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VSI C Run-Time Library Reference Manual for OpenVMS Systems

Document Number: DO-VIBHAA-011
Publication Date: April 2024
Software Version:
VSI C Version 7.4-1 for OpenVMS
Operating System and Version:
VSI OpenVMS IA-64 Version 8.4-1H1 or higher
VSI OpenVMS Alpha Version 8.4-2L1 or higher
VSI OpenVMS x86-64 Version 9.2-1 or higher

Preface

This manual describes the VSI C Run-Time Library (C RTL) for OpenVMS Alpha, OpenVMS Integrity server, and OpenVMS x86-64 operating systems.

This manual provides reference information about the C RTL functions and macros that perform input/output (I/O) operations, character and string manipulation, mathematical operations, error detection, subprocess creation, system access, screen management, and emulation of selected UNIX features. It also notes portability concerns between operating systems, where applicable.

The VSI C Run-Time Library contains XPG4-compliant internationalization support, providing functions to help you develop software that can run in different languages and cultures.

The complete VSI C Run-Time Library needed for use with the VSI C and VSI C++ compilers is distributed with the OpenVMS Alpha, OpenVMS Integrity server, and OpenVMS x86-64 operating systems in both shared image and object module library form.

1. About VSI

VMS Software, Inc. (VSI) is an independent software company licensed by Hewlett Packard Enterprise to develop and support the OpenVMS operating system.

2. Intended Audience

This manual is intended for experienced and novice programmers who need reference information on the functions and macros found in the C RTL.

3. Document Structure

This manual has the following chapters, reference section, and appendixes:

  • Chapter 1 provides an overview of the C RTL.

  • Chapter 2 discusses the Standard I/O, Terminal I/O, and UNIX I/O functions.

  • Chapter 3 describes the character, string, and argument-list functions.

  • Chapter 4 describes the error-handling and signal-handling functions.

  • Chapter 5 explains the functions used to create subprocesses.

  • Chapter 6 describes the Curses Screen Management functions.

  • Chapter 7 discusses the math functions.

  • Chapter 8 explains the memory allocation functions.

  • Chapter 10 describes the functions used to interact with the operating system.

  • Chapter 11 gives an introduction to the facilities provided in the VSI C environment on OpenVMS systems for developing international software.

  • Chapter 12 describes the date/time functions.

  • Chapter 13 describes symbolic links and POSIX pathname support.

  • The Reference Section describes all the functions in the C RTL.

  • Appendix A contains version-dependency tables that list the C RTL functions supported on different OpenVMS versions.

  • Appendix B lists the function prototypes that are duplicated in more than one header file.

4. Related Documents

The following documents may be useful when programming in VSI C for OpenVMS systems:

  • VSI C User Manual—For C programmers who need information on using VSI C for OpenVMS systems.

  • VSI C Reference Manual—Provides language reference information for VSI C on VSI OpenVMS systems.

  • VSI TCP/IP Services for OpenVMS Sockets API and System Services Programming—For information on the socket routines used for writing Internet application programs for the OpenVMS product or other implementations of the TCP/IP protocol.

  • VSI TCP/IP Services for OpenVMS Guide to IPv6—For information on TCP/IP Services for OpenVMS IPv6 features, how to install and configure IPv6 on your system, changes in the socket application programming interface (API), and how to port your applications to run in an IPv6 environment.

  • X/Open Portability Guide, Issue 3—Documents what is commonly known as the XPG3 specification.

  • X/Open CAE Specification System Interfaces and Headers, Issue 4—Documents what is commonly known as the XPG4 specification.

  • X/Open CAE Specification, System Interfaces and Headers, Issue 4, Version 2—Documents what is commonly known as XPG4 V2.

  • X/Open CAE Specification, System Interfaces and Headers, Issue 5—Documents what is commonly known as the XPG5 specification.

  • Technical Standard. System Interfaces, Issue 6—Combined Open Group Technical Standard and IEEE standard. IEEE Std 1003.1-2001, sometimes known as XPG6.

  • Standard for Information Technology - Portable Operating System Interface (POSIX) - Part 1: System Application Program Interface (API) - Amendment 2: Threads Extension [C Language]—Documents what is also known as POSIX 1003.1c-1995.

  • ISO/IEC 9945-2:1993 - Information Technology - Portable Operating System Interface (POSIX) - Part 2: Shell and Utilities—Documents what is also known as ISO POSIX-2.

  • ISO/IEC 9945-1:1990 - Information Technology - Portable Operating System Interface (POSIX) - Part 1: System Application Programming Interface (API) (C Language)—Documents what is also known as ISO POSIX-1.

  • ANSI/ISO/IEC 9899:1999 - Programming Languages - C—The C99 standard, published by ISO in December, 1999 and adopted as an ANSI standard in April, 2000.

  • ISO/IEC 9899:1990-1994 - Programming Languages - C, Amendment 1:Integrity—Documents what is also known as ISO C, Amendment 1.

  • ISO/IEC 9899:1990[1992] - Programming Languages - C—Documents what is also known as ISO C. The normative part is the same as X3.159-1989, American National Standard for Information Systems - Programming Language C, also known as ANSI C.

5. OpenVMS Documentation

The full VSI OpenVMS documentation set can be found on the VMS Software Documentation webpage at https://docs.vmssoftware.com.

6. VSI Encourages Your Comments

You may send comments or suggestions regarding this manual or any VSI document by sending electronic mail to the following Internet address: . Users who have VSI OpenVMS support contracts through VSI can contact for help with this product.

7. Typographical Conventions

The conventions found in the following table are used in this document.
ConventionMeaning
OpenVMS systems

Refers to the OpenVMS operating system on all supported platforms, unless otherwise specified.

Ctrl/x

While holding down the Ctrl key, press the key specified by x.

  • switch statement
  • int data type
  • fprintf function
  • <stdio.h> header file

Monospace type identifies language keywords and the names of C RTL functions and header files. Monospace type is also used when referring to a specific variable name used in an example.

arg1

Italic type indicates a placeholder, such as an argument or parameter name.

float x;
   .
   .
   .
x = 5;

A vertical ellipsis indicates that not all of the text of a program or program output is illustrated. Only relevant material is shown in the example.

option, ...

A horizontal ellipsis indicates that additional parameters, options, or values can be entered. A comma that precedes the ellipsis indicates that successive items must be separated by commas.

[output-source, ...]

Square brackets, in function synopses and a few other contexts, indicate that a syntactic element is optional. Square brackets are not optional, however, when used to delimit a directory name in an OpenVMS file specification or when used to delimit the dimensions of a multidimensional array in VSI C source code.

[a | b]

Brackets surrounding two or more items separated by a vertical bar ( | ) indicate a choice; you must choose one of the two syntactic elements.

Δ

A delta symbol is used in some contexts to indicate a single ASCII space character.

8. Platform Labels

A platform is a combination of operating system and hardware that provides a distinct environment. This manual contains information applicable to the OpenVMS operating system running on x86-64, Itanium, and Alpha processors.

The information in this manual applies to all OpenVMS operating systems, except when specifically labeled as follows:
LabelExplanation
(Alpha system)

Specific to an HPE Alpha system running the OpenVMS Alpha operating system.

(Integrity server system)

Specific to an HPE Integrity server running the OpenVMS Integrity server operating system.

(x86-64 system)Specific to an x86-64 server running the OpenVMS x86-64 operating environment.

Chapter 1. Introduction

The ISO/ANSI C standard defines a library of functions, as well as related types and macros, to be provided with any implementation of ANSI C. The VSI C Reference Manual describes the ANSI-conformant library features common to all VSI C platforms. The VSI C Run-Time Library Reference Manual for OpenVMS Systems provides a more detailed description of these routines and their use in the OpenVMS environment. It also documents additional header files, functions, types, and macros that are available on the OpenVMS system.

All library functions are declared in a header file. To make the contents of a header file available to your program, include the header file with an #include preprocessor directive. For example:
#include <stdlib.h>

Each header file contains function prototypes for a set of related functions, and defines any types and macros needed for their use.

To list the header files, use the following commands:
$ LIBRARY/LIST SYS$LIBRARY:SYS$STARLET_C.TLB
$ LIBRARY/LIST SYS$LIBRARY:DECC$RTLDEF.TLB
$ DIR SYS$COMMON:[DECC$LIB.REFERENCE.DECC$RTLDEF]*.H;
$ DIR SYS$LIBRARY:*.H;
The first command lists the text module form of the header files for the OpenVMS system interfaces. The second lists the text module form of the header files for the VSI C language interface. The third lists *.H header files for the VSI C language interfaces. The fourth lists *.H header files for layered products and other applications.

Note

The SYS$COMMON:[DECC$LIB.REFERENCE.DECC$RTLDEF] directory is only a reference area for your viewing. The compiler still looks in the *.TLB files for #include file searches.

However, duplicate files (such as <stdio.h>) found in SYS$LIBRARY probably support the VAX C Version 3.2 environment and should not be used with VSI C.

Function definitions themselves are not included in the header files, but are contained in the VSI C Run-Time Library (C RTL) shipped with the OpenVMS operating system. Before using the C RTL, you must be familiar with the following topics:

  • The linking process

  • The macro substitution process

  • The difference between function definitions and function calls

  • The format of valid file specifications

  • The OpenVMS-specific methods of input and output (I/O)

  • The VSI C for OpenVMS extensions and nonstandard features

A knowledge of all these topics is necessary to effectively use the C RTL. This chapter shows the connections between these topics and the C RTL. Read this chapter before any of the other chapters in this manual.

The primary purpose of the C RTL is to provide a means for C programs to perform I/O operations; the C language itself has no facilities for reading and writing information. In addition to I/O support, the C RTL also provides a means to perform many other tasks.

Chapters 2 through 11 describe the various tasks supported by the C RTL. The Reference Section alphabetically lists and describes all the functions and macros available to perform these tasks.

1.1. Using the VSI C Run-Time Library (C RTL)

When working with the C RTL, you must be aware of some implementation specifics.

First, if you plan to use C RTL functions in your C programs, make sure that a function named main or a function that uses the main_program option exists in your program. For more information, see the VSI C Reference Manual or the VSI C User Manual.

Second, the C RTL functions are executed at run time, but references to these functions are resolved at link time. When you link your program, the OpenVMS linker resolves all references to C RTL functions by searching any shareable code libraries or object code libraries specified on the LINK command line.

You can use the C RTL as a shareable image or you can use the C RTL object libraries.

When you use the C RTL as a shareable image, the code for the RTL resides in an image file in SYS$SHARE and is shared by all VSI C programs. After execution, control returns to your program. This process has a number of advantages:

  • You reduce the size of a program's executable image.

  • The program's image takes up less disk space.

  • The program swaps in and out of memory faster due to decreased size.

  • With VSI C and VSI C++, you no longer need to define an options file when linking your program against the shareable image. Linking against the RTL shareable image is now much simpler than it was with VAX C. In fact, it is the default method of linking to the C RTL.

When linking to the C RTL, you do not need to define any LNK$LIBRARY logicals. In fact, you should deassign LNK$LIBRARY because linking with the shareable image is more convenient than linking with the C RTL object libraries.

See your OpenVMS, VSI C, or VSI C++ release notes for any supplemental information about linking with the C RTL.

1.3.  C RTL Function Prototypes and Syntax

After learning how to link object modules and include header files, you must learn how to reference VSI C functions in your program. The remaining chapters in this manual provide detailed descriptions of the C RTL functions.

1.3.1. Function Prototypes

In all chapters, the syntax describing each function follows the standard convention for defining a function. This syntax is called a function prototype (or just prototype). The prototype is a compact representation of the order of a function's arguments (if any), the types of the arguments, and the type of the value returned by a function. We recommend the use of prototypes.

If the return value of the function cannot be easily represented by a C data-type keyword, look for a description of the return values in the explanatory text. The prototype descriptions provide insight into the functionality of the function. These descriptions may not describe how to call the function in your source code.

For example, consider the prototype for the feof function:
#include <stdio.h>
int feof(FILE *file_ptr);
This syntax shows the following information:

  • The feof prototype resides in the <stdio.h> header file. To use feof, you must include this header file. (Declaring C RTL functions yourself is not recommended.)

  • The feof function returns a value of data type int.

  • There is one argument, file_ptr, that is of type "pointer to FILE". FILE is defined in the <stdio.h> header file.

To use feof in a program, include <stdio.h> anywhere before the function call to feof, as in the following example:
#include <stdio.h>                 /* Include Standard I/O     */

main()
{

    FILE *infile;                  /* Define a file pointer    */
       .
       .
       .                           /* Call the function feof   */
    while ( ! feof(infile) )       /* Until EOF reached        */
       {                           /* Perform file operations  */
          .
          .
          .
       }
}

1.3.2. Syntax Conventions for Function Prototypes

Since some library functions take a varying number of parameters, syntax descriptions for function prototypes adhere to the following conventions:

  • Ellipses (…) are used to indicate a varying number of parameters.

  • In cases where the type of a parameter may vary, its type is not shown in the syntax.

Consider the printf syntax description:
#include <stdio.h>
int printf(const char *format_specification, ...);

The syntax description for printf shows that you can specify one or more optional parameters. The remaining information about printf parameters is in the description of the function.

1.3.3. UNIX Style File Specifications

The C RTL functions and macros often manipulate files. One of the major portability problems is the different file specifications used on various systems. Since many C applications are ported to and from UNIX systems, it is convenient for all compilers to be able to read and understand UNIX system file specifications.

The following file specification conversion functions are included in the C RTL to assist in porting C programs from UNIX systems to OpenVMS systems:

  • decc$match_wild
  • decc$translate_vms
  • decc$fix_time
  • decc$to_vms
  • decc$from_vms

The advantage of including these file specification conversion functions in the C RTL is that you do not have to rewrite C programs containing UNIX system file specifications. VSI C can translate most valid UNIX system file specifications to OpenVMS file specifications.

Please note the differences between the UNIX system and OpenVMS file specifications, as well as the method used by the RTL to access files. For example, the RTL accepts a valid OpenVMS specification and most valid UNIX file specifications, but the RTL cannot accept a combination of both. Table 1.1 shows the differences between UNIX system and OpenVMS system file specification delimiters.
Table 1.1. UNIX and OpenVMS File Specification Delimiters

Description

OpenVMS System

UNIX System

Node delimiter

::

!/

Device delimiter

:

/

Directory path delimiter

[ ]

/

Subdirectory delimiter

[ . ]

/

File extension delimiter

.

.

File version delimiter

;

Not applicable

For example, Table 1.2 shows the formats of two valid specifications and one invalid specification.
Table 1.2. Valid and Invalid UNIX and OpenVMS File Specifications

System

File Specification

Valid/Invalid

OpenVMS

BEATLE::DBA0:[MCCARTNEY]SONGS.LIS

Valid

UNIX

beatle!/usr1/mccartney/songs.lis

Valid

—

BEATLE::DBA0:[MCCARTNEY.C]/songs.lis

Invalid

When VSI C translates file specifications, it looks for both OpenVMS and UNIX system file specifications. Consequently, there may be differences between how VSI C translates UNIX system file specifications and how UNIX systems translate the same UNIX file specification.

For example, if the two methods of file specification are combined, as in Table 1.2, C RTL can interpret [MCCARTNEY.C]/songs.lis as either [MCCARTNEY]songs.lis or [C]songs.lis. Therefore, when VSI C encounters a mixed file specification, an error occurs.

UNIX systems use the same delimiter for the device name, the directory names, and the filename. Due to the ambiguity of UNIX file specifications, VSI C may not translate a valid UNIX system file specification according to your expectations.

For instance, the OpenVMS system equivalent of /bin/today can be either [BIN]TODAY or [BIN.TODAY]. VSI C can make the correct interpretation only from the files present. If a file specification conforms to UNIX system filename syntax for a single file or directory, it is converted to the equivalent OpenVMS filename if one of the following conditions is true:

  • If the specification corresponds to an existing OpenVMS directory, it is converted to that directory name. For example, /dev/dir/sub is converted to DEV:[DIR.SUB] if DEV:[DIR.SUB] exists.

  • If the specification corresponds to an existing OpenVMS filename, it is converted to that filename. For example, /dev/dir/file is converted to DEV:[DIR]FILE if DEV:[DIR]FILE exists.

  • If the specification corresponds to a nonexistent OpenVMS filename, but the given device and directory exist, it is converted to a filename. For example, /dev/dir/file is converted to DEV:[DIR]FILE if DEV:[DIR] exists.


Note

Beginning with OpenVMS Version 7.3, you can instruct the C RTL to interpret the leading part of a UNIX style file specification as either a subdirectory name or a device name.

As with previous releases, the default translation of foo/bar (UNIX style name) is FOO:BAR (OpenVMS style device name).

To request translation of foo/bar (UNIX style name) to [.FOO]BAR (OpenVMS style subdirectory name), define the logical name DECC$DISABLE_TO_VMS_LOGNAME_TRANSLATION to ENABLE. DECC$DISABLE_TO_VMS_LOGNAME_TRANSLATION is checked only once per image activation, not on a file-by-file basis. Defining this logical affects not only the decc$to_vms function, but all C RTL functions that accept both UNIX style and OpenVMS style filenames as an argument.

In the UNIX system environment, you reference files with a numeric file descriptor. Some file descriptors reference Standard I/O devices; some descriptors reference actual files. If the file descriptor belongs to an unopened file, the C RTL opens the file. VSI C equates file descriptors with the following OpenVMS logical names:

File Descriptor

OpenVMS Logical

Meaning

0

SYS$INPUT

Standard input

1

SYS$OUTPUT

Standard output

2

SYS$ERROR

Standard error

1.3.4. Extended File Specifications

The ODS-5 volume structure provides enhanced support for mixed UNIX and OpenVMS style filenames. It supports long filenames, allows the use of a wider range of characters within filenames, and preserves case within filenames. With OpenVMS Alpha Version 7.3-1, the C RTL has greatly improved support of ODS-5 characters, with 250 of the 256 characters supported, as opposed to only 214 supported previously. Also, filenames without file types can now be accessed.

To enable the new support, you must define one or more C RTL feature logical names. These names include the following:
  • DECC$EFS_CHARSET
  • DECC$DISABLE_TO_VMS_LOGNAME_TRANSLATION
  • DECC$FILENAME_UNIX_NO_VERSION
  • DECC$FILENAME_UNIX_REPORT
  • DECC$READDIR_DROPDOTNOTYPE
  • DECC$RENAME_NO_INHERIT

See Section 1.5 for more information on these and other feature logical names.

1.4. Feature-Test Macros for Header-File Control

Feature-test macros provide a means for writing portable programs. They ensure that the C RTL symbolic names used by a program do not clash with the symbolic names supplied by the implementation.

The C RTL header files are coded to support the use of a number of feature-test macros. When an application defines a feature-test macro, the C RTL header files supply the symbols and prototypes defined by that feature-test macro and nothing else. If a program does not define such a macro, the C RTL header files define symbols without restriction.

The feature-test macros supported by the C RTL fall into the following broad categories for controlling the visibility of symbols in header files according to the following:

  • Standards

  • Multiple-version support

  • Compatibility

1.4.1. Standards Macros

The C RTL implements parts of the following standards:

  • X/Open CAE Specification, System Interfaces and Headers, Issue 4, Version 2, also known as XPG4 V2.

  • X/Open CAE Specification, System Interfaces and Headers, Issue 4, also known as XPG4.

  • Standard for Information Technology - Portable Operating System Interface (POSIX) - Part 1: System Application Program Interface (API) – Amendment 2: Threads Extension [C Language], also known as POSIX 1003.1c-1995 or IEEE 1003.1c-1995.

  • ISO/IEC 9945-2:1993 - Information Technology - Portable Operating System Interface (POSIX) - Part 2: Shell and Utilities, also known as ISO POSIX-2.

  • ISO/IEC 9945-1:1990 - Information Technology - Portable Operating System Interface (POSIX) - Part 1: System Application Programming Interface (API) (C Language), also known as ISO POSIX-1.

  • ANSI/ISO/IEC 9899:1999 - The C99 standard, published by ISO in December, 1999 and adopted as an ANSI standard in April, 2000.

  • ISO/IEC 9899:1990-1994 - Programming Languages - C, Amendment 1: Integrity, also known as ISO C, Amendment 1.

  • ISO/IEC 9899:1990 - Programming Languages - C, also known as ISO C. The normative part is the same as X3.159-1989, American National Standard for Information Systems - Programming Language C, also known as ANSI C.

1.4.2. Selecting a Standard

You can define a feature-test macro to select each standard. You can do this either with a #define preprocessor directive in your C source before the inclusion of any header file, or with the /DEFINE qualifier on the CC command line.

Table 1.3 lists and describes the C RTL feature-test macros that control standards support.
Table 1.3. Feature Test Macros — Standards

Macro Name

Standard Selected

Other Standards Implied

Description

_XOPEN_SOURCE_
EXTENDED

XPG4 V2

XPG4, ISO POSIX-2, ISO POSIX-1, ANSI C

Makes visible XPG4-extended features, including traditional UNIX based interfaces not previously adopted by X/Open.

_XOPEN_SOURCE

XPG4(X/Open Issue 4)

ISO POSIX-2, ISO POSIX-1, ANSI C

Makes visible XPG4 standard symbols and causes _POSIX_C_SOURCE to be set to 2 if it is not already defined with a value greater than 2.? ?

_XOPEN_SOURCE=500

X/Open Issue 5

ISO POSIX-2, ISO POSIX-1, ANSI C

Makes visible X/Open Issue 5 standard symbols and causes _POSIX_C_SOURCE to be set to 2 if it is not already defined with a value greater than 2.? ?

_XOPEN_SOURCE=600

X/Open Issue 6

ISO POSIX-2, ISO POSIX-1, ANSI C

Makes visible X/Open Issue 6 standard symbols and causes _POSIX_C_SOURCE to be set to 2 if it is not already defined with a value greater than 2.? ?

_POSIX_C_SOURCE==199506

IEEE 1003.1c-1995

ISO POSIX-2, ISO POSIX-1, ANSI C

Header files defined by ANSI C make visible those symbols required by IEEE 1003.1c-1995.

_POSIX_C_SOURCE==2

ISO POSIX-2

ISO POSIX-1, ANSI C

Header files defined by ANSI C make visible those symbols required by ISO POSIX-2 plus those required by ISO POSIX-1.

_POSIX_C_SOURCE==1

ISO POSIX-1

ANSI C

Header files defined by ANSI C make visible those symbols required by ISO POSIX-1.

__STDC_VERSION__==199409

ISO C amdt 1

ANSI C

Makes ISO C Amendment 1 symbols visible.

_ANSI_C_SOURCE

ANSI C

–

Makes ANSI C standard symbols visible.

__HIDE_FORBIDDEN_NAMES

When defined to the value 1, causes the C RTL headers that are named in the C standard to be configured such that they define only those identifiers that are specified as being defined by those headers under the version of the C standard in effect for the compilation, unless additional features are explicitly requested by other configuration macros (_XOPEN_SOURCE, for example).

The C and C++ compilers will predefine this macro when certain language standard conformance features are selected, but the user can override any such predefinition by specifying /UNDEFINE=_ _HIDE_FORBIDDEN_ NAMES on the command line (or using #undef before including any headers). Conversely, the user can explicitly define the macro before including any headers, regardless of the language standard selected for the compiler.

Features not defined by one of the previously named standards are considered VSI C extensions and are selected by not defining any standards-related, feature-test macros.

If you do not explicitly define feature test macros to control header file definitions, you implicitly include all defined symbols as well as VSI C extensions.

1.4.3. Interactions with the /STANDARD Qualifier

The /STANDARD qualifier selects the dialect of the C language supported.

With the exception of /STANDARD=ANSI89 and /STANDARD=ISOC94, the selection of C dialect and the selection of C RTL APIs to use are independent choices. All other values for /STANDARD cause the entire set of APIs to be available, including extensions.

Specifying /STANDARD=ANSI89 restricts the default API set to the ANSI C set. In this case, to select a broader set of APIs, you must also specify the appropriate feature-test macro. To select the ANSI C dialect and all APIs, including extensions, undefine __HIDE_FORBIDDEN_NAMES before including any header file.

Compiling with /STANDARD=ISOC94 sets __STDC_VERSION__ to 199409. Conflicts that arise when compiling with both XPG4 and ISO C Amendment 1 resolve in favor of ISO C Amendment 1. XPG4 extensions to ISO C Amendment 1 are selected by defining _XOPEN_SOURCE.

The following examples help clarify these rules:
  • The fdopen function is an ISO POSIX-1 extension to <stdio.h>. Therefore, <stdio.h> defines fdopen only if one or more of the following is true:

    • The program including it is not compiled in strict ANSI C mode (/STANDARD=ANSI89).

    • _POSIX_C_SOURCE is defined as 1 or greater.

    • _XOPEN_SOURCE is defined.

    • _XOPEN_SOURCE_EXTENDED is defined.

  • The popen function is an ISO POSIX-2 extension to <stdio.h>. Therefore, <stdio.h> defines popen only if one or more of the following is true:

    • The program including it is not compiled in strict ANSI C mode (/STANDARD=ANSI89).

    • _POSIX_C_SOURCE is defined as 2 or greater.

    • _XOPEN_SOURCE is defined.

    • _XOPEN_SOURCE_EXTENDED is defined.

  • The getw function is an X/Open extension to <stdio.h>. Therefore, <stdio.h> defines getw only if one or more of the following is true:

    • The program is not compiled in strict ANSI C mode (/STANDARD=ANSI89).

    • _XOPEN_SOURCE is defined.

    • _XOPEN_SOURCE_EXTENDED is defined.

  • The X/Open Extended symbolic constants _SC_PAGESIZE, _SC_PAGE_SIZE, _SC_ATEXIT_MAX, and _SC_IOV_MAX were added to <unistd.h> to support the sysconffunction. However, these constants are not defined by _POSIX_C_SOURCE.

    The <unistd.h> header file defines these constants only if a program does not define _POSIX_C_SOURCE and does define _XOPEN_SOURCE_EXTENDED.

    If _POSIX_C_SOURCE is defined, these constants are not visible in <unistd.h>. Note that _POSIX_C_SOURCE is defined only for programs compiled in strict ANSI C mode.

  • The fgetname function is a C RTL extension to <stdio.h>. Therefore, <stdio.h> defines fgetname only if the program is not compiled in strict ANSI C mode (/STANDARD=ANSI89).

  • The macro _PTHREAD_KEYS_MAX is defined by POSIX 1003.1c-1995. This macro is made visible in <limits.h> when compiling for this standard with _POSIX_C_SOURCE == 199506 defined, or by default when compiling without any standards-defining, feature-test macros.

  • The macro WCHAR_MAX defined in <wchar.h> is required by ISO C Amendment 1 but not by XPG4. Therefore:

    • Compiling for ISO C Amendment 1 makes this symbol visible, but compiling for XPG4 compliance does not.

    • Compiling for both ISO C Amendment 1 and XPG4 makes this symbol visible.

    Similarly, the functions wcsftime and wcstok in <wchar.h> are defined slightly differently by the ISO C Amendment 1 and XPG4:

    • Compiling for ISO C Amendment 1 makes the ISO C Amendment 1 prototypes visible.

    • Compiling for XPG4 compliance makes the XPG4 prototypes visible.

    • Compiling for both ISO C Amendment 1 and XPG4 selects the ISO C prototypes because conflicts resulting from this mode of compilation resolve in favor of ISO C.

    • Compiling without any standard selecting feature test macros makes ISO C Amendment 1 features visible.

    In this example, compiling with no standard-selecting feature-test macros makes WCHAR_MAX and the ISO C Amendment 1 prototypes for wcsftime and wcstok visible.

  • The wcswidth and wcwidth functions areXPG4 extensions to ISO C Amendment 1. Their prototypes are in <wchar.h>.

    These symbols are visible if:

    • Compiling for XPG4 compliance by defining _XOPEN_SOURCE or _XOPEN_SOURCE_EXTENDED.

    • Compiling for DEC C Version 4.0 compatibility or on pre-OpenVMS Version 7.0 systems.

    • Compiling with no standard-selecting feature-test macros.

    • Compiling for both ISO C Amendment 1 and XPG4 compilance because these symbols are XPG4 extensions to ISO C Amendment 1.

    Compiling for strict ISO C Amendment 1 does not make them visible.

1.4.4. Multiple-Version-Support Macros

1.4.4.1. The __VMS_VER Macro

By default, the header files enable APIs in the C RTL provided by the version of the operating system on which the compilation occurs. This is accomplished by the predefined setting of the __VMS_VER macro, as described in the VSI C User Manual. For example, compiling on OpenVMS Version 6.2 causes only C RTL APIs from Version 6.2 and earlier to be made available.

Another example of the use of the __VMS_VER macro is support for the 64-bit versions of C RTL functions available with OpenVMS Alpha Version 7.0 and higher. In all header files, functions that provide 64-bit support are conditionalized so that they are visible only if __VMS_VER indicates a version of OpenVMS that is greater than or equal to 7.0.

To target an older version of the operating system, do the following:

  1. Define a logical DECC$SHR to point to the old version of DECC$SHR. The compiler uses a table from DECC$SHR to perform routine name prefixing.

  2. Override the value of __VMS_VER by defining the macro __VMS_VER_OVERRIDE on the command line and setting its value to a number that represents the version of OpenVMS that you are compiling for. For example, to compile for OpenVMS Version 7.0, add the following switch to your compile command:
    /DEFINE=(__VMS_VER_0VERRIDE=70000000)
    This will set the value of __VMS_VER to 70000000.

    Defining __VMS_VER_OVERRIDE without a value sets __VMS_VER to the maximum value.

Targeting a newer version of the operating system might not always be possible. For some versions, you can expect that the new DECC$SHR.EXE will require new features of the operating system that are not present. For such versions, the defining of the logical DECC$SHR in Step 1 would cause the compilation to fail.

1.4.4.2. The __CRTL_VER Macro

The __CRTL_VER macro allows you to compile applications on an OpenVMS system with one version of the C RTL or C RTL ECO installed and execute them on OpenVMS systems with a different version of the C RTL or C RTL ECO.

The __CRTL_VER macro is defined by the compiler and is set to a value equal to the version of the C RTL on the current system. The current value of __CRTL_VER is set to 80500000.

If you compile an application that is intended to be executed on a system with a lower version of the C RTL, override the value of _CRTL_VER macro to enable functions and features that are only available on the system with the lower version of the C RTL.

You can override the value of __CRTL_VER by defining __CRTL_VER_OVERRIDE on the compile command line. For example, to set the value of __CRTL_VER to 80400000, use the following compiler switch:
/DEFINE=(__CRTL_VER_OVERRIDE=80400000)

Defining __CRTL_VER_OVERRIDE without a value sets __CRTL_VER to the maximum value.

1.4.5. Compatibility Modes

The following predefined macros are used to select header-file compatibility with previous versions of DEC C or the OpenVMS operating system:

  • _DECC_V4_SOURCE

  • _VMS_V6_SOURCE

There are two types of incompatibilities that can be controlled in the header files:

  • To conform to standards, some changes are source-code incompatible but binary compatible. To select DEC C Version 4.0 source compatibility, use the _DECC_V4_SOURCE macro.

  • Other changes to conform to standards introduce a binary or run-time incompatibility.

    In general, programs that recompile get new behaviors. In these cases, use the _VMS_V6_SOURCE feature test macro to retain previous behaviors.

    However, for the exit, kill, and wait functions, the OpenVMS Version 7.0 changes to make these routines ISO POSIX-1 compliant were considered too incompatible to become the default. Therefore, in these cases the default behavior is the same as on pre-OpenVMS Version 7.0 systems. To access the versions of these routines that comply with ISO POSIX-1, use the _POSIX_EXIT feature test macro.

The following examples help clarify the use of these macros:
  • To conform to the ISO POSIX-1 standard, typedefs for the following have been added to <types.h>:
       dev_t         off_t
   gid_t         pid_t
   ino_t         size_t
   mode_t        ssize_t
   nlink_t       uid_t

    Previous development environments using a version of DEC C earlier than Version 5.2 may have compensated for the lack of these typedefs in <types.h> by adding them to another module. If this is the case on your system, then compiling with the <types.h> provided with DEC C Version 5.2 might cause compilation errors.

    To maintain your current environment and include the DEC C Version 5.2 <types.h>, compile with _DECC_V4_SOURCE defined. This will omit incompatible references from the DEC C Version 5.2 headers. In <types.h>, for example, the previously listed typedefs will not be visible.

  • As of OpenVMS Version 7.0, the C RTL getuid and geteuid functions are defined to return an OpenVMS UIC (user identification code) that contains both the group and member portions of the UIC. In previous versions of the DEC C RTL, these functions returned only the member number from the UIC code.

    Note that the prototypes for getuid and geteuid in <unistd.h> (as required by the ISO POSIX-1 standard) and in <unixlib.h> (for C RTL compatibility) have not changed. By default, newly compiled programs that call getuid and geteuid get the new definitions. That is, these functions will return an OpenVMS UIC.

    To let programs retain the pre-OpenVMS Version 7.0 behavior of getuid and geteuid, compile with the _VMS_V6_SOURCE feature-test macro defined.

  • As of OpenVMS Version 7.0, the C RTL exit function is defined with ISO POSIX-1 semantics. As a result, the input status argument to exit takes a number between 0 and 255. (Prior to this, exit could take an OpenVMS condition code in its status parameter.)

    By default, the behavior for exit on OpenVMS systems is the same as before: exit accepts an OpenVMS condition code. To enable the ISO POSIX-1 compatible exit function, compile with the _POSIX_EXIT feature-test macro defined.

1.4.6. Curses and Socket Compatibility Macros

The following feature-test macros are used to control the Curses and Socket subsets of the C RTL library:

  • _BSD44_CURSES

    This macro selects the Curses package from the 4.4BSD Berkeley Software Distribution.

  • _VMS_CURSES

    This macro selects a Curses package based on the VAX C compiler. This is the default Curses package.

  • _SOCKADDR_LEN

    This macro is used to select 4.4BSD-compatible and XPG4 V2-compatible socket interfaces. These interfaces require support in your underlying TCP/IP software. Contact your TCP/IP vendor to inquire if the version of TCP/IP software you run supports 4.4BSD sockets.

Strict XPG4 V2 compliance requires the 4.4BSD-compatible socket interface. Therefore, if _XOPEN_SOURCE_EXTENDED is defined on OpenVMS Version 7.0 or higher, _SOCKADDR_LEN is defined to be 1.

The following examples help clarify the use of these macros:

  • Symbolic constants like AE, AL, AS, AM, BC, which represent pointers to termcap fields used by the BSD Curses package, are only visible in <curses.h> if _BSD44_CURSES is defined.

  • The <socket.h> header file defines a 4.4BSD sockaddr structure only if _SOCKADDR_LEN or _XOPEN_SOURCE_EXTENDED is defined. Otherwise, <socket.h> defines a pre-4.4BSD sockaddr structure. If _SOCKADDR_LEN is defined and _XOPEN_SOURCE_EXTENDED is not defined.

    The <socket.h> header file also defines an osockaddr structure, which is a 4.3BSD sockaddr structure to be used for compatibility purposes. Since XPG4 V2 does not define an osockaddr structure, it is not visible in _XOPEN_SOURCE_EXTENDED mode.

1.4.7. 2 GB File Size Macro

The C RTL provides support for compiling applications to use file sizes and offsets that are 2 GB and larger. This is accomplished by allowing file offsets of 64-bit integers.

The fseeko and ftello functions, which have the same behavior as fseek and ftell, accept or return values of type off_t, which allows for a 64-bit variant of off_t to be used.

C RTL functions lseek, mmap, ftuncate, truncate, stat, fstat, and ftw can also accommodate a 64-bit file offset.

The new 64-bit interfaces can be selected at compile time by defining the _LARGEFILE feature macro.

1.4.8. 32-Bit UID and GID Macro

The C RTL supports 32-bit User Identification (UID) and Group Identification (GID). When an application is compiled to use 32-bit UID/GID, the UID and GID are derived from the UIC as in previous versions of the operating system.

To compile an application for 16-bit UID/GID support on systems that by default use 32-bit UIDs/GIDs, define the _DECC_SHORT_GID_T macro to 1.

Not specifying _DECC_SHORT_GID_T provides long (32-bit) UID/GID.

Compiling on older OpenVMS systems where long UID/GID is not supported, or compiling for legacy compatibility (_DECC_V4_SOURCE for VSI C Version 4 or _VMS_V6_SOURCE for OpenVMS Version 6), forces use of short (16-bit) UID/GID.

1.4.9. Standard-Compliant stat Structure

The C RTL supports an X/Open standard-compliant definition of the stat structure and associated definitions. To use these new definitions, applications must compile with the _USE_STD_STAT feature-test macro defined. Use of _USE_STD_STAT specifies long (32-bit) GIDs.

When compiled with _USE_STD_STAT, the stat structure includes these changes:

  • Type ino_t is defined as an unsigned quadword int. Without _USE_STD_STAT, it is an unsigned short.

  • Type dev_t is defined as a 64-bit integer. Without _USE_STD_STAT, it is a 32-bit character pointer.

  • Type off_t is defined as a 64-bit integer, as if the _LARGEFILE macro has been defined. Without _USE_STD_STAT, off_t is a 32-bit integer.

  • Fields st_dev and st_rdev will have unique values per device. Without _USE_STD_STAT, uniqueness is not assured.

  • Fields st_blksize and st_blocks are added. Without _USE_STD_STAT, these fields do not exist.

1.4.10. Using Legacy _toupper and _tolower Behavior

As of OpenVMS Version 8.3, to comply with the C99 ANSI standard and X/Open Specification, the _tolower and _toupper macros by default do not evaluate their parameter more than once. They simply call their respective tolower or toupper function. This avoids side effects (such as i++ or function calls) where the user can tell how many times an expression is evaluated.

To retain the older, optimized behavior of the _tolower and _toupper macros, compile with /DEFINE=_FAST_TOUPPER. Then, as in previous releases, these macros optimize the call to avoid the overhead of a runtime call. However, the macro's parameter is evaluated more than once to determine how to calculate the result, possibly creating unwanted side effects.

1.4.11. Using Faster, Inlined Put and Get Functions

Compiling with the _ _UNIX_PUTC macro defined enables an optimization that sets the following I/O functions to use faster, in lined functions:
fgetc
fputc
putc
putchar
fgetc_unlocked
fputc_unlocked
putc_unlocked
putchar_unlocked

1.4.12. POSIX Style Exit

The VSI C and C++ Version 7.1 and higher compilers have a /MAIN=POSIX_EXIT qualifier that defines the _POSIX_EXIT macro and causes the main program to call __posix_exit instead of exit when returning from the main program.

This qualifier should be used with programs ported from UNIX that do not explicitly call exit and do not use OpenVMS specific exit codes.

For older compilers, the following sample code can be used to force the existing main module to have a different name so that a simple main program will call it but force the exit status to be through the __posix_exit call.

The replacement main function can be in a different module, so that /DEFINE="main=real_main" is all that is needed for modifying the build of the existing main function.
#define _POSIX_EXIT 1

#include <stdlib.h>

int real_main(int argc, char **argv);

/* Make sure POSIXized exit is used */
int main(int argc, char **argv)
{
int ret_status;

   ret_status = real_main(argc, argv);

exit (ret_status);
}
#define main real_main

Unless your C program is intentionally using OpenVMS status codes for exit values, it is strongly recommended that both the _POSIX_EXIT macro be defined and, if needed, the /MAIN=POSIX_EXIT or the alternative main replacement be used so that DCL, BASH, and the accounting file get usable exit values.

1.5. Enabling C RTL Features Using Feature Logical Names

The C RTL provides an extensive list of feature switches that can be set using DECC$ logical names. These switches affect the behavior of a C application at run time.

The feature switches introduce new behaviors and also preserve old behaviors that have been deprecated.

You enable most features by setting a logical name to ENABLE and disable a feature by setting the logical name to DISABLE:
$ DEFINE DECC$feature ENABLE

DEFINE DECC$feature DISABLE
Some feature logical names can be set to a numeric value. For example:
$ DEFINE DECC$PIPE_BUFFER_SIZE 32768

Notes

  • Do not set C RTL feature logical names for the system. Set them only for the applications that need them, because other applications including OpenVMS components depend on the default behavior of these logical names.

  • Older feature logicals from earlier releases of the C RTL were documented as supplying "any equivalence string" to enable a feature. While this was true at one time, we now strongly recommend that you use ENABLE for setting these feature logicals and DISABLE for disabling them. Failure to do so may produce unexpected results.

    The reason for this is twofold:

    • In previous versions of the C RTL, any equivalence string, even DISABLE, may have enabled a feature logical.

    • In subsequent and current versions of the C RTL, the following equivalence strings will disable a feature logical. Do not use them to enable a feature logical.
      • DISABLE
      • 0 (zero)
      • F
      • FALSE
      • N
      • NO

      Any other string not on this list will enable a feature logical. The unintentionally misspelled string "DSABLE", for example, will enable a feature logical.

The C RTL also provides several functions to manage feature logicals within your applications:
decc$feature_get
decc$feature_get_value
decc$feature_get_index
decc$feature_get_name
decc$feature_set
decc$feature_set_value
decc$feature_show
decc$feature_show_all

See the Reference Section for more information on these functions.

Table 1.4 lists the C RTL feature logical names, grouped by the type of features they control.
Table 1.4. C RTL Feature Logical Names

Feature Logical Name

Default

Performance Optimizations

DECC$ENABLE_GETENV_CACHE

DISABLE

DECC$LOCALE_CACHE_SIZE

0

DECC$TZ_CACHE_SIZE

2

Legacy Behaviors

DECC$ALLOW_UNPRIVILEGED_NICE

DISABLE

DECC$NO_ROOTED_SEARCH_LISTS

DISABLE

DECC$PRINTF_USES_VAX_ROUND

DISABLE

DECC$THREAD_DATA_AST_SAFE

DISABLE

DECC$V62_RECORD_GENERATION

DISABLE

DECC$WRITE_SHORT_RECORDS

DISABLE

DECC$XPG4_STRPTIME

DISABLE

File Attributes

DECC$DEFAULT_LRL

32767

DECC$DEFAULT_UDF_RECORD

DISABLE

DECC$FIXED_LENGTH_SEEK_TO_EOF

DISABLE

DECC$ACL_ACCESS_CHECK

DISABLE

DECC$PRN_PRE_BYTE

DISABLE

Mailboxes

DECC$MAILBOX_CTX_STM

DISABLE

Changes for UNIX Conformance

DECC$SELECT_IGNORES_INVALID_FD

DISABLE

DECC$STRTOL_ERANGE

DISABLE

DECC$VALIDATE_SIGNAL_IN_KILL

DISABLE

General UNIX Enhancements

DECC$UNIX_LEVEL

DISABLE

DECC$ARGV_PARSE_STYLE

DISABLE

DECC$PIPE_BUFFER_SIZE

512

DECC$PIPE_BUFFER_QUOTA

512

DECC$STREAM_PIPE

DISABLE

DECC$POPEN_NO_CRLF_REC_ATTR

DISABLE

DECC$STDIO_CTX_EOL

DISABLE

DECC$USE_RAB64

DISABLE

DECC$GLOB_UNIX_STYLE

DISABLE

Enhancements for UNIX Style Filenames

DECC$DISABLE_TO_VMS_LOGNAME_TRANSLATION

DISABLE

DECC$EFS_CHARSET

DISABLE

DECC$ENABLE_TO_VMS_LOGNAME_CACHE

ENABLE

DECC$FILENAME_ENCODING_UTF8

DISABLE

DECC$FILENAME_UNIX_NO_VERSION

DISABLE

DECC$FILENAME_UNIX_REPORT

DISABLE

DECC$READDIR_DROPDOTNOTYPE

DISABLE

DECC$RENAME_NO_INHERIT

DISABLE

DECC$RENAME_ALLOW_DIR

DISABLE

Enhancements for UNIX Style File Attributes

DECC$EFS_FILE_TIMESTAMPS

DISABLE

DECC$EXEC_FILEATTR_INHERITANCE

DISABLE

DECC$FILE_OWNER_UNIX

DISABLE

DECC$FILE_PERMISSION_UNIX

DISABLE

DECC$FILE_SHARING

DISABLE

UNIX Compliance Mode

DECC$DETACHED_CHILD_PROCESS

DISABLE

DECC$FILENAME_UNIX_ONLY

DISABLE

DECC$POSIX_STYLE_UID

DISABLE

DECC$USE_JPI$_CREATOR

DISABLE

New Behaviors for POSIX Conformance

DECC$ALLOW_REMOVE_OPEN_FILES

DISABLE

DECC$POSIX_SEEK_STREAM_FILE

DISABLE

DECC$UMASK

RMS default

File-Name Handling

DECC$POSIX_COMPLIANT_PATHNAMES

DISABLE

DECC$DISABLE_POSIX_ROOT

ENABLE

DECC$EFS_CASE_PRESERVE

DISABLE

DECC$EFS_CASE_SPECIAL

DISABLE

DECC$EFS_NO_DOTS_IN_DIRNAME

DISABLE

DECC$READDIR_KEEPDOTDIR

DISABLE

DECC$UNIX_PATH_BEFORE_LOGNAME

DISABLE

An alphabetic listing and description of the C RTL feature logical names follows. Unless otherwise stated, the feature logicals are enabled with ENABLE and disabled with DISABLE.

DECC$ACL_ACCESS_CHECK

The DECC$ACL_ACCESS_CHECK feature logical controls the behavior of the access function.

With DECC$ACL_ACCESS_CHECK enabled, the access function checks both UIC protection and OpenVMS Access Control Lists (ACLs).

With DECC$ACL_ACCESS_CHECK disabled, the access function checks only UIC protection.

DECC$ALLOW_REMOVE_OPEN_FILES

The DECC$ALLOW_REMOVE_OPEN_FILES feature logical controls the behavior of the remove function on open files. Ordinarily, the operation fails. However, POSIX conformance dictates that the operation succeed.

With DECC$ALLOW_REMOVE_OPEN_FILES enabled, this POSIX conformant behavior is achieved.

DECC$ALLOW_UNPRIVILEGED_NICE

With DECC$ALLOW_UNPRIVILEGED_NICE enabled, the nice function exhibits its legacy behavior of not checking the privilege of the calling process (that is, any user may lower the nice value to increase process priorities). Also, when the caller sets a priority above MAX_PRIORITY, the nice value is set to the base priority.

With DECC$ALLOW_UNPRIVILEGED_NICE disabled, the nice function conforms to the X/Open standard of checking the privilege of the calling process (only users with ALTPRI privilege can lower the nice value to increase process priorities), and when the caller sets a priority above MAX_PRIORITY, the nice value is set to MAX_PRIORITY.

DECC$ARGV_PARSE_STYLE

With DECC$ARGV_PARSE_STYLE enabled, case is preserved in command-line arguments when the process has been set up for extended DCL parsing using SETPROCESS/PARSE_STYLE=EXTENDED.

DECC$ARGV_PARSE_STYLE must be defined externally as a logical name or set in a function called using the LIB$INITIALIZE mechanism because it is evaluated before function main is called.

DECC$DEFAULT_LRL

DECC$DEFAULT_LRL specifies the default value for the RMS attribute for the longest record length. The default value 32767 is the largest record size supported by RMS.

Default: 32767

Maximum: 32767

DECC$DEFAULT_UDF_RECORD

With DECC$DEFAULT_UDF_RECORD enabled, file access mode defaults to RECORD instead of STREAM mode for all files except STREAMLF.

DECC$DETACHED_CHILD_PROCESS

With DECC$DETACHED_CHILD_PROCESS enabled, child processes created using vfork and exec are created as detached processes instead of subprocesses.

This feature has only limited support. In some cases the console cannot be shared between the parent process and the detached process, which can cause exec to fail.

DECC$DISABLE_POSIX_ROOT

With DECC$DISABLE_POSIX_ROOT enabled, support for the POSIX root directory defined by SYS$POSIX_ROOT is disabled.

With DECC$DISABLE_POSIX_ROOT disabled, the SYS$POSIX_ROOT logical name is interpreted as the equivalent of the file path "/". If a UNIX path starting with a slash (/) is given and the value after the leading slash cannot be translated as a logical name, SYS$POSIX_ROOT is used as the parent directory for the specified UNIX file path.

The C RTL supports a UNIX style root that behaves like a real directory. This allows such actions as:
% cd /
% mkdir /dirname
% tar -xvf tarfile.tar /dirname
% ls /
Previously, the C RTL did not recognize "/" as a directory name. The normal processing for a file path starting with "/" was to interpret the first element as a logical name or device name. If this failed, there was special processing for the name /dev/null and names starting with /bin and /tmp:
/dev/null       NLA0:
/bin            SYS$SYSTEM:
/tmp            SYS$SCRATCH:

These behaviors are retained for compatibility purposes. In addition, support has been added to the C RTL for the logical name SYS$POSIX_ROOT as an equivalent to "/".

To enable this feature for use by the C RTL, define SYS$POSIX_ROOT as a concealed logical name. For example:
$ DEFINE/TRANSLATION=(CONCEALED,TERMINAL) SYS$POSIX_ROOT "$1$DKA0:[SYS0.abc.]"
To disable this feature:
$ DEFINE DECC$DISABLE_POSIX_ROOT DISABLE
Enabling SYS$POSIX_ROOT results in the following behavior:

  • If the existing translation of a UNIX path starting with "/" fails and SYS$POSIX_ROOT is defined, the name is interpreted as if it starts with /sys$posix_root.

  • When converting from an OpenVMS to a UNIX style filename, and the OpenVMS name starts with "SYS$POSIX_ROOT:", then the "SYS$POSIX_ROOT:" is removed. For example, SYS$POSIX_ROOT:[dirname] becomes /dirname. If the resulting name could be interpreted as a logical name or one of the special cases previously listed, the result is /./dirname instead of /dirname.

DECC$DISABLE_TO_VMS_LOGNAME_TRANSLATION

With DECC$DISABLE_TO_VMS_LOGNAME_TRANSLATION enabled, the conversion routine decc$to_vms will only treat the first element of a UNIX style name as a logical name if there is a leading slash (/).

DECC$EFS_CASE_PRESERVE

With DECC$EFS_CASE_PRESERVE enabled, case is preserved for filenames on ODS-5 disks.

With DECC$EFS_CASE_PRESERVE disabled, UNIX style filenames are always reported in lowercase.

However, note that enabling DECC$EFS_CASE_SPECIAL overrides the setting for DECC$EFS_CASE_PRESERVE.

DECC$EFS_CASE_SPECIAL

With DECC$EFS_CASE_SPECIAL enabled, case is preserved only for filenames containing lowercase. If an element of a filename contains all uppercase letters, it is reported in all lowercase in UNIX style.

When enabled, DECC$EFS_CASE_SPECIAL overrides the value of DECC$EFS_CASE_PRESERVE.

DECC$EFS_CHARSET
With DECC$EFS_CHARSET enabled, UNIX names can contain ODS-5 extended characters. Support includes multiple dots and all ASCII characters in the range 0 to 255, except the following:
<NUL>      /         *"         ?
Unless DECC$FILENAME_UNIX_ONLY is enabled, some characters can be interpreted as OpenVMS characters depending on context. They are:
:         ^[         ;<
DECC$EFS_CHARSET might be necessary for existing applications that make assumptions about filenames based on the presence of certain characters, because the following nonstandard and undocumented C RTL extensions do not work when EFS extended character-set support is enabled:

  • $HOME is interpreted as the user's login directory

    With DECC$EFS_CHARSET enabled, $HOME is treated literally and may be in an OpenVMS or UNIX style filename.

  • ~name is interpreted as the login directory for user name

    With DECC$EFS_CHARSET enabled, ~name is treated literally and can be in an OpenVMS or UNIX style filename.

  • Wild card regular expressions in the form [a-z]

    With DECC$EFS_CHARSET enabled, square brackets are acceptable in OpenVMS and UNIX style filenames. For instance, in a function such as open, abc[a-z]ef.txt is interpreted as a UNIX style name equivalent to the OpenVMS style name abc^[a-z^]ef.txt, and [a-z]bc is interpreted asan OpenVMS style name equivalent to the UNIX style name /sys$disk/a-z/bc.

With DECC$EFS_CHARSET enabled, the following encoding for EFS extended characters is supported when converting from an OpenVMS style filename to a UNIX style filename:

  • All ODS-2 compatible names

  • All encoding for 8-bit characters, either as single byte or using two-digit hexadecimal form ^ab. In a UNIX path these are always represented as a single byte.

  • Encoding for DEL (^7F)

  • The following characters when preceded by a caret:
    space ! , _ & ' ( ) + @ { } ; # [ ] % ^ = $ - ~ .
  • The following characters when not preceded by a caret:
    $  -  ~  .

  • The implementation supports the conversion from OpenVMS to UNIX needed for functions readdir, ftw, getname, fgetname, getcwd, and others.


Note

There are some special cases in C RTL filename processing. For example:

  • Pathnames ending in ^.dir are treated as directories, and when translated, these characters are truncated from the string.

  • Pathnames beginning with ^/ treat the next token as a logical name or a directory from the root.

The following sample program shows these nuances:
#include <stdio.h>
#include <dirent.h>
#include <unixlib.h>
#include <string.h>
main()
{
  char adir[80];
  DIR *dir;
  struct dirent *dp;
  int decc_feature_efs_charset_index = 0;
  int decc_feature_efs_charset_default_val = 0;

  if (
      ( (decc_feature_efs_charset_index =
        decc$feature_get_index("DECC$EFS_CHARSET")) == -1 )
      ||
      ( (decc_feature_efs_charset_default_val =
        decc$feature_get_value(decc_feature_efs_charset_index, 0)) == -1 )
      ||
      ( (decc$feature_set_value(decc_feature_efs_charset_index, 1, TRUE) == -1))
     )
    {
      printf("Error setting up DECC$EFS_CHARSET macro\n");
    }

  strcpy(adir, "SYS$SYSDEVICE:[SSHTEST.TEST.a^,test^.dir^;22]");
  printf("\n\nFor %s\n", adir);
mrb:  dir = opendir(adir);
  if(dir)
    {
      do
        {
          dp = readdir(dir);
          if(dp->d_name) printf("%s\n", dp->d_name);
        } while (dp);
    }

  closedir(dir);

  strcpy(adir, "SYS$SYSDEVICE:[SSHTEST.TEST.a^,test^.dir]");
  printf("\n\nFor %s\n", adir);
  dir = opendir(adir);
  if(dir)
    {
      do
        {
          dp = readdir(dir);
          if(dp->d_name) printf("%s\n", dp->d_name);
        } while (dp);
    }

  closedir(dir);

  strcpy(adir, "SYS$SYSDEVICE:[SSHTEST.TEST.a^\\test]");
  printf("\n\nFor %s\n", adir);
  dir = opendir(adir);
  if(dir)
    {
      do
        {
          dp = readdir(dir);
          if(dp->d_name) printf("%s\n", dp->d_name);
        } while (dp);
    }

  strcpy(adir, "SYS$SYSDEVICE:[SSHTEST.TEST.copies]");
  printf("\n\nFor %s\n", adir);
  dir = opendir(adir);
  if(dir)
    {
      do
        {
          dp = readdir(dir);
          if(dp->d_name) printf("%s\n", dp->d_name);
        } while (dp);
    }

  closedir(dir);

  strcpy(adir, "/SYS$SYSDEVICE/SSHTEST/TEST/copies");
  printf("\n\nFor %s\n", adir);
  dir = opendir(adir);
  if(dir)
    {
      do
        {
          dp = readdir(dir);
          if(dp->d_name) printf("%s\n", dp->d_name);
        } while (dp);
    }

  closedir(dir);

}
DECC$EFS_FILE_TIMESTAMPS

With DECC$EFS_FILE_TIMESTAMPS enabled, stat and fstat report new ODS-5 access time (st_atime), attribute revision time (st_ctime) and modification time (st_mtime) for files on ODS-5 volumes that have the extended file times enabled using SET VOLUME/VOLUME=ACCESS_DATES.

If DECC$EFS_FILE_TIMESTAMPS is disabled, or the volume is not ODS-5, or the volume does not have support for these additional times enabled, st_ctime continues to be the file creation time and st_atime the same as the st_mtime.

The utime and utimes functions support these ODS-5 times in the same way as stat.

DECC$EFS_NO_DOTS_IN_DIRNAME

With support for extended characters in filenames for ODS-5, a name such as NAME.EXT can be interpreted as NAME.EXT.DIR. Determining if directory [.name^.ext] exists adds overhead to UNIX name translation when support for extended character support in UNIX filenames is enabled.

Enabling the DECC$EFS_NO_DOTS_IN_DIRNAME feature logical suppresses the interpretation of a filename containing dots as a directory name. With this logical enabled, NAME.EXT is assumed to be a filename; no check is made for directory [.name^.ext].

DECC$ENABLE_GETENV_CACHE

The C RTL supplements the list of environment variables in the environ table with all logical names and DCL symbols available to the process.

By default, whenever getenv is called for a name not in the environ table, an attempt is made to resolve this as a logical name and, if this fails, as a DCL symbol.

With DECC$ENABLE_GETENV_CACHE enabled, once a logical name or DCL name has been successfully translated, its value is stored in a cache. When the same name is requested in a future call to getenv, the value is returned from the cache instead of reevaluating the logical name or DCL symbol.

DECC$ENABLE_TO_VMS_LOGNAME_CACHE

Use the DECC$ENABLE_TO_VMS_LOGNAME_CACHE to improve the performance of UNIX name translation. The value is the life of each cache entry in seconds. The equivalence string ENABLE is evaluated as 1 second.

Define DECC$ENABLE_TO_VMS_LOGNAME_CACHE to 1 to enable the cache with a 1-second life for each entry.

Define DECC$ENABLE_TO_VMS_LOGNAME_CACHE to 2 to enable the cache with a 2-second life for each entry.

Define DECC$ENABLE_TO_VMS_LOGNAME_CACHE to -1 to enable the cache without a cache entry expiration.

DECC$EXEC_FILEATTR_INHERITANCE

The DECC$EXEC_FILEATTR_INHERITANCE feature logical affects child processes that are C programs.

For versions of OpenVMS before Version 7.3-2, DECC$EXEC_FILEATTR_INHERITANCE is either enabled or disabled:

  • With DECC$EXEC_FILEATTR_INHERITANCE enabled, the current file pointer and the file open mode is passed to the child process in exec calls.

  • With this logical name disabled, the child process does not inherit append mode or the file position.

For OpenVMS Version 7.3-2 and higher, DECC$EXEC_FILEATTR_INHERITANCE can be defined to 1 or 2, or be disabled:

  • With DECC$EXEC_FILEATTR_INHERITANCE defined to 1, a child process inherits file positioning for all file access modes except append.

  • With DECC$EXEC_FILEATTR_INHERITANCE defined to 2, a child process inherits file positioning for all file access modes including append.

  • With DECC$EXEC_FILEATTR_INHERITANCE disabled, a child process does not inherit the file position for any access modes.

DECC$FILENAME_ENCODING_UTF8

C RTL routines that deal with filenames now support filenames in UTF-8 encoding when given in UNIX style.

For example, on an ODS-5 disk the OpenVMS DIRECTORY command supports a filename with the following characters: 
disk:[mydir]^U65E5^U672C^U8A9E.txt

This filename contains three UCS-2 characters (call them xxx, yyy, and zzz for typographical purposes) meaning "day", "origin", and "language", respectively.

With UTF-8 support enabled, a C program can now read the filename from the VMS directory and use that filename as an UTF-8 encoded string.

For example, opendir("/disk/mydir") followed by a readdir will place the following into the d_name field of the supplied dirent structure:
"\xE6\x97\xA5\xE6\x9C\xAC\xE8\xAA\x9E.txt"
One of the following calls can then open this file: 
open("/disk/mydir/\xE6\x97\xA5\xE6\x9C\xAC\xE8\xAA\x9E.txt",O_RDWR,0)
open("/disk/mydir/xxxyyyzzz.txt", O_RDWR,0)

The "\xE6\x97\xA5" above is the byte stream E697A5, which represents the xxx character in UTF-8 encoding. See the following example, where the actual characters comprising the filename are shown:

Figure 1.2. Unicode Example
Unicode Example

This feature enhances the UNIX portability of international software that uses UTF-8 encoded filenames.

The DECC$FILENAME_ENCODING_UTF8 feature logical controls whether or not the C RTL allows and correctly interprets Unicode UTF-8 encoding for filenames given in UNIX style.

This logical is undefined by default, and the C RTL behavior is to accept filenames as ASCII and Latin-1 format.

This feature works only on ODS-5 disks. Therefore, to enable Unicode UTF-8 encoding, you must define both the DECC$FILENAME_ENCODING_UTF8 and DECC$EFS_CHARSET logicals to ENABLE.

DECC$FILENAME_UNIX_ONLY
With DECC$FILENAME_UNIX_ONLY enabled, filenames are never interpreted as OpenVMS style names. This prevents any interpretation of the following as OpenVMS special characters:
:   [   ^
DECC$FILENAME_UNIX_NO_VERSION

With DECC$FILENAME_UNIX_NO_VERSION enabled, OpenVMS version numbers are not supported in UNIX style filenames.

With DECC$FILENAME_UNIX_NO_VERSION disabled, in UNIX style names, version numbers are reported preceded by a period (.).

DECC$FILENAME_UNIX_REPORT

With DECC$FILENAME_UNIX_REPORT enabled, all filenames are reported in UNIX style unless the caller specifically selects OpenVMS style. This applies to getpwnam, getpwuid, argv[0], getname, fgetname, and tempnam.

With DECC$FILENAME_UNIX_REPORT disabled, unless specified in the function call, filenames are reported in OpenVMS style.

DECC$FILE_OWNER_UNIX

When DECC$FILE_OWNER_UNIX is enabled, the owner for a new file or directory is always based on the effective UIC. When an earlier version of the file exists, the owner for the new file is inherited from this.

When disabled, the owner for a new file is set following VMS rules and may inherit the owner from the parent directory.

DECC$FILE_PERMISSION_UNIX

With DECC$FILE_PERMISSION_UNIX enabled, the file permissions for new files and directories are set according to the file creation mode and umask. This includes mode 0777. When an earlier version of the file exists, the file permissions for the new file are inherited from the earlier version. This mode sets DELETE permission for a new directory when WRITE permission is enabled.

With DECC$FILE_PERMISSION_UNIX disabled, modes 0 and 0777 indicate using RMS default protection or protection from the previous version of the file. Permissions for new directories also follow OpenVMS rules, including disabling DELETE permissions.

DECC$FILE_SHARING

With DECC$FILE_SHARING enabled, all files are opened with full sharing enabled (FAB$M_DEL | FAB$M_GET | FAB$M_PUT | FAB$M_UPD). This is set as a logical OR with any sharing mode specified by the caller.

DECC$FIXED_LENGTH_SEEK_TO_EOF

With DECC$FIXED_LENGTH_SEEK_TO_EOF enabled, lseek, fseeko, and fseek with the direction parameter set to SEEK_END will position relative to the last byte in the file for files with fixed-length records.

With DECC$FIXED_LENGTH_SEEK_TO_EOF disabled, lseek, fseek, and fseeko when called with SEEK_EOF on files with fixed-length records, will position relative to the end of the last record in the file.

DECC$GLOB_UNIX_STYLE

Enabling DECC$GLOB_UNIX_STYLE selects the UNIX mode of the glob function, which uses UNIX style filenames and wildcards instead of OpenVMS style filenames and wildcards.

DECC$LOCALE_CACHE_SIZE

DECC$LOCALE_CACHE_SIZE defines how much memory, in categories, to allocate for caching locale data. The default value is 0, which disables the locale cache.

Default: 0

Maximum: 2147483647

DECC$MAILBOX_CTX_STM

By default, an open on a local mailbox that is not a pipe treats mailbox records as having a record attribute of FAB$M_CR.

With DECC$MAILBOX_CTX_STM enabled, the record attribute FAB$M_CR is not set.

DECC$NO_ROOTED_SEARCH_LISTS
When the decc$to_vms function evaluates a UNIX style path string, if it determines the first element to be a logical name, then:

  • For rooted logicals or devices, it appends ":[000000]" to the logical name.

    For example, if log1 is a rooted logical ($DEFINE LOG1[DIR_NAME.]) then /log1/filename.ext translates to LOG1:[000000]FILENAME.EXT.

  • For nonrooted logicals, it appends just a colon (:) to the logical name.

    For example, if log2 is a nonrooted logical ($ DEFINE LOG2[DIR_NAME]), then /log2/filename.ext translates to LOG2:FILENAME.EXT.

  • If the first element is a search-list logical, the translation proceeds by evaluating the first element in the search list, and translating the path as previously described.

The preceding three cases lead to predictable, expected results.

In the case where the first element is a search list that consists of a mixture of rooted and nonrooted logicals, translating paths as described previously can lead to different behavior from that of older versions of OpenVMS (before OpenVMS Version 7.3-1):

  • Before OpenVMS Version 7.3-1, regardless of the contents of the logical, the decc$to_vms function appended only a colon (:). For search lists that consisted of a mixture of rooted and nonrooted logicals, this resulted in certain expected behaviors.

  • For OpenVMS Version 7.3-1 and later, if the first element of the mixed search list is a rooted logical, then decc$to_vms appends ":[000000]" to the logical name, resulting in different behavior from that of OpenVMS releases prior to Version 7.3-1.

DECC$NO_ROOTED_SEARCH_LISTS controls how the decc$to_vms function resolves search-list logicals and provides a means to restore the OpenVMS behavior prior to Version 7.3-1.

With DECC$NO_ROOTED_SEARCH_LISTS enabled:

  • If a logical is detected in a file specification, and it is a search list, then a colon (:) is appended when forming the OpenVMS file specification.

  • If it is not a search list, the behavior is the same as with DECC$NO_ROOTED_SEARCH_LISTS disabled.

Enabling this feature logical provides the pre-Version 7.3-1 behavior for search list logicals.

With DECC$NO_ROOTED_SEARCH_LISTS disabled:

  • If a logical is detected in a file specification, and it is a rooted logical (or a search list whose first element is a rooted logical), then ":[000000]" is appended when forming the OpenVMS file specification.

  • If it is a nonrooted logical (or a search list whose first element is a nonrooted logical), then just a colon (:) is appended.

Disabling this feature logical provides the behavior for OpenVMS Version 7.3-1 and later.

DECC$PIPE_BUFFER_QUOTA

OpenVMS Version 7.3-2 adds an optional fourth argument of type int to the pipe function to specify the buffer quota of the pipe's mailbox. In previous OpenVMS versions, the buffer quota was equal to the buffer size.

DECC$PIPE_BUFFER_QUOTA lets you specify a buffer quota to use for the pipe function if the optional fourth argument of that function is omitted.

If the optional pipe fourth argument is omitted and DECC$PIPE_BUFFER_QUOTA is not defined, then the buffer quota defaults to the buffer size, as before.

Default: 512

Minimum: 512

Maximum: 2147483647

DECC$PIPE_BUFFER_SIZE

The system default buffer size of 512 bytes for pipe write operations can limit performance and generate extra line feeds when handling messages longer than 512 bytes.

DECC$PIPE_BUFFER_SIZE allows a larger buffer size to be used for pipe functions such as pipe and popen. A value of 512 to 65535 bytes can be specified.

If DECC$PIPE_BUFFER_SIZE is not specified, the default buffer size 512 is used.

Default: 512

Minimum: 512

Maximum: 65535

DECC$POPEN_NO_CRLF_REC_ATTR

With DECC$POPEN_NO_CRLF_REC_ATTR disabled, a pipe opened with the popen function has its record attributes set to CR/LF carriage control (fab$b_rat |= FAB$M_CR). This is the default behavior.

With DECC$POPEN_NO_CRLF_REC_ATTR enabled, CR/LF carriage control is prevented from being added to the pipe records. This is compatible with UNIX behavior, but be aware that enabling this feature might result in undesired behavior from other functions, such as gets, that rely on the carriage-return character.

DECC$POSIX_COMPLIANT_PATHNAMES

With DECC$POSIX_COMPLIANT_PATHNAMES enabled, an application is allowed to present POSIX-compliant pathnames to any C RTL function that accepts a pathname.

By default DECC$POSIX_COMPLIANT_PATHNAMES is disabled, and the usual C RTL behavior prevails. This disabled mode includes interpretation of pathnames as UNIX style specifications and uses rules that are different and unrelated to POSIX-compliant pathname processing.

To enable DECC$POSIX_COMPLIANT_PATHNAMES, set it to one of the following values:

1

All pathnames are designated as POSIX style.

2

Pathnames that end in ":" or contain any of the bracket characters " []<>", and that can be successfully parsed by the SYS$FILESCAN service, are designated as OpenVMS style. Otherwise, they are designated as POSIX style.

3

The pathnames "." and "..", or pathnames that contain "/"are designated as POSIX style. Otherwise, they are designated as OpenVMS style.

4

All pathnames are designated as OpenVMS style.

See Section 13.3.1 for more information

DECC$POSIX_SEEK_STREAM_FILE

With DECC$POSIX_SEEK_STREAM_FILE enabled, positioning beyond end-of-file on STREAM files does not write to the file until the next write. If the write is beyond the current end-of-file, this positions beyond the old end-of-file, and the start position for the write is filled with zeros.

With DECC$POSIX_SEEK_STREAM_FILE disabled, positioning beyond end-of-file will immediately write zeros to the file from the current end-of-file to the new position.

DECC$POSIX_STYLE_UID

With DECC$POSIX_STYLE_UID enabled, 32-bit UIDs and GIDs are interpreted as POSIX style identifiers.

With this logical name disabled, UIDs and GIDs are derived from the process UIC.

This feature is only available on OpenVMS systems providing POSIX style UID and GID support.

DECC$PRINTF_USES_VAX_ROUND

With DECC$PRINTF_USES_VAX_ROUND enabled, the F and E format specifiers of printf use VAX rounding rules for programs compiled with IEEE float.

DECC$PRN_PRE_BYTE

A change introduced by Hewlett Packard Enterprise (HPE) during OpenVMS V8.4 maintenance allowed systems that used the CIFS product (SAMBA) to display files in the appropriate format. However, that change affected files with PRINT carriage control (also known as FORTRAN carriage control). For some environments, the print codes that are removed when transferring files between systems cause incorrect printing behavior resulting in form feeds being lost.

When enabled, DECC$PRN_PRE_BYTE converts the print codes in files that have PRINT file carriage control to their ASCII control code equivalents. CIFS then sends them to the client.

Enabling DECC$PRN_PRE_BYTE, in addition to enabling the logical DECC$TERM_REC_CRLF, which is used by CIFS, correctly includes the print codes on transferred files.

To enable the DECC$PRN_PRE_BYTE logical feature, set it to ENABLE.
$ DEFINE/SYSTEM DECC$PRN_PRE_BYTE ENABLE
DECC$READDIR_DROPDOTNOTYPE

With DECC$READDIR_DROPDOTNOTYPE enabled, readdir when reporting files in UNIX style only reports the trailing period (.) for files with no file type when the filename contains a period.

With this logical name disabled, all files without a file type are reported with a trailing period.

DECC$READDIR_KEEPDOTDIR

The default behavior when reporting files in UNIX style from readdir is to report directories without a file type.

With DECC$READDIR_KEEPDOTDIR enabled, directories are reported in UNIX style with a file type of ".DIR".

DECC$RENAME_NO_INHERIT
DECC$RENAME_NO_INHERIT provides more UNIX compliant behavior in the rename function. With DECC$RENAME_NO_INHERIT enabled, the following behaviors are enforced:

  • If the old argument points to the pathname of a file that is not a directory, the new argument will not point to the pathname of a directory.

  • The new argument cannot point to a directory that exists.

  • If the old argument points to the pathname of a directory, the new argument will not point to the pathname of a file that is not a directory.

  • The new name for the file does not inherit anything from the old name. The new name must be specified completely. For example:

    Renaming "A.A" to "B" yields "B"

With this logical name disabled, you get the expected OpenVMS behavior. For example:

Renaming "A.A" to "B" yields "B.A"

DECC$RENAME_ALLOW_DIR
Enabling DECC$RENAME_ALLOW_DIR restores the prior OpenVMS behavior of the rename function by allowing conversion to a directory specification when the second argument is an ambiguous file specification passed as a logical name. The ambiguity is whether the logical name is a UNIX or OpenVMS file specification. Consider the following example with DECC$RENAME_ALLOW_DIR enabled:
rename("file.ext", "logical_name") /* where logical_name = dev:[dir.subdir] */
                                   /* and :[dir.subdir] exists.             */
This results in: 
dev:[dir.subdir]file.ext

This example renames a file from one directory into another directory, which is the same behavior as in legacy versions of OpenVMS (versions before 7.3-1). Also in this example, if dev:[dir.subdir] does not exist, rename returns an error.

Disabling DECC$RENAME_ALLOW_DIR provides a more UNIX compliant conversion of the "logical_name" argument of rename. Consider the following example with DECC$RENAME_ALLOW_DIR disabled: 
rename("file.ext", "logical_name") /* where logical_name = dev:[dir.subdir] */
This results in:
dev:[dir]subdir.ext

This example renames the file using the subdir part of the "logical_name" argument as the new filename because on UNIX systems, renaming a file to a directory is not allowed. So rename internally converts the "logical_name" to a filename, and dev:[dir]subdir is the most reasonable conversion it can perform.

This new feature switch has a side effect of causing rename to a directory to take precedence over rename to a file. Consider this example: 
rename ( "file1.ext", "dir2" )      /* dir2 is not a logical */

With DECC$RENAME_ALLOW_DIR disabled, this example results in dir2.ext, regardless of whether or not subdirectory [.dir2] exists.

With DECC$RENAME_ALLOW_DIR enabled, this example results in dir2.ext only if subdirectory [.dir2] does not exist. If subdirectory [.dir2] does exist, the result is [.dir2]file1.ext.

Note

If DECC$RENAME_NO_INHERIT is enabled, UNIX compliant behavior is expected, so DECC$RENAME_ALLOW_DIR is ignored, and renaming a file to a directory is not allowed.

DECC$SELECT_IGNORES_INVALID_FD

With DECC$SELECT_IGNORES_INVALID_FD disabled, select and poll fail with errno set to EBADF when an invalid file descriptor is specified in one of the descriptor sets.

With DECC$SELECT_IGNORES_INVALID_FD enabled, select and poll ignore invalid file descriptors.

DECC$STDIO_CTX_EOL

With DECC$STDIO_CTX_EOL enabled, writing to stdout and stderr for stream access is deferred until a terminator is seen or the buffer is full.

With DECC$STDIO_CTX_EOL disabled, each fwrite generates a separate write, which for mailbox and record files generates a separate record.

DECC$STREAM_PIPE

With DECC$STREAM_PIPE enabled, the C RTL pipe function uses the more UNIX compatible stream I/O.

With DECC$STREAM_PIPE disabled, pipe uses the OpenVMS legacy record I/O. This is the default.

DECC$STRTOL_ERANGE

With DECC$STRTOL_ERANGE enabled, the strtol behavior for an ERANGE error is corrected to consume all remaining digits in the string.

With DECC$STRTOL_ERANGE disabled, the legacy behavior of leaving the pointer at the failing digit is preserved.

DECC$THREAD_DATA_AST_SAFE

The C RTL has a mode that allocates storage for thread-specific data allocated by threads at non-AST level separate for data allocated for ASTs. In this mode, each access to thread-specific data requires a call to LIB$AST_IN_PROG, which can add significant overhead when accessing thread-specific data in the C RTL.

The alternate mode protects thread-specific data only if another function has it locked. This protects data that is in use within the C RTL, but does not protect the caller from an AST changing the data pointed to.

This latter mode is now the C RTL default for the strtok, ecvt, and fcvt functions.

You can select the legacy AST safe mode by enabling DECC$THREAD_DATA_AST_SAFE.

DECC$TZ_CACHE_SIZE

DECC$TZ_CACHE_SIZE specifies the number of time zones that can be held in memory.

Default: 2

Maximum: 2147483647

DECC$UMASK

DECC$UMASK specifies the default value for the permission mask umask. By default, a parent C program sets the umask from the RMS default permissions for the process. A child process inherits the parent's value for umask.

To enter the value as an octal value, add the leading zero; otherwise, it is translated as a decimal value. For example: 
$ DEFINE DECC$UMASK 026

Maximum: 0777

DECC$UNIX_LEVEL

With the DECC$UNIX_LEVEL logical name, you can manage multiple C RTL feature logical names at once. By setting a value for DECC$UNIX_LEVEL from 1 to 100, you determine the default value for groups of feature logical names. The value you set has a cumulative effect: the higher the value, the more groups that are affected. Setting a value of 20, for example, enables all the feature logicals associated with a DECC$UNIX_LEVEL of 20, 10, and 1.

The principal logical names affecting UNIX like behavior are grouped as follows:
  • 1 General corrections
  • 10 Enhancements
  • 20 UNIX style filenames
  • 30 UNIX style file attributes
  • 90 Full UNIX behavior - No concessions to OpenVMS

Level 30 is appropriate for UNIX like programs such as BASH and GNV.

The DECC$UNIX_LEVEL values and associated groups of affected feature logical names are: 
General Corrections          (DECC$UNIX_LEVEL 1)

   DECC$FIXED_LENGTH_SEEK_TO_EOF   1
   DECC$POSIX_SEEK_STREAM_FILE     1
   DECC$SELECT_IGNORES_INVALID_FD  1
   DECC$STRTOL_ERANGE              1
   DECC$VALIDATE_SIGNAL_IN_KILL    1

General Enhancements        (DECC$UNIX_LEVEL 10)

   DECC$ARGV_PARSE_STYLE           1
   DECC$EFS_CASE_PRESERVE          1
   DECC$STDIO_CTX_EOL              1
   DECC$PIPE_BUFFER_SIZE           4096
   DECC$USE_RAB64                  1

UNIX style filenames       (DECC$UNIX_LEVEL 20)

   DECC$DISABLE_TO_VMS_LOGNAME_TRANSLATION 1
   DECC$EFS_CHARSET                1
   DECC$FILENAME_UNIX_NO_VERSION   1
   DECC$FILENAME_UNIX_REPORT       1
   DECC$READDIR_DROPDOTNOTYPE      1
   DECC$RENAME_NO_INHERIT          1
   DECC$GLOB_UNIX_STYLE

UNIX like file attributes     (DECC$UNIX_LEVEL 30)

   DECC$EFS_FILE_TIMESTAMPS        1
   DECC$EXEC_FILEATTR_INHERITANCE  1
   DECC$FILE_OWNER_UNIX            1
   DECC$FILE_PERMISSION_UNIX       1
   DECC$FILE_SHARING               1

UNIX compliant behavior       (DECC$UNIX_LEVEL 90)

   DECC$FILENAME_UNIX_ONLY         1
   DECC$POSIX_STYLE_UID            1
   DECC$USE_JPI$_CREATOR           1
   DECC$DETACHED_CHILD_PROCESS     1

Notes

  • Defining a logical name for an individual feature logical supersedes the default value established by DECC$UNIX_LEVEL for that feature.

  • Future revisions of the C RTL may add new feature logicals to a given DECC$UNIX_LEVEL. For applications that specify that UNIX level, the effect is to enable those new feature logicals by default.

DECC$UNIX_PATH_BEFORE_LOGNAME

With DECC$UNIX_PATH_BEFORE_LOGNAME enabled, when translating a UNIX filename not starting with a leading slash (/), an attempt is made to match this to a file or directory in the current directory. If this is not found and the name is valid as a logical name in an OpenVMS filename, an attempt is made to translate the logical name and, if found, is used as part of the resulting filename.

Enabling DECC$UNIX_PATH_BEFORE_LOGNAME overrides the setting for DECC$DISABLE_TO_VMS_LOGNAME_TRANSLATION.

DECC$USE_JPI$_CREATOR

When enabled, DECC$USE_JPI$_CREATOR determines the parent process ID in getppid by calling $GETJPI using item JPI$_CREATOR instead of JPI$_OWNER.

This feature is only available on systems supporting POSIX style session identifiers.

DECC$USE_RAB64

With DECC$USE_RAB64 enabled, open functions allocate a RAB64 structure instead of the traditional RAB structure.

This provides latent support for file buffers in 64-bit memory.

DECC$VALIDATE_SIGNAL_IN_KILL

With DECC$VALIDATE_SIGNAL_IN_KILL enabled, a signal value that is in the range 0 to _SIG_MAX but is not supported by the C RTL generates an error with errno set to EINVAL, which makes the behavior the same as for raise.

With this logical name disabled, validation of signals is restricted to checking that the signal value is in the range 0 to _SIG_MAX. If sys$sigprc fails, errno is set based on sys$sigprc exit status.

DECC$V62_RECORD_GENERATION

OpenVMS Versions 6.2 and higher can output record files using different rules.

With DECC$V62_RECORD_GENERATION enabled, the output mechanism follows the rules used for OpenVMS Version 6.2.

DECC$WRITE_SHORT_RECORDS

The DECC$WRITE_SHORT_RECORDS feature logical supports a previous change to the fwrite function (to accommodate writing records with size less than the maximum record size), while retaining the legacy way of writing records to a fixed-length file as the default behavior:

With DECC$WRITE_SHORT_RECORDS enabled, short-sized records (records with size less than the maximum record size) written at EOF are padded with zeros to align records on record boundaries. This is the behavior seen in OpenVMS Version 7.3-1 and some ACRTL ECOs of that time period.

With DECC$WRITE_SHORT_RECORDS disabled, the legacy behavior of writing records with no padding is implemented. This is the recommended and default behavior.

DECC$XPG4_STRPTIME

XPG5 support for strptime introduces pivoting year support so that years in the range 0 to 68 are in the 21st century, and years in the range 69-99 are in the 20th century.

With DECC$XPG4_STRPTIME enabled, XPG5 support for the pivoting year is disabled and all years in the range 0 to 99 are in the current century.

1.6. 32-Bit UIDs/GIDs and POSIX Style Identifiers

Where supported in versions of the OpenVMS operating system, POSIX style identifiers refers to the User Identifier (UID), Group Identifier (GID), and Process Group. The scope includes real and effective identifiers.

The support for POSIX style identifiers in the C RTL requires 32-bit user and group ID support and also depends on features in the base version of OpenVMS. POSIX style IDs are supported by OpenVMS Version 7.3-2 and higher.

To use POSIX style identifiers on OpenVMS versions that support them requires applications to be compiled for 32-bit UID/GID. On OpenVMS versions where 32-bit UID/GID is the default, the user or application must still enable POSIX style IDs by defining the DECC$POSIX_STYLE_UID feature logical name:
$ DEFINE DECC$POSIX_STYLE_UID ENABLE

With POSIX style IDs enabled, at compile time you can selectively invoke the traditional (UIC-based) definition for an individual function by explicitly calling it by its decc$-prefixed entry point (as opposed to the decc$__long_gid_-prefixed entry point, which provides the POSIX style behavior).

To disable POSIX style IDs:
$ DEFINE DECC$POSIX_STYLE_UID DISABLE

OpenVMS Version 7.3-2 and higher supports POSIX style IDs as well as 32-bit UID/GIDs. When an application is compiled to use 32-bit UID/GIDs, the UID and GID are derived from the UIC as in previous versions of the operating system. In some cases, such as with the getgroups function, more information may be returned when the application supports 32-bit GIDs.

To compile an application for 16-bit UID/GID support on systems that by default use 32-bit UIDs/GIDs, define the _DECC_SHORT_GID_T macro to 1.

1.7. Input and Output on OpenVMS Systems

After you learn how to link with the C RTL and call VSI C functions and macros, you can use the C RTL for its primary purpose: input/output (I/O).

Since every system has different methods of I/O, familiarize yourself with the OpenVMS specific methods of file access. In this way, you will be equipped to predict functional differences when porting your source program from one operating system to another.

Figure 1.3 shows the I/O methods available with the C RTL. The OpenVMS system services communicate directly with the OpenVMS operating system, so they are closest to the operating system. The OpenVMS Record Management Services (RMS) functions use the system services, which manipulate the operating system. The VSI C Standard I/O and UNIX I/O functions and macros use the RMS functions. Since the C RTL Standard I/O and UNIX I/O functions and macros must go through several layers of function calls before the system is manipulated, they are furthest from the operating system.

Figure 1.3. I/O Interface from C Programs
I/O Interface from C Programs

The C programming language was developed on the UNIX operating system, and the Standard I/O functions were designed to provide a convenient method of I/O that would be powerful enough to be efficient for most applications, and also be portable so that the functions could be used on any system running C language compilers.

The C RTL adds functionality to this original specification. Since, as implemented in the C RTL, the Standard I/O functions recognize line terminators, the C RTL Standard I/O functions are particularly useful for text manipulation. The C RTL also implements some of the Standard I/O functions as preprocessor-defined macros.

In a similar manner, the UNIX I/O functions originally were designed to provide a more direct access to the UNIX operating systems. These functions were meant to use a numeric file descriptor to represent a file. A UNIX system represents all peripheral devices as files to provide a uniform method of access.

The C RTL adds functionality to the original specification. The UNIX I/O functions, as implemented in VSI C, are particularly useful for manipulating binary data. The C RTL also implements some of the UNIX I/O functions as preprocessor-defined macros.

The C RTL includes the Standard I/O functions that should exist on all C compilers, and also the UNIX I/O functions to maintain compatibility with as many other implementations of C as possible. However, both Standard I/O and UNIX I/O use RMS to access files. To understand how the Standard I/O and UNIX I/O functions manipulate RMS formatted files, learn the fundamentals of RMS. See Section 1.7.1 for more information about Standard I/O and UNIX I/O in relationship to RMS files. For an introduction to RMS, see the VSI OpenVMS Guide to OpenVMS File Applications.

Before deciding which method is appropriate for you, first ask this question: Are you concerned with UNIX compatibility or with developing code that will run solely under the OpenVMS operating system?

  • If UNIX compatibility is important, you probably want to use the highest levels of I/O—Standard I/O and UNIX I/O—because that level is largely independent of the operating system. Also, the highest level is easier to learn quickly, an important consideration if you are a new programmer.

  • If UNIX compatibility is not important to you or if you require the sophisticated file processing that the Standard I/O and UNIX I/O methods do not provide, you might find RMS desirable.

If you are writing system-level software, you may need to access the OpenVMS operating system directly through calls to system services. For example, you may need to access a user-written device driver directly through the Queue I/O Request System Service ($QIO). To do this, use the OpenVMS level of I/O; this level is recommended if you are an experienced OpenVMS programmer. For examples of programs that call OpenVMS system services, see the VSI C User Manual.

You may never use the RMS or the OpenVMS system services. The Standard I/O and UNIX I/O functions are efficient enough for a large number of applications. Figure 1.4 shows the dependency of the Standard I/O and the UNIX I/O functions on RMS, and the various methods of I/O available to you.

Figure 1.4. Mapping Standard I/O and UNIX I/O to RMS
Mapping Standard I/O and UNIX I/O to RMS

1.7.1. RMS Record and File Formats

To understand the capabilities and the restrictions of the Standard I/O and UNIX I/O functions and macros, you need to understand OpenVMS Record Management Services (RMS).

RMS supports the following file organizations:

  • Sequential

  • Relative

  • Indexed

Sequential files have consecutive records with no empty records in between; relative files have fixed-length cells that may or may not contain a record; and indexed files have records that contain data, carriage-control information, and keys that permit various orders of access.

The C RTL functions can access only sequential files. If you wish to use the other file organizations, you must use the RMS functions. For more information about the RMS functions, see the VSI C User Manual.

RMS is not concerned with the contents of records, but it is concerned about the record format, which is the way a record physically appears on the recording surface of the storage medium.

RMS supports the following record formats:

  • Fixed-length

  • Variable-length

  • Variable with fixed-length control (VFC)

  • Stream

You can specify a fixed-length record format at the time of file creation. This means that all records occupy the same amount of space in the file. You cannot change the record format once you create the file.

The length of records in variable-length, VFC, and stream file formats can vary up to a maximum size that must be specified when you create the file. With variable-length record or VFC format files, the size of the record is held in a header section at the beginning of the data record. With stream files, RMS terminates the records when it encounters a specific character, such as a carriage-control or line-feed character. Stream files are useful for storing text.

RMS allows you to specify carriage-control attributes for records in a file. Such attributes include the implied carriage-return or the Fortran formatted records. RMS interprets these carriage controls when the file is output to a terminal, a line printer, or other device. The carriage-control information is not stored in the data records.

By default, files inherit the RMS record format, maximum record size and record attributes, from the previous version of the file, if one exists; to an OpenVMS system programmer, the inherited attributes are known as FAB$B_RFM, FAB$W_MRS and FAB$B_RAT. If no previous versions exist, the newly created file defaults to stream format with line-feed record separator and implied carriage-return attributes. (This manual refers to this type of file as a stream file.) You can manipulate stream files using the Standard I/O and the UNIX I/O functions of the C RTL. When using these files and fixed-record files with no carriage control, there is no restriction on the ability to seek to any random byte of the file using the fseek or the lseek functions. However, if the file has one of the other RMS record formats, such as variable-length record format, then these functions, due to RMS restrictions, can seek only to record boundaries. Use the default VAX stream format unless you need to create or access files to be used with other VAX languages or utilities.

1.7.2. Access to RMS Files

RMS sequential files can be opened in record mode or stream mode. By default, STREAM_LF files are opened in stream mode; all other file types are opened in record mode. When opening a file, you can override these defaults by specifying the optional argument "ctx=rec" to force record mode, or "ctx=stm" to force stream mode. RMS relative and indexed files are always opened in record mode. The access mode determines the behavior of various I/O functions in the C RTL.

One of the file types defined by RMS is an RMS-11 stream format file, corresponding to a value of FAB$C_STM for the record format. The definition of this format is such that the RMS record operation SYS$GET removes leading null bytes from each record. Because this file type is processed in record mode by the C RTL, it is unsuitable as a file format for binary data unless it is explicitly opened with "ctx=stm", in which case the raw bytes of data from the file are returned.

Note

In OpenVMS Version 7.0 the default LRL value on stream files was changed from 0 to 32767. This change caused significant performance degradation on certain file operations such as sort.

This is no longer a problem. The C RTL now lets you define the logical DECC$DEFAULT_LRL to change the default record-length value on stream files.

The C RTL first looks for this logical. If it is found and it translates to a numeric value between 0 and 32767, that value is used for the default LRL.

To restore the behavior prior to OpenVMS Version 7.0, enter the following command:
$ DEFINE DECC$DEFAULT_LRL 0

1.7.2.1. Accessing RMS Files in Stream Mode

Stream access to RMS files is done with the block I/O facilities of RMS. Stream input is performed from RMS files by passing each byte of the on-disk representation of the file to your program. Stream output to RMS files is done by passing each byte from your program to the file. The C RTL performs no special processing on the data.

When opening a file in stream mode, the C RTL allocates a large internal buffer area. Data is read from the file using a single read into the buffer area and then passing the data to your program as needed. Data is written to the file when the internal buffer is full or when the fflush function is called.

1.7.2.2. Accessing RMS Record Files in Record Mode

Record access to record files is done with the record I/O facilities of RMS. The C RTL emulates a byte stream by translating carriage-control characters during the process of reading and writing records. Random access is allowed to all record files, but positioning (with fseek and lseek) must be on a record boundary for VFC files, variable record files, or files with non-null carriage control. Positioning a record file causes all buffered input to be discarded and buffered output to be written to the file.

Record input from RMS record files is emulated by the C RTL in two steps:

  1. The C RTL reads a logical record from the file.

    If the record format is variable length with fixed control (RFM = VFC), and the record attributes are not print carriage control (RAT is not PRN), then the C RTL concatenates the fixed-control area to the beginning of the record.

  2. The C RTL expands the record to simulate a stream of bytes by translating the record's carriage-control information (if any).

In RMS terms, the C RTL translates the record's carriage-control information using one of the following methods:

  • If the record attribute is implied carriage control (RAT = CR), then the C RTL appends a new-line character to the record.

    This new-line character is considered an integral part of the record, which means for example, that it can be obtained by the fgetc function and is considered a line terminator by the fgets function. Since fgets reads the file up to the new-line character, for RAT=CR files this function cannot retrieve a string that crosses the record boundaries.

  • If the record attributes are print carriage control (RAT = PRN), then the C RTL expands and concatenates the prefix and postfix carriage controls before and after the record.

    This translation is done according to rules specified by RMS, with one exception: if the prefix character is x01 and the postfix character is x8D, then nothing is attached to the beginning of the record and a single new-line character is attached to the end of it. This is done because this prefix/postfix combination is normally used to represent a line.

  • If the record attributes are Fortran carriage control (RAT = FTN), then the C RTL removes the initial control byte and attaches the appropriate carriage-control characters before and after the data as defined by RMS, with the exception of the space and default carriage-control characters. In these cases, which are used to represent a line, the C RTL appends a single new-line character to the data.

    The mapping of Fortran carriage-control can be disabled by using "ctx=nocvt".

  • If the record attributes are null (RAT = NONE) and the input is coming from a terminal, then the C RTL appends the terminating character to the record. If the terminator is a carriage return or Ctrl/Z, then VSI C translates the character to a new-line character ( \n).

    If the input is coming from a nonterminal file, then the C RTL passes the record unchanged to your program with no additional prefix or postfix characters.

As you read from the file, the C RTL delivers a stream of bytes resulting from the translations. Information that is not read from an expanded record by one function call is delivered on the next input function call.

The C RTL performs record output to RMS record files in two steps.

The first part of the record output emulation is the formation of a logical record. As you write bytes to a record file, the emulator examines the information being written for record boundaries. The handling of information in the byte stream depends on the attributes of the destination file or device, as follows:

  • For all files, if the number of output bytes is greater than the internal buffer allocated by the C RTL, a record is output.

  • For files with fixed record length (RFM = FIX) or for files opened with "ctx=bin" or "ctx=xplct", a record is output only when the internal buffer is filled or when the flush function is called.

  • For files with STREAM_CR record format (RFM = STMCR), the C RTL outputs a record when it encounters a carriage-return character ( \r).

  • For files with STREAM record format (RFM = STM) the C RTL outputs a record when it encounters a new-line (\n), form feed (\f), or vertical tab (\v) character.

  • For all other file types, the C RTL outputs a record when it encounters a new-line ( \n) character.

The second part of record output emulation is to write the logical record formed during the first step. The C RTL forms the output record as follows:

  • If the record attribute is carriage control (R AT = CR), and if the logical record ends with a new-line character ( \n), the C RTL drops the new-line character and writes the logical record with implied carriage control.

  • If the record attribute is print carriage control (RAT = PRN), then the C RTL writes the record with print carriage control according to the rules specified by RMS. If the logical record ends with a single new-line character (\n), the C RTL maps the new-line character to an x01 prefix and x8D postfix character. This is the reverse of the translation for record input files with print carriage-control attributes.

  • If the record attributes are Fortran carriage control (RAT = FTN), then the C RTL removes any prefix and/or postfix carriage-control characters and concatenates a single carriage-control byte to the beginning of the record as defined by RMS, with one exception: If the output record ends in a new-line character ( \n), the C RTL will remove the new-line character and use the space carriage-control byte. This is the reverse of the translation for record input files with Fortran carriage-control attributes.

    The mapping of Fortran carriage-control can be disabled by using "ctx=nocvt".

  • If the logical record is to be written to a terminal device and the last character of the record is a new-line character ( \n) the C RTL replaces the new-line character with a carriage-return ( \r), and attaches a line-feed character ( \n) to the front of the record. The C RTL then writes out the record with no carriage control.

  • If the output file record format is variable length with fixed control (RFM = VFC), and the record attributes do not include print carriage control (RAT is not PRN), then the C RTL takes the beginning of the logical record to be the fixed-control header, and reduces the number of bytes written out by the length of the header. These bytes are then used to construct the fixed-control header. If there are too few bytes in the logical record, an error is signaled.

1.7.2.2.1. Accessing Variable-Length or VFC Record Files in Record Mode

When you access a variable-length or VFC record file in record mode, many I/O functions behave differently than they would if they were being used with stream mode. This section describes these differences.

In general, the new-line character ( \n) is the record separator for all record modes. On output, when a new-line character is encountered, a record is generated unless you specify an optional argument (such as "ctx=bin"or "ctx=xplct") that affects the interpretation of new lines.

The read and decc$record_read functions always read at most one record. The write and decc$record_write functions always generate at least one record.

decc$record_read and decc$record_write are equivalent, respectively, to read and write, except that they work with file pointers rather than file descriptors.

Unlike the read function, which reads at most one record, the fread function can span records. Rather than read number_items records (where number_items is the third parameter to fread), fread tries to read the number of bytes equal to number_items × size_of_item (where size_of_item is the second parameter to fread). The value returned by fread is equal to the number of bytes read divided by size_of_item.

However, the fwrite function always generates at least number_items records.

The fgets and gets functions read to either a new-line character or a record boundary.

The fflush function always generates a record if there is unwritten data in the buffer. The same is true of close, fclose, fseek, lseek, rewind, and fsetpos, all of which perform implicit fflush functions.

A record is also generated whenever an attempt is made to write more characters than allowed by the maximum record size.

For more information on these functions, see the Reference Section.

1.7.2.2.2. Accessing Fixed-Length Record Files in Record Mode

When accessing a fixed-length record file in record mode, the I/O functions generally behave as described in Section 1.7.2.2.1.

The write, fwrite, and decc$record_write functions will fail if given a record size that is not an integral multiple of the maximum record size, unless the file was opened with the "ctx=xplct" optional argument specified. All other output functions will generate records at every nth byte, where n is the maximum record size.

If a new record is forced by fflush, the data in the buffer is padded to the maximum record size with null characters.

Note

This padding can cause problems for programs that seek to the end-of-file. For example, if a program were to append data to a file, then seek backwards in the file (causing an fflush to occur), and then seek to the end-of-file again, a zero-filled "hole" will have been created between the previous end-of-file and the new end-of-file if the previous end-of-file was not on a record boundary.

1.7.2.3. Example – Difference Between Stream Mode and Record Mode

Example 1.1 demonstrates the difference between stream mode and record mode access.
Example 1.1. Differences Between Stream Mode and Record Mode Access
/*      CHAP_1_STREAM_RECORD.C                       */

/* This program demonstrates the difference between  */
/* record mode and stream mode input/output.         */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void process_records(const char *fspec, FILE * fp);

main()
{
    FILE *fp;

    fp = fopen("example-fixed.dat", "w", "rfm=fix", "mrs=40", "rat=none");
    if (fp == NULL) {
        perror("example-fixed");
        exit(EXIT_FAILURE);
    }
    printf("Record mode\n");
    process_records("example-fixed.dat", fp);
    fclose(fp);

    printf("\nStream mode\n");
    fp = fopen("example-streamlf.dat", "w");
    if (fp == NULL) {
        perror("example-streamlf");
        exit(EXIT_FAILURE);
    }
    process_records("example-streamlf.dat", fp);
    fclose(fp);
}

void process_records(const char *fspec, FILE * fp)
{
    int i,
        sts;

    char buffer[40];

    /* Write records of all 1's, all 2's and all 3's */
    for (i = 0; i < 3; i++) {
        memset(buffer, '1' + i, 40);
        sts = fwrite(buffer, 40, 1, fp);
        if (sts != 1) {
            perror("fwrite");
            exit(EXIT_FAILURE);
        }
    }

    /* Rewind the file and write 10 characters of A's, then 10 B's, */
    /* then 10 C's.                                                 */
    /*                                                              */
    /* For stream mode, each fwrite call outputs 10 characters      */
    /* and advances the file position 10 characters                 */
    /* characters.                                                  */
    /*                                                              */
    /* For record mode, each fwrite merges the 10 characters  into  */
    /* the existing 40-character record, updates the record and     */
    /* advances the file position 40 characters to the next record. */
    rewind(fp);
    for (i = 0; i < 3; i++) {
        memset(buffer, 'A' + i, 10);
        sts = fwrite(buffer, 10, 1, fp);
        if (sts != 1) {
            perror("fwrite2");
            exit(EXIT_FAILURE);
        }
    }

    /* Now reopen the file and output the records. */

    fclose(fp);
    fp = fopen(fspec, "r");
    for (i = 0; i < 3; i++) {
        sts = fread(buffer, 40, 1, fp);
        if (sts != 1)
            perror("fread");
            printf("%.40s\n", buffer);
    }

    return;
}
Running this program produces the following output:
Record Mode
AAAAAAAAAA111111111111111111111111111111
BBBBBBBBBB222222222222222222222222222222
CCCCCCCCCC333333333333333333333333333333

Stream mode
AAAAAAAAAABBBBBBBBBBCCCCCCCCCC1111111111
2222222222222222222222222222222222222222
3333333333333333333333333333333333333333

1.8. Specific Portability Concerns

One of the last tasks in preparing to use the C RTL, if you are going to port your source programs across systems, is to be aware of specific differences between the C RTL and the run-time libraries of other implementations of the C language. This section describes some of the problems that you might encounter when porting programs to and from an OpenVMS system. Although portability is closely tied to the implementation of the C RTL, this section also contains information on the portability of other VSI C for OpenVMS constructs.

The C RTL provides ANSI C defined library functions as well as many commonly available APIs and a few OpenVMS extensions. See Section 1.4 for specific standards, portions of which are implemented by the C RTL. Attempts have been made to maintain complete portability in functionality whenever possible. Many of the Standard I/O and UNIX I/O functions and macros contained in the C RTL are functionally equivalent to those of other implementations.

The RTL function and macro descriptions elaborate on issues presented in this section and describe concerns not documented here.

The following list documents issues of concern if you wish to port C programs to the OpenVMS environment:

  • VSI C for OpenVMS Systems does not implement the global symbols end, edata, and etext.

  • There are differences in how OpenVMS and UNIX systems lay out virtual memory. In some UNIX systems, the address space between 0 and the break address is accessible to your program. In OpenVMS systems, the first page of memory is not accessible.

    For example, if a program tries to reference location 0 on an OpenVMS system, a hardware error (ACCVIO) is returned and the program terminates abnormally. OpenVMS systems reserve the first page of address space to catch incorrect pointer references, such as a reference to a location pointed to by a null pointer. For this reason, some existing programs that run on some UNIX systems may fail and you should modify them, as necessary. (Tru64 UNIX and OpenVMS, however, are compatible in this regard.)

  • Some C programmers code all external declarations in #include files. Then, specific declarations that require initialization are redeclared in the relevant module. This practice causes the VSI C compiler to issue a warning message about multiply declared variables in the same compilation. One way to avoid this warning is to make the redeclared symbols extern variables in the #include files.

  • VSI C does not support asm calls on OpenVMS VAX and Integrity server systems. They are supported on OpenVMS Alpha systems. See the VSI C User Manual for more information on intrinsic functions.

  • Some C programs call the counted string functions strcmpn and strcpyn. These names are not used by VSI C for OpenVMS systems. Instead, you can define macros that expand the strcmpn and strcpyn names into the equivalent, ANSI-compliant names strncmp and strncpy.

  • The VSI C for OpenVMS compiler does not support the following initialization form: 
    int  foo  123;

    Programs using this form of initialization must be changed.

  • VSI C for OpenVMS systems predefines several compile-time macros such as _ _vax, _ _alpha, _ _ia64 _ _32BITS, _ _vms, _ _vaxc, _ _VMS_VER, _ _DECC_VER, _ _D_FLOAT, _ _G_FLOAT, _ _IEEE_FLOAT, _ _X_FLOAT, and others. These predefined macros are useful for programs that must be compatible on other machines and operating systems. For more information, see the predefined macro chapter of the VSI C User Manual.

  • The ANSI C language does not guarantee any memory order for the variables in a declaration. For example:
    int  a, b, c;

  • Depending on the type of external linkage requested, extern variables in a program may be treated differently using VSI C on OpenVMS systems than they would on UNIX systems. See the VSI C User Manual for more information.

  • The dollar sign ($) is a legal character in VSI C for OpenVMS identifiers, and can be used as the first character.

  • The ANSI C language does not define any order for evaluating expressions in function parameter lists or for many kinds of expressions. The way in which different C compilers evaluate an expression is only important when the expression has side effects. Consider the following examples: 
    a[i]  =  i++;

    x = func_y() + func_z();

    f(p++, p++)

    Neither VSI C nor any other C compiler can guarantee that such expressions evaluate in the same order on all C compilers.

  • The size of a VSI C variable of type int is 32bits on OpenVMS systems. You will have to modify programs that are written for other machines and that assume a different size for a variable of type int. A variable of type long is the same size (32 bits) as a variable of type int.

  • The C language defines structure alignment to be dependent on the machine for which the compiler is designed. On OpenVMS Alpha systems, VSI C aligns structure members on natural boundaries, unless #pragma nomember_alignment is specified. Other implementations may align structure members differently.

  • References to structure members in VSI C cannot be vague. For more information, see the VSI C Reference Manual.

  • Registers are allocated based upon how often a variable is used, but the register keyword gives the compiler a strong hint that you want to place a particular variable into a register. Whenever possible, the variable is placed into a register. Any scalar variable with the storage class auto or register can be allocated to a register as long as the variable's address is not taken with the ampersand operator (&) and it is not a member of a structure or union.

1.8.1. Reentrancy

The C RTL supports an improved and enhanced reentrancy. The following types of reentrancy are supported:

  • AST reentrancy uses the _BBSSI built-in function to perform simple locking around critical sections of RTL code, but it may also disable asynchronous system traps (ASTs) in locked regions of code. This type of locking should be used when AST code contains calls to C RTL I/O routines.

    Failure to specify AST reentrancy might cause I/O routines to fail, setting errno to EALREADY.

  • MULTITHREAD reentrancy is designed to be used in threaded programs such as those that use the POSIX threads library. It performs threads locking and never disables ASTs. The POSIX Threads library must be available on your system to use this form of reentrancy.

  • TOLERANT reentrancy uses the _BBSSI built-in function to perform simple locking around critical sections of RTL code, but ASTs are not disabled. This type of locking should be used when ASTs are used and must be delivered immediately.

  • NONE gives optimal performance in the C RTL, but does absolutely no locking around critical sections of RTL code. It should only be used in a single-threaded environment when there is no chance that the thread of execution will be interrupted by an AST that would call the C RTL.

For non-threaded processes, the default reentrancy type is TOLERANT. When the threads library is loaded, the reentrancy level is implicitly set to C$C_MULTITHREAD, and the application cannot change it after that.

You can set the reentrancy type by compiling with the /REENTRANCY command-line qualifier or by calling the decc$set_reentrancy function. This function must be called exclusively from non-AST level.

When programming an application using multiple threads or ASTs, consider three classes of functions:

  • Functions with no internal data

  • Functions with thread-local internal data

  • Functions with processwide internal data

Most functions have no internal data at all. For these functions, synchronization is necessary only if the parameter is used by the application in multiple threads or in both AST and non-AST contexts. For example, although the strcat function is ordinarily safe, the following is an example of unsafe usage:
extern char buffer[100];
void routine1(char *data) {
    strcat( buffer, data );
}

If routine1 executed concurrently in multiple threads, or if routine1 is interrupted by an AST routine that calls it,the results of the strcat call are unpredictable.

The second class of functions are those that have thread-local static data. Typically, these are routines in the library that return a string where the application is not permitted to free the storage for the string. These routines are thread-safe but not AST-reentrant. This means they can safely be called concurrently, and each thread will have its own copy of the data. They cannot be called from AST routines if it is possible that the same routine was executing in non-AST context. The routines in this class are:
asctime        stat
ctermid        strerror
ctime          strtok
cuserid        VAXC$ESTABLISH
gmtime         the errno variable
localtime      wcstok
perror

All the socket functions are also included in this list if the TCP/IP product in use is thread-safe.

The third class of functions are those that affect processwide data. These functions are neither thread-safe nor AST-reentrant. For example, sigsetmask establishes the processwide signal mask. Consider a routine like the following: 
void update_data
base()
{
    int old_mask;

    old_mask = sigsetmask( 1 << (SIGINT - 1));
        /* Do work here that should not be aborted. */
    sigsetmask( old_mask );
}

If update_database was called concurrently in multiple threads, thread 1 might unblock SIGINT while thread 2 was still performing work that should not be aborted.

The routines in this class are:

  • All the signal routines

  • All the exec routines

  • The exit, _exit, nice, system, wait, getitimer, setitimer, and setlocale routines.


Note

Generally, UTC-based time functions can affect in-memory time-zone information, which is processwide data. However, if the system time zone remains the same during the execution of the application (which is the common case) and the cache of time-zone files is enabled (which is the default), then the _r variant of the time functions asctime_r, ctime_r, gmtime_r and localtime_r is both thread-safe and AST-reentrant.

If, however, the system time zone can change during the execution of the application or the cache of time-zone files is not enabled, then both variants of the UTC-based time functions belong to the third class of functions, which are neither thread-safe nor AST-reentrant.

Some functions remain inherently nonthread-safe regardless of the reentrancy type. They are:
execl      exit
execle     _exit
execlp     nice
execv      system
execve     vfork
execvp

1.8.2. Multithread Restrictions

Mixing the multithread programming model and the OpenVMS AST programming model in the same application is not recommended. The application has no mechanism to control which thread gets interrupted by an AST. This can result in are source deadlock if the thread holds a resource that is also needed by the AST routine. The following functions use mutexes. To avoid a potential resource deadlock, do not call them from AST functions in a multithreaded application.

  • All the I/O functions

  • All the socket functions

  • All the signal functions

  • vfork, exec, wait, system

  • catgets

  • set_new_handler (C++ only)

  • getenv

  • rand and srand

  • exit and _exit

  • clock

  • nice

  • times

  • ctime, localtime, asctime, mktime

1.9. 64-Bit Pointer Support

This section is for application developers who need to use 64-bit virtual memory addressing on OpenVMS Alpha Version 7.0 or higher.

OpenVMS Alpha 64-bit virtual addressing support makes the 64-bit virtual address space defined by the Alpha architecture available to both the OpenVMS operating system and its users. It also allows per-process virtual addressing for accessing dynamically mapped data beyond traditional 32-bit limits.

The VSI C Run-Time Library on OpenVMS Alpha Version 7.0 systems and higher includes the following features in support of 64-bit pointers:

  • Guaranteed binary and source compatibility of existing programs

  • No impact on applications that are not modified to exploit 64-bit support

  • Enhanced memory allocation routines that allocate 64-bit memory

  • Widened function parameters to accommodate 64-bit pointers

  • Dual implementations of functions that need to know the pointer size used by the caller

  • New information available to the DEC C Version 5.2 compiler or higher to seamlessly call the correct implementation

  • Ability to explicitly call either the 32-bit or 64-bit form of functions for applications that mix pointer sizes

  • A single shareable image for use by 32-bit and 64-bit applications

1.9.1. Using the VSI C Run-Time Library

The VSI C Run-Time library on OpenVMS Alpha Version 7.0 systems and higher can generate and accept 64-bit pointers. Functions that require a second interface to be used with 64-bit pointers reside in the same object libraries and shareable images as their 32-bit counterparts. No new object libraries or shareable images are introduced. Using 64-bit pointers does not require changes to your link command or link options files.

The VSI C 64-bit environment allows an application to use both 32-bit and 64-bit addresses. For more information about how to manipulate pointer sizes, see the /POINTER_SIZE qualifier and #pragma pointer_size and #pragma required_pointer_size preprocessor directives in the VSI C User Manual.

The /POINTER_SIZE qualifier requires you to specify a value of 32 or 64. This value is used as the default pointer size within the compilation unit. You can compile one set of modules using 32-bit pointers and another set using 64-bit pointers. Care must be taken when these two separate groups of modules call each other.

Use of the /POINTER_SIZE qualifier also influences the processing of C RTL header files. For those functions that have a 32-bit and 64-bit implementation, specifying /POINTER_SIZE enables function prototypes to access both functions, regardless of the actual value supplied to the qualifier. In addition, the value specified to the qualifier determines the default implementation to call during that compilation unit.

The #pragma pointer_size and #pragma required_pointer_size preprocessor directives can be used to change the pointer size in effect within a compilation unit. You can default pointers to 32-bit pointers and then declare specific pointers within the module as 64-bit pointers. You would also need to specifically call the _malloc64 form of malloc to obtain memory from the 64-bit memory area.

1.9.2. Obtaining 64-Bit Pointers to Memory

The C RTL has many functions that return pointers to newly allocated memory. In each of these functions, the application owns the memory pointed to and is responsible for freeing that memory.

Functions that allocate memory are:
  • malloc
  • calloc
  • realloc
  • strdup
Each of these functions have a 32-bit and a 64-bit implementation. When the /POINTER_SIZE qualifier is used, the following functions can also be called:
  • _malloc32, _malloc64
  • _calloc32, _calloc64
  • _realloc32, _realloc64
  • _strdup32, _strdup64

When /POINTER_SIZE=32 is specified, all malloc calls default to _malloc32.

When /POINTER_SIZE=64 is specified, all malloc calls default to _malloc64.

Regardless of whether the application calls a 32-bit or 64-bit memory allocation routine, there is still a single free function. This function accepts either pointer size.

Be aware that the memory allocation functions are the only ones that return pointers to 64-bit memory. All C RTL structure pointers returned to the calling application (such as a FILE, WINDOW, or DIR) are always 32-bit pointers. This allows both 32-bit and 64-bit callers to pass these structure pointers within the application.

1.9.3. VSI C Header Files

The header files distributed with OpenVMS support 64-bit pointers. Each function prototype whose signature contains a pointer is constructed to indicate the size of the pointer accepted.

A 32-bit pointer can be passed as an argument to functions that accept either a 32-bit or 64-bit pointer for that argument.

A 64-bit pointer, however, cannot be passed as an argument to a function that accepts a 32-bit pointer. Attempts to do this are diagnosed by the compiler with a MAYLOSEDATA message. The diagnostic message IMPLICITFUNC means the compiler can do no additional pointer-size validation for calls to that function. If this function is a C RTL function, refer to the reference section of this manual for the name of the header file that defines that function.

You might find the following pointer-size compiler diagnostics useful:

  • %CC-IMPLICITFUNC

    A function prototype was not found before using the specified function. The compiler and run-time system rely on prototype definitions to detect incorrect pointer-size usage. Failure to include the proper header files can lead to incorrect results and/or pointer truncation.

  • %CC-MAYLOSEDATA

    A truncation is necessary to do this operation. The operation could be passing a 64-bit pointer to a function that does not support a 64-bit pointer in the given context. It could also be a function returning a 64-bit pointer to a calling application that is trying to store that return value in a 32-bit pointer.

  • %CC-MAYHIDELOSS

    This message (when enabled) helps expose real MAYLOSEDATA messages that are being suppressed because of a cast operation. To enable this warning, compile with the qualifier /WARNINGS=ENABLE=MAYHIDELOSS.

1.9.4. Functions Affected

The C RTL accommodates applications that use only 32-bit pointers, only 64-bit pointers, or combinations of both. To use 64-bit memory, you must, at a minimum, recompile and relink an application. The amount of source code change required depends on the application itself, calls to other run-time libraries, and the combinations of pointer sizes used.

With respect to 64-bit pointer support, the functions in the C RTL fall into four categories:

  • Functions not impacted by choice of pointer size

  • Functions enhanced to accept either pointer size

  • Functions having a 32-bit and 64-bit implementation

  • Functions that accept only 32-bit pointers

From an application developer's perspective, the first two types of functions are the easiest to use in either a single- or mixed-pointer mode.

The third type requires no modifications when used in a single-pointer compilation, but might require source code changes when used in a mixed-pointer mode.

The fourth type requires careful attention whenever 64-bit pointers are used.

1.9.4.1. No Pointer-Size Impact

The choice of pointer size has no impact on a function if its prototype contains no pointer-related parameters or return values. The mathematical functions are good examples of this.

Even some functions in this category that do have pointers in their prototype are not impacted by pointer size. For example, strerror has the prototype:
char * strerror (int error_number);

This function returns a pointer to a character string, but this string is allocated by the C RTL. As a result, to support both 32-bit and 64-bit applications, these types of pointers are guaranteed to fit in a 32-bit pointer.

1.9.4.2. Functions Accepting Both Pointer Sizes

The Alpha architecture supports 64-bit pointers. The OpenVMS Alpha calling standard specifies that all arguments are actually passed as 64-bit values. Before OpenVMS Alpha Version 7.0, all 32-bit addresses passed to procedures were sign-extended into this 64-bit parameter. The called function declared the parameters as 32-bit addresses, which caused the compiler to generate 32-bit instructions (such as LDL) to manipulate these parameters.

Many functions in the C RTL are enhanced to receive the full 64-bit address. For example, consider strlen:
size_t strlen (const char *string);

The only pointer in this function is the character-string pointer. If the caller passes a 32-bit pointer, the function works with the sign-extended 64-bit address. If the caller passes a 64-bit address, the function works directly with that address.

The C RTL continues to have only a single entry point for functions in this category. There are no source-code changes required to add any of the four pointer-size options for functions of this type. The OpenVMS documentation refers to these functions as 64-bit friendly.

1.9.4.3. Functions with Two Implementations

There are many reasons why a function might need one implementation for 32-bit pointers and another for 64-bit pointers. Some of these reasons include:

  • The pointer size of the return value is the same size as the pointer size of one of the arguments. If the argument is 32 bits, the return value is 32 bits. If the argument is 64 bits, the return value is 64 bits.

  • One of the arguments is a pointer to an object whose size is pointer-size sensitive. To know how many bytes are being pointed to, the function must know if the code was compiled in 32-bit or 64-bit pointer-size mode.

  • The function returns the address of dynamically allocated memory. The memory is allocated in 32-bit space when compiled for 32-bit pointers, and is allocated in 64-bit space when compiled for 64-bit pointers.

From the application developer's point of view, there are three function prototypes for each of these functions. The <string.h> header file contains many functions whose return value is dependent upon the pointer size used as the first argument to the function call. For example, consider the memset function. The header file defines three entry points for this function: 
void * memset   (void *memory_pointer, int character, size_t size);
void *_memset32 (void *memory_pointer, int character, size_t size);
void *_memset64 (void *memory_pointer, int character, size_t size);

The first prototype is the function that your application would currently call if using this function. The compiler changes a call to memset into a call to either _memset32 when compiled with /POINTER_SIZE=32, or _memset64 when compiled with /POINTER_SIZE=64.

You can override this default behavior by directly calling either the 32-bit or the 64-bit form of the function. This accommodates applications using mixed-pointer sizes, regardless of the default pointer size specified with the /POINTER_SIZE qualifier.

If the application is compiled without specifying the /POINTER_SIZE qualifier, neither the 32-bit specific nor the 64-bit specific function prototypes are defined. In this case, the compiler automatically calls the 32-bit interface for all interfaces having dual implementations.

Table 1.5 shows the C RTL functions that have dual implementations to support 64-bit pointer size. When compiling with the /POINTER_SIZE qualifier, calls to the unmodified function names are changed to calls to the function interface that matches the pointer size specified on the qualifier.
Table 1.5. Functions with Dual Implementations
basename
 
bsearch
 
calloc
 
catgets
ctermid
 
cuserid
 
dirname
 
fgetname
fgets
 
fgetws
 
gcvt
 
getcwd
getname
 
getpwent
 
getpwnam
 
getpwnam_r
getpwuid
 
getpwuid_r
 
gets
 
index
longname
 
malloc
 
mbsrtowcs
 
memccpy
memchr
 
memcpy
 
memmove
 
memset
mktemp
 
mmap
 
qsort
 
readv
realloc
 
rindex
 
strcat
 
strchr
strcpy
 
strdup
 
strncat
 
strncpy
strpbrk
 
strptime
 
strrchr
 
strsep
strstr
 
strtod
 
strtok
 
strtok_r
strtol
 
strtoll
 
strtoq
 
strtoul
strtoull
 
strtouq
 
tmpnam
 
wcscat
wcschr
 
wcscpy
 
wcsncat
 
wcsncpy
wcspbrk
 
wcsrchr
 
wcsrtombs
 
wcsstr
wcstok
 
wcstol
 
wcstoul
 
wcswcs
wmemchr
 
wmemcpy
 
wmemmove
 
wmemset
writev
 
glob
 
globfree

Table 1.6 shows the TCP/IP socket routines that have dual implementations to support 64-bit pointer size.
Table 1.6. Socket Routines with Dual Implementations
freeaddrinfo
 
getaddrinfo
recvmsg
 
sendmsg

1.9.4.4. Socket Transfers Greater than 64 KB

Starting with OpenVMS Version 8.3, support is added for socket transfers greater than 64 KB for the following socket routines:
send
 
recv
 
read
sendto
 
recvfrom
 
write
sendmsg
 
recvmsg

1.9.4.5. Functions Requiring Explicit use of 64-Bit Structures

A few functions require explicit use of 64-bit structures when compiling /POINTER_SIZE=LONG. This is necessary for functions that have recently had 64-bit support added to avoid unexpected run-time errors by inadvertently mixing 32-bit and 64-bit versions of structures.

Consider the following two functions:
sendmsg recvmsg

These functions previously offered 32-bit support only, even when compiled with /POINTER_SIZE=LONG. In order to preserve the previous behavior of 32-bit pointer support in those functions even when compiled with /POINTER_SIZE=LONG, these two functions do not follow the normal convention for 32-bit and 64-bit support as documented in the previous section.

The following variants of these functions, and the corresponding structures they use, have been added to the C RTL to provide 64-bit support:
Function       Structure
--------       ---------
__recvmsg32    __msghdr32
__recvmsg64    __msghdr64
__sendmsg32    __msghdr32
__sendmsg64    __msghdr64
When compiling the standard versions of these functions, the following behavior occurs:

  • With /POINTER_SIZE=32 specified, the compiler converts the call to the 32-bit version of the function. For example, recvmsg is converted to __recvmsg32.

  • With /POINTER_SIZE=64 specified, the compiler converts the call to the 64-bit version of the function. For example, recvmsg is converted to __recvmsg64.

  • When the /POINTER_SIZE qualifier is not specified, neither the 32-bit-specific nor the 64-bit-specific function prototypes are defined.

However, a similar conversion of the corresponding structures does not occur for these functions. This behavior is necessary because these structures existed before OpenVMS Version 7.3-2 as 32-bit versions only, even when compiled with /POINTER_SIZE=LONG. Implicitly changing the size of the structure could result in unexpected run-time errors.

When compiling programs that use the standard version of these functions for 64-bit support, you must use the 64-bit-specific definition of the related structure. With /POINTER_SIZE=64 specified, compiling a program with the standard function name and standard structure definition will result in compiler PTRMISMATCH warning messages.

For example, you insert the recvmsg routine into your program along with the standard definition of the msghdr structure. Compiling the program with /POINTER=64 or /POINTER=LONG results in the following warning messages being displayed:
struct msghdr msgin;
int retval = recvmsg(sock, &msgin, flag);

recvmsg(sock, &msgin, flag);
....^
%CC-W-PTRMISMATCH, In this statement, the referenced type of the pointer
value "&msgin" is "long pointer to struct msghdr", which is not compatible
with "long pointer to struct __msghdr64".
When compiling for 64 bits, you need to use the 64-bit-specific version of the related structure. In the previous example, the declaration of the msgin structure could be changed to the following: 
struct __msghdr64 *msgin;
Or, to provide flexibility between 32-bit and 64-bit compilations, the msgin structure could be declared as follows:
#if __INITIAL_POINTER_SIZE == 64
struct __msghdr64 *msgin;
#else
struct __msghdr32 *msgin;
#endif

1.9.4.6. Functions Restricted to 32-Bit Pointers

A few functions in the C RTL do not support 64-bit pointers. If you try to pass a 64-bit pointer to one of these functions, the compiler generates a %CC-W-MAYLOSEDATA warning. Applications compiled with /POINTER_SIZE=64 might need to be modified to avoid passing 64-bit pointers to these functions.

Table 1.7 shows the functions restricted to using 32-bit pointers. The C RTL offers no 64-bit support for these functions. You must ensure that only 32-bit pointers are used with these functions.
Table 1.7. Functions Restricted to 32-Bit Pointers
atexit
 
initstate
iconv
 
Table 1.8 shows functions that make callbacks to user-supplied functions as part of processing that function call. The callback procedures are not passed 64-bit pointers.
Table 1.8. Callbacks that Pass Only 32-Bit Pointers
decc$from_vms
 
decc$to_vms
ftw
 
tputs

1.9.5. Reading Header Files

This section introduces the pointer-size manipulations used in the C RTL header files. Use the following examples to become more proficient in reading these header files and to help modify your own header files.

:#if __INITIAL_POINTER_SIZE 1
#   if (__VMS_VER < 70000000) || !defined ALPHA 2
#      error " Pointer size usage not permitted before OpenVMS Alpha V7.0"
#   endif
#   pragma __pointer_size __save 3
#   pragma __pointer_size 32 4
#endif
:
:
#if __INITIAL_POINTER_SIZE 5
#   pragma __pointer_size 64
#endif
:
:
#if __INITIAL_POINTER_SIZE 6
#   pragma __pointer_size __restore
#endif
:

All VSI C compilers that support the /POINTER_SIZE qualifier predefine the __INITIAL_POINTER_SIZE macro. The C RTL header files take advantage of the ANSI rule that if a macro is not defined, it has an implicit value of 0.

The macro is defined as 32 or 64 when the /POINTER_SIZE qualifier is used. It is defined as 0 if the qualifier is not used. The statement at 1 can be read as "if the user has specified either /POINTER_SIZE=32 or /POINTER_SIZE=64 on the command line".

The C compiler is supported on many OpenVMS versions. The lines at 2 generate an error message if the target of the compilation is one that does not support 64-bit pointers.

A header file cannot assume anything about the actual pointer-size context in effect at the time the header file is included. Furthermore, the VSI C compiler offers only the _ _INITIAL_POINTER_SIZE macro and a mechanism to change the pointer size, but not a way to determine the current pointer size.

All header files that have a dependency on pointer sizes are responsible for saving 3, initializing 4, altering 5, and restoring 6 the pointer-size context.
:#ifndef __CHAR_PTR32 1
#   define __CHAR_PTR32 1
    typedef char * __char_ptr32;
    typedef const char * __const_char_ptr32;
#endif
:
:
#if __INITIAL_POINTER_SIZE
#   pragma __pointer_size 64
#endif
:
:
#ifndef __CHAR_PTR64 2
#   define __CHAR_PTR64 1
    typedef char * __char_ptr64;
    typedef const char * __const_char_ptr64;
#endif
:

Some function prototypes need to refer to a 32-bit pointer when in a 64-bit pointer-size context. Other function prototypes need to refer to a 64-bit pointer when in a 32-bit pointer-size context.

VSI C binds the pointer size used in a typedef at the time the typedef is made. Assuming this header file is compiled with no /POINTER_SIZE qualifier or with /POINTER_SIZE=SHORT, the typedef declaration of __char_ptr32 1 is made in a 32-bit context. The typedef declaration of __char_ptr64 2 is made in a 64-bit context.
:
#if __INITIAL_POINTER_SIZE
#   if (__VMS_VER < 70000000) || !defined __ALPHA
#      error " Pointer size usage not permitted before OpenVMS Alpha V7.0"
#   endif
#   pragma __pointer_size __save
#   pragma __pointer_size 32
#endif
:
1
:
#if __INITIAL_POINTER_SIZE 2
#   pragma __pointer_size 64
#endif
:
3
:
int abs (int __j); 4
:
__char_ptr32 strerror (int __errnum); 5
:

Before declaring function prototypes that support 64-bit pointers, the pointer context is changed 2 from 32-bit pointers to 64-bit pointers.

Functions restricted to 32-bit pointers are placed in the 32-bit pointer context section 1 of the header file. All other functions are placed in the 64-bit context section 3 of the header file.

Functions that have no pointer-size impact (4 and 5) are located in the 64-bit section. Functions that have no pointer-size impact except for a 32-bit address return value 5 are also in the 64-bit section, and use the 32-bit specific typedefs previously discussed.
:
#if __INITIAL_POINTER_SIZE
#   pragma __pointer_size 64
#endif
:
:
#if __INITIAL_POINTER_SIZE == 32 1
#   pragma __pointer_size 32
#endif
:
char *strcat (char *__s1, __const_char_ptr64 __s2); 2
:
#if __INITIAL_POINTER_SIZE
#   pragma __pointer_size 32
    :
    char *_strcat32  (char *__s1, __const_char_ptr64 __s2); 3
    :
#   pragma __pointer_size 64
    :
    char *_strcat64  (char *__s1, const char *__s2); 4
    :
#endif
:

This example shows declarations of functions that have both a 32-bit and 64-bit implementation. These declarations are located in the 64-bit section of the header file.

The normal interface to the function 2 is declared using the pointer size specified on the /POINTER_SIZE qualifier. Because the header file is in 64-bit pointer context and because of the statements at 1, the declaration at 2 is made using the same pointer-size context as the /POINTER_SIZE qualifier.

The 32-bit specific interface 3 and the 64-bit specific interface 4 are declared in 32-bit and 64-bit pointer-size context, respectively.

Chapter 2. Understanding Input and Output

There are three types of input and output (I/O) in the VSI C Run-Time Library (C RTL): UNIX, Standard, and Terminal. Table 2.1 lists all the I/O functions and macros found in the C RTL. For more detailed information on each function and macro, see the Reference Section.
Table 2.1. I/O Functions and Macros

Function or Macro

Description

UNIX I/O – Opening and Closing Files

close

Closes the file associated with a file descriptor.

creat

Creates a new file.

  • dup
  • dup2

Allocate a new descriptor that refers to a file specified by a file descriptor returned by open, creat, or pipe.

open

Opens a file and positions it at its beginning.

UNIX I/O – Reading from Files

read

Reads bytes from a file and places them in a buffer.

UNIX I/O – Writing to Files

write

Writes a specified number of bytes from a buffer to a file.

UNIX I/O – Maneuvering in Files

lseek

Positions a stream file to an arbitrary byte position and returns the new position as an int.

UNIX I/O – Additional X/Open I/O Functions and Macros

  • fstat
  • stat

Access information about the file descriptor or the file specification.

  • flockfile
  • ftrylockfile
  • funlockfile

File-pointer-locking functions.

fsync

Writes to disk any buffered information for the specified file.

getname

Returns the file specification associated with a file descriptor.

isapipe

Returns 1 if the file descriptor is associated with a pipe and 0 if it is not.

isatty

Returns 1 if the specified file descriptor is associated with a terminal and 0 if it is not.

lwait

Waits for completion of pending asynchronous I/O.

ttyname

Returns a pointer to the null-terminated name of the terminal device associated with file descriptor 0, the default input device.

Standard I/O – Opening and Closing Files

fclose

Closes a function by flushing any buffers associated with the file control block, and freeing the file control block and buffers previously associated with the file pointer.

fdopen

Associates a file pointer with a file descriptor returned by an open, creat, dup, dup2, or pipe function.

fopen

Opens a file by returning the address of a FILE structure.

freopen

Substitutes the file, named by a file specification, for the open file addressed by a file pointer.

Standard I/O – Reading from Files

  • fgetc
  • getc
  • fgetwc
  • getw
  • getwc

Return characters from a specified file.

  • fgets
  • fgetws

Read a line from a specified file and stores the string in an argument.

fread

Reads a specified number of items from a file.

  • getline
  • getwline
  • getdelim
  • getwdelim

Read characters from an input stream.

  • fscanf
  • fwscanf
  • vfscanf
  • vfwscanf

Perform formatted input from a specified file.

  • sscanf
  • swscanf
  • vsscanf
  • vswscanf

Perform formatted input from a character string in memory.

  • ungetc
  • ungetwc

Push back a character into the input stream and leave the stream positioned before the character.

Standard I/O – Writing to Files

  • fprintf
  • fwprintf
  • vfprintf
  • vfwprintf

Perform formatted output to a specified file.

  • fputc
  • putc
  • putw
  • putwc
  • fputwc

Write characters to a specified file.

  • fputs
  • fputws

Write a character string to a file without copying the string's null terminator.

fwrite

Writes a specified number of items to a file.

  • sprintf
  • swprintf
  • vsprintf
  • vswprintf

Perform formatted output to a string in memory.

Standard I/O – Maneuvering in Files

fflush

Sends any buffered information for the specified file to RMS.

fgetpos

Stores the current value of the file position indicator for the stream.

fsetpos

Sets the file position indicator for the stream according to the value of the object pointed to.

  • fseek
  • fseeko

Position the file to the specified byte offset in the file.

  • ftell
  • ftello

Return the current byte offset to the specified stream file.

rewind

Sets the file to its beginning.

Standard I/O – Additional Standard I/O Functions and Macros

access

Checks a file to see whether a specified access mode is allowed.

clearerr

Resets the error and end-of-file indications for a file.

feof

Tests a file to see if the end-of-file has been reached.

ferror

Returns a nonzero integer if an error has occurred while reading or writing a file.

fgetname

Returns the file specification associated with a file pointer.

fileno

Returns an integer file descriptor that identifies the specified file.

ftruncate

Truncates a file at the specified position.

fwait

Waits for completion of pending asynchronous I/O.

fwide

Sets the orientation a stream.

  • mktemp
  • mkostemp

Create a unique filename from a template.

  • remove
  • delete

Delete a file.

rename

Gives a new name to an existing file.

  • setbuf
  • setvbuf

Associate a buffer with an input or output file.

tmpfile

Creates a temporary file that is opened for update.

tmpnam

Creates a character string that can be used in place of the file-name argument in other function calls.

Terminal I/O – Reading from Files

  • getchar
  • getwchar

Read a single character from the standard input (stdin).

gets

Reads a line from the standard input (stdin).

  • scanf
  • wscanf
  • vscanf
  • vwscanf

Perform formatted input from the standard input.

Terminal I/O – Writing to Files

  • printf
  • wprintf
  • vprintf
  • vwprintf

Perform formatted output to the standard output (stdout).

  • putchar
  • putwchar

Write a single character to the standard output and return the character.

puts

Writes a character string to the standard output followed by a new-line character.

2.1. Using RMS from RTL Routines

When you create a file using the C RTL I/O functions and macros, you can supply values for many RMS file attributes, including:

  • Allocation quantity

  • Block size

  • Default file extension

  • Default filename

  • File access context options

  • File-processing options

  • File-sharing options

  • Multiblock count

  • Multibuffer count

  • Maximum record size

  • Record attributes

  • Record format

  • Record-processing options

See the description of the creat function in the Reference Section for information on these values.

Other functions that allow you to set these values include open, fopen, and freopen.

For more information about RMS, see the VSI C User Manual.

2.2. UNIX I/O and Standard I/O

UNIX I/O functions are UNIX system services, now standardized by ISO POSIX-1 (the ISO Portable Operating System Interface).

UNIX I/O functions use file descriptors to access files. A file descriptor is an integer that identifies the file. A file descriptor is declared in the following way, where file_desc is the name of the file descriptor:
int  file_desc;
UNIX I/O functions, such as creat, associate the file descriptor with a file. Consider the following example:
file_desc1 = creat("INFILE.DAT", 0, "rat=cr", "rfm=var");
This statement creates the file, INFILE.DAT, with file access mode 0, carriage-return control, variable-length records, and it associates the variable file_desc1 with the file. When the file is accessed for other operations, such as reading or writing, the file descriptor is used to refer to the file. For example:
write(file_desc1, buffer, sizeof(buffer));

This statement writes the contents of the buffer to INFILE.DAT.

There may be circumstances when you should use UNIX I/O functions and macros instead of the Standard I/O functions and macros. For a detailed discussion of both forms of I/O and how they manipulate the RMS file formats, see Chapter 1.

Standard I/O functions are specified by the ANSI C Standard.

Standard I/O functions add buffering to the features of UNIX I/O and use file pointers to access files. A file pointer is an object of type FILE *, which is a typedef defined in the <stdio.h> header file as follows:
typedef  struct  _iobuf  *FILE;

The _iobuf identifier is also defined in <stdio.h>.

To declare a file pointer, use the following:
FILE  *file_ptr;
Use the Standard I/O fopen function to create or open an existing file. For example:
#include <stdio.h>

main()
{
   FILE  *outfile;
   outfile  =  fopen("DISKFILE.DAT", "w+");
      .
      .
      .
}

Here, the file DISKFILE.DAT is opened for write-update access.

The C RTL provides the following functions for converting between file descriptors and file pointers:

  • fileno – returns the file descriptor associated with the specified file pointer.

  • fdopen – associates a file pointer with a file descriptor returned by an open, creat, dup, dup2, or pipe function.

2.3. Wide-Character Versus Byte I/O Functions

The wide-character I/O functions provide operations similar to most of the byte I/O functions, except that the fundamental units internal to the wide-character functions are wide characters.

However, the external representation (in files) is a sequence of multibyte characters, not wide characters. For the wide-character formatted input and output functions:

  • The wide-character formatted input functions (such as fwscanf) always read a sequence of multibyte characters from files, regardless of the specified directive and, before any further processing, convert this sequence to a sequence of wide characters.

  • The wide-character formatted output functions (such as fwprintf) write wide characters to output files by first converting wide-character argument types to a sequence of multibyte characters, then calling the underlying operating system output primitives.

Byte I/O functions cannot handle state-dependent encodings. Wide-character I/O functions can. They accomplish this by associating each wide-character stream with a conversion-state object of type mbstate_t.

The wide-character I/O functions are:
fgetwc        fputwc        fwscanf       fwprintf       ungetwc
fgetws        fputws        wscanf        wprintf
getwc         putwc                       vfwprintf
getwchar      putwchar                    vwprintf
The byte I/O functions are:
fgetc         fputc         fscanf        fprintf         ungetc
fgets         fputs         scanf         printf          fread
getc          putc                        vfprinf         fwrite
gets          puts                        vprintf
getchar       putchar

The wide-character input functions read multibyte characters from the stream and convert them to wide characters as if they were read by successive calls to the fgetwc function. Each conversion occurs as if a call were made to the mbrtowc function with the conversion state described by the stream's own mbstate_t object.

The wide-character output functions convert wide characters to multibyte characters and write them to the stream as if they were written by successive calls to the fputwc function. Each conversion occurs as if a call were made to the wcrtomb function, with the conversion state described by the I/O stream's own mbstate_t object.

If a wide-character I/O function encounters an invalid multibyte character, the function sets errno to the value EILSEQ.

2.4. Conversion Specifications

Several of the Standard I/O functions (including the Terminal I/O functions) use conversion specifications to specify data formats for I/O. These functions are the formatted-input and formatted-output functions. Consider the following example:
int     x = 5.0;
FILE    *outfile;
   .
   .
   .
fprintf(outfile, "The answer is %d.\n", x);

The decimal value of the variable x replaces the conversion specification %d in the string to be written to the file associated with the identifier outfile.

Each conversion specification begins with a percent sign (%) and ends with a conversion specifier, which is a character that specifies the type of conversion to be performed. Optional characters can appear between the percent sign and the conversion specifier.

For the wide-character formatted I/O functions, the conversion specification is a string of wide characters. For the byte I/O equivalent functions, it is a string of bytes.

Sections 2.4.1 and 2.4.2 describe these optional characters and conversion specifiers.

2.4.1. Converting Input Information

The format specification string for the input of information can include three kinds of items:

  • White-space characters (spaces, tabs, and new-line characters), which match optional white-space characters in the input field.

  • Ordinary characters (not %), which must match the next nonwhite-space character in the input.

  • Conversion specifications, which govern the conversion of the characters in an input field and their assignment to an object indicated by a corresponding input pointer.

Each input pointer is an address expression indicating an object whose type matches that of a corresponding conversion specification. Conversion specifications form part of the format string. The indicated object is the target that receives the input value. There must be as many input pointers as there are conversion specifications, and the addressed objects must match the types of the conversion specifications.

A conversion specification consists of the following characters, in the order listed:

  • A percent character (%) or the sequence %n$ (where n is an integer),

    The sequence %n$ denotes that the conversion is applied to the nth input pointer listed, where n is a decimal integer between [1, NL_ARGMAX] (see the <limits.h> header file). For example, a conversion specification beginning with %5$ means that the conversion will be applied to the fifth input pointer listed after the format specification. The sequence %$ is invalid.

    If the conversion specification does not begin with the sequence %n$, the conversion specification is matched to its input pointer in left-to-right order. You should only use one type of conversion specification (% or %n$) in a format specification.

  • One or more optional characters (see Table 2.2).

  • A conversion specifier (see Table 2.3).

Table 2.2 shows the characters you can use between the percent sign (%) (or the sequence %n$), and the conversion specifier. These characters are optional but, if specified, must occur in the order shown in Table 2.2.
Table 2.2. Optional Characters Between % (or %n$) and the Input Conversion Specifier

Character

Meaning

*

An assignment-suppressing character.

field width

A nonzero decimal integer that specifies the maximum field width.

For the wide-character input functions, the field width is measured in wide characters.

For the byte input functions, the field width is measured in bytes, unless the directive is one of the following: 
%lc, %ls, %C, %S, %[

In these cases, the field width is measured in multibyte character units.

For programs compiled with /L_DOUBLE=64 (that is, compiled without the default /L_DOUBLE=128), the maximum field width is 1024.

h, l, or L (or ll)

Precede a conversion specifier of d, i, or n with an h if the corresponding argument is a pointer to shortint rather than a pointer to int; with an l (lowercase ell) if it is a pointer to long int; or, for OpenVMS Alpha systems only, with an L or ll (two lowercase ells) if it is a pointer to __int64.

Precede a conversion specifier of o, u, or x with an h if the corresponding argument is a pointer to unsigned short int rather than a pointer to unsigned int; with an l if it is a pointer to unsigned long int; or, for OpenVMS Alpha systems only, with an L or ll if it is a pointer to unsigned __int64.

Precede a conversion specifier of c, s, or [ with an l (lowercase ell) if the corresponding argument is a pointer to a wchar_t.

Finally, precede a conversion specifier of e, f, or g with an l (lowercase ell) if the corresponding argument is a pointer to double rather than a pointer to float, or with an L if it is a pointer to long double.

If an h, l, L, or ll appears with any other conversion specifier, then the behavior is undefined.

Table 2.3 describes the conversion specifiers for formatted input.
Table 2.3. Conversion Specifiers for Formatted Input

Specifier

Input Type?

Description

d

Expects a decimal integer in the input whose format is the same as expected for the subject sequence of the strtol function with the value 10 for the base argument. The corresponding argument must be a pointer to int.

i

Expects an integer whose type is determined by the leading input characters. A leading 0 is equated to octal, a leading 0X or 0x is equated to hexadecimal, and all other forms are equated to decimal. The corresponding argument must be a pointer to int.

o

Expects an octal integer in the input (with or without a leading 0). The corresponding argument must be a pointer to int.

u

Expects a decimal integer in the input whose format is the same as expected for the subject sequence of the strtoul function with the value 10 for the base argument.

x

Expects a hexadecimal integer in the input (with or without a leading 0x). The corresponding argument must be a pointer to unsignedint.

c

Byte

Expects a single byte in the input. The corresponding argument must be a pointer to char.

If a field width precedes the c conversion specifier, then the number of characters specified by the field width is read. In this case, the corresponding argument must be a pointer to an array of char.

If the optional character l (lowercase ell) precedes this conversion specifier, then the specifier expects a multibyte character in the input which is converted into a wide-character code.

The corresponding argument must be a pointer to type wchar_t. If a field width also precedes the c conversion specifier, then the number of characters specified by the field width is read. In this case, the corresponding argument must be a pointer to an array of wchar_t.

Wide-character

Expects a sequence of the number of characters specified in the optional field width; this is 1 if not specified.

If no l (lowercase ell) precedes the c specifier, then the corresponding argument must be a pointer to an array of char.

If an l (lowercase ell) precedes the c specifier, then the corresponding argument must be a pointer to an array of wchar_t.

C

Byte

The specifier expects a multibyte character in the input, which is converted into a wide-character code. The corresponding argument must be a pointer to type wchar_t.

If a field width also precedes the C conversion specifier, then the number of characters specified by the field width is read. In this case, the corresponding argument must be a pointer to an array of wchar_t.

Wide-character

Expects a sequence of the number of characters specified in the optional field width; this is 1 if not specified. The corresponding argument must be a pointer to an array of wchar_t.

s

Byte

Expects a sequences of bytes in the input. The corresponding argument must be a pointer to an array of characters that is large enough to contain the sequence and a terminating null character (\0) that is automatically added. The input field is terminated by a space, tab, or new-line character.

If the optional character l (ell) precedes this conversion specifier, then the specifier expects a sequence of multibyte characters in the input, which are converted to wide-character codes. The corresponding argument must be a pointer to an array of wide characters (type wchar_t) that is large enough to contain the sequence plus the terminating null wide-character code that is automatically added. The input field is terminated by a space, tab, or new-line character.

Wide-character

Expects (conceptually) a sequence of nonwhite-space characters in the input.

If no l (lowercase ell) precedes the s specifier, then the corresponding argument must be a pointer to an array of char large enough to contain the sequence plus the terminating null byte that is automatically added.

If an l (lowercase ell) precedes the s specifier, then the corresponding argument must be a pointer to an array of wchar_t large enough to contain the sequence plus the terminating null wide character that is automatically added.

S

Byte

The specifier expects a sequence of multibyte characters in the input, which are converted to wide-character codes. The corresponding argument must be a pointer to an array of wide characters (type wchar_t) that is large enough to contain the sequence plus a terminating null wide-character code that is added automatically. The input field is terminated by a space, tab, or new-line character.

Wide-character

Expects a sequence of nonwhite-space characters in the input. The corresponding argument must be a pointer to an array of wchar_t large enough to contain the sequence plus the terminating null wide character that is automatically added.

e, f, g

Expects a floating-point number in the input. The corresponding argument must be a pointer to float. The input format for floating-point numbers is: [±]nnn[radix][ddd][{E |e}[±]nn]. The n's and d's are decimal digits (as many as indicated by the field width minus the signs and the letter E). The radix character is defined in the current locale.

[...]

Expects a nonempty sequence of characters that is not delimited by a white-space character. The brackets enclose a set of characters (the scanset) expected in the input sequence. Any character in the input sequence that does not match a character in the scanset terminates the character sequence.

All characters between the brackets comprise the scanset, unless the first character after the left bracket is a circumflex (^). In this case, the scanset contains all characters other than those that appear between the circumflex and the right bracket. Any character that does appear between the circumflex and the right bracket will terminate the input character sequence.

If the conversion specifier begins with [] or [^], then the right bracket character is in the scanset and the next right bracket character is the matching right bracket that ends the specification; otherwise, the first right bracket character ends the specification.

Byte

If an l (lowercase ell) does not precede the [ specifier, then the characters in the scanset must be single-byte characters only. In this case, the corresponding argument must be a pointer to an array of char large enough to accept the sequence and the terminating null byte that is automatically added.

If an l (lowercase ell) does precede the [ specifier, then the characters in the input sequence are considered to be multibyte characters, which are then converted to a wide-character sequence for further processing. If character ranges are specified in the scanset, then the processing is done according to the LC_COLLATE category of the current program's locale. In this case, the corresponding argument must be a pointer to an array of wchar_t large enough to accept the sequence and the terminating null wide character that is automatically added.

Wide-character

If no l (lowercase ell) precedes the [ conversion specifier, then processing is the same as described for the byte-input type of the %l[ specifier, except that the corresponding argument must be an array of char large enough to accept the multibyte sequence plus the terminating null byte that is automatically added.

If an l (lowercase ell) precedes the [ conversion specifier, then processing is the same as in the preceding paragraph except that the corresponding argument must be an array of wchar_t large enough to accept the wide-character sequence plus the terminating null wide character that is automatically added.

p

Requires an argument that is a pointer to void. The input value is interpreted as a hexadecimal value.

n

No input is consumed. The corresponding argument is a pointer to an integer. The integer is assigned the number of characters read from the input stream so far by this call to the formatted input function. Execution of a %n directive does not increment the assignment count returned when the formatted input function completes execution.

%

Matches a single percent symbol. No conversion or assignment takes place. The complete conversion specification would be %%.

Remarks

  • You can change the delimiters of the input field with the bracket ([ ]) conversion specification. Otherwise, an input field is defined as a string of nonwhite-space characters. It extends either to the next white-space character or until the field width, if specified, is exhausted. The function reads across line and record boundaries, since the new-line character is a white-space character.

  • A call to one of the input conversion functions resumes searching immediately after the last character processed by a previous call.

  • If the assignment-suppression character (*) appears in the format specification, no assignment is made. The corresponding input field is interpreted and then skipped.

  • The arguments must be pointers or other address-valued expressions, since VSI C permits only calls by value. To read a number in decimal format and assign its value to n, you must use the following form: 
    scanf("%d", &n)
    You cannot use the following form:
    scanf("%d", n)
  • White space in a format specification matches optional white space in the input field. Consider the following format specification:
    field = %x
    This format specification matches the following forms:
    field = 5218
field=5218
field= 5218
field =5218
    These forms do not match the following example:
    fiel d=5218

2.4.2. Converting Output Information

The format specification string for the output of information can contain:

  • Ordinary characters, which are copied to the output.

  • Conversion specifications, each of which causes the conversion of a corresponding output source to a character string in a particular format Conversion specifications are matched to output sources in left-to-right order.

A conversion specification consists of the following, in the order listed:

  • A percent character (%) or the sequence %n$.

    The sequence %n$ denotes that the conversion is applied to the nth output source listed, where n is a decimal integer between [1, NL_ARGMAX] (see the <limits.h> header file). For example, a conversion specification beginning with %5$ means that the conversion will be applied to the fifth output source listed after the format specification.

    If the conversion specification does not begin with the sequence %n$, the conversion specification is matched to its output source in left-to-right order. You should only use one type of conversion specification (% or %n$) in a format specification.

  • One or more optional characters (see Table 2.4).

  • A conversion specifier (see Table 2.5) concludes the conversion specification.

For examples of conversion specifications, see the sample programs in Section 2.6.

Table 2.4 shows the characters you can use between the percent sign (%) (or the sequence %n$) and the conversion specifier. These characters are optional, but if specified, they must occur in the order shown in Table 2.4.
Table 2.4. Optional Characters Between % (or %n$) and the Output Conversion Specifier

Character

Meaning

flags

You can use the following flag characters, alone or in any combined order, to modify the conversion specification:

' (single quote)

Requests that a numeric conversion is formatted with the thousands separator character. Only the numbers to the left of the radix character are formatted with the separator character. The character used as a separator and the positioning of the separators are defined in the program's current locale.

– (hyphen)

Left-justifies the converted output source in its field.

+

Requests that an explicit sign be present on a signed conversion. If this flag is not specified, the result of a signed conversion begins with a sign only when a negative value is converted.

space

Prefixes a space to the result of a signed conversion, if the first character of the conversion is not a sign, or if the conversion results in no characters. If you specify both the space and the + flag, the space flag is ignored.

#

Requests an alternate conversion format. Depending on the conversion specified, different actions will occur.

For the o (octal) conversion, the precision is increased to force the first digit to be a zero.

For the x (or X) conversion, a nonzero result is prefixed with 0x (or 0X).

For e, E, f, F, g, and G conversions, the result contains a decimal point even at the end of an integer value.

For g and G conversions, trailing zeros are not trimmed.

For other conversions, the effect of # is undefined.

0

Uses zeros rather than spaces to pad the field width for d, i, o, u, x, X, e, E, f, F, g, and G conversions.

If both the 0 and the – flags are specified, then the 0 flag is ignored.

For d, i, o, u, x, and X conversions, if a precision is specified, the 0 flag is ignored.

For other conversions, the behavior of the 0 flag is undefined.

field width

The minimum field width can be designated by a decimal integer constant, or by an output source. To specify an output source, use an asterisk (*) or the sequence *n$, where n refers to the nth output source listed after the format specification.

The minimum field width is considered after the conversion is done according to all the other components of the format directive. This component affects the padding of the conversion result as follows:

If the result of the conversion is wider than the minimum field, write it out.

If the result of the conversion is narrower than the minimum width, pad it to make up the field width. Pad with spaces by default. Pad with zeros if the 0 flag is specified; this does not mean that the width is an octal number. Padding is on the left by default, and on the right if a minus sign is specified.

For the wide-character output functions, the field width is measured in wide characters; for the byte output functions, it is measured in bytes.

For programs compiled with /L_DOUBLE=64 (that is, compiled without the default /L_DOUBLE=128), the maximum field width is 1024.

. (period)

Separates the field width from the precision.

precision
The precision defines any of the following:

  • Minimum number of digits to appear for d, i, o, u, x, and X conversions

  • Number of digits to appear after the decimal-point character for e, E, and f conversions

  • Maximum number of significant digits for g and G conversions

  • Maximum number of characters to be written from a string in an s or S conversion

If a precision appears with any other conversion specifier, the behavior is undefined.

Precision can be designated by a decimal integer constant, or by an output source. To specify an output source, use an asterisk (*) or the sequence *n$, where n refers to the nth output source listed after the format specification.

If only the period is specified, the precision is taken as 0.

h

An h specifies that a following d, i, o, u, x, or X conversion specifier applies to a short int or an unsigned short int argument.

An h specifies that a following n conversion specifier applies to a pointer to a short int argument.

hh

An hh specifies that a following d, i, o, u, x, or X conversion specifier applies to a signed char or an unsigned char argument.

j

A j specifies that a following d, i, o, u, x, or X conversion specifier applies to an intmax_t argument.

l

An l (lowercase ell) specifies that a following d, i, o, u, x, or X conversion specifier applies to a long int or an unsigned long int argument.

An l specifies that a following n conversion specifier applies to a pointer to a long int argument.

An l specifies that a following c or s conversion specifier applies to a wchar_t argument.

L (or ll)

An L or ll (two lowercase ells) specifies that a following d, i, o, u, x, or X conversion specifier applies to an __int64 or unsigned __int64 argument.

An L specifies that a following e, E, f, F, g, or G conversion specifier applies to a long double argument.

t

A t specifies that a following d, i, o, u, x, or X conversion specifier applies to a ptrdiff_t argument.

z

A z specifies that a following d, i, o, u, x, or X conversion specifier applies to a size_t argument.

Remarks


  • If an h, hh, j, l, L (or ll), t, or z appears with any other conversion specifier, the behavior is undefined.

  • On OpenVMS Alpha systems, VSI C int values are equivalent to long values.

Table 2.5 describes the conversion specifiers for formatted output.
Table 2.5. Conversion Specifiers for Formatted Output

Specifier

Output Type?

Description

d, i

Converts an int argument to signed decimal format.

o

Converts an unsigned int argument to unsigned octal format.

u

Converts an unsigned int argument to unsigned decimal format (giving a number in the range 0 to 4,294,967,295).

x, X

Converts an unsigned int argument to unsigned hexadecimal format (with or without a leading 0x). The letters abcdef are used for x conversion, and the letters ABCDEF are used for X conversion.

f, F

Converts a float or double argument to the format [–]mmm.nnnnnn. The number of n's is equal to the precision specification as follows:

  • If no precision is specified, the default is 6.

  • If the precision is 0 and the # flag is specified, the decimal point appears but no n's appear.

  • If the precision is 0 and the # flag is not specified, the decimal point also does not appear.

  • If a decimal point appears, at least one digit appears before it.

The value is rounded to the appropriate number of digits.

e, E

Converts a float or double argument to the format [–]m.nnnnnn E ±xx. The number of n's is specified by the precision. If no precision is specified, the default is 6. If the precision is explicitly 0 and the # flag is specified, the decimal point appears but no n's appear. If the precision is explicitly 0 and the # flag is not specified, the decimal point also does not appear. An 'e' is printed for e conversion; an 'E' is printed for E conversion. The exponent always contains at least two digits. If the value is 0, the exponent is 0.

g, G

Converts a float or double argument to format f or e (or E if the G conversion specifier is used), with the precision specifying the number of significant digits. If the precision is 0, it is taken as 1. The format used depends on the value of the argument: format e (or E) is used only if the exponent resulting from such a conversion is less than –4, or is greater than or equal to the precision; otherwise, format f is used. Trailing zeros are suppressed in the fractional portion of the result. A decimal point appears only if it is followed by a digit.

c

Byte

Converts an int argument to an unsigned char, and writes the resulting byte.

If the optional character l (lowercase ell) precedes this conversion specifier, then the specifier converts a wchar_t argument to an array of bytes representing the character, and writes the resulting character. If the field width is specified and the resulting character occupies fewer bytes than the field width, then it will be padded to the given width with space characters. If the precision is specified, then the behavior is undefined.

Wide-character

If an l (lowercase ell) does not precede the c specifier, then the int argument is converted to a wide character as if by calling btowc, and the resulting character is written.

If an l (lowercase ell) precedes the c specifier, then the specifier converts a wchar_t argument to an array of bytes representing the character, and writes the resulting character. If the field width is specified and the resulting character occupies fewer characters than the field width, it will be padded to the given width with space characters. If the precision is specified, the behavior is undefined.

C

Byte

Converts a wchar_t argument to an array of bytes representing the character, and writes the resulting character. If the field width is specified and the resulting character occupies fewer bytes than the field width, then it will be padded to the given width with space characters. If the precision is specified, then the behavior is undefined.

Wide-character

Converts a wchar_t argument to an array of bytes representing the character, and writes the resulting character. If the field width is specified and the resulting character occupies fewer wide characters than the field width, then it will be padded to the given width with space characters. If the precision is specified, then the behavior is undefined.

s

Byte

Requires an argument that is a pointer to an array of characters of type char. The argument is used to write characters until a null character is encountered or until the number of characters indicated by the precision specification is exhausted. If the precision specification is 0 or omitted, then all characters up to a null are output.

If the optional character l (lowercase ell) precedes this conversion specifier, then the specifier converts an array of wide-character codes to multibyte characters, and writes the multibyte characters. Requires an argument that is a pointer to an array of wide characters of type wchar_t. Characters are written until a null wide character is encountered or until the number of bytes indicated by the precision specification is exhausted. If the precision specification is omitted or is greater than the size of the array of converted bytes, then the array of wide characters must be terminated by a null wide character.

Wide-character

If an l (lowercase ell) does not precede the s specifier, then the specifier converts an array of multibyte characters, as if by calling mbrtowc for each multibyte character, and writes the resulting characters until a null wide character is encountered or the number of wide characters indicated by the precision specification is exhausted. If the precision specification is omitted or is greater than the size of the array of converted characters, then the converted array must be terminated by a null wide character.

If an l precedes this conversion specifier, then the argument is a pointer to an array of wchar_t. Characters from this array are written until a null wide character is encountered or the number of wide characters indicated by the precision specification is exhausted. If the precision specification is omitted or is greater than the size of the array, then the array must be terminated by a null wide character.

S

Byte

Converts an array of wide-character codes to multibyte characters, and writes the multibyte characters. Requires an argument that is a pointer to an array of wide characters of type wchar_t. Characters are written until a null wide character is encountered or until the number of bytes indicated by the precision specification is exhausted. If the precision specification is omitted or is greater than the size of the array of converted bytes, then the array of wide characters must be terminated by a null wide character.

Wide-character

The argument is a pointer to an array of wchar_t. Characters from this array are written until a null wide character is encountered or the number of wide characters indicated by the precision specification is exhausted. If the precision specification is omitted or is greater than the size of the array, then the array must be terminated by a null wide character.

p

Requires an argument that is a pointer to void. The value of the pointer is output as a hexadecimal number.

n

Requires an argument that is a pointer to an integer. The integer is assigned the number of characters written to the output stream so far by this call to the formatted output function. No argument is converted.

%

Writes out the percent symbol. No conversion is performed. The complete conversion specification would be %%.

2.5. Terminal I/O

VSI C defines three file pointers that allow you to perform I/O to and from the logical devices usually associated with your terminal (for interactive jobs) or a batch stream (for batch jobs). In the OpenVMS environment, the three permanent process files SYS$INPUT, SYS$OUTPUT, and SYS$ERROR perform the same functions for both interactive and batch jobs. Terminal I/O refers to both terminal and batch stream I/O. The file pointers stdin, stdout, and stderr are defined when you include the <stdio.h> header file using the #include preprocessor directive.

The stdin file pointer is associated with the terminal to perform input. This file is equivalent to SYS$INPUT. The stdout file pointer is associated with the terminal to perform output. This file is equivalent to SYS$OUTPUT. The stderr file pointer is associated with the terminal to report run-time errors. This file is equivalent to SYS$ERROR.

There are three file descriptors that refer to the terminal. The file descriptor 0 is equivalent to SYS$INPUT, 1 is equivalent to SYS$OUTPUT, and 2 is equivalent to SYS$ERROR.

When performing I/O at the terminal, you can use Standard I/O functions and macros (specifying the pointers stdin, stdout, or stderr as arguments), you can use UNIX I/O functions (giving the corresponding file descriptor as an argument), or you can use the Terminal I/O functions and macros. There is no functional advantage to using one type of I/O over another; the Terminal I/O functions might save keystrokes since there are no arguments.

2.6. Program Examples

This section gives some program examples that show how the I/O functions can be used in applications.

Example 2.1 shows the printf function.
Example 2.1. Output of the Conversion Specifications
/*      CHAP_2_OUT_CONV.C                               */

/* This program uses the printf function to print the   */
/* various conversion specifications and their effect   */
/* on the output.                                       */

/* Include the proper header files in case printf has   */
/* to return EOF.                                       */

#include <stdlib.h>
#include <stdio.h>
#include <wchar.h>

#define WIDE_STR_SIZE 20

main()
{
    double val = 123345.5;
    char c = 'C';
    int i = -1500000000;
    char *s = "thomasina";
    wchar_t wc;
    wchar_t ws[WIDE_STR_SIZE];

    /* Produce a wide character and a wide character string */

    if (mbtowc(&wc, "W", 1) == -1) {
        perror("mbtowc");
        exit(EXIT_FAILURE);
    }

    if (mbstowcs(ws, "THOMASINA", WIDE_STR_SIZE) == -1) {
        perror("mbstowcs");
        exit(EXIT_FAILURE);
    }

    /* Print the specification code, a colon, two tabs, and the  */
    /* formatted output value delimited by the angle bracket     */
    /* characters (<>).                                          */

    printf("%%9.4f:\t\t<%9.4f>\n", val);
    printf("%%9f:\t\t<%9f>\n", val);
    printf("%%9.0f:\t\t<%9.0f>\n", val);
    printf("%%-9.0f:\t\t<%-9.0f>\n\n", val);

    printf("%%11.6e:\t\t<%11.6e>\n", val);
    printf("%%11e:\t\t<%11e>\n", val);
    printf("%%11.0e:\t\t<%11.0e>\n", val);
    printf("%%-11.0e:\t\t<%-11.0e>\n\n", val);

    printf("%%11g:\t\t<%11g>\n", val);
    printf("%%9g:\t\t<%9g>\n\n", val);

    printf("%%d:\t\t<%d>\n", c);
    printf("%%c:\t\t<%c>\n", c);
    printf("%%o:\t\t<%o>\n", c);
    printf("%%x:\t\t<%x>\n\n", c);

    printf("%%d:\t\t<%d>\n", i);
    printf("%%u:\t\t<%u>\n", i);
    printf("%%x:\t\t<%x>\n\n", i);

    printf("%%s:\t\t<%s>\n", s);
    printf("%%-9.6s:\t\t<%-9.6s>\n", s);
    printf("%%-*.*s:\t\t<%-*.*s>\n", 9, 5, s);
    printf("%%6.0s:\t\t<%6.0s>\n\n", s);
    printf("%%C:\t\t<%C>\n", wc);
    printf("%%S:\t\t<%S>\n", ws);
    printf("%%-9.6S:\t\t<%-9.6S>\n", ws);
    printf("%%-*.*S:\t\t<%-*.*S>\n", 9, 5, ws);
    printf("%%6.0S:\t\t<%6.0S>\n\n", ws);
}
Running Example 2.1 produces the following output:
$ RUN  EXAMPLE
%9.4f:          <123345.5000>
%9f:            <123345.500000>
%9.0f:          <   123346>
%-9.0f:         <123346   >
%11.6e:         <1.233455e+05>
%11e:           <1.233455e+05>
%11.0e:         <      1e+05>
%-11.0e:        <1e+05      >
%11g:           <     123346>
%9g:            <   123346>
%d:             <67>
%c:             <C>
%o:             <103>
%x:             <43>
%d:             <-1500000000>
%u:             <2794967296>
%x:             <a697d100>
%s:             <thomasina>
%-9.6s:         <thomas   >
%-*.*s:         <thoma    >
%6.0s:          <      >
%C:             <W>
%S:             <THOMASINA>
%-9.6S:         <THOMAS   >
%-*.*S:         <THOMA    >
%6.0S:          <      >
$
Example 2.2 shows the use of the fopen, ftell, sprintf, fputs, fseek, fgets, and fclose functions.
Example 2.2. Using the Standard I/O Functions
/*      CHAP_2_STDIO.C  */

/* This program establishes a file pointer, writes lines from   */
/* a buffer to the file, moves the file pointer to the second   */
/* record, copies the record to the buffer, and then prints     */
/* the buffer to the screen.                                    */

#include <stdio.h>
#include <stdlib.h>

main()
{
    char buffer[32];
    int i,
        pos;
    FILE *fptr;

    /*  Set file pointer.            */
    fptr = fopen("data.dat", "w+");
    if (fptr == NULL) {
        perror("fopen");
        exit(EXIT_FAILURE);
    }

    for (i = 1; i < 5; i++) {
        if (i == 2)     /*  Get position of record 2. */
            pos = ftell(fptr);
        /*  Print a line to the buffer.  */
        sprintf(buffer, "test data line %d\n", i);
        /*  Print buffer to the record.  */
        fputs(buffer, fptr);
    }

    /*  Go to record number 2.       */
    if (fseek(fptr, pos, 0) < 0) {
        perror("fseek");        /*  Exit on fseek error. */
        exit(EXIT_FAILURE);
    }

    /*  Read record 2 in the buffer. */
    if (fgets(buffer, 32, fptr) == NULL) {
        perror("fgets");        /*  Exit on fgets error.  */
        exit(EXIT_FAILURE);
    }
    /*  Print the buffer.       */
    printf("Data in record 2 is: %s", buffer);
    fclose(fptr);       /*  Close the file.     */
}
Running Example 2.2 produces the following result: 
$ RUN  EXAMPLE
Data in record 2 is: test data line 2
The output to DATA.DAT from Example 2.2 is: 
test data line 1
test data line 2
test data line 3
test data line 4

Example 2.3. Using Wide Character I/O Functions
/*      CHAP_2_WC_IO.C                                          */

/* This program establishes a file pointer, writes lines from   */
/* a buffer to the file using wide-character codes, moves the   */
/* file pointer to the second record, copies the record to the  */
/* wide-character buffer, and then prints the buffer to the     */
/* screen.                                                      */

#include <stdio.h>
#include <stdlib.h>
#include <wchar.h>

main()
{
    char flat_buffer[32];
    wchar_t wide_buffer[32];
    wchar_t format[32];
    int i,
        pos;
    FILE *fptr;

    /*  Set file pointer.            */
    fptr = fopen("data.dat", "w+");
    if (fptr == NULL) {
        perror("fopen");
        exit(EXIT_FAILURE);
    }

    for (i = 1; i < 5; i++) {
        if (i == 2)     /*  Get position of record 2. */
            pos = ftell(fptr);
        /*  Print a line to the buffer.  */
        sprintf(flat_buffer, "test data line %d\n", i);
        if (mbstowcs(wide_buffer, flat_buffer, 32) == -1) {
            perror("mbstowcs");
            exit(EXIT_FAILURE);
        }

        /*  Print buffer to the record.  */
        fputws(wide_buffer, fptr);
    }

    /*  Go to record number 2. */
    if (fseek(fptr, pos, 0) < 0) {
        perror("fseek");        /*  Exit on fseek error. */
        exit(EXIT_FAILURE);
    }

    /*  Put record 2 in the buffer.  */
    if (fgetws(wide_buffer, 32, fptr) == NULL) {
        perror("fgetws");       /*  Exit on fgets error. */
        exit(EXIT_FAILURE);
    }
    /*  Print the buffer. */
    printf("Data in record 2 is: %S", wide_buffer);
    fclose(fptr);               /*  Close the file.  */
}
Running Example 2.3 produces the following result:
$ RUN  EXAMPLE
Data in record 2 is: test data line 2
The output to DATA.DAT from Example 2.3 is:
test data line 1
test data line 2
test data line 3
test data line 4
Example 2.4 shows the use of both a file pointer and a file descriptor to access a single file.
Example 2.4. I/O Using File Descriptors and Pointers
/*      CHAP_2_FILE_DIS_AND_POINTER.C                           */

/* The following example creates a file with variable-length    */
/* records (rfm=var) and the carriage-return attribute (rat=cr).*/
/*                                                              */
/* The program uses creat to create and open the file, and      */
/* fdopen to associate the file descriptor with a file pointer. */
/* After using the fdopen function, the file must be referenced */
/* using the Standard I/O functions.                            */

#include <unixio.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define ERROR 0
#define ERROR1 -1
#define BUFFSIZE 132

main()
{
    char buffer[BUFFSIZE];
    int fildes;
    FILE *fp;

    if ((fildes = creat("data.dat", 0, "rat=cr",
                        "rfm=var")) == ERROR1) {
        perror("DATA.DAT: creat() failed\n");
        exit(EXIT_FAILURE);
    }

    if ((fp = fdopen(fildes, "w")) == NULL) {
        perror("DATA.DAT: fdopen() failed\n");
        exit(EXIT_FAILURE);
    }
    while (fgets(buffer, BUFFSIZE, stdin) != NULL)
        if (fwrite(buffer, strlen(buffer), 1, fp) == ERROR) {
            perror("DATA.DAT: fwrite() failed\n");
            exit(EXIT_FAILURE);
        }

    if (fclose(fp) == EOF) {
        perror("DATA.DAT: fclose() failed\n");
        exit(EXIT_FAILURE);
    }
}

Chapter 3. Character, String, and Argument-List Functions

Table 3.1 describes the character, string, and argument-list functions in the VSI C Run-Time Library (C RTL). Although further discussion follows in this chapter, see the Reference Section for more detailed information on each function.
Table 3.1. Character, String, and Argument-List Functions

Function

Description

Character Classification

  • isalnum
  • iswalnum

Return a nonzero integer if its argument is one of the alphanumeric characters in the current locale.

  • isalpha
  • iswalpha

Return a nonzero integer if its argument is one of the alphabetic characters in the current locale.

isascii

Returns a nonzero integer if its argument is any ASCII character.

  • iscntrl
  • iswcntrl

Return a nonzero integer if its argument is a control character in the current locale.

  • isdigit
  • iswdigit

Return a nonzero integer if its argument is a digit character in the current locale.

  • isgraph
  • iswgraph

Return a nonzero integer if its argument is a graphic character in the current locale.

  • islower
  • iswlower

Return a nonzero integer if its argument is a lowercase character in the current locale.

  • isprint
  • iswprint

Return a nonzero integer if its argument is a printing character in the current locale.

  • ispunct
  • iswpunct

Return a nonzero integer if its argument is a punctuation character in the current locale.

  • isspace
  • iswspace

Return a nonzero integer if its argument is a white-space character in the current locale.

  • isupper
  • iswupper

Return a nonzero integer if its argument is an uppercase character in the current locale.

iswctype

Returns a nonzero integer if its argument has the specified property.

  • isxdigit
  • iswxdigit

Return a nonzero integer if its argument is a hexadecimal digit (0 to 9, A to F, or a to f ).

Character Conversion

btowc

Converts a one-byte multibyte character to a wide character in the initial shift state.

  • ecvt
  • fcvt
  • gcvt

Convert an argument to a null-terminated string of ASCII digits and return the address of the string.

  • index
  • rindex

Search for a character in a string.

  • mblen
  • mbrlen

Determine the number of bytes in a multibyte character.

mbsinit

Determines whether an mbstate_t object describes an initial conversion state.

mbstowcs

Converts a sequence of multibyte characters into a sequence of corresponding codes.

toascii

Converts its argument, an 8-bit ASCII character, to a 7-bit ASCII character.

  • tolower
  • _tolower
  • towlower

Convert its argument, an uppercase character, to lowercase.

  • toupper
  • _toupper
  • towupper

Convert its argument, a lowercase character, to uppercase.

towctrans

Maps one wide character to another according to a specified mapping descriptor.

wcstombs

Converts a sequence of wide-character codes corresponding to multibyte characters to a sequence of multibyte characters.

wctob

Determines if a wide character corresponds to a single-byte multibyte character and returns its multibyte character representation.

wctomb

Converts a wide character to its multibyte character representation.

wctrans

Returns the description of a mapping, corresponding to specified property, that can be later used in a call to towctrans.

wctype

Converts a valid character class defined for the current locale to an object of type wctype_t.

String Manipulation

atof

Converts a given string to a double-precision number.

  • atoi
  • atol

Convert a given string of ASCII characters to the appropriate numeric values.

  • atoll
  • atoq

Convert a given string of ASCII characters to an __int64.

basename

Return the last component of a path name.

dirname

Report the parent directory name of a file path name.

  • strcat
  • strncat
  • wcscat
  • wcsncat

Append one string to the end of another string.

  • strchr
  • strrchr
  • wcschr
  • wcsrchr

Return the address of the first or last occurrence of a given character in a null-terminated string.

  • strcmp
  • strncmp
  • strcoll
  • wcscmp
  • wcsncmp
  • wcscoll

Compare two character strings and returns a negative, zero, or positive integer indicating that the values of the individual characters in the first string are less than, equal to, or greater than the values in the second string.

  • strcpy
  • strncpy
  • wcscpy
  • wcsncpy

Copies all or part of one string into another.

  • strxfrm
  • wcsxfrm

Transform a multibyte string to another string ready for comparisons using the strcmp or wcscmp function.

  • strcspn
  • wcscspn

Search a string for a character that is in a specified set of characters.

  • strlen
  • wcslen

Return the length of a string of characters. The returned length does not include the terminating null character ( \0).

  • strpbrk
  • wcspbrk

Search a string for the occurrence of one of a specified set of characters.

  • strspn
  • wcsspn

Search a string for the occurrence of a character that is not in a specified set of characters.

  • strstr
  • wcswcs

Search a string for the first occurrence of a specified set of characters.

  • strtod
  • wcstod

Convert a given string to a double-precision number.

  • strtok
  • wcstok

Locate text tokens in a given string.

  • strtol
  • wcstol

Convert the initial portion of a string to a signed long integer.

  • strtoll
  • strtoq

Convert the initial portion of a string to signed __int64.

  • strtoul
  • wcstoul

Convert the initial portion of a string to an unsigned long integer.

  • strtoull
  • strtouq

Convert the initial portion of the string pointed to by the pointer to the character string to an unsigned __int64.

String Handling—Accessing Binary Data

bcmp

Compares byte strings.

bcopy

Copies byte strings.

bzero

Copies nulls into byte strings.

  • memchr
  • wmemchr

Locate the first occurrence of the specified byte within the initial length of the object to be searched.

  • memcmp
  • wmemcmp

Compare two objects byte by byte.

  • memcpy
  • memmove
  • mempcpy
  • wmemcpy
  • wmemmove

Copy a specified number of bytes from one object to another.

  • memset
  • wmemset

Set a specified number of bytes in a given object to a given value.

Argument-List Handling—Accessing a Variable-Length Argument List

va_arg

Returns the next item in the argument list.

va_copy

Copies one argument list to another.

va_count

Returns the number of quadwords (Alpha only) in the argument list.

va_end

Finishes the va_start session.

  • va_start
  • va_start_1

Initialize a variable to the beginning of the argument list.

  • vfprintf
  • vprintf
  • vsprintf

Print formatted output based on an argument list.

3.1. Character-Classification Functions

The character-classification functions take a single argument on which they perform a logical operation. The argument can have any value; it does not have to be an ASCII character. The isascii function determines if the argument is an ASCII character (0 through 177 octal). The other functions determine whether the argument is a particular type of ASCII character, such as a graphic character or digit. The isw* functions test wide characters. Character-classification information is in the LC_CTYPE category of the program's current locale.

For all functions, a positive return value indicates TRUE. A return value of0 indicates FALSE.

To briefly reference the character-classification functions in a subsequent table, each function is assigned a number, as shown in Table 3.2.
Table 3.2. Character-Classification Functions

Function Number

Function

Function Number

Function

1

isalnum

7

islower

2

isalpha

8

isprint

3

isascii

9

ispunct

4

iscntrl

10

isspace

5

isdigit

11

isupper

6

isgraph

12

isxdigit

Table 3.3 lists the numbers of the functions (as assigned in Table 3.2) that return the value TRUE for each of the given ASCII characters. The numeric code represents the octal value of each of the ASCII characters.
Table 3.3. ASCII Characters and the Character-Classification Functions

ASCII Values

Function Numbers

ASCII Values

Function Numbers

NUL 00

3,4

@ 100

3,6,8,9

SOH 01

3,4

A 101

1,2,3,6,8,11,12

STX 02

3,4

B 102

1,2,3,6,8,11,12

ETX 03

3,4

C 103

1,2,3,6,8,11,12

EOT 04

3,4

D 104

1,2,3,6,8,11,12

ENQ 05

3,4

E 105

1,2,3,6,8,11,12

ACK 06

3,4

F 106

1,2,3,6,8,11,12

BEL 07

3,4

G 107

1,2,3,6,8,11

BS 10

3,4

H 110

1,2,3,6,8,11

HT 11

3,4,10

I 111

1,2,3,6,8,11

LF 12

3,4,10

J 112

1,2,3,6,8,11

VT 13

3,4,10

K 113

1,2,3,6,8,11

FF 14

3,4,10

L 114

1,2,3,6,8,11

CR 15

3,4,10

M 115

1,2,3,6,8,11

SO 16

3,4

N 116

1,2,3,6,8,11

SI 17

3,4

O 117

1,2,3,6,8,11

DLE 20

3,4

P 120

1,2,3,6,8,11

DC1 21

3,4

Q 121

1,2,3,6,8,11

DC2 22

3,4

R 122

1,2,3,6,8,11

DC3 23

3,4

S 123

1,2,3,6,8,11

DC4 24

3,4

T 124

1,2,3,6,8,11

NAK 25

3,4

U 125

1,2,3,6,8,11

SYN 26

3,4

V 126

1,2,3,6,8,11

ETB 27

3,4

W 127

1,2,3,6,8,11

CAN 30

3,4

X 130

1,2,3,6,8,11

EM 31

3,4

Y 131

1,2,3,6,8,11

SUB 32

3,4

Z 132

1,2,3,6,8,11

ESC 33

3,4

[ 133

3,6,8,9

FS 34

3,4

\ 134

3,6,8,9

GS 35

3,4

] 135

3,6,8,9

RS 36

3,4

^ 136

3,6,8,9

US 37

3,4

– 137

3,6,8,9

SP 40

3,8,10

` 140

3,6,8,9

! 41

3,6,8,9

a 141

1,2,3,6,7,8,12

" 42

3,6,8,9

b 142

1,2,3,6,7,8,12

# 43

3,6,8,9

c 143

1,2,3,6,7,8,12

$ 44

3,6,8,9

d 144

1,2,3,6,7,8,12

% 45

3,6,8,9

e 145

1,2,3,6,7,8,12

& 46

3,6,8,9

f 146

1,2,3,6,7,8,12

’ 47

3,6,8,9

g 147

1,2,3,6,7,8

( 50

3,6,8,9

h 150

1,2,3,6,7,8

) 51

3,6,8,9

i 151

1,2,3,6,7,8

* 52

3,6,8,9

j 152

1,2,3,6,7,8

+ 53

3,6,8,9

k 153

1,2,3,6,7,8

' 54

3,6,8,9

l 154

1,2,3,6,7,8

- 55

3,6,8,9

m 155

1,2,3,6,7,8

. 56

3,6,8,9

n 156

1,2,3,6,7,8

/ 57

3,6,8,9

o 157

1,2,3,6,7,8

0 60

1,3,5,6,8,12

p 160

1,2,3,6,7,8

1 61

1,3,5,6,8,12

q 161

1,2,3,6,7,8

2 62

1,3,5,6,8,12

r 162

1,2,3,6,7,8

3 63

1,3,5,6,8,12

s 163

1,2,3,6,7,8

4 64

1,3,5,6,8,12

t 164

1,2,3,6,7,8

5 65

1,3,5,6,8,12

u 165

1,2,3,6,7,8

6 66

1,3,5,6,8,12

v 166

1,2,3,6,7,8

7 67

1,3,5,6,8,12

w 167

1,2,3,6,7,8

8 70

1,3,5,6,8,12

x 170

1,2,3,5,6,8

9 71

1,3,5,6,8,12

y 171

1,2,3,5,6,8

: 72

3,6,8,9

z 172

1,2,3,5,6,8

; 73

3,6,8,9

{ 173

3,6,8,9

< 74

3,6,8,9

| 174

3,6,8,9

= 75

3,6,8,9

} 175

3,6,8,9

> 76

3,6,8,9

~ 176

3,6,8,9

? 77

3,6,8,9

DEL 177

3,4

Example 3.1 shows how the character-classification functions are used.
Example 3.1. Character-Classification Functions
/*       CHAP_3_CHARCLASS.C                                     */

/* This example uses the isalpha, isdigit, and isspace          */
/* functions to count the number of occurrences of letters,     */
/* digits, and white-space characters entered through the       */
/* standard input (stdin).                                      */

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>

main()
{
    char c;
    int i = 0,
        j = 0,
        k = 0;

    while ((c = getchar()) != EOF) {
        if (isalpha(c))
            i++;
        if (isdigit(c))
            j++;
        if (isspace(c))
            k++;
    }

    printf("Number of letters: %d\n", i);
    printf("Number of digits:  %d\n", j);
    printf("Number of spaces:  %d\n", k);
}
The sample input and output from Example 3.1 follows:
$ RUN  EXAMPLE1
I saw 35 people riding bicycles on Main Street.Return
Ctrl/Z
Number of letters: 36
Number of digits:  2
Number of spaces:  8
$

3.2. Character-Conversion Functions

The character-conversion functions convert one type of character to another type. These functions include:
ecvt         _tolower
fcvt         toupper
gcvt         _toupper
mbtowc       towctrans
mbrtowc      wctrans
mbsrtowcs    wcrtomb
toascii      wcsrtombs
tolower

For more information on each of these functions, see the Reference Section.

Example 3.2 shows how to use the ecvt function.
Example 3.2. Converting Double Values to an ASCII String
/*     CHAP_3_CHARCONV.C                                        */

/* This program uses the ecvt function to convert a double      */
/* value to a string. The program then prints the string.       */

#include <stdio.h>
#include <stdlib.h>
#include <unixlib.h>
#include <string.h>

main()
{

    double val;         /* Value to be converted */

    int sign,           /* Variables for sign   */
        point;          /* and decimal place    */

    /*  Array for the converted string  */
    static char string[20];

    val = -3.1297830e-10;

    printf("original value: %e\n", val);
    if (sign)
        printf("value is negative\n");
    else
        printf("value is positive\n");
    printf("decimal point at %d\n", point);
}
The output from Example 3.2 is as follows:
$ RUN  EXAMPLE2
original value: -3.129783e-10
converted string: 31298
value is negative
decimal point at -9
$
Example 3.3 shows how to use the toupper and tolower functions.
Example 3.3. Changing Characters to and from Uppercase Letters
/*     CHAP_3_CONV_UPPERLOWER.C                                 */

/* This program uses the functions toupper and tolower to       */
/* convert uppercase to lowercase and lowercase to uppercase    */
/* using input from the standard input (stdin).                 */

#include <ctype.h>
#include <stdio.h>      /*  To use EOF identifier */
#include <stdlib.h>

main()
{
    char c,
         ch;

    while ((c = getchar()) != EOF) {
        if (c >= 'A' && c <= 'Z')
            ch = tolower(c);
        else
            ch = toupper(c);
        putchar(ch);
    }
}
Sample input and output from Example 3.3 are as follows:
$ RUN  EXAMPLE3
LET'S GO TO THE welcome INN.Ctrl/Z
let's go to the WELCOME inn.
$

3.3. String and Argument-List Functions

The C RTL contains a group of functions that manipulate strings. Some of these functions concatenate strings; others search a string for specific characters or perform some other comparison, such as determining the equality of two strings.

The C RTL also contains a set of functions that allow you to copy buffers containing binary data.

The set of functions defined and declared in the <varargs.h> and the <stdarg.h> header files provide a method of accessing variable-length argument lists. The <stdarg.h> functions are defined by the ANSI C Standard and are more portable than those defined in <varargs.h>.

The C RTL functions such as printf and execl, for example, use variable-length argument lists. User-defined functions with variable-length argument lists that do not use <varargs.h> or <stdarg.h> are not portable due to the different argument-passing conventions of various machines.

The <stdarg.h> header file does not contain va_alist and va_dcl. The following shows a syntax example when using <stdarg.h>:
function_name(int arg1, ...)
{
va_list ap;
. . .
When using <varargs.h>:

  • The identifier va_alist is a parameter in the function definition.

  • va_dcl declares the parameter va_alist, a declaration that is not terminated with a semicolon (;).

  • The type va_list is used in the declaration of the variable used to traverse the list. You must declare at least one variable of type va_list when using <varargs.h>.

These names and declarations have the following syntax: 
function_name(int arg1, ...)
{
va_list ap;
.
.
.

3.4. Program Examples

Example 3.4 shows how to use the strcat and strncat functions.
Example 3.4. Concatenating Two Strings
/*        CHAP_3_CONCAT.C                                      */

/*  This example uses strcat and strncat to concatenate two    */
/*  strings.                                                   */

#include <stdio.h>
#include <string.h>

main()
{
    static char string1[80] = "Concatenates ";
    static char string2[] = "two strings ";
    static char string3[] = "up to a maximum of characters.";
    static char string4[] = "imum number of characters";

    printf("strcat:\t%s\n", strcat(string1, string2));
    printf("strncat ( 0):\t%s\n", strncat(string1, string3, 0));
    printf("strncat (11):\t%s\n", strncat(string1, string3, 11));
    printf("strncat (40):\t%s\n", strncat(string1, string4, 40));
}
Example 3.4 produces the following output:
$ RUN  EXAMPLE1
strcat: Concatenates two strings
strncat ( 0): Concatenates two strings
strncat (11): Concatenates two strings up to a max
strncat (40): Concatenates two strings up to a maximum number of characters.
$
Example 3.5 shows how to use the strcspn function.
The sample output, to the file strcspn.out, in Example 3.5 is as follows:
$ RUN  EXAMPLE2 strcspn with null charset:  6
strcspn with null string:  0
strcspn("xabc","abc"):  1
strcspn("abc","def"):  3
Example 3.6 shows how to use the <stdarg.h> functions and definitions.
Example 3.6. Using the <stdarg.h> Functions and Definitions
/*        CHAP_3_STDARG.C                                       */

/* This routine accepts a variable number of string arguments,  */
/* preceded by a count of the number of such strings. It        */
/* allocates enough space in which to concatenate all of the    */
/* strings, concatenates them together, and returns the address */
/* of the new string. It returns NULL if there are no string    */
/* arguments, or if they are all null strings.                  */

#include <stdarg.h>       /* Include appropriate header files   */
#include <stdlib.h>       /* for the "example" call in main.    */
#include <string.h>
#include <stdio.h>

/* NSTRINGS is the maximum number of string arguments accepted  */
/* (arbitrary).                                                 */

#define NSTRINGS 10

char *concatenate(int n,...)
{
    va_list ap;         /* Declare the argument pointer. */

    char *list[NSTRINGS],
        *string;
    int index = 0,
        size = 0;

    /* Check that the number of arguments is within range.   */

    if (n <= 0)
        return NULL;
    if (n > NSTRINGS)
        n = NSTRINGS;

    va_start(ap, n);    /* Initialize the argument pointer.  */

    do {
        /* Extract the next argument and save it. */

        list[index] = va_arg(ap, char *);

        size += strlen(list[index]);
    } while (++index < n);

    va_end(ap); /* Terminate use of ap. */

    if (size == 0)
        return NULL;

    string = malloc(size + 1);
    string[0] = '\0';

    /* Append each argument to the end of the growing result    */
    /*  string.                                                 */

    for (index = 0; index < n; ++index)
        strcat(string, list[index]);

    return string;
}

/* An example of calling this routine is */

main() {
    char *ret_string ;

    ret_string = concatenate(7, "This ", "message ", "is ",
                                "built with ", "a", " variable arg",
                                " list.") ;

    puts(ret_string) ;
}
The call to Example 3.6 produces the following output:
This message is built with a variable arg list.

Chapter 4. Error and Signal Handling

Table 4.1 lists and describes all the error- and signal-handling functions found in the VSI C Run-Time Library (C RTL). For more detailed information on each function, see the Reference Section.
Table 4.1. Error- and Signal-Handling Functions

Function

Description

abort

Raises the signal SIGABRT that terminates the execution of the program.

assert

Puts diagnostics into programs.

atexit

Registers a function to be called at program termination.

exit, _exit

Terminates the current program.

perror

Writes a short error message to stderr describing the current errno value.

strerror

Maps the error code in errno to an error message string.

alarm

Sends the signal SIGALARM to the invoking process after the number of seconds indicated by its argument has elapsed.

gsignal

Generates a specified software signal.

kill

Sends a SIGKILL signal to the process specified by a process ID.

longjmp

Transfers control from a nested series of function invocations back to a predefined point without returning normally.

pause

Causes the process to wait until it receives a signal.

raise

Generates a specified signal.

setjmp

Establishes the context for a later transfer of control from a nested series of function invocations, without returning normally.

sigaction

Specifies the action to take upon delivery of a signal.

sigaddset

Adds the specified individual signal.

sigblock

Causes the signals in its argument to be added to the current set of signals being blocked from delivery.

sigdelset

Deletes a specified individual signal.

sigemptyset

Initializes the signal set to exclude all signals.

sigfillset

Initializes the signal set to include all signals.

sighold

Adds the specified signal to the calling process's signal mask.

sigignore

Sets the disposition of the specified signal to SIG_IGN.

sigismember

Tests whether a specified signal is a member of the signal set.

siglongjmp

Nonlocal go to with signal handling.

sigmask

Constructs the mask for a given signal number.

signal

Catches or ignores a signal.

sigpause

Blocks a specified set of signals and then waits for a signal that was not blocked.

sigpending

Examines pending signals.

sigprocmask

Sets the current signal mask.

sigrelse

Removes the specified signal from the calling process's signal mask.

sigsetjmp

Sets the jump point for a nonlocal go to.

sigsetmask

Establishes the signals that are blocked from delivery.

sigsuspend

Atomically changes the set of blocked signals and waits for a signal.

sigtimedwait

Suspends a calling thread and waits for queued signals to arrive.

sigvec

Permanently assigns a handler for a specific signal.

sigwait

Suspends a calling thread and waits for queued signals to arrive.

sigwaitinfo

Suspends a calling thread and waits for queued signals to arrive.

ssignal

Allows you to specify the action to be taken when a particular signal is raised.

VAXC$ESTABLISH

Establishes an application exception handler in a way that is compatible with C RTL exception handling.

4.1. Error Handling

When an error occurs during a call to any of the C RTL functions, the function returns an unsuccessful status. Many RTL routines also set the external variable errno to a value that indicates the reason for the failure. You should always check the return value for an error situation.

The <errno.h> header file declares errno and symbolically defines the possible error codes. By including the <errno.h> header file in your program, you can check for specific error codes after a C RTL function call.

At program startup, the value of errno is 0. The value of errno can be set to a nonzero value by many C RTL functions. It is not reset to 0 by any C RTL function, so it is only valid to use errno after a C RTL function call has been made and a failure status returned. Table 4.2 lists the symbolic values that may be assigned to errno by the C RTL.
Table 4.2. The Error Code Symbolic Values

Symbolic Constant

Description

E2BIG

Argument list too long

EACCES

Permission denied

EADDRINUSE

Address already in use

EADDRNOTAVAIL

Can't assign requested address

EAFNOSUPPORT

Address family not supported

EAGAIN

No more processes

EALIGN

Alignment error

EALREADY

Operation already in progress

EBADF

Bad file number

EBADCAT

Bad message catalog format

EBADMSG

Corrupted message detected

EBUSY

Mount device busy

ECANCELED

Operation canceled

ECHILD

No children

ECONNABORTED

Software caused connection abort

ECONNREFUSED

Connection refused

ECONNRESET

Connection reset by peer

EDEADLK

Resource deadlock avoided

EDESTADDRREQ

Destination address required

EDOM

Math argument

EDQUOT

Disk quota exceeded

EEXIST

File exists

EFAIL

Cannot start operation

EFAULT

Bad address

EFBIG

File too large

EFTYPE

Inappropriate operation for file type

EHOSTDOWN

Host is down

EHOSTUNREACH

No route to host

EIDRM

Identifier removed

EILSEQ

Illegal byte sequence

EINPROGRESS

Operation now in progress

EINPROG

Asynchronous operation in progress

EINTR

Interrupted system call

EINVAL

Invalid argument

EIO

I/O error

EISCONN

Socket is already connected

EISDIR

Is a directory

ELOOP

Too many levels of symbolic links

EMFILE

Too many open files

EMLINK

Too many links

EMSGSIZE

Message too long

ENAMETOOLONG

Filename too long

ENETDOWN

Network is down

ENETRESET

Network dropped connection on reset

ENETUNREACH

Network is unreachable

ENFILE

File table overflow

ENOBUFS

No buffer space available

ENODEV

No such device

ENOENT

No such file or directory

ENOEXEC

Exec format error

ENOLCK

No locks available

ENOMEM

Not enough core

ENOMSG

No message of desired type

ENOPROTOOPT

Protocol not available

ENOSPC

No space left on device

ENOSYS

Function not implemented

ENOTBLK

Block device required

ENOTCONN

Socket is not connected

ENOTDIR

Not a directory

ENOTEMPTY

Directory not empty

ENOTSOCK

Socket operation on nonsocket

ENOTSUP

Function not implemented

ENOTTY

Not a typewriter

ENWAIT

No waiting processes

ENXIO

No such device or address

EOPNOTSUPP

Operation not supported on socket

EPERM

Not owner

EPFNOSUPPORT

Protocol family not supported

EPIPE

Broken pipe

EPROCLIM

Too many processes

EPROTONOSUPPORT

Protocol not supported

EPROTOTYPE

Protocol wrong type for socket

ERANGE

Result too large

EREMOTE

Too many levels of remote in path

EROFS

Read-only file system

ESHUTDOWN

Can't send after socket shutdown

ESOCKTNOSUPPORT

Socket type not supported

ESPIPE

Illegal seek

ESRCH

No such process

ESTALE

Stale NFS file handle

ETIMEDOUT

Connection timed out

ETOOMANYREFS

Too many references: can't splice

ETXTBSY

Text file busy

EUSERS

Too many users

EVMSERR

OpenVMS specific non-translatable error code

EWOULDBLOCK

I/O operation would block channel

EXDEV

Cross-device link

You can translate the error codes to a message, similar to that found in UNIX systems, by using the perror or strerror function. If errno is set to EVMSERR, perror cannot translate the error code and prints the following message, followed by the OpenVMS error message associated with the value:
%s:nontranslatable vms error code: xxxxxx vms message:

In the message, %s is the string you supply to perror ; xxxxxx is the OpenVMS condition value.

If errno is set to EVMSERR, then the OpenVMS condition value is available in the vaxc$errno variable declared in the <errno.h> header file. The vaxc$errno variable is guaranteed to have a valid value only if errno is set to EVMSERR; if errno is set to a value other than EVMSERR, the value of vaxc$errno is undefined.

See the strerror function in the Reference Section for another way to translate error codes.

4.2. Signal Handling

A signal is a form of software interrupt to the normal execution of a user process. Signals occur as a result of a variety of events, including any of the following:

  • Typing Ctrl/C at a terminal

  • Certain programming errors

  • A call to the gsignal or raise function

  • A wake-up action

4.2.1. OpenVMS Versus UNIX Terminology

Both OpenVMS and UNIX systems provide signal-handling mechanisms that behave differently but use similar terminology. With the C RTL, you can program using either signal-handling mechanism. Before describing the signal-handling routines, some terminology must be established.

The UNIX term for a software interrupt is signal. A routine called by the UNIX system to process a signal is termed a signal handler.

A software interrupt on an OpenVMS system is referred to as a signal, condition, or exception. A routine called by the OpenVMS system to process software interrupts is termed a signal handler, condition handler, or exception handler.

To prevent confusion, the terms signal and signal handler in this manual refer to UNIX interrupts and interrupt processing routines, while the terms exception and exception handler refer to OpenVMS interrupts and interrupt processing routines.

4.2.2. UNIX Signals and the C RTL

Signals are represented by mnemonics defined in the <signal.h> header file. Table 4.3 lists the supported signal mnemonics and the corresponding event that causes each signal to be generated on the OpenVMS operating system.
Table 4.3. C RTL Signals

Name

Description

Generated by

SIGABRT?

Abort

abort()

SIGALRM

Alarm clock

Timer AST, alarm routine

SIGBUS

Bus error

Access violation or change mode user

SIGCHLD

Child process stopped

Child process terminated or stopped

SIGEMT

EMT instruction

Compatibility mode trap or opcode reserved to customer

SIGFPE

Floating-point exception

Floating-point overflow/underflow

SIGHUP

Hang up

Data set hang up

SIGILL?

Illegal instruction

Illegal instruction, reserved operand, or reserved address mode

SIGINT?

Interrupt

OpenVMS Ctrl/C interrupt

SIGIOT?

IOT instruction

Opcode reserved to customer

SIGKILL? ?

Kill

External signal only

SIGQUIT?

Quit

Not implemented.

SIGPIPE

Broken pipe

Write to a pipe with no readers.

SIGSEGV

Segment violation

Length violation or change mode user

SIGSYS

System call error

Bad argument to system call

SIGTERM

Software terminate

External signal only

SIGTRAP?

Trace trap

TBIT trace trap or breakpoint fault instruction

SIGUSR1

User-defined signal

Explicit program call to raise the signal

SIGUSR2

User-defined signal

Explicit program call to raise the signal

SIGWINCH?

Window size changed

Explicit program call to raise the signal

By default, when a signal (except for SIGCHLD) occurs, the process is terminated. However, you can choose to have the signal ignored by using one of the following functions:
  • sigaction
  • signal
  • sigvec
  • ssignal
You can have the signal blocked by using one of the following functions:
  • sigblock
  • sigsetmask
  • sigprocmask
  • sigsuspend
  • sigpause

Table 4.3 indicates those signals that cannot be ignored or blocked.

You can also establish a signal handler to catch and process a signal by using one of the following functions:
  • sigaction
  • signal
  • sigvec
  • ssignal

Unless noted in Table 4.3, each signal can be reset. A signal is reset if the signal handler function calls signal or ssignal to re-establish itself to catch the signal. Example 4.1 shows how to establish a signal handler and reset the signal.

The calling interface to a signal handler is:
void handler (int sigint);

Where sigint is the signal number of the raised signal that caused this handler to be called.

A signal handler installed with sigvec remains installed until it is changed.

A signal handler installed with signal or signal remains installed until the signal is generated.

A signal handler can be installed for more than one signal. Use the sigaction routine with the SA_RESETHAND flag to control this.

4.2.3. Signal-Handling Concepts

A signal is said to be generated for (or sent to) a process when the event that causes the signal first occurs. Examples of such events include detection of hardware faults, timer expiration, and terminal activity, as well as the invocation of kill. In some circumstances, the same event generates signals for multiple processes.

Each process has an action to be taken in response to each signal defined by the system. A signal is said to be delivered to a process when the appropriate action for the process and signal is taken.

During the time between the generation of a signal and its delivery, the signal is said to be pending. Ordinarily, this interval cannot be detected by an application. However, a signal can be blocked from delivery to a process:

  • If the action associated with a blocked signal is anything other than to ignore the signal, and if that signal is generated for the process, the signal remains pending until either it is unblocked or the action associated with it is set to ignore the signal.

  • If the action associated with a blocked signal is to ignore the signal and if that signal is generated for the process, it is unspecified whether the signal is discarded immediately upon generation or remains pending.

Each process has a signal mask that defines the set of signals currently blocked from delivery to it. The signal mask for a process is initialized from that of its parent. The sigaction, sigprocmask, and sigsuspend functions control the manipulation of the signal mask.

The determination of which action is taken in response to a signal is made at the time the signal is delivered, allowing for any changes since the time of generation. This determination is independent of the means by which the signal was originally generated. If a subsequent occurrence of a pending signal is generated, it is implementation-dependent as to whether the signal is delivered more than once. The C RTL delivers the signal only once. The order in which multiple, simultaneously pending signals are delivered to a process is unspecified.

4.2.4. Signal Actions

This section applies to the sigaction, signal, sigvec, and ssignal functions.

There are three types of action that can be associated with a signal:
  • SIG_DFL
  • SIG_IGN
  • pointer to a function
Initially, all signals are set to SIG_DFL or SIG_IGN prior to entry of the main routine (see the exec functions.) The actions prescribed by these values are:

  • SIG_DFL — signal-specific default action

    • The default actions for the signals defined in this document are specified under <signal.h>.

    • If the default action is to stop the process, the execution of that process is temporarily suspended. When a process stops, a SIGCHLD signal is generated for its parent process, unless the parent process has set the SA_NOCLDSTOP flag. While a process is stopped, any additional signals that are sent to the process are not delivered until the process is continued, except SIGKILL which always terminates the receiving process. A process that is a member of an orphaned process group is not allowed to stop in response to the SIGSTOP, SIGTTIN, or SIGTTOU signals. In cases where delivery of one of these signals would stop such a process, the signal is discarded.

    • Setting a signal action to SIG_DFL for a signal that is pending and whose default action is to ignore the signal (for example, SIGCHLD), causes the pending signal to be discarded, whether or not it is blocked.

  • SIG_IGN — ignore signal

    • Delivery of the signal has no effect on the process. The behavior of a process is undefined after it ignores a SIGFPE, SIGILL, or SIGSEGV signal that was not generated by kill or raise.

    • The system does not allow the action for the SIGKILL or SIGSTOP signals to be set to SIG_IGN.

    • Setting a signal action to SIG_IGN for a signal that is pending causes the pending signal to be discarded, whether or not it is blocked.

    • If a process sets the action for the SIGCHLD signal to SIG_IGN, the behavior is unspecified.

  • pointer to a function — catch signal

    • On delivery of the signal, the receiving process executes the signal-catching function at the specified address. After returning from the signal-catching function, the receiving process resumes execution at the point at which it was interrupted.

    • Specify the signal-catching function as:
      void func(int signo);

      Here, func is the specified signal-catching function and signo is the signal number of the signal being delivered.

    • The behavior of a process is undefined after it returns normally from a signal-catching function for a SIGFPE, SIGKILL, or SIGSEGV signal that was not generated by kill or raise.

    • The system does not allow a process to catch the signals SIGKILL and SIGSTOP.

    • If a process establishes a signal-catching function for the SIGCHLD signal while it has a terminated child process for which it has not waited, it is unspecified whether a SIGCHLD signal is generated to indicate that child process.

4.2.5. Signal Handling and OpenVMS Exception Handling

This section discusses how C RTL signal handling is implemented with and interacts with OpenVMS exception handling. Information in this section allows you to write OpenVMS exception handlers that do not conflict with C RTL signal handling. For information on OpenVMS exception handling, see the OpenVMS Procedure Calling and Condition Handling Standard.

The C RTL implements signals with OpenVMS exceptions. When gsignal or raise is called, the signal number is translated to a particular OpenVMS exception, which is used in a call to LIB$SIGNAL. This mechanism is necessary to catch an OpenVMS exception resulting from a user error and translate it into a corresponding UNIX signal. For example, an ACCVIO resulting from a write to a NULL pointer is translated to a SIGBUS or SIGSEGV signal.

Tables 4.4 and 4.5 list the C RTL signal names, the corresponding OpenVMS Alpha and Integrity server system exceptions, the event that generates the signal, and the optional signal code for use with the gsignal and raise functions.

To call a signal handler that you have established with signal or sigvec, the C RTL intercepts the OpenVMS exceptions that correspond to signals by having an OpenVMS exception handler in the main routine of the program. If your program has a main function, then this exception handler is automatically established. If you do not have a main function, or if your main function is written in a language other than VSI C, then you must invoke the VAXC$CRTL_INIT routine to establish this handler.

The C RTL uses OpenVMS exceptions to implement the setjmp and longjmp functions. When the longjmp function is called, a C$_LONGJMP OpenVMS exception is signaled. To prevent the C$_LONGJMP exception from being interfered with by user exception handlers, use the VAXC$ESTABLISH routine to establish user OpenVMS exception handlers instead of calling LIB$ESTABLISH. The C$_LONGJMP mnemonic is defined in the <errnodef.h> header file.

If you want to use OpenVMS exception handlers and UNIX signals in your C program, your OpenVMS exception handler must be prepared to accept and resignal the OpenVMS exceptions listed in Table 4.4 (Alpha only), as well as the C$_LONGJMP exception and any C$ facility exception that might be introduced in future versions of the C RTL. This is because UNIX signals are global in context, whereas OpenVMS exceptions are stack-frame based.

Consequently, an OpenVMS exception handler always receives the exception that corresponds to the UNIX signal before the C RTL exception handler in the main routine does. By resignalling the OpenVMS exception, you allow the C RTL exception handler to receive the exception. You can intercept any of those OpenVMS exceptions yourself, but in doing so you will disable the corresponding UNIX signal.
Table 4.4. C RTL Signals and Corresponding OpenVMS Alpha Exceptions (Alpha Only)

Name

OpenVMS Exception

Generated By

Code

SIGABRT

SS$_OPCCUS

The abort function

–

SIGALRM

SS$_ASTFLT

The alarm function

–

SIGBUS

SS$_ACCVIO

Access violation

–

SIGBUS

SS$_CMODUSER

Change mode user

–

SIGCHLD

C$_SIGCHLD

Child process stopped

–

SIGEMT

SS$_COMPAT

Compatibility mode trap

–

SIGFPE

SS$_DECDIV

Decimal divide trap

FPE_DECDIV_TRAP

SIGFPE

SS$_DECINV

Decimal invalid operand trap

FPE_DECINV_TRAP

SIGFPE

SS$_DECOVF

Decimal overflow trap

FPE_DECOVF_TRAP

SIGFPE

SS$_HPARITH

Floating/decimal division by 0

FPE_FLTDIV_TRAP

SIGFPE

SS$_HPARITH

Floating overflow trap

FPE_FLTOVF_TRAP

SIGFPE

SS$_HPARITH

Floating underflow trap

FPE_FLTUND_TRAP

SIGFPE

SS$_HPARITH

Integer overflow

FPE_INTOVF_TRAP

SIGFPE

SS$_HPARITH

Invalid operand

FPE_INVOPR_TRAP

SIGFPE

SS$_HPARITH

Inexact result

FPE_INXRES_TRAP

SIGFPE

SS$_INTDIV

Integer div by zero

FPE_INTDIV_TRAP

SIGFPE

SS$_SUBRNG

Subscript out of range

FPE_SUBRNG_TRAP

SIGFPE

SS$_SUBRNG1

Subscript1 out of range

FPE_SUBRNG1_TRAP

SIGFPE

SS$_SUBRNG2

Subscript2 out of range

FPE_SUBRNG2_TRAP

SIGFPE

SS$_SUBRNG3

Subscript3 out of range

FPE_SUBRNG3_TRAP

SIGFPE

SS$_SUBRNG4

Subscript4 out of range

FPE_SUBRNG4_TRAP

SIGFPE

SS$_SUBRNG5

Subscript5 out of range

FPE_SUBRNG5_TRAP

SIGFPE

SS$_SUBRNG6

Subscript6 out of range

FPE_SUBRNG6_TRAP

SIGFPE

SS$_SUBRNG7

Subscript7 out of range

FPE_SUBRNG7_TRAP

SIGHUP

SS$_HANGUP

Data set hangup

–

SIGILL

SS$_OPCDEC

Reserved instruction

ILL_PRIVIN_FAULT

SIGILL

SS$_ROPRAND

Reserved operand

ILL_RESOP_FAULT

SIGINT

SS$_CONTROLC

OpenVMS Ctrl/C interrupt

–

SIGIOT

SS$_OPCCUS

Customer-reserved opcode

–

SIGKILL

SS$_ABORT

External signal only

–

SIGQUIT

SS$_CONTROLY

The raise function

–

SIGPIPE

SS$_NOMBX

No mailbox

–

SIGPIPE

C$_SIGPIPE

Broken pipe

–

SIGSEGV

SS$_ACCVIO

Length violation

–

SIGSEGV

SS$_CMODSUPR

Change mode supervisor

–

SIGSYS

SS$_BADPARAM

Bad argument to system call

–

SIGTERM

Not implemented

–

–

SIGTRAP

SS$_BREAK

Breakpoint fault instruction

–

SIGUSR1

C$_SIGUSR1

The raise function

–

SIGUSR2

C$_SIGUSR2

The raise function

–

SIGWINCH ?

C$_SIGWINCH ?

The raise function

–


OpenVMS Alpha Signal-Handling Notes

  • While all signals that exist on OpenVMS VAX systems also exist on OpenVMS Alpha systems, the corresponding OpenVMS exceptions and code is different in a number of cases because on Alpha processors there are two new OpenVMS exceptions and several others that are obsolete.

  • All floating-point exceptions on OpenVMS Alpha systems are signaled by the OpenVMS exception SS$_HPARITH (high-performance arithmetic trap). The particular type of trap that occurred is translated by the C RTL through use of the exception summary longword, which is set when a high-performance arithmetic trap is signaled.


Table 4.5. C RTL Signals and Corresponding OpenVMS Integrity server system Exceptions (Integrity servers Only)

Name

OpenVMS Exception

Generated By

Code

SIGABRT

SS$_OPCCUS

The abort function

–

SIGALRM

SS$_ASTFLT

The alarm function

–

SIGBUS

SS$_ACCVIO

Access violation

–

SIGBUS

SS$_CMODUSER

Change mode user

–

SIGCHLD

C$_SIGCHLD

Child process stopped

–

SIGEMT

SS$_COMPAT

Compatibility mode trap

–

SIGFPE

SS$_DECOVF

Decimal overflow trap

FPE_DECOVF_TRAP

SIGFPE

SS$_DECDIV

Decimal divide trap

FPE_DECDIV_TRAP

SIGFPE

SS$_DECINV

Decimal invalid operand trap

FPE_DECINV_TRAP

SIGFPE

SS$_FLTDENORMAL

Denormal operand fault

FPE_FLTDENORMAL

_FAULT

SIGFPE

SS$_FLTDIV

Floating/decimal division by 0

FPE_FLTDIV_TRAP

SIGFPE

SS$_FLTDIV_F

Floating divide by 0 fault

FPE_FLTDIV_FAULT

SIGFPE

SS$_FLTINE

Inexact operation trap

FPE_FLTINE_TRAP

SIGFPE

SS$_FLTINV

Invalid operation trap

FPE_FLTINV_TRAP

SIGFPE

SS$_FLTINV_F

Invalid operation fault

FPE_FLTINV_FAULT

SIGFPE

SS$_FLTOVF

Floating overflow trap

FPE_FLTOVF_TRAP

SIGFPE

SS$_FLTUND

Floating underflow trap

FPE_FLTUND_TRAP

SIGFPE

SS$_INTDIV

Integer division by 0

FPE_INTDIV_TRAP

SIGFPE

SS$_INTOVF

Integer overflow

FPE_INTOVF_TRAP

SIGFPE

SS$_SUBRNG

Subscript-range

FPE_SUBRNG_TRAP

SIGHUP

SS$_HANGUP

Data set hangup

–

SIGILL

SS$_OPCDEC

Reserved instruction

ILL_PRIVIN_FAULT

SIGILL

SS$_ROPRAND

Reserved operand

ILL_RESOP_FAULT

SIGINT

SS$_CONTROLC

OpenVMS Ctrl/C interrupt

–

SIGIOT

SS$_OPCCUS

Customer-reserved opcode

–

SIGKILL

SS$_ABORT

External signal only

–

SIGQUIT

SS$_CONTROLY

The raise function

–

SIGPIPE

SS$_NOMBX

No mailbox

–

SIGPIPE

C$_SIGPIPE

Broken pipe

–

SIGSEGV

SS$_ACCVIO

Length violation

–

SIGSEGV

SS$_CMODSUPR

Change mode supervisor

–

SIGSYS

SS$_BADPARAM

Bad argument to system call

–

SIGTERM

Not implemented

–

–

SIGTRAP

SS$_TBIT

TBIT trace trap

–

SIGTRAP

SS$_BREAK

Breakpoint fault instruction

–

SIGUSR1

C$_SIGUSR1

The raise function

–

SIGUSR2

C$_SIGUSR2

The raise function

–

SIGWINCH

C$_SIGWINCH

The raisefunction

–

4.3. Program Example

Example 4.1 shows how the signal, alarm, and pause functions operate. It also shows how to establish a signal handler to catch a signal, which prevents program termination.
Example 4.1. Suspending and Resuming Programs
/*    CHAP_4_SUSPEND_RESUME.C                                   */

/* This program shows how to alternately suspend and resume a   */
/* program using the signal, alarm, and pause functions.        */

#define SECONDS 5

#include <stdio.h>
#include <signal.h>

int number_of_alarms = 5;       /*  Set alarm counter.            */

void alarm_action(int);

main()
{
    signal(SIGALRM, alarm_action); /*  Establish a signal handler. */
                                   /*  to catch the SIGALRM signal.*/

    alarm(SECONDS);     /* Set alarm clock for 5 seconds. */

    pause();    /*  Suspend the process until     *
                 *  the signal is received.       */
}

void alarm_action(int x)
{
    printf("\t<%d\007>", number_of_alarms); /*  Print the value of  */
                                            /*  the alarm counter.  */

    signal(SIGALRM, alarm_action);      /*  Reset the signal.       */

    alarm(SECONDS);     /*  Set the alarm clock.      */

    if (--number_of_alarms)     /*  Decrement alarm counter.  */
        pause();
}
Here is the sample output from Example 4.1:
$ RUN  EXAMPLE
       <5>   <4>   <3>   <2>   <1>

Chapter 5. Subprocess Functions

The VSI C Run-Time Library (C RTL) provides functions that allow you to create subprocesses from a VSI C program. The creating process is called the parent and the created subprocess is called the child.

To create a child process within the parent process, use the exec functions (execl, execle, execv, execve, execlp, and execvp) and the vfork function. Other functions are available to allow the parent and child to read and write data across processes (pipe) and to allow for synchronization of the two processes (wait). This chapter describes how to implement and use these functions.

The parent process can execute VSI C programs in its children, either synchronously or asynchronously. The number of children that can run simultaneously is determined by the /PRCLM user authorization quota established for each user on your system. Other quotas that may affect the use of subprocesses are /ENQLM (Queue Entry Limit), /ASTLM (AST Waits Limit), and /FILLM (Open File Limit).

This chapter discusses the subprocess functions. Table 5.1 lists and describes all the subprocess functions found in the C RTL. For more detailed information on each function, see the Reference Section.
Table 5.1. Subprocess Functions

Function

Description

Implementation of Child Processes

system

Passes a given string to the host environment to be executed by a command processor.

vfork

Creates an independent child process.

The exec Functions

  • execl
  • execle
  • execlp
  • execv
  • execve
  • execvp

Pass the name of the image to be activated in a child process.

Synchronizing Process

  • wait
  • wait3
  • wait4
  • waitpid

Suspend the parent process until a value is returned from a child.

Interprocess Communication

pipe

Allows for communication between a parent and child.

5.1. Implementing Child Processes in VSI C

Child processes are created by VSI C functions with the OpenVMS LIB$SPAWN RTL routine. (See the VMS Run-Time Library Routines Volume for information on LIB$SPAWN.) Using LIB$SPAWN allows you to create multiple levels of child processes; the parent's children can also spawn children, and so on, up to the limits allowed by the user authorization quotas discussed in the introduction to this chapter.

Child processes can only execute other VSI C programs. Other native-mode OpenVMS languages do not share the ability of VSI C to communicate between processes; if they do, they do not use the same mechanisms. The parent process must be run under an VSI supported command-language interpreter (CLI), such as DCL. You cannot run the parent as a detached process or under control of a user-supplied CLI.

Enabling the DECC$DETACHED_CHILD_PROCESS feature logical allows child processes to be created as detached processes instead of subprocesses. This feature has only limited support. In some cases, the console cannot be shared between the parent process and the detached process, which can cause exec to fail.

Parent and child processes communicate through a mailbox as shown in Figure 5.1. This mailbox transfers the context in which the child will run. This context mailbox passes information to the child that it inherits from the parent, such as the names and file descriptors of all the files opened by the parent and the current location within those files. The mailbox is deleted by the parent when the child image exits.

Note

The mailbox created by the vfork and exec functions is temporary. The logical name of this mailbox is VAXC$EXECMBX and is reserved for use by the C RTL.

The mailbox is created with a maximum message size and a buffer quota of 512 bytes each, unless the buffer size and quota are explicitly specified with the DECC$PIPE_BUFFER_SIZE or DECC$PIPE_BUFFER_QUOTA feature logicals, or with the bufsize or bufquota parameters of the pipe function. See the pipe function for more information.

You need the TMPMBX privilege to create a mailbox with these RTL functions. Since TMPMBX is the privilege required by the DCL commands PRINT and SUBMIT, most users on a system have this privilege. To see what system privileges you have, enter a SHOW PROCESS/PRIVILEGES command.

You cannot change the characteristics of these mailboxes. For more information on mailboxes, see the VSI OpenVMS I/O User's Reference Manual.

5.2. The exec Functions

There are six exec functions that you can call to execute an VSI C image in the child process. These functions expect that vfork has been called to set up a return address. The exec functions will call vfork if the parent process did not.

When vfork is called by the parent, the exec function returns to the parent process. When vfork was called by an exec function, the exec function returns to itself, waits for the child to exit, and then exits the parent process. The exec function does not return to the parent process unless the parent calls vfork to save the return address.

In OpenVMS Version 7.2, the exec functions were enhanced to activate either executable images or DCL command procedures. If no file extension is specified in the file_name argument, the functions first search for the file with the .EXE file extension and then for the file with the .COM file extension. If both the executable image and the command procedure with the same name exist, you must explicitly specify the .COM file extension to force activating the command procedure.

For a DCL command procedure, the exec functions pass the first eight arg0, arg1, ..., arguments specified in the exec call to the command procedure as P1, P2, ... parameters, preserving the case.

Unlike UNIX based systems, the exec functions in the C RTL cannot always determine if the specified executable image or command procedure exists and can be activated and executed. Therefore, the exec functions might appear to succeed even though the specified file cannot be executed by the child process.

The status of the child process, returned to the parent process, indicates that the error occurred. You can retrieve this error code by using one of the functions from the wait family of functions.

Note

The vfork and exec functions in the C RTL on OpenVMS systems work differently than on UNIX systems:

  • On UNIX systems, vfork creates a child process, suspends the parent, and starts the child running where the parent left off.

  • On OpenVMS systems, vfork establishes context later used by an exec function, but it is the exec function, not vfork, that starts a process running the specified program.

For a programmer, the key differences are:

  • On OpenVMS systems, code between the call to vfork and the call to an exec function runs in the parent process.

    On UNIX systems, this code runs in the child process.

  • On OpenVMS systems, the child inherits open file descriptors and so on, at the point where the exec function is called.

    On UNIX systems, this occurs at the point where vfork is called.

5.2.1. exec Processing

The exec functions use the LIB$SPAWN routine to create the subprocess and activate the child image within the subprocess. This child process inherits the parent's environment, including all defined logical names and command-line interpreter symbols.

By default, child processes also inherit the default (working) directory of their parent process. However, you can use the decc$set_child_default_dir function to set the default directory for a child process as it begins execution. For more information about the decc$set_child_default_dir function, see the Reference Section.

The exec functions use the logical name VAXC$EXECMBX to communicate between parent and child; this logical name must not exist outside the context of the parent image.

The exec functions pass the following information to the child:

  • The parent's umask value, which specifies whether any access is to be disallowed when a new file is created. For more information about the umask function, see the Reference Section.

  • The file-name string associated with each file descriptor and the current position within each file. The child opens the file and calls lseek to position the file to the same location as the parent. If the file is a record file, the child is positioned on a record boundary, regardless of the parent's position within the record. For more information about file descriptors, see Chapter 2. For more information on the lseek function, see the Reference Section.

    This information is sent to the child for all descriptors known to the parent including all descriptors for open files, null descriptors, and duplicate descriptors.

    File pointers are not transferred to the child. For files opened by a file pointer in the parent, only their corresponding file descriptors are passed to the child. The fdopen function must be called to associate a file pointer with the file descriptor if the child will access the file-by-file pointer. For more information about the fdopen function, see the Reference Section.

    The DECC$EXEC_FILEATTR_INHERITANCE feature logical can be used to control whether or not a child process inherits file positioning, and if so, for which access modes. For more information on DECC$EXEC_FILEATTR_INHERITANCE, see Section 1.5.

  • The signal database. Only SIG_IGN (ignore) actions are inherited. Actions specified as routines are changed to SIG_DFL (default) because the parent's signal-handling routines are inaccessible to the child.

  • The environment and argument vectors.

When everything is transmitted to the child, exec processing is complete. Control in the parent process then returns to the address saved by vfork and the child's process ID is returned to the parent.

See Section 4.2.4 for a discussion of signal actions and the SIGCHLD signal.

5.2.2. exec Error Conditions

The exec functions will fail if LIB$SPAWN cannot create the subprocess. Conditions that can cause a failure include exceeding the subprocess quota or finding the communications by the context mailbox between the parent and child to be broken. Exceeding some quotas will not cause LIB$SPAWN to fail, but will put LIB$SPAWN into a wait state that can cause the parent process to hang. An example of such a quota is the Open File Limit quota.

You will need an Open File Limit quota of at least 20 files, with an average of three times the number of concurrent processes that your program will run. If you use more than one open pipe at a time, or perform I/O on several files at one time, this quota may need to be even higher. See your system manager if this quota needs to be increased.

When an exec function fails, a value of -1 is returned. After such a failure, the parent is expected to call either the exit or _exit function. Both functions then return to the parent's vfork call, which returns the child's process ID. In this case, the child process ID returned by the exec function is less than zero. For more information about the exit function, see the Reference Section.

5.3. Synchronizing Processes

A child process is terminated when the parent process terminates. Therefore, the parent process must check the status of its child processes before exiting. This is done using the C RTL function wait.

5.4. Interprocess Communication

A channel through which parent and child processes communicate is called a pipe. Use the pipe function to create a pipe.

5.5. Program Examples

Example 5.1 shows the basic procedures for executing an image in a child process. The child process in Example 5.1 prints a message 10 times.
Example 5.1. Creating the Child Process
/*      chap_5_exec_image.c     */

/* This example creates the child process.  The only    */
/* functionality given to the child is the ability to   */
/* print a message 10 times.                            */

#include <climsgdef.h>  /* CLI status values  */
#include <stdio.h>
#include <perror.h>
#include <processes.h>
#include <stdlib.h>

static const char *child_name = "chap_5_exec_image_child.exe" ;

main()
{
   int status,
       cstatus;

   /* NOTE:                                            */
   /*    Any local automatic variables, even those     */
   /*    having the volatile attribute, may have       */
   /*    indeterminant values if they are modified     */
   /*    between the vfork() call and the matching     */
   /*    exec() call.                                  */

1   if ((status = vfork()) != 0) {
       /* This is either an error or                   */
       /* the "second" vfork return, taking us "back"  */
       /* to parent mode.                              */
2       if (status < 0)
            printf("Parent - Child process failed\n");
       else {
            printf("Parent - Waiting for Child\n");
3            if ((status = wait(&cstatus)) == -1)
               perror("Parent - Wait failed");
4            else if (cstatus == CLI$_IMAGEFNF)
               printf("Parent - Child does not exist\n");
            else
               printf("Parent - Child final status: %d\n", cstatus);
        }
    }
5    else {  /* The FIRST Vfork return is zero, do the exec */
           printf("Parent - Starting Child\n");
           if ((status = execl(child_name, 0)) == -1) {
               perror("Parent - Execl failed");
               exit(EXIT_FAILURE);
         }
    }
}

----------------------------------------------------------
/*      CHAP_5_EXEC_IMAGE_CHILD.C                    */

/* This is the child program that writes a message   */
/* through the parent to "stdout"                    */

#include <stdio.h>

main()
{
    int i;

    for (i = 0; i < 10; i++)
        printf("Child - executing\n");
    return (255) ;    /* Set an unusual success stat */
}
Key to Example 5.1:

1

The vfork function is called to set up the return address for the exec call.

The vfork function is normally used in the expression of an if statement. This construct allows you to take advantage of the double return aspect of vfork, since one return value is 0 and the other is nonzero.

5

A 0 return value is returned the first time vfork is called and the parent executes the else clause associated with the vfork call, which calls execl.

2

A negative child process ID is returned when an exec function fails. The return value is checked for these conditions.

3

The wait function is used to synchronize the parent and child processes.

4

Since the exec functions can indicate success up to this point even if the image to be activated in the child does not exist, the parent checks the child's return status for the predefined status, CLI$_IMAGEFNF (file not found).

In Example 5.2, the parent passes arguments to the child process.
Example 5.2. Passing Arguments to the Child Process
/*       CHAP_5_CHILDARG.C                                           */

/* In this example, the arguments are placed in an array, gargv,     */
/* but they can be passed to the child explicitly as a zero-         */
/* terminated series of character strings. The child program in this */
/* example writes the arguments that have been passed it to stdout.  */

#include <climsgdef.h>
#include <stdio.h>
#include <stdlib.h>
#include <perror.h>
#include <processes.h>

const char *child_name = "chap_5_childarg_child.exe" ;

main()
{
    int status,
        cstatus;
    char *gargv[] =
    {"Child", "ARGC1", "ARGC2", "Parent", 0};

    if ((status = vfork()) != 0) {
        if (status < -1)
            printf("Parent - Child process failed\n");
        else {
            printf("Parent - waiting for Child\n");
            if ((status = wait(&cstatus)) == -1)
                perror("Parent - Wait failed");
            else if (cstatus == CLI$_IMAGEFNF)
                printf("Parent - Child does not exist\n");
            else
                printf("Parent - Child final status: %x\n",
                       cstatus);
        }
    }
    else {
        printf("Parent - Starting Child\n");
        if ((status = execv(child_name, gargv)) == -1) {
            perror("Parent - Exec failed");
            exit(EXIT_FAILURE);
        }
    }
}

--------------------------------------------------------
/*       CHAP_5_CHILDARG_CHILD.C                      */

/* This is a child program that echo's its arguments   */

#include <stdio.h>

main(argc, argv)
    int argc;
    char *argv[];
{
    int i;

    printf("Program name: %s\n", argv[0]);

    for (i = 1; i < argc; i++)
        printf("Argument %d: %s\n", i, argv[i]);
    return(255) ;
}
Example 5.3 shows how to use the wait function to check the final status of multiple children being run simultaneously.
Example 5.3. Checking the Status of Child Processes
/*        CHAP_5_CHECK_STAT.C                                   */

/* In this example 5 child processes are started.  The wait()   */
/* function is placed in a separate for loop so that it is      */
/* called once for each child. If wait() were called within     */
/* the first for loop, the parent would wait for one child to   */
/* terminate before executing the next child. If there were     */
/* only one wait request, any child still running when the      */
/* parent exits would terminate prematurely.                    */

#include <climsgdef.h>
#include <stdio.h>
#include <stdlib.h>
#include <perror.h>
#include <processes.h>

const char *child_name = "chap_5_check_stat_child.exe" ;

main()
{
    int status,
        cstatus,
        i;

    for (i = 0; i < 5; i++) {
        if ((status = vfork()) == 0) {
            printf("Parent - Starting Child %d\n", i);
            if ((status = execl(child_name, 0)) == -1) {
                perror("Parent - Exec failed");
                exit(EXIT_FAILURE);
            }
        }
        else if (status < -1)
            printf("Parent - Child process failed\n");
    }

    printf("Parent - Waiting for children\n");

    for (i = 0; i < 5; i++) {
        if ((status = wait(&cstatus)) == -1)
            perror("Parent - Wait failed");
        else if (cstatus == CLI$_IMAGEFNF)
            printf("Parent - Child does not exist\n");
        else
            printf("Parent - Child %X final status: %d\n",
                   status, cstatus);
    }
}
Example 5.4 shows how to use the pipe and dup2 functions to communicate between a parent and child process through specific file descriptors. The #define preprocessor directive defines the preprocessor constants inpipe and outpipe as the names of file descriptors 11 and 12.
Example 5.4. Communicating Through a Pipe
/*        CHAP_5_PIPE.C                                         */

/* In this example, the parent writes a string to the pipe for  */
/* the child to read.  The child then writes the string back    */
/* to the pipe for the parent to read.  The wait function is    */
/* called before the parent reads the string that the child has */
/* passed back through the pipe.  Otherwise, the reads and      */
/* writes will not be synchronized.                             */

#include <perror.h>
#include <climsgdef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <processes.h>
#include <unixio.h>

#define inpipe 11
#define outpipe 12

const char *child_name = "chap_5_pipe_child.exe" ;

main()
{
    int pipes[2];
    int mode,
        status,
        cstatus,
        len;
    char *outbuf,
        *inbuf;

    if ((outbuf = malloc(512)) == 0) {
        printf("Parent - Outbuf allocation failed\n");
        exit(EXIT_FAILURE);
    }

    if ((inbuf = malloc(512)) == 0) {
        printf("Parent - Inbuf allocation failed\n");
        exit(EXIT_FAILURE);
    }
    if (pipe(pipes) == -1) {
        printf("Parent - Pipe allocation failed\n");
        exit(EXIT_FAILURE);
    }

    dup2(pipes[0], inpipe);
    dup2(pipes[1], outpipe);
    strcpy(outbuf, "This is a test of two-way pipes.\n");

    status = vfork();

    switch (status) {
    case 0:
        printf("Parent - Starting child\n");
        if ((status = execl(child_name, 0)) == -1) {
            printf("Parent - Exec failed");
            exit(EXIT_FAILURE);
        }
        break;

    case -1:
        printf("Parent - Child process failed\n");
        break;

    default:
        printf("Parent - Writing to child\n");

        if (write(outpipe, outbuf, strlen(outbuf) + 1) == -1) {
            perror("Parent - Write failed");
            exit(EXIT_FAILURE);
        }
        else {
            if ((status = wait(&cstatus)) == -1)
                perror("Parent - Wait failed");

            if (cstatus == CLI$_IMAGEFNF)
                printf("Parent - Child does not exist\n");
            else {
                printf("Parent - Reading from child\n");
                if ((len = read(inpipe, inbuf, 512)) <= 0) {
                    perror("Parent - Read failed");
                    exit(EXIT_FAILURE);
                }
                else {
                    printf("Parent: %s\n", inbuf);
                    printf("Parent - Child final status: %d\n",
                            cstatus);
                }
            }
        }
        break;
    }
}

------------------------------------------------------------------
/*        CHAP_5_PIPE_CHILD.C                                   */

/* This is a child program which reads from a pipe and writes   */
/* the received message back to its parent.                     */

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

#define inpipe 11
#define outpipe 12

main()
{
    char *buffer;
    int len;

    if ((buffer = malloc(512)) == 0) {
        perror("Child - Buffer allocation failed\n");
        exit(EXIT_FAILURE);
    }

    printf("Child - Reading from parent\n");
    if ((len = read(inpipe, buffer, 512)) <= 0) {
        perror("Child - Read failed");
        exit(EXIT_FAILURE);
    }
    else {
        printf("Child: %s\n", buffer);
        printf("Child - Writing to parent\n");
        if (write(outpipe, buffer, strlen(buffer) + 1) == -1) {
            perror("Child - Write failed");
            exit(EXIT_FAILURE);
        }
    }
    exit(EXIT_SUCCESS);
}

Chapter 6. Curses Screen Management Functions and Macros

This chapter describes the screen management routines available with VSI C for OpenVMS Systems.

The OpenVMS Curses screen management package is supported on all OpenVMS systems.

On OpenVMS Alpha systems, two screen management packages are supported: OpenVMS Curses and a more UNIX compatible package based on the Berkeley Standard Distribution (BSD) Curses software.? See Section 6.1 for more information.

Furthermore, the C RTL offers a Curses package based on the 4.4BSD Berkeley Software Distribution. Documentation on the 4.4BSD Curses package can be found in Screen Updating and Cursor Movement Optimization: A Library Package, by Kenneth C.R.C. Arnold.

The functions and macros in the OpenVMS and BSD-based Curses packages are nearly the same. Most differences between them are called out in this chapter. Otherwise, this chapter makes no distinction between the two Curses packages, and refers to "Curses" or the "Curses functions and macros".

6.1. Using the BSD-Based Curses Package (Alpha only)

The <curses.h> header file required to use the BSD-based Curses implementation is provided with the VSI C compiler on OpenVMS Alpha systems.

Existing programs are not affected by the BSD-based Curses functions because the OpenVMS Curses functions are still available as the default Curses package. (Note that is a change from previous versions of VSI C, where BSD-based Curses was the default.)

To get the 4.4BSD Curses implementation, you must compile modules that include <curses.h> with the following qualifier:
  • /DEFINE=_BSD44_CURSES

The BSD-based Curses functions do not provide the support required to call the OpenVMS SMG$ routines with the pasteboard and keyboard allocated by the Curses functions. Consequently, Curses programs that rely on calling SMG$ entry points, as well as Curses functions, must continue to use the OpenVMS Curses implementation.

The BSD-based Curses implementation is not interoperable with the old implementation. Attempts to mix calls to the new functions and the old functions will result in incorrect output displayed on the screen and could result in an exception from an SMG$ routine.

6.2. Curses Overview

Curses, the VSI C Screen Management Package, is composed of C RTL functions and macros that create and modify defined sections of the terminal screen and optimize cursor movement. Using the screen management package, you can develop a user interface that is both visually attractive and user-friendly. Curses is terminal-independent and provides simplified terminal screen formatting and efficient cursor movement.

Most Curses functions and macros are listed in pairs where the first routine is a macro and the second is a function beginning with the prefix “w,”for “window.” These prefixes are delimited by brackets ([ ]). For example, [w]addstr designates the addstr macro and the waddstr function. The macros default to the window stdscr; the functions accept a specified window as an argument.

To access the Curses functions and macros, include the <curses.h> header file.

The terminal-independent Screen Management Software, which is part of the OpenVMS RTL, is used to implement Curses. For portability purposes,most functions and macros are designed to perform in a manner similar to other C implementations. However, the Curses routines depend on the OpenVMS system and its Screen Management Software, so performance of some functions and macros could differ slightly from those of other implementations.

Some functions and macros available on other systems are not available with the C RTL Curses package.

Some functions, such as [w]clrattr, [w]insstr, mv[w]insstr, and [w]setattr are specific to VSI C for OpenVMS systems and are not portable.

Table 6.1 lists all of the Curses functions and macros found in the C RTL. For more detailed information on each function and macro, see the Reference Section.
Table 6.1. Curses Functions and Macros

Function or Macro

Description

[w]addch

Adds a character to the window at the current position of the cursor.

[w]addstr

Adds a string to the window at the current position of the cursor.

box

Draws a box around the window.

[w]clear

Erases the contents of the specified window and resets the cursor to coordinates (0,0).

clearok

Sets the clear flag for the window.

[w]clrattr

Deactivates the video display attribute within the window.

[w]clrtobot

Erases the contents of the window from the current position of the cursor to the bottom of the window.

[w]clrtoeol

Erases the contents of the window from the current cursor position to the end of the line on the specified window.

[no]crmode

Sets and unsets the terminal from c break mode.

[w]delch

Deletes the character on the specified window at the current position of the cursor.

[w]deleteln

Deletes the line at the current position of the cursor.

delwin

Deletes the specified window from memory.

[no]echo

Sets the terminal so that characters mayor may not be echoed on the terminal screen.

endwin

Clears the terminal screen and frees any virtual memory allocated to Curses data structures.

[w]erase

Erases the window by painting it with blanks.

[w]getch

Gets a character from the terminal screen and echoes it on the specified window.

[w]getstr

Gets a string from the terminal screen,stores it in a character variable, and echoes it on the specified window.

getyx

Puts the (y,x) coordinates of the current cursor position on the window in the variables y and x.

[w]inch

Returns the character at the current cursor position on the specified window without making changes to the window.

initscr

Initializes the terminal-type data and all screen functions.

[w]insch

Inserts a character at the current cursor position in the specified window.

[w]insertln

Inserts a line above the line containing the current cursor position.

[w]insstr

Inserts a string at the current cursor position on the specified window.

leaveok

Leaves the cursor at the current coordinates after an update to the window.

longname

Assigns the full terminal name to a character name that must be large enough to hold the character string.

[w]move

Changes the current cursor position on the specified window.

mv[w]addch

Moves the cursor and adds a character to the specified window.

mv[w]addstr

Moves the cursor and adds a string to the specified window.

mvcur

Moves the terminal's cursor.

mv[w]delch

Moves the cursor and deletes a character on the specified window.

mv[w]getch

Moves the cursor, gets a character from the terminal screen, and echoes it on the specified window.

mv[w]getstr

Moves the cursor, gets a string from the terminal screen, stores it in a variable, and echoes it on the specified window.

mv[w]inch

Moves the cursor and returns the character on the specified window without making changes to the window.

mv[w]insch

Moves the cursor and inserts a character in the specified window.

mv[w]insstr

Moves the cursor and inserts a string in the specified window.

mvwin

Moves the starting position of the window to the specified coordinates.

newwin

Creates a new window with lines and columns starting at the coordinates on the terminal screen.

[no]nl

Provided only for UNIX software compatibility and has no functionality in the OpenVMS environment.

overlay

Writes the contents of one window that will fit over the contents of another window, beginning at the starting coordinates of both windows.

overwrite

Writes the contents of one window,insofar as it will fit, over the contents of another window beginning at the starting coordinates of both windows.

[w]printw

Performs a printf on the window starting at the current position of the cursor.

[no]raw

Provided only for UNIX software compatibility and has no functionality in the OpenVMS environment.

[w]refresh

Repaints the specified window on the terminal screen.

[w]scanw

Performs a scanf on the window.

scroll

Moves all the lines on the window up one line.

scrollok

Sets the scroll flag for the specified window.

[w]setattr

Activates the video display attribute within the window.

[w]standend

Deactivates the boldface attribute for the specified window.

[w]standout

Activates the boldface attribute of the specified window.

subwin

Creates a new sub window with lines and columns starting at the coordinates on the terminal screen.

touchwin

Places the most recently edited version of the specified window on the terminal screen.

wrapok

OpenVMS Curses only. Allows the wrapping of a word from the right border of the window to the beginning of the next line.

6.3. Curses Terminology

This section explains some of the Curses terminology and shows you how Curses looks on the terminal screen.

Consider a Curses application as being a series of overlapping windows. Window overlapping is called occlusion. To distinguish the boundaries of these occluding windows, you can outline the rectangular windows with specified characters, or you can turn on the reverse video option (make the window a light background with dark writing).

6.3.1. Predefined Windows (stdscr and curscr)

Initially, two windows the size of the terminal screen are predefined by Curses. These windows are called stdscr and curscr. The stdscr window is defined for your use. Many Curses macros default to this window. For example, if you draw a box around stdscr, move the cursor to the left-corner area of the screen, write a string to stdscr, and then display stdscr on the terminal screen, your display will look like that in Figure 6.1.

Figure 6.1. An Example of the stdscr Window
An Example of the stdscr Window

The second predefined window, curscr, is designed for internal Curses work; it is an image of what is currently displayed on the terminal screen. The only VSI C for OpenVMS Curses function that will accept this window as an argument is clearok. Do not write to or read from curscr. Use stdscr and user-defined windows for all your Curses applications.

6.3.2. User-Defined Windows

You can occlude stdscr with your own windows. The size and location of each window is given in terms of the number of lines, the number of columns, and the starting position.

The lines and columns of the terminal screen form a coordinate system, or grid, on which the windows are formed. You specify the starting position of a window with the (y,x) coordinates on the terminal screen where the upper left corner of the window is located. The coordinates (0,0) on the terminal screen, for example, are the upper left corner of the screen.

The entire area of the window must be within the terminal screen borders;windows can be as small as a single character or as large as the entire terminal screen. You can create as many windows as memory allows.

When writing to or deleting from windows, changes do not appear on the terminal screen until the window is refreshed. When refreshing a window, you place the updated window onto the terminal screen, which leaves the rest of the screen unaltered.

All user-defined windows, by default, occlude stdscr. You can create two or more windows that occlude each other as well as stdscr. When writing data to one occluding window, the data is not written to the underlying window.

You can create overlapping windows (called subwindows). A declared window must contain the entire area of its subwindow. When writing data to a subwindow or to the portion of the window overlapped by the subwindow, both windows contain the new data. For instance, if you write data to a subwindow and then delete that subwindow, the data is still present on the underlying window.

If you create a window that occludes stdscr and a subwindow of stdscr, your terminal screen will look like Figure 6.2.

Figure 6.2. Displaying Windows and Subwindows
Displaying Windows and Subwindows

If you delete both the user-defined window and the subwindow, and then update the terminal screen with the new image, your terminal screen will look like Figure 6.3.

Figure 6.3. Updating the Terminal Screen
Updating the Terminal Screen

The string written on the window is deleted, but the string written on the subwindow remains on stdscr.

6.4. Getting Started with Curses

There are commands that you must use to initialize and restore the terminal screen when using Curses Screen Management functions and macros. Also, there are predefined variables and constants on which Curses depends. Example 6.1 shows how to set up a program using Curses.
Example 6.1. A Curses Program
1#include <curses.h>

2WINDOW  *win1, *win2, *win3;

main()
{
3   initscr();
      .
      .
      .
   endwin();
}
Key to Example 6.1:

1

The preprocessor directive includes the <curses.h> header file, which defines the data structures and variables used to implement Curses. The <curses.h> header file includes the <stdio.h> header file, so it is not necessary to duplicate this action by including <stdio.h> again in the program source code. You must include <curses.h> to use any of the Curses functions or macros.

2

In the example, WINDOW is a data structure defined in <curses.h>. You must declare each user-specified window in this manner. In Example 6.1, the three defined windows are win1, win2, and win3.

3

The initscr and endwin functions begin and end the window editing session. The initscr function clears the terminal screen (for OpenVMS Curses only; BSD-based Curses does not clear the screen), and allocates space for the windows stdscr and curscr. The endwin function deletes all windows and clears the terminal screen.

Most Curses users wish to define and modify windows. Example 6.2 shows you how to define and write to a single window.
Example 6.2. Manipulating Windows
#include <curses.h>

WINDOW  *win1, *win2, *win3;

main()
{
   initscr();

1   win1 = newwin(24, 80, 0, 0);
2   mvwaddstr(win1, 2, 2, "HELLO");
      .
      .
      .
   endwin();
}
Key to Example 6.2:

1

The newwin function defines a window 24 rows high and 80 columns wide with a starting position at coordinates (0,0), the upper left corner of the terminal screen. The program assigns these attributes to win1. The coordinates are specified as follows: (lines,columns) or (y,x).

2

The mvwaddstr macro performs the same task as a call to the separate macros move and addstr. The mvwaddstr macro moves the cursor to the specified coordinates and writes a string onto stdscr.


Note

Most Curses macros update stdscr by default. Curses functions that update other windows have the same name as the macros but with the added prefix “w”. For example, the addstr macro adds a given string to stdscr at the current cursor position. The waddstr function adds a given string to a specified window at the current cursor position.

When updating a window, specify the cursor position relative to the origin of the window, not the origin of the terminal screen. For example, if a window has a starting position of (10,10) and you want to add a character to the window at its starting position,specify the coordinates (0,0), not (10,10).

The string HELLO in Example 6.2 does not appear on the terminal screen until you refresh the screen. You accomplish this by using the wrefresh function. Example 6.3 shows how to display the contents of win1 on the terminal screen.
Example 6.3. Refreshing the Terminal Screen
#include <curses.h>

WINDOW  *win1, *win2, *win3;

main()
{
   initscr();

   win1 = newwin(22, 60, 0, 0);
   mvwaddstr(win1, 2, 2, "HELLO");
   wrefresh(win1);
      .
      .
      .
   endwin();
}

The wrefresh function updates just the region of the specified window on the terminal screen. When the program is executed, the string HELLO appears on the terminal screen until the program executes the endwin function. The wrefresh function only refreshes the part of the window on the terminal screen that is not overlapped by another window. If win1 was overlapped by another window and you want all of win1 to be displayed on the terminal screen, call the touchwin function.

6.5. Predefined Variables and Constants

The <curses.h> header file defines variables and constants useful for implementing Curses (see Table 6.2).
Table 6.2. Curses Predefined Variables and #define Constants

Name

Type

Description

curscr

WINDOW *

Window of current screen

stdscr

WINDOW *

Default window

LINES

int

Number of lines on the terminal screen

COLS

int

Number of columns on the terminal screen

ERR

—

Flag (0 ) for failed routines

OK

—

Flag (1 ) for successful routines

TRUE

—

Boolean true flag (1 )

FALSE

—

Boolean false flag (0 )

_BLINK

—

Parameter for setattr and clrattr

_BOLD

—

Parameter for setattr and clrattr

_REVERSE

—

Parameter for setattr and clrattr

_UNDERLINE

—

Parameter for setattr and clrattr

For example, you can use the predefined macro ERR to test the success or failure of a Curses function. Example 6.4 shows how to perform such a test.
Example 6.4. Curses Predefined Variables
#include <curses.h>

WINDOW  *win1, *win2, *win3;

main()
{
   initscr();
   win1 = newwin(10, 10, 1, 5);
      .
      .
      .
   if (mvwin(win1, 1, 10) == ERR)
      addstr("The MVWIN function failed.");
      .
      .
      .
   endwin();
}

In Example 6.4, if the mvwin function fails, the program adds a string to stdscr that explains the outcome. The Curses mvwin function moves the starting position of a window.

6.6. Cursor Movement

In the UNIX system environment, you can use Curses functions to move the cursor across the terminal screen. With other implementations, you can either allow Curses to move the cursor using the move function, or you can specify the origin and the destination of the cursor to the mvcur function, which moves the cursor in a more efficient manner.

In VSI C for OpenVMS systems, the two functions are functionally equivalent and move the cursor with the same efficiency.

Example 6.5 shows how to use the move and mvcur functions.
Example 6.5. The Cursor Movement Functions
#include <curses.h>

main()
{
   initscr();
      .
      .
      .
1   clear();
2   move(10, 10);
3   move(LINES/2, COLS/2);
4   mvcur(0, COLS-1, LINES-1, 0);
      .
      .
      .
   endwin();
}
Key to Example 6.5:

1

The clear macro erases stdscr and positions the cursor at coordinates (0,0).

2

The first occurrence of move moves the cursor to coordinates (10,10).

3

The second occurrence of move uses the predefined variables LINES and COLS to calculate the center of the screen (by calculating the value of half the number of LINES and COLS on the screen).

4

The mvcur function forces absolute addressing. This function can address the lower left corner of the screen by claiming that the cursor is presently in the upper right corner. You can use this method if you are unsure of the current position of the cursor, but move works just as well.

6.7. Program Example

The following program example shows the effects of many of the Curses macros and functions. You can find explanations of the individual lines of code, if not self-explanatory, in the comments to the right of the particular line. Detailed discussions of the functions follow the source code listing.

Example 6.6 shows the definition and manipulation of one user-defined window and stdscr.
Example 6.6. stdscr and Occluding Windows
/*        CHAP_6_STDSCR_OCCLUDE.C                       */

/* This program defines one window: win1.  win1 is      */
/* located towards the center of the default window     */
/* stdscr.  When writing to an occluding window (win1)  */
/* that is later erased, the writing is erased as well. */

#include <curses.h>     /* Include header file.         */

WINDOW *win1;                   /* Define windows.      */

main()
{
    char str[80];               /* Variable declaration.*/

    initscr();  /* Set up Curses.   */
    noecho();   /* Turn off echo.   */

    /* Create window.             */
    win1 = newwin(10, 20, 10, 10);

    box(stdscr, '|', '-');  /* Draw a box around stdscr. */
    box(win1, '|', '-');    /* Draw a box around win1.   */

    refresh();  /* Display stdscr on screen.  */

    wrefresh(win1);     /* Display win1 on screen.  */

1   getstr(str);      /* Pause. Type a few words!   */

   mvaddstr(22, 1, str);
2   getch();
     /* Add string to win1.        */

    mvwaddstr(win1, 5, 5, "Hello");
    wrefresh(win1);     /* Add win1 to terminal scr.  */

    getch();    /* Pause.  Press Return.      */

    delwin(win1);       /* Delete win1.           */

3   touchwin(stdscr); /* Refresh all of stdscr.     */

   getch();                   /* Pause.  Press Return.      */
   endwin();                  /* Ends session.              */
}
Key to Example 6.6:

1

The program waits for input. The echo was disabled using the noecho macro, so the words that you type do not appear on stdscr. However, the macro stores the words in the variable str for use elsewhere in the program.

2

The getch macro causes the program to pause. When you are finished viewing the screen, press Return so the program can resume. The getch macro refreshes stdscr on the terminal screen without calling refresh. The screen appears like Figure 6.4.

Figure 6.4. An Example of the getch Macro
An Example of the getch Macro

3

The touchwin function refreshes the screen so that all of stdscr is visible and the deleted occluding window no longer appears on the screen.

Chapter 7. Math Functions

Table 7.1 lists and describes the math functions in the VSI C Run-Time Library (C RTL). For more detailed information on each function, see the Reference Section.
Table 7.1. Math Functions

Function

Description

abs

Returns the absolute value of an integer.

acos

Returns the arc cosine of its radian argument, in the range [0, π] radians.

acosd

Returns the arc cosine of its radian argument, in the range [0,180] degrees.

acosh

Returns the hyperbolic arc cosine of its argument.

asin

Returns the arc sine of its radian argument in the range [-π/2,π/2] radians.

asind

Returns the arc sine of its radian argument, in the range [-90,90] degrees.

asinh

Returns the hyperbolic arc sine of its argument.

atan

Returns the arc tangent of its radian argument, in the range [-π/2,π/2] radians.

atand

Returns the arc tangent of its radian argument, in the range [-90,90] degrees.

atan2

Returns the arc tangent of y/ x (its two radian arguments), in the range [ - π, π] radians.

atand2

Returns the arc tangent of y/ x (its two radian arguments), in the range [ -180,180] degrees.

atanh

Returns the hyperbolic arc tangent of its radian argument.

cabs

Returns the absolute value of a complex number as: sqrt (x2 + y2).

cbrt

Returns the rounded cube root of its argument.

ceil

Returns the smallest integer greater than or equal to its argument.

copysign

Returns its first argument with the same sign as its second.

cos

Returns the cosine of its radian argument in radians.

cosd

Returns the cosine of its radian argument in degrees.

cosh

Returns the hyperbolic cosine of its argument.

cot

Returns the cotangent of its radian argument in radians.

cotd

Returns the cotangent of its radian argument in degrees.

  • drand48
  • erand48
  • jrand48
  • lrand48
  • mrand48
  • nrand48

Generate uniformly distributed pseudorandom number sequences. Return 48-bit, non-negative, double-precision floating-point values.

erf

Returns the error function of its argument.

erfc

Returns (1.0−erf(x)).

exp

Returns the base e raised to the power of the argument.

expm1

Returns exp(x)−1.

fabs

Returns the absolute value of a floating-point value.

finite

Returns 1 if its argument is a finite number; 0 if not.

floor

Returns the largest integer less than or equal to its argument.

fmod

Computes the floating-point remainder of its first argument divided by its second.

fp_class

Determines the class of IEEE floating-point values, returning a constant from the <fp_class.h> header file.

isnan

Test for NaN. Returns 1 if its argument is a NaN; 0 if not.

  • j0
  • j1
  • jn

Compute Bessel functions of the first kind.

frexp

Calculates the fractional and exponent parts of a floating-point value.

hypot

Returns the square root of the sum of the squares of two arguments.

initstate

Initializes random number generators.

labs

Returns the absolute value of an integer as a long int.

lcong48

Initializes a 48-bit uniformly distributed pseudorandom number sequence.

lgamma

Computes the logarithm of the gamma function.

  • qabs
  • llabs

Return the absolute value of an __int64 integer.

ldexp

Returns its first argument multiplied by 2 raised to the power of its second argument.

  • ldiv
  • div

Return the quotient and remainder after the division of their arguments.

  • qdiv
  • lldiv

Return the quotient and remainder after the division of their arguments.

  • log
  • log2
  • log10

Return the logarithm of their arguments.

log1p

Computes ln(1+ x) accurately.

logb

Returns the radix-independent exponent of its argument.

nextafter

Returns the next machine-representable number following x in the direction of y.

nint

Returns the nearest integral value to the argument.

modf

Returns the positive fractional part of its first argument and assigns the integral part to the object whose address is specified by the second argument.

pow

Returns the first argument raised to the power of the second.

  • rand
  • srand

Return pseudorandom numbers in the range 0 to 231 −1.

  • random
  • srandom

Generate pseudorandom numbers in a more random sequence.

rint

Rounds its argument to an integral value according to the current IEEE rounding direction specified by the user.

scalb

Returns the exponent of a floating-point number.

  • seed48
  • srand48

Initialize a 48-bit random number generator.

setstate

Restarts and changes random number generators.

sin

Returns the sine of its radian argument in radians.

sind

Returns the sine of its radian argument in degrees.

sinh

Returns the hyperbolic sine of its argument.

sqrt

Returns the square root of its argument.

tan

Returns the tangent of its radian argument in radians.

tand

Returns the tangent of its radian argument in degrees.

tanh

Returns the hyperbolic tangent of its argument.

trunc

Truncates its argument to an integral value.

unordered

Returns 1 if either or both of its arguments is a NaN; 0, if not.

  • y0
  • y1
  • yn

Compute Bessel functions of the second kind.

7.1. Math Function Variants – float, long double

Additional math routine variants are supported for VSI C. They are defined in <math.h> and are float and long double variants of the routines listed in Table 7.1.

Float variants take float arguments and return float values. Their names have an f suffix. For example:
float cosf (float x);
float tandf (float x);
Long double variants take long double arguments and return long double values. Their names have an l suffix. For example: 
long double cosl (long double x);
long double tandl (long double x);

All math routine variants are included in the Reference Section of this manual.

Note that for programs compiled without /L_DOUBLE=64 (that is, compiled with the default /L_DOUBLE=128), the long double variants of these C RTL math routines map to the X_FLOAT entry points.

7.2. Error Detection

To help you detect run-time errors, the <errno.h> header file defines the following two symbolic values that are returned by many (but not all) of the mathematical functions:

  • EDOM indicates that an argument is inappropriate; the argument is not within the function's domain.

  • ERANGE indicates that a result is out of range; the argument is too large or too small to be represented by the machine.

When using the math functions, you can check the external variable errno for either or both of these values and take the appropriate action if an error occurs.

The following program example checks the variable errno for the value EDOM, which indicates that a negative number was specified as input to the function sqrt:
#include <errno.h>
#include <math.h>
#include <stdio.h>

main()
{
   double input, square_root;

   printf("Enter a number: ");
   scanf("%le", &input);
   errno = 0;
   square_root = sqrt(input);

   if (errno == EDOM)
      perror("Input was negative");
   else
      printf("Square root of %e = %e\n",
              input, square_root);
}

If you did not check errno for this symbolic value, the sqrt function returns 0 when a negative number is entered. For more information about the <errno.h> header file, see Chapter 4.

7.3. The <fp.h> Header File

The <fp.h> header file implements some of the features defined by the Numerical C Extensions Group of the ANSI X3J11 committee. You might find this useful for applications that make extensive use of floating-point functions.

Some of the double-precision functions listed in this chapter return the value ±HUGE_VAL (defined in either <math.h> or <fp.h>) if the result is out of range. The float version of those functions return the value HUGE_VALF (defined only in <fp.h>) for the same conditions. The long double version returns the value HUGE_VALL (also defined in <fp.h>).

For programs compiled to enable IEEE infinity and NaN values, the values HUGE_VAL, HUGE_VALF, and HUGE_VALL are expressions, not compile-time constants. Initializations such as the following cause a compile-time error:
$ CREATE IEEE_INFINITY.C
#include <fp.h>

double my_huge_val = HUGE_VAL
^Z
$ CC /FLOAT=IEEE/IEEE=DENORM IEEE_INFINITY

double my_huge_val = HUGE_VAL;
.....................^
%CC-E-NEEDCONSTEXPR, In the initializer for my_huge_val, "decc$gt_dbl_infinity"
is not constant, but occurs in a context that requires a constant expression.
at line number 3 in file WORK1$:[RTL]IEEE_INFINITY.C;1
$

When using both <math.h> and <fp.h>, be aware that <math.h> defines a function isnan and <fp.h> defines a macro by the same name. Whichever header is included first in the application will resolve a reference to isnan.

7.4. Example

Example 7.1 shows how the tan, sin, and cos functions operate.
Example 7.1. Calculating and Verifying a Tangent Value
/*        CHAP_7_MATH_EXAMPLE.C                                 */

/* This example uses two functions --- mytan and main ---       */
/* to calculate the tangent value of a number, and to check     */
/* the calculation using the sin and cos functions.             */

#include <math.h>
#include <stdio.h>

/* This function calculates the tangent using the sin and       */
/* cos functions.                                               */

double mytan(x)
    double x;
{
    double y,
           y1,
           y2;

    y1 = sin(x);
    y2 = cos(x);

    if (y2 == 0)
        y = 0;
    else
        y = y1 / y2;

    return y;
}
main()
{
    double x;

    /*  Print values: compare   */
    for (x = 0.0; x < 1.5; x += 0.1)
        printf("tan of %4.1f = %6.2f\t%6.2f\n", x, mytan(x), tan(x));
}
Example 7.1 produces the following output:
$ RUN  EXAMPLE
tan of  0.0 =   0.00      0.00
tan of  0.1 =   0.10      0.10
tan of  0.2 =   0.20      0.20
tan of  0.3 =   0.31      0.31
tan of  0.4 =   0.42      0.42
tan of  0.5 =   0.55      0.55
tan of  0.6 =   0.68      0.68
tan of  0.7 =   0.84      0.84
tan of  0.8 =   1.03      1.03
tan of  0.9 =   1.26      1.26
tan of  1.0 =   1.56      1.56
tan of  1.1 =   1.96      1.96
tan of  1.2 =   2.57      2.57
tan of  1.3 =   3.60      3.60
tan of  1.4 =   5.80      5.80
$

Chapter 8. Memory Allocation Functions

Table 8.1 lists and describes all the memory allocation functions found in the VSI C Run-Time Library (C RTL). For a more detailed description of each function, see the Reference Section.
Table 8.1. Memory Allocation Functions

Function

Description

  • alloca
  • calloc
  • malloc

Allocate an area of memory.

  • brk
  • sbrk

Determine the lowest virtual address that is not used with the program.

  • cfree
  • free

Make available for reallocation the area allocated by a previous calloc, malloc, or realloc call.

realloc

Changes the size of the area pointed to by the first argument to the number of bytes given by the second argument.

strdup

Duplicates a string.

All C RTL functions requiring additional storage from the heap get that storage using the C RTL memory allocation functions malloc, calloc, realloc, free, and cfree. Memory allocated by these functions is quadword-aligned.

The ANSI C standard does not include cfree. For this reason, it is preferable to free memory using the functionally equivalent free function.

The alloca function allocates the memory on the stack. The memory is automatically freed when the function that calls alloca returns to its caller.

The brk and sbrk functions assume that memory can be allocated contiguously from the top of your address space. However, the malloc function and RMS may allocate space from this same address space. Do not use the brk and sbrk functions in conjunction with RMS and C RTL routines that use malloc.

Previous versions of the VAX C RTL documentation indicated that the memory allocation routines used the OpenVMS RTL functions LIB$GET_VM and LIB$FREE_VM to acquire and return dynamic memory. This is no longer the case; interaction between these routines and the C RTL memory allocation routines is no longer problematic (although LIB$SHOW_VM can no longer be used to track C RTL malloc and free usage).

The C RTL memory allocation functions calloc, malloc, realloc, and free are based on the LIB$ routines LIB$VM_CALLOC, LIB$VM_MALLOC, LIB$VM_REALLOC and LIB$VM_FREE, respectively.

The routines VAXC$CALLOC_OPT, VAXC$CFREE_OPT, VAXC$FREE_OPT, VAXC$MALLOC_OPT, and VAXC$REALLOC_OPT are now obsolete and should not be used in new development. However, versions of these routines that are equivalent to the standard C memory allocation routines are provided for backward compatibility.

8.1. Program Example

Example 8.1 shows the use of the malloc, calloc, and free functions.
Example 8.1. Allocating and Deallocating Memory for Structures
/*        CHAP_8_MEM_MANAGEMENT.C                               */

/* This example takes lines of input from the terminal until    */
/* it encounters a Ctrl/Z, places the strings into an           */
/* allocated buffer, copies the strings to memory allocated for */
/* structures, prints the lines back to the screen, and then    */
/* deallocates all the memory used for the structures.          */

#include  <stdlib.h>
#include  <stdio.h>
#define   MAX_LINE_LENGTH  80

struct line_rec {               /*  Declare the structure.   */
    struct line_rec *next;      /*  Pointer to next line.    */
    char *data;                 /*  A line from terminal.    */
};

int main(void)
{
    char *buffer;

    /* Define pointers to        */
    /*  structure (input lines). */

    struct line_rec *first_line = NULL,
            *next_line,
            *last_line = NULL;

    /* Buffer points to memory.  */
    buffer = malloc(MAX_LINE_LENGTH);

    if (buffer == NULL) {       /* If error ...  */
        perror("malloc");
        exit(EXIT_FAILURE);
    }

    while (gets(buffer) != NULL) {      /* While not Ctrl/Z ...  */
        /* Allocate for input line.  */
        next_line = calloc(1, sizeof (struct line_rec));

        if (next_line == NULL) {
            perror("calloc");
            exit(EXIT_FAILURE);
        }

        /* Put line in data area.    */
        next_line->data = buffer;

        if (last_line == NULL)  /* Reset pointers.   */
            first_line = next_line;
        else
            last_line->next = next_line;

        last_line = next_line;
        /* Allocate space for the     */
        /*  next input line.          */
        buffer = malloc(MAX_LINE_LENGTH);

        if (buffer == NULL) {
            perror("malloc");
            exit(EXIT_FAILURE);
        }
    }
    free(buffer);       /* Last buffer always unused. */
    next_line = first_line;     /* Pointer to beginning.  */

    while (next_line != NULL) {
        puts(next_line->data);  /* Write line to screen.  */
        free(next_line->data);  /* Deallocate a line.     */
        last_line = next_line;
        next_line = next_line->next;
        free(last_line);
    }

    exit(EXIT_SUCCESS);
}
The sample input and output for Example 8.1 are as follows:
$ RUN  EXAMPLE
line one
line two
Ctrl/Z
EXIT
line one
line two
$

Chapter 9. Shared Memory Functions

This chapter lists and describes all shared memory functions found in the VSI C Run-Time Library (C RTL), as well as current prerequisites, limitations, and restrictions for System V Shared Memory.
Table 9.1. Shared Memory Functions

Function

Description

shmget

Gets a shared memory segment.

shmctl

Shared memory control operations.

shmat

Shared memory attach operation.

shmdt

Shared memory detach operation.

shm_open

Opens a shared memory object.

shm_unlink

Removes a shared memory object.

9.1. System V Shared Memory Limitations

The following are the current limits in System V Shared Memory:

  • Maximum number (SHMMNI) of System V Shared Memory segments allowed in a system is 1024.

  • Maximum size (SHMMAX) of System V Shared Memory segment allowed is 512 MB.

  • Minimum size (SHMMIN) of System V Shared Memory segment allowed is 1 byte.

    Note

    The global section mapped for System V Shared Memory segment is a multiple of 8 KB. For example, System V Shared Memory segment of size 1 byte will have an 8 KB global section.

9.2. Prerequisites

System V Shared Memory interfaces use file-backed global sections. These functions either create or delete the files based on request. The files are created in SYS$SPECIFIC:[DECC$SYSV_SHM]. The System Manager or Administrator must create the directory using the following command before using the Shared Memory Functions:

$ CREATE /DIRECTORY SYS$SPECIFIC:[DECC$SYSV_SHM]  -
  /OWNER_UIC = [SYSTEM]  -
  /PROTECTION = (S:RWE, O:RWE, G:RWE, W:RWE)

Note

If the SYS$SPECIFIC:[DECC$SYSV_SHM] directory does not exist, the directory SYS$SPECIFIC:[PSX$SEMAPHORES] will be used.

9.3. Restrictions

The following are the current restrictions:

  • If an application passes its valid non-zero virtual address to the shmat() function, the current implementation expects this address to be a 32 bit virtual address; a 64 bit virtual address is not supported.

  • System V Shared Memory Functions are implemented using file-backed global sections; hence each shared memory segment created would internally create a file to back the data for the section on system device (SYS$SYSDEVICE), and shared memory control operation with IPC_RMID deletes the file. So, the System Administrator must provide sufficient disk space on SYS$SYSDEVICE based on the usage of shared memory segments.

  • Performance of shared memory functions depends on the size of segments so the application that uses these functions may experience delay when they are used for the first time. If the same segments are used frequently without IPC_RMID, then this delay will not be seen because with no IPC_RMID in use, the file will not be deleted, and thus will exist until it is deleted.

  • Current release guarantees the initialization of shared memory segments with zero values only when the following conditions are true:

    • The High-Water Marking is enabled on the SYS$SYSDEVICE device.

    • The application is using $ERAPAT (erase pattern) system service, and the erase pattern generated for disk storage type is zero.

    In every other case, the initial contents of each shared memory segment created may or may not be initialized with zero values.

Note

For the following error cases, you must increase the value of the GBLSECTIONS SYSGEN parameter:

  • The shmget() function returns ENOMEM (value=12) or ENOSPC (value=28).

    ENOMEM indicates 'Not enough core' and ENOSPC indicates no space left on device.

  • The shmat() function returns ENOMEM (value=12).

Internally, shared memory uses global sections. Hence, a system having a large number of shared memory segments may result in exhaustion of GBLSECTIONS.

Chapter 10. System Functions

The C programming language is a good choice if you wish to write operating systems. For example, much of the UNIX operating system is written in C. When writing system programs, it is sometimes necessary to retrieve or modify the environment in which the program is running. This chapter describes the VSI C Run-Time Library (C RTL) functions that accomplish this and other system tasks.

Table 10.1 lists and describes all the system functions found in the C RTL. For a more detailed description of each function, see the Reference Section.
Table 10.1. System Functions

Function

Description

System Functions – Searching and Sorting Utilities

bsearch

Performs a binary search on an array of sorted objects for a specified object.

  • qsort
  • qsort_r

Sort an array of objects in place by implementing the quick-sort algorithm.

System Functions – Retrieving Process Information

ctermid

Returns a character string giving the equivalence string of SYS$COMMAND, which is the name of the controlling terminal.

cuserid

Returns a pointer to a character string containing the name of the user who initiated the current process.

getcwd

Returns a pointer to the file specification for the current working directory.

  • getegid
  • geteuid
  • getgid
  • getuid

Return, in OpenVMS terms, group and member numbers from the user-identification code (UIC).

getenv

Searches the environment array for the current process and returns the value associated with a specified environment.

getlogin

Gets the login name of the user associated with the current session.

getpid

Returns the process ID of the current process.

getppid

Returns the parent process ID of the calling process.

getpwnam

Accesses user-name information in the user database.

getpwuid

Accesses user-ID information in the user database.

System Functions – Changing Process Information

chdir

Changes the default directory.

chmod

Changes the file protection of a file.

chown

Changes the owner user identification code (UIC ) of a file.

mkdir

Creates a directory.

nice

Increases or decreases the process priority to the process base priority by the amount of the argument.

putenv

Sets an environmental variable.

setenv

Inserts or resets the environment variable name in the current environment list.

  • setgid
  • setuid

Implemented for program portability and have no functionality.

  • sleep
  • usleep

Suspend the execution of the current process for at least the number of seconds indicated by its argument.

umask

Creates a file protection mask that is used whenever a new file is created. It returns the old mask value.

System Functions – Retrieving and Converting Date/Time Information

asctime

Converts a broken-down time into a 26-character string.

clock

Determines the CPU time, in microseconds, used since the beginning of the program execution.

clock_getres

Gets the resolution for the specified clock.

clock_gettime

Returns the current time (in seconds and nanoseconds) for the specified clock.

clock_settime

Sets the specified clock.

ctime

Converts a time, in seconds, to an ASCII string in the form generated by the asctime function.

decc$fix_time

Converts OpenVMS binary system times to UNIX binary times.

difftime

Computes the difference, in seconds, between the two times specified by its arguments.

ftime

Returns the elapsed time since 00:00:00, January 1, 1970, in the structure timeb.

getclock

Gets the current value of the systemwide clock.

getdate

Converts a formatted string to a time/date structure.

getitimer

Returns the value of interval timers.

gettimeofday

Gets the date and time.

gmtime

Converts time units to broken-down UTC time.

localtime

Converts a time (expressed as the number of seconds elapsed since 00:00:00, January 1, 1970) into hours, minutes, seconds, and so on.

mktime

Converts a local-time structure into time since the Epoch.

nanosleep

High-resolution sleep (REALTIME). Suspends a process from execution for the specified timer interval.

setitimer

Sets the value of interval timers.

  • strftime
  • wcsftime

Place characters into an array, as controlled by a specified format string.

strptime

Converts a character string into date and time values.

time

Returns the time elapsed since 00:00:00, January 1, 1970, in seconds.

times

Returns the accumulated times of the current process and of its terminated child processes.

tzset

Sets and accesses time-zone conversion.

ualarm

Sets or changes the timeout of interval timers.

wcsftime

Uses date and time information stored in a tm structure to create a wide-character output string.

System Function – Miscellaneous

VAXC$CRTL_INIT

Initializes the run-time environment and establishes an exit and condition handler, which makes it possible for C RTL functions to be called from other languages.

Example 10.1 shows how the cuserid function is used.
Example 10.1. Accessing the User Name
/*        CHAP_9_GET_USER.C                                   */

/* Using cuserid, this program returns the user name.         */

#include <stdio.h>

main()
{
    static char string[L_cuserid];

    cuserid(string);
    printf("Initiating user: %s\n", string);
}
If a user named TOLLIVER runs the program, the following is displayed on stdout: 
$ RUN  EXAMPLE1
Initiating user: TOLLIVER
Example 10.2 shows how the getenv function is used.
Example 10.2. Accessing Terminal Information
/*        CHAP_9_GETTERM.C                              */

/* Using getenv, this program returns the terminal.     */

#include <stdio.h>
#include <stdlib.h>

main()
{
    printf("Terminal type: %s\n", getenv("TERM"));
}
Running Example 10.2 on a VT100 terminal in 132-column mode displays the following:
$ RUN  EXAMPLE3
Terminal type: vt100-132
Example 10.3 shows how to use getenv to find the user's default login directory and how to use chdir to change to that directory.
Example 10.3. Manipulating the Default Directory
/*       CHAP_9_CHANGE_DIR.C                                    */

/* This program performs the equivalent of the DCL command      */
/* SET DEFAULT SYS$LOGIN. However, once the program exits, the  */
/* directory is reset to the directory from which the program   */
/* was run.                                                     */

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>

main()
{
    char *dir;
    int i;

    dir = getenv("HOME");
    if ((i = chdir(dir)) != 0) {
        perror("Cannot set directory");
        exit(0);
    }

    printf("Current directory: %s\n", dir);
}
Running Example 10.3 displays the following: 
$ RUN EXAMPLE4
Current directory: dba0:[tolliver]
$
Example 10.4 shows how to use the time, localtime, and strftime functions to print the correct date and time at the terminal.
Example 10.4. Printing the Date and Time
/*        CHAP_9_DATE_TIME.C                                    */

/* The time function returns the time in seconds; the localtime */
/* function converts the time to hours, minutes, and so on;     */
/* the strftime function uses these values to obtain a string   */
/* in the desired format.                                       */

#include <time.h>
#include <stdio.h>

#define MAX_STRING 80

main()
{
    struct tm *time_structure;
    time_t time_val;
    char output_str[MAX_STRING];

    time(&time_val);
    time_structure = localtime(&time_val);

    /* Print the date  */

    strftime(output_str, MAX_STRING,
             "Today is %A, %B %d, %Y", time_structure);

    printf("%s\n", output_str);

    /* Print the time using a 12-hour clock format. */

    strftime(output_str, MAX_STRING,
             "The time is %I:%M %p", time_structure);

    printf("%s\n", output_str);
}
Running Example 10.4 displays the following:
$ RUN  EXAMPLE5
Today is Thursday, May 20, 1993
The time is 10:18 AM
$

Chapter 11. Developing International Software

This chapter describes typical features of international software and the features provided with the VSI C Run-Time Library (C RTL) that enable you to design and implement international software.

See the Reference Section for more detailed information on the functions described in this chapter.

11.1. Internationalization Support

The C RTL has added capabilities to allow application developers to create international software. The C RTL obtains information about a language and a culture by reading this information from locale files.

11.1.1. Installation

If you are using these C RTL capabilities, you must install a separate kit to provide these files to your system. See the appendix "Installing OpenVMS Internationalization data kit" in the OpenVMS Upgrade and Installation Guide.

On OpenVMS Alpha systems the save set is provided on the Layered Product CD, and is named VMSI18N0nn or ALPVMSI18N0n_07nn.

To install this save set, follow the standard OpenVMS installation procedures using this save-set name as the name of the kit. There are several categories of locales that you can select to install. You can select as many locales as you need by answering the following prompts: 
* Do you want European and US support? [YES]?
* Do you want Chinese GB18030 support (locale and Unicode converters) [YES]?
* Do you want Chinese support? [YES]?
* Do you want Japanese support? [YES]?
* Do you want Korean support? [YES]?
* Do you want Thai support? [YES]?
* Do you want the Unicode converters? [YES]?

This kit also has an Installation Verification Procedure that we recommend you run to verify the correct installation of the kit.

11.1.2. Unicode Support

In OpenVMS Version 7.2, the VSI C Run-Time Library added the Universal Unicode locale, which is distributed with the OpenVMS system, not with the VMSI18N0nn kit. The name of the Unicode locale is:
   UTF8-20

Like those locales shipped with the VMSI18N0nn kit, the Unicode locale is located at the standard location referred to by the SYS$I18N_LOCALE logical name.

The UTF8-20 Unicode is based on Unicode standard Version V2.0. The Unicode locale uses UCS-4 as wide-character encoding and UTF-8 as multibyte character encodings.

C RTL also includes converters that perform conversions between Unicode and any other supported character sets. The expanded set of converters includes converters for UCS-2, UCS-4, and UTF-8 Unicode encoding. The Unicode converters can be used by the ICONV CONVERT utility and by the iconv family of functions in the VSI C Run-Time Library.

In OpenVMS Version 7.2, the VSI C Run-Time Library added Unicode character set converters for Microsoft Code Page 437.

11.2. Features of International Software

International software is software that can support multiple languages and cultures. An international program should be able to:

  • Display messages in the user's own language. This includes screen displays, error messages, and prompts.

  • Handle culture-specific information such as:

    • Date and time formatting

      The conventions for representing dates and times vary from one country to another. For example, in the US the month is given first; in the UK the day is specified first. Therefore, the date 12/5/1993 is interpreted as December 5, 1993 in the US, and as May 12, 1993 in the UK.

    • Numeric formatting

      The character that represents the decimal point (the radix character) and the thousands separator character vary from one country to another. For example, in the UK the period (.) is used to represent the radix character, and the comma is used as a separator. However, in Germany, the comma is used as the radix character and the period is the separator character. Therefore, the number 2,345.67 in the UK is the same as 2.345,67 in Germany.

    • Monetary formatting

      Currency values are represented by different symbols and can be formatted using a variety of separator characters, depending on the currency.

  • Handle different coded character sets (not just ASCII).

  • Handle a mixture of single and multibyte characters.

  • Provide multipass string comparisons.

    String comparison functions such as strcmp compare strings by comparing the code point values of the characters in the strings. However, some languages require more complex comparisons to correctly sort strings.

To meet the previous requirements, an application should not make any assumptions about the language, local customs, or the coded character set used. All this localization data should be defined separately from the program, and only bound to it at run time.

The rest of this chapter describes how you can create international software using VSI C.

11.3. Developing International Software Using VSI C

The VSI C environment provides the following facilities to create international software:

  • A method for separating localization data from a program.

    Localization data is held in a database known as a locale. This stores all the language and culture information required by a program. See Section 11.4 for details of the structure of locales.

    A program specifies what locales to use by calling the setlocale function. See Section 11.5 for more information.

  • A method of separating message text from the program source.

    This is achieved using message catalogs that store all the messages for an application. The message catalog is linked to the application at run time. This means that the messages can be translated into different languages and then the required language version is selected at run time. See Section 11.6.

  • C RTL functions that are sensitive to localization data.

    The C RTL includes functions for:

  • A special wide-character data type defined in the C RTL makes it easier to handle codesets that have a mixture of single and multibyte characters. A set of functions is also defined to support this wide-character data type. See Section 11.9.

11.4. Locales

A locale consists of different categories, each of which determines one aspect of the international environment. Table 11.1 lists the categories in a locale and describes the information in each.
Table 11.1. Locale Categories

Category

Description

LC_COLLATE

Contains information about collating sequences.

LC_CTYPE

Contains information about character classification.

LC_MESSAGES

Defines the answers that are expected in response to yes/no prompts.

LC_MONETARY

Contains monetary formatting information.

LC_NUMERIC

Contains information about formatting numbers.

LC_TIME

Contains time and date information.

The locales provided reside in the directory defined by the SYS$I18N_LOCALE logical name. The file-naming convention for locales is:
language_country_codeset.locale
Where:

  • language is the mnemonic for the language. For example, EN indicates an English locale.

  • country is the mnemonic for the country. For example, GB indicates a British locale.

  • codeset is the name of the ISO standard codeset for the locale. For example, ISO8859-1 is the ISO 8859 codeset for the Western European languages. See Section 11.7 for more information about the codesets supported.

11.5. Using the setlocale Function to Set Up an International Environment

An application sets up its international environment at run time by calling the setlocale function. The international environment is set up in one of two ways:

  • The environment is defined by one locale. In this case, each of the locale categories is defined by the same locale.

  • Categories are defined separately. This lets you define a mixed environment that uses different locales depending on the operation performed. For example, if an English user has some Spanish files that are to be processed by an application, the LC_COLLATE category could be defined by a Spanish locale while the other categories are defined by an English locale. To do this you would call setlocale once for each category.

The syntax for the setlocale function is:
char *setlocale(int category, const char *locale)
Where:

  • category is either the name of a category, or LC_ALL. Specifying LC_ALL means that all the categories are defined by the same locale. Specify a category name to set up a mixed environment.

  • locale is one of the following:

    • The name of the locale to use.

      If you want users to specify the locale interactively, your application could prompt the user for a locale name, and then pass the name as an argument to the setlocale function. A locale name has the following format:
         language_country.codeset[@modifier]

      For example, setlocale(LC_COLLATE, "en_US.ISO8859-1") selects the locale en_US.ISO8859-1 for the LC_COLLATE category.

    • ""

      This causes the function to use logical names to determine the locale for the category specified. See the section called “Specifying the Locale Using Logical Names” for details.

If an application does not call the setlocale function, the default locale is the C locale. This allows such applications to call those functions that use information in the current locale.

Specifying the Locale Using Logical Names

If the setlocale function is called with "" as the locale argument, the function checks for a number of logical names to determine the locale name for the category specified.

There are a number of logical names that users can set up to define their international environment:

  • Logical name corresponding to a category

    For example, the LC_NUMERIC logical name defines the locale associated with the LC_NUMERIC category within the user's environment.

  • LC_ALL

  • LANG

    The LANG logical name defines the user's language.

In addition to the logical names defined by a user, there are a number of systemwide logical names, set up during system startup, that define the default international environment for all users on a system:

  • SYS$ category

    Where category is the name of a category. This specifies the system default for that category.

  • SYS$LC_ALL

  • SYS$LANG

The setlocale function checks for user-defined logical names first, and if these are not defined, it checks the system logical names.

11.6. Using Message Catalogs

An important requirement for international software is that it should be able to communicate with the user in the user's own language. The messaging system enables program messages to be created separately from the program source, and linked to the program at run time.

Messages are defined in a message text source file, and compiled into a message catalog using the GENCAT command. The message catalog is accessed by a program using the functions provided in the C RTL.

The functions provided to access the messages in a catalog are:

  • The catopen function, which opens a specified catalog ready for use.

  • The catgets function, which enables the program to read a specific message from a catalog.

  • The catclose function, which closes a specified catalog. Open message catalogs are also closed by the exit function.

For information on generating message catalogs, see the GENCAT command description in the OpenVMS system documentation.

11.7. Handling Different Character Sets

The C RTL supports a number of state-independent codesets and codeset encoding schemes that contain the ASCII encoded Portable Character Set. It does not support state-dependent codesets. The codesets supported are:

  • ISO8859- n

    where n = 1,2,5,7,8 or 9. This covers codesets for North America, Europe (West and East), Israel, and Turkey.

  • eucJP, SJIS, DECKANJI, SDECKANJI: Codesets used in Japan.

  • eucTW, DECHANYU, BIG5, DECHANZI: Chinese codesets used in China (PRC), Hong-Kong, and Taiwan.

  • DECKOREAN: Codeset used in Korea.

11.7.1. Charmap File

The characters in a codeset are defined in a charmap file. The charmap files supplied by VSI are located in the directory defined by the SYS$I18N_LOCALE logical name. The file type for a charmap file is .CMAP.

11.7.2. Converter Functions

As well as supporting different coded character sets, the C RTL provides the following converter functions that enable you to convert characters from one codeset to another:

  • iconv_open—Specifies the type of conversion. It allocates a conversion descriptor required by the iconv function.

  • iconv—Converts characters in a file to the equivalent characters in a different codeset. The converted characters are stored in a separate file.

  • iconv_close—Deallocates a conversion descriptor and the resources allocated to the descriptor.

11.7.3. Using Codeset Converter Files

The file-naming convention for codeset converters is:
fromcode_tocode.iconv

Where fromcode is the name of the source codeset, and tocode is the name of the codeset to which characters are converted.

You can add codeset converters to a given system by installing the converter files in the directory pointed by the logical name SYS$I18N_ICONV.

Codeset converter files can be implemented either as table-based conversion files or as algorithm-based converter files created as OpenVMS shareable images.

Creating a Table-Based Conversion File

The following summarizes the necessary steps to create a table-based codeset converter file:

  1. Create a text file that describes the mapping between any character from the source codeset to the target codeset. For the format of this file, see the DCL command ICONV COMPILE in the OpenVMS New Features Manual, which processes such a file and creates a codeset converter table file.

  2. Copy the resulting file from the previous step to the directory pointed by the logical SYS$I18N_ICONV, assuming you have the privilege to do so.

Creating an Algorithm-Based Conversion File

To create an algorithm-based codeset converter file implemented as a shareable image, follow these steps:
  1. Create C source files that implement the codeset converter. The API is documented in the public header file <iconv.h> as follows:

    • The universal entry point _u_iconv_open is called by the C RTL routine iconv_open to initialize a conversion.

    • _u_iconv_open returns to iconv_open a pointer to the structure __iconv_extern_obj_t.

    • Within this structure, the converter exports its own conversion entry point and conversion close routine, which are called by the C RTL routines iconv and iconv_close, respectively.

    • The major and minor identifier fields are required by iconv_open to test for a possible mismatch between the library and the converter. The converter usually assigns the constants __ICONV_MAJOR and __ICONV_MINOR, defined in the <iconv.h> header file.

    • The field tcs_mb_cur_max is used only by the DCL command ICONV CONVERT to optimize its buffer usage. This field reflects the maximum number of bytes that comprise a single character in the target codeset, including the shift sequence (if any).

  2. Compile and link the modules that comprise the codeset converter as an OpenVMS shareable image, making sure that the filename adheres to the preceding conventions.

  3. Copy the resulting file from the previous step to the directory pointed by the logical SYS$I18N_ICONV, assuming you have the privilege to do so.

Some Final Notes

By default, SYS$I18N_ICONV is a search list where the first directory in the list SYS$SYSROOT:[SYS$I18N.ICONV.USER] is meant for use as a site-specific repository for iconv codeset converters.

The number of codesets and locales installed vary from system to system. Check the SYS$I18N directory tree for the codesets, converters, and locales installed on your system.

11.8. Handling Culture-Specific Information

Each locale contains the following cultural information:

  • Date and time information

    The LC_TIME category defines the conventions for writing date and time, the names of the days of the week, and the names of months of the year.

  • Numeric information

    The LC_NUMERIC category defines the conventions for formatting non-monetary values.

  • Monetary information

    The LC_MONETARY category defines currency symbols and the conventions used to format monetary values.

  • Yes and no responses

    The LC_MESSAGES category defines the strings expected in response to yes/no questions.

You can extract some of this cultural information using the nl_langinfo function and the localeconv function. See Section 11.8.1.

11.8.1. Extracting Cultural Information From a Locale

The nl_langinfo function returns a pointer to a string that contains an item of information obtained from the program's current locale. The information you can extract from the locale is:

  • Date and time formats

  • The names of the days of the week, and months of the year in the local language

  • The radix character

  • The character used to separate groups of digits in non-monetary values

  • The currency symbol

  • The name of the codeset for the locale

  • The strings defined for responses to yes/no questions

The localeconv function returns a pointer to a data structure that contains numeric formatting and monetary formatting data from the LC_NUMERIC and LC_MONETARY categories.

11.8.2. Date and Time Formatting Functions

The functions that use the date and time information are:

  • strftime—Takes date and time values stored in a data structure and formats them into an output string. The format of the output string is controlled by a format string.

  • strptime—Converts a string (of type char) into date and time values. A format string defines how the string is interpreted.

  • wcsftime—Does the same as strftime except that it creates a wide-character string.

11.8.3. Monetary Formatting Function

The strfmon function uses the monetary information in a locale to convert a number of values into a string. The format of the string is controlled by a format string.

11.8.4. Numeric Formatting

The information in LC_NUMERIC is used by various functions. For example, strtod, wcstod, and the print and scan functions determine the radix character from the LC_NUMERIC category.

11.9. Functions for Handling Wide Characters

A character can be represented by single-byte or multibyte values depending on the codeset. To make it easier to handle both single-byte and multibyte characters in the same way, the C RTL defines a wide-character data type, wchar_t. This data type can store characters that are represented by 1-, 2-, 3-, or 4-byte values.

The functions provided to support wide characters are:

11.9.1. Character Classification Functions

The LC_CTYPE category in a locale classifies the characters in the locale's codeset into different types (alphabetic, numeric, lowercase, uppercase, and so on). There are two sets of functions, one for wide characters and one for single-byte characters, that test whether a character is of a specific type. The is* functions test single-byte characters, and the isw* functions test wide characters.

For example, the iswalnum function tests if a wide character is classed as either alphabetic or numeric. It returns a nonzero value if the character is one of these types. For more information about the classification functions, see Chapter 3 and the Reference Section.

11.9.2. Case Conversion Functions

The LC_CTYPE category defines mapping between pairs of characters of the locale. The most common character mapping is between uppercase and lowercase characters. However, a locale can support more than just case mappings.

Two functions are provided to map one character to another according to the information in the LC_CTYPE category of the locale:

  • wctrans—Looks for the named mapping (predefined in the locale) between characters.

  • towctrans—Maps one character to another according to the named mapping given to the wctrans function.

Two functions are provided for character case mapping:

  • towlower—Maps an uppercase wide character to its lowercase equivalent.

  • towupper—Maps a lowercase wide character to its uppercase equivalent.

For more information about these functions, see the Reference Section.

11.9.3. Functions for Input and Output of Wide Characters

The set of input and output functions manages wide characters and wide-character strings.

Read Functions

The functions for reading wide characters and wide-character strings are fgetwc, fgetws, getwc, and getwchar.

There is also an ungetwc function that pushes a wide character back into the input stream.

Write Functions

The functions for writing wide characters and wide-character strings are fputwc, fputws, putwc, and putwchar.

Scan Functions

All the scan functions allow for a culture-specific radix character, as defined in the LC_NUMERIC category of the current locale.

The %lc, %C, %ls, and %S conversion specifiers enable the scan functions fwscanf, wscanf, swscanf, fscanf, scanf, and sscanf to read in wide characters.

All the print functions can format numeric values according to the data in the LC_NUMERIC category of the current locale.

The %lc, %C and %ls, %S conversion specifiers used with print functions convert wide characters to multibyte characters and print the resulting characters.

See Chapter 2 for details of all input and output functions.

11.9.4. Functions for Converting Multibyte and Wide Characters

Wide characters are used internally by an application to manage single-byte or multibyte characters. However, text files are generally stored in multibyte character format. To process these files, the multibyte characters need converting to wide-character format. This can be achieved using the following functions:

  • mbtowc, mbrtowc, btowc—Convert one multibyte character to a wide character.

  • mbsrtowcs, mbstowcs—Convert a multibyte character string to a wide-character string.

Similarly, the following functions convert wide characters into their multibyte equivalent:

  • wcrtomb, wctomb, wctob—Convert a single wide character to a multibyte character.

  • wcsrtombs, wcstombs—Convert a wide-character string to a multibyte character string.

Associated with these conversion functions, the mblen and mbrlen functions are used to determine the size of a multibyte character.

Several of the wide-character functions take an argument of type "pointer to mbstate_t", where mbstate_t is an opaque datatype (like FILE or fpos_t) intended to keep the conversion state for the state-dependent codesets.

11.9.5. Functions for Manipulating Wide-Character Strings and Arrays

The C RTL contains a set of functions (the wcs* and wmem* functions) that manipulate wide-character strings. For example, the wcscat function appends a wide-character string to the end of another string in the same way that the strcat function works on character strings of type char.

See Chapter 3 for details of the string manipulation functions.

11.10. Collating Functions

In an international environment, string comparison functions need to allow for multipass collations. The collation requirements include:

  • Ordering accented characters.

  • Collating a character sequence as a single character. For example, ch in Spanish should be collated after c but before d.

  • Collating a single character as a two-character sequence.

  • Ignoring some characters.

Collating information is stored in the LC_COLLATE category of a locale. The C RTL includes the strcoll and wcscoll functions that use this collating information to compare two strings.

Multipass collations by strcoll or wcscoll can be slower than using the strcmp or wcscmp functions. If your program needs to do many string comparisons using strcoll or wcscoll, it may be quicker to transform the strings once, using the strxfrm or wcsxfrm function, and then use the strcmp or wcscmp function.

The term collation refers to the relative order of characters. The collation order is locale-specific and might ignore some characters. For example, an American dictionary ignores the hyphen in words and lists take-out between takeoff and takeover.

Comparison, on the other hand, refers to the examination of characters for sameness or difference. For example, takeout and take-out are different words, although they may collate the same.

Suppose an application sorts a list of words so it can later perform a binary search on the list to quickly retrieve a word. Using strcmp, take-in, take-out, and take-up would be grouped in one part of the table. Using strcoll and a locale that ignores hyphens, take-out would be grouped with takeoff and takeover, and would be considered a duplicate of takeout. To avoid a binary search finding takeout as a duplicate of take-out, an application would most likely use strcmp rather than strcoll for forming a binary tree.

Chapter 12. Date/Time Functions

This chapter describes the date/time functions available with VSI C for OpenVMS Systems. For more detailed information on each function, see the Reference Section.
Table 12.1. Date/Time Functions

Function

Description

asctime

Converts a broken-down time from localtime into a 26-character string.

ctime

Converts a time, in seconds, since 00:00:00, January 1, 1970 to an ASCII string of the form generated by the asctime function.

ftime

Returns the elapsed time since 00:00:00, January 1, 1970 in the structure pointed to by its argument.

getclock

Gets the current value of the systemwide clock.

gettimeofday

Gets the date and time.

gmtime

Converts time units to GMT (Greenwich Mean Time).

localtime

Converts a time (expressed as the number of seconds elapsed since 00:00:00, January 1, 1970) into hours, minutes, seconds, and so on.

mktime

Converts a local time structure to a calendar time value.

time

Returns the time elapsed since 00:00:00, January 1, 1970, in seconds.

tzset

Sets and accesses time-zone conversion.

Also, the time-related information returned by fstat and stat uses the new date/time model described in Section 12.1.

12.1. Date/Time Support Models

Beginning with OpenVMS Version 7.0, the C RTL changed its date/time support model from one based on local time to one based on Universal Coordinated Time (UTC). This allows the C RTL to implement ANSI C/POSIX functionality that previously could not be implemented. A UTC time-based model also makes the C RTL compatible with the behavior of the Tru64 UNIX time functions.

By default, newly compiled programs will generate entry points into UTC-based date/time routines.

For compatibility with OpenVMS systems prior to Version 7.0, previously compiled programs that relink on an OpenVMS Version 7.0 system will retain local-time-based date/time support. Relinking alone will not access UTC support.

Compiling programs with the _DECC_V4_SOURCE and _VMS_V6_SOURCE feature-test macros defined will also enable local-time-based entry points. That is, the new OpenVMS Version 7.0 date/time functions will not be enabled.

Functions with both UTC-based and local-time-based entry points are:
ctime           mktime
fstat           stat
ftime           strftime
gmtime          time
localtime       wcsftime

Note

Introducing a UTC-based, date/time model implies a certain loss of performance because time-related functions supporting UTC must read and interpret time-zone files instead of doing simple computations in memory as was done for the date/time model based on local time.

To decrease this performance degradation, OpenVMS Version 7.1 and higher can maintain the processwide cache of time-zone files. The size of the cache (that is, the number of files in the memory) is determined by the value of the DECC$TZ_CACHE_SIZE logical name. The default value is 2.

Because the time-zone files are relatively small (about 3 blocks each), consider defining DECC$TZ_CACHE_SIZE as the maximum number of time zones used by the application. For example, the default cache size fits an application that does not switch time zones during the run and runs on a system where the TZ environment variable is defined with both Standard and Summer time zone.

12.2. Overview of Date/Time Functions

In the UTC-based model, times are represented as seconds since the Epoch. The Epoch is defined as the time 0 hours, 0 minutes, 0 seconds, January 1, 1970 UTC. Seconds since the Epoch is a value interpreted as the number of seconds between a specified time and the Epoch.

The functions time and ftime return the time as seconds since the Epoch.

The functions ctime, gmtime, and localtime take as their argument a time value that represents the time in seconds from the Epoch.

The function mktime converts a broken-down time, expressed as local time, into a time value in terms of seconds since the Epoch.

The values st_ctime, st_atime, and st_mtime returned in the stat structure by the stat and fstat functions are also in terms of UTC.

Time support new to OpenVMS Version 7.0 includes the functions tzset, gettimeofday, and getclock, and the external variables tzname, timezone, and daylight.

The UTC-based time model enables the C RTL to:

  • Implement the ANSI C gmtime function, which returns a structure in terms of GMT time.

  • Specify the ANSI tm_isdst field of the tm structure, which specifies whether daylight savings time is in effect.

  • Provide time-related POSIX and X/Open extensions (such as the tzset function (which lets you get time information from any time zone), and the external variables tzname, timezone, and daylight.

  • Correctly compute the local time for times in the past, something that the time functions like localtime need to do.

  • Enable localtime and gmtime, through the use of feature-test macros (see Section 1.4), to return two additional fields: tm_zone (an abbreviation of the time-zone name) and tm_gmtoff (the offset from UTC in seconds) in the tm structure they return.

12.3. C RTL Date/Time Computations – UTC and Local Time

Universal Coordinated Time (UTC) is an international standard for measuring time of day. Under the UTC time standard, zero hour occurs when the Greenwich Meridian is at midnight. UTC has the advantage of always increasing, unlike local time, which can go backwards/forwards depending on daylight saving time.

Also, UTC has two additional components:

  • A measure of inaccuracy (optional)

  • A time-differential factor, which is an offset applied to UTC to derive local time.

    The time-differential factor associates each local time zone with UTC; the time differential factor is applied to UTC to derive local time. (Local times can vary up to –12 hours West of the Greenwich Meridian and +13 hours East of it).

For the C RTL time support to work correctly on OpenVMS Version 7.0 and higher, the following must be in place:

  • Your OpenVMS system must be correctly configured to use a valid OpenVMS TDF. Make sure this is set correctly by checking the value of the SYS$TIMEZONE_DIFFERENTIAL logical. This logical should contain the time difference added to UTC to arrive at your local time.

  • Your OpenVMS installation must correctly set the local time zone that describes the location that you want to be your default local time zone. In general, this is the local time zone in which your system is running.

For more information, see the section on setting up your system to compensate for different time zones in your OpenVMS System Manager's Manual: Essentials.

The C RTL uses local time-zone conversion rules to compute local time from UTC, as follows:

  1. The C RTL internally computes time in terms of UTC.

  2. The C RTL then uses time-zone conversion rules to compute a time-differential factor to apply to UTC to derive local time. See the tzset function in the Reference Section of this manual for more information on the time-zone conversion rules.

By default, the time-zone conversion rules used for computing local time from UTC are specified in time-zone files defined by the SYS$LOCALTIME and SYS$POSIXRULES system logicals. These logicals are set during an OpenVMS installation to point to time-zone files that represent the system's best approximation to local wall-clock time:

  • SYS$LOCALTIME defines the time-zone file containing the default conversion rules used by the C RTL to compute local time.

  • SYS$POSIXRULES defines the time-zone file that specifies the default rules to be applied to POSIX style time zones that do not specify when to change to summer time and back.

SYS$POSIXRULES can be the same as SYS$LOCALTIME. See the tzset function for more information.

12.4. Time-Zone Conversion Rule Files

The time-zone files pointed to by the SYS$LOCALTIME and SYS$POSIXRULES logicals are part of a public-domain, time-zone support package installed on OpenVMS Version 7.0 and higher systems.

This support package includes a series of source files that describe the time-zone conversion rules for computing local time from UTC in worldwide time zones. OpenVMS Version 7.0 and higher systems provide a time-zone compiler called ZIC. The ZIC compiler compiles time-zone source files into binary files that the C RTL reads to acquire time-zone conversion specifications. For more information on the format of these source files, see the OpenVMS system documentation for ZIC.

The time-zone files are organized as follows:

  • The root time-zone directory is SYS$COMMON:[SYS$TIMEZONE.SYSTEM]. The system logical SYS$TZDIR is set during installation to point to this area.

  • Time-zone source files are found in SYS$COMMON:[SYS$TIMEZONE.SYSTEM.SOURCES].

  • Binary time-zone files use SYS$COMMON:[SYS$TIMEZONE.SYSTEM] as their root directory. Some binaries reside in this directory while others reside in its subdirectories.

  • Binaries residing in subdirectories are time-zone files that represent specific time zones in a larger geographic area. For example, SYS$COMMON:[SYS$TIMEZONE.SYSTEM] contains a subdirectory for the United States and a subdirectory for Canada, because each of these geographic locations contains several time zones. Each time zone in the US is represented by a time-zone file in the Unites States subdirectory. Each time zone in Canada is represented by a time-zone file in the Canada subdirectory.

Several of the time-zone files have names based on acronyms for the areas that they represent. Table 12.2 lists these acronyms.
Table 12.2. Time-zone Filename Acronyms

Time-Zone Acronym

Description

CET

Central European Time

EET

Eastern European Time

Factory

Specifies No Time Zone

GB-Eire

Great Britain/Ireland

GMT

Greenwich Mean Time

NZ

New Zealand

NZ-CHAT

New Zealand, Chatham Islands

MET

Middle European Time

PRC

Peoples Republic of China

ROC

Republic of China

ROK

Republic of Korea

SystemV

Specific to System V operating system

UCT

Universal Coordinated Time

US

United States

UTC

Universal Coordinated Time

Universal

Universal Coordinated Time

W-SU

Middle European Time

WET

Western European Time

A mechanism is available for you to define and implement your own time-zone rules. For more information, see the OpenVMS system documentation on the ZIC compiler and the description of tzset in the reference section of this manual.

Also, the SYS$LOCALTIME and SYS$POSIXRULES system logicals can be redefined to user-supplied time zones.

12.5. Sample Date/Time Scenario

The following example and explanation shows how to use the C RTL time functions to print the current time: 
#include <stdio.h>
#include <time.h>

main ()
{
  time_t t;

  t = time((time_t)0);
  printf ("The current time is: %s\n",asctime (localtime (&t)));
}
This example:

  1. Calls the time function to get the current time in seconds since the Epoch, in terms of UTC.

  2. Passes this value to the localtime function, which uses time-conversion information as specified by tzset to determine which time-zone conversion rules should be used to compute local time from UTC. By default, these rules are specified in the file defined by SYS$LOCALTIME:

    1. For a user in the Eastern United States interested in their local time, SYS$LOCALTIME would be defined during installation to SYS$COMMON:[SYS$ZONEINFO.US]EASTERN, the time-zone file containing conversion rules for the Eastern U.S. time zone.

    2. If the local time falls during daylight savings time (DST), SYS$COMMON:[SYS$ZONEINFO.US]EASTERN indicates that a time differential factor of -4 hours needs to be applied to UTC to get local time.

      If the local time falls during Eastern standard time (EST), SYS$COMMON:[SYS$ZONEINFO.US]EASTERN indicates that a time differential factor of -5 hours needs to be applied to UTC to get local time.

    3. The C RTL applies -4 (DST) or -5 (EST) to UTC, and localtime returns the local time in terms of a tm structure.

  3. Pass this tm structure to the asctime function to print the local time in a readable format.

Reference Section

This section describes the functions contained in the VSI C Run-Time Library (C RTL), listed alphabetically.

a64l

a64l — Converts a character string to a long integer.

Format

#include <stdlib.h>
long a64l (const char *s);

Argument

s

A pointer to the character string that is to be converted to a long integer.

Description

The a64l and l64a functions are used to maintain numbers stored in base-64 ASCII characters as follows:

  • a64l converts a character string to a long integer.

  • l64a converts a long integer to a character string.

Each character used for storing a long integer represents a numeric value from 0 through 63. Up to six characters can be used to represent a long integer.

The characters are translated as follows:

  • A period (.) represents 0.

  • A slash (/) represents 1.

  • The numbers 0 through 9 represent 2 through 11.

  • Uppercase letters A through Z represent 12 through 37.

  • Lowercase letters a through z represent 38 through 63.

The a64l function takes a pointer to a base-64 representation, in which the first digit is the least significant, and returns a corresponding long value. If the string pointed to by the s parameter exceeds six characters, a64l uses only the first six characters.

If the first six characters of the string contain a null terminator, a64l uses only characters preceding the null terminator.

The a64l function translates a character string from left to right with the least significant number on the left, decoding each character as a 6-bit base-64 number.

If s is the NULL pointer or if the string pointed to by s was not generated by a previous call to l64a, the behavior of a64l is unspecified.

See also l64a.

Return Values

n

Upon successful completion, the long value resulting from conversion of the input string.

0L

Indicates that the string pointed to by s is an empty string.

abort

abort — Sends the signal SIGABRT that terminates execution of the program.

Format

#include <stdlib.h>
void abort (void);

abs

abs — Returns the absolute value of an integer.

Format

#include <stdlib.h>
int abs (int x);

Argument

x

An integer.

Return Value

x

The absolute value of the input argument. If the argument is LONG_MIN, abs returns LONG_MIN because –LONG_MIN cannot fit in an int variable.

access

access — Checks a file to see whether a specified access mode is allowed. The access function does not accept network files as arguments.

Format

#include <unistd.h>
int access (const char *file_spec, int mode);

Arguments

file_spec

A character string that gives an OpenVMS or UNIX style file specification. The usual defaults and logical name translations are applied to the file specification.

mode

Interpreted as shown in Table 33.
Table 33. Interpretation of the mode Argument

Mode Argument

Access Mode

F_OK

Tests to see if the file exists

X_OK

Execute

W_OK

Write (implies delete access)

R_OK

Read

Combinations of access modes are indicated by ORing the values. For example, to check to see if a file has RWED access mode, invoke access as follows: 
access (file_spec, R_OK | W_OK | X_OK);

Description

The access function checks a file to see whether a specified access mode is allowed. If the DECC$ACL_ACCESS_CHECK feature logical is enabled, this function checks OpenVMS Access Control Lists (ACLs) as well as the UIC protection.

Return Values

0

Indicates that the access is allowed.

-1

Indicates that the access is not allowed.

Example

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>

main()
{
    if (access("sys$login:login.com", F_OK)) {
        perror("ACCESS - FAILED");
        exit(2);
    }
}

acos

acos — Returns the arc cosine of its argument.

Format

#include <math.h>
double acos (double x);
float acosf (float x); 
long double acosl (long double x); 
double acosd (double x); 
float acosdf (float x); 
long double acosdl (long double x);

Argument

x

A radian expressed as a real value in the domain [-1,1].

Description

The acos functions compute the principal value of the arc cosine of x in the range [0, π] radians for x in the domain [-1,1].

The acosd functions compute the principal value of the arc cosine of x in the range [0,180] degrees for x in the domain [-1,1].

For abs(x) > 1, the value of acos( x) is 0, and errno is set to EDOM.

acosh

acosh — Returns the hyperbolic arc cosine of its argument.

Format

#include <math.h>
double acosh (double x);
float acoshf (float x);
long double acoshl (long double x);

Argument

x

A radian expressed as a real value in the domain [1, +Infinity].

Description

The acosh functions return the hyperbolic arc cosine of x for x in the domain [1, +Infinity], where acosh(x) = ln(x + sqrt(x**2 - 1)).

The acosh function is the inverse function of cosh where acosh(cosh(x)) = | x|.

x < 1 is an invalid argument.

[w]addch

[w]addch — Add a character to the window at the current position of the cursor.

Format

#include <curses.h>
int addch (char ch);
int waddch (WINDOW *win, char ch);

Arguments

win

A pointer to the window.

ch

The character to be added. A new-line character (\n) clears the line to the end, and moves the cursor to the next line at the same x coordinate. A return character (\r) moves the cursor to the beginning of the line on the window. A tab character (\t) moves the cursor to the next tabstop within the window.

Description

When the waddch function is used on a subwindow, it writes the character onto the underlying window as well.

The addch routine performs the same function as waddch, but on the stdscr window.

The cursor is moved after the character is written to the screen.

Return Values

OK

Indicates success.

ERR

Indicates that writing the character would cause the screen to scroll illegally. For more information, see the scrollok function.

[w]addstr

[w]addstr — Add the string pointed to by str to the window at the current position of the cursor.

Format

#include <curses.h>
int addstr (char *str);
int waddstr (WINDOW *win, char *str);

Arguments

win

A pointer to the window.

str

A pointer to a character string.

Description

When the waddstr function is used on a subwindow, the string is written onto the underlying window as well.

The addstr routine performs the same function as waddstr, but on the stdscr window.

The cursor position changes as a result of calling this routine.

Return Values

OK

Indicates success.

ERR

Indicates that the function causes the screen to scroll illegally, but it places as much of the string onto the window as possible. For more information, see the scrollok function.

alarm

alarm — Sends the signal SIGALRM (defined in the <signal.h> header file) to the invoking process after the number of seconds indicated by its argument has elapsed.

Format

#include <unistd.h>
unsigned int alarm (unsigned int seconds); (ISO POSIX-1)
int alarm (unsigned int seconds); (Compatibility)

Argument

seconds

Has a maximum limit of LONG_MAX seconds.

Description

Calling the alarm function with a 0 argument cancels any pending alarms.

Unless it is intercepted or ignored, the signal generated by alarm terminates the process. Successive alarm calls reinitialize the alarm clock. Alarms are not stacked.

Because the clock has a 1-second resolution, the signal may occur up to 1 second early. If the SIGALRM signal is intercepted, resumption of execution may be held up due to scheduling delays.

When the SIGALRM signal is generated, a call to SYS$WAKE is generated whether or not the process is hibernating. The pending wake causes the current pause() to return immediately (after completing any function that catches the SIGALRM).

Return Value

n

The number of seconds remaining from a previous alarm request.

alloca

alloca — Allocates memory on the stack.

Format

#include <alloca.h>
void *alloca (unsigned int size);

Arguments

size

The total number of bytes to be allocated.

Description

The alloca function allocates size bytes from the stack frame of the caller. The memory is automatically freed when the function that calls alloca returns to its caller. See the VSI C User Manual for the description of the __ALLOCA macro.

Return Value

x

Returns a pointer to the allocated memory.

asctime, asctime_r

asctime, asctime_r — Converts a broken-down time in a tm structure into a 26-character string in the following form: Sun Sep 16 01:03:52 1984 \n \0. All fields have a constant width.

Format

#include <time.h>
char *asctime (const struct tm *timeptr);
char *asctime_r (const struct tm *timeptr, char *buffer); (ISO POSIX-1)

Arguments

timeptr

A pointer to a structure of type tm, which contains the broken-down time.

The tm structure is defined in the <time.h> header file, and also shown in Table 36 in the description of localtime.

buffer

A pointer to a character array that is at least 26 bytes long. This array is used to store the generated date-and-time string.

Description

The asctime and asctime_r functions convert the contents of tm into a 26-character string and returns a pointer to the string.

The difference between asctime_r and asctime is that the former puts the result into a user-specified buffer. The latter puts the result into thread-specific static memory allocated by the C RTL, which can be overwritten by subsequent calls to ctime or asctime; you must make a copy if you want to save it.

On success, asctime returns a pointer to the string; asctime_r returns its second argument. On failure, these functions return the NULL pointer.

See the localtime function for a list of the members in tm.

Note

Generally speaking, UTC-based time functions can affect in-memory timezone information, which is processwide data. However, if the system time zone remains the same during the execution of the application (which is the common case) and the cache of timezone files is enabled (which is the default), then the _r variant of the time functions asctime_r, ctime_r, gmtime_r and localtime_r, is both thread-safe and AST-reentrant.

If, however, the system time zone can change during the execution of the application or the cache of timezone files is not enabled, then both variants of the UTC-based time functions belong to the third class of functions, which are neither thread-safe nor AST-reentrant.

Return Values

x

A pointer to the string, if successful.

NULL

Indicates failure.

asin

asin — Returns the arc sine of its argument.

Format

#include <math.h>
double asin (double x);
float asinf (float x); 
long double asinl (long double x); 
double asind (double x); 
float asindf (float x); 
long double asindl (long double x);

Argument

x

A radian expressed as a real number in the domain [-1,1].

Description

The asin functions compute the principal value of the arc sine of x in the range [- π/2, π/2] radians for x in the domain [-1,1].

The asind functions compute the principal value of the arc sine of x in the range [-90,90] degrees for x in the domain [-1,1].

When abs(x) is greater than 1.0, the value of asin( x) is 0, and errno is set to EDOM.

asinh

asinh — Returns the hyperbolic arc sine of its argument.

Format

#include <math.h>
double asinh (double x);
float asinhf (float x);
long double asinhl (long double x);

Argument

x

A radian expressed as a real value in the domain [-Infinity,+Infinity].

Description

The asinh functions return the hyperbolic arc sine of x for x in the domain [-Infinity, +Infinity], where asinh(x) = ln(x + sqrt(x**2+ 1)).

The asinh function is the inverse function of sinh where asinh(sinh(x)) = x.

assert

assert — Used for implementing run-time diagnostics in programs.

Format

#include <assert.h>
void assert (int expression);

Argument

expression

An expression that has an int type.

Description

When assert is executed, if expression is false (that is, it evaluates to 0), assert writes information about the particular call that failed (including the text of the argument, the name of the source file, and the source line number; the latter two are, respectively, the values of the preprocessing macros __FILE__ and __LINE__) to the standard error file in an implementation-defined format. Then, it calls the abort function.

The assert function writes a message in the following form:
Assertion failed:  expression, file aaa, line nnn
If expression is true (that is, it evaluates to nonzero) or if the signal SIGABRT is being ignored, assert returns no value.

Note

If a null character ('\0') is part of the expression being asserted, then only the text up to and including the null character is printed, since the null character effectively terminates the string being output.

Compiling with the CC command qualifier /DEFINE=NDEBUG or with the preprocessor directive #define NDEBUG ahead of the #include assert statement causes the assert function to have no effect.

Example

#include <stdio.h>
#include <assert.h>

main()
{
    printf("Only this and the assert\n");
    assert(1 == 2);     /* expression is FALSE */

    /* abort should be called so the printf will not happen. */

    printf("FAIL abort did not execute");
}

atan

atan — Returns the arc tangent of its radian argument, in the range [-π/2, π/2] radians.

Format

#include <math.h>
double atan (double x);
float atanf (float x);
long double atanl (long double x);
double atand (double x);
float atandf (float x);
long double atandl (long double x);

Argument

x

A radian expressed as a real number.

Description

The atan functions compute the principal value of the arc tangent of x in the range [- π/2, π/2] radians.

The atand functions compute the principal value of the arc tangent of x in the range [-90,90] degrees.

atan2

atan2 — Returns the arc tangent of y/x (its two radian arguments), in the range [-π, π] radians.

Format

#include <math.h>
double atan2 (double y, double x);
float atan2f (float y, float x);
long double atan2l (long double y, long double x);
double atand2 (double y, double x);
float atand2f (float y, float x);
long double atand2l (long double y, long double x);

Arguments

y

A radian expressed as a real number.

x

A radian expressed as a real number.

Description

The atan2 functions compute the principal value of the arc tangent of y/ x in the range [- π, π] radians. The sign of atan2 and atan2f is determined by the sign of y. The value of atan2( y, x) is computed as follows, where f is the number of fraction bits associated with the data type:

Value of Input Arguments

Angle Returned

x = 0 or y/x > 2**( f+1)

π/2 * (sign y)

x > 0 and y/x <= 2**( f+1)

atan(y/x)

x < 0 and y/x <= 2**( f+1)

π * (sign y) + atan(y/x)

The atand2 functions compute the principal value of the arc tangent of y/ x in the range [-180,180] degrees. The sign of atand2 and atand2f is determined by the sign of y.

The following are invalid arguments for the atan2 and atand2 functions:

Function

Exceptional Argument

atan2, atan2f, atan2l

x = y = 0

atan2, atan2f, atan2l

| x | = | y | = Infinity

atand2, atand2f, atand2l

x = y = 0

atand2, atand2f, atand2l

| x | = | y | = Infinity

atanh

atanh — Returns the hyperbolic arc tangent of its argument.

Format

#include <math.h>
double atanh (double x);
float atanhf (float x);
long double atanhl (long double x);

Argument

x

A radian expressed as a real value in the domain [-1,1].

Description

The atanh functions return the hyperbolic arc tangent of x. The atanh function is the inverse function of tanh where atanh(tanh(x)) = x.

|x| > 1 is an invalid argument.

atexit

atexit — Registers a function that is called without arguments at program termination.

Format

#include <stdlib.h>
int atexit (void (*func) (void));

Argument

func

A pointer to the function to be registered.

Return Values

0

Indicates that the registration has succeeded.

nonzero

Indicates failure.

Restriction

The longjmp function cannot be executed from within the handler, because the destination address of the longjmp no longer exists.

Example

#include <stdlib.h>
#include <stdio.h>

static void hw(void);

main()
{
    atexit(hw);
}

static void hw()
{
        puts("Hello, world\n");
}
Running this example produces the following output:
Hello, world

atof

atof — Converts an ASCII character string to a double-precision number.

Format

#include <stdlib.h>
double atof (const char *nptr);

Argument

nptr

A pointer to the character string to be converted to a double-precision number. The string is interpreted by the same rules that are used to interpret floating constants.

Description

The string to be converted has the following format: 
[white-spaces][+|-]digits[radix-character][digits][e|E[+|-]integer]

Where radix-character is defined in the current locale.

The first unrecognized character ends the conversion.

This function is equivalent to strtod(nptr, (char**) NULL).

Return Values

x

The converted value.

0

Indicates an underflow or the conversion could not be performed. The function sets errno to ERANGE or EINVAL, respectively.

±HUGE_VAL

Overflow occurred; errno is set to ERANGE.

atoi, atol

atoi, atol — Convert strings of ASCII characters to the appropriate numeric values.

Format

#include <stdlib.h>
int atoi (const char *nptr);
long int atol (const char *nptr);

Argument

nptr

A pointer to the character string to be converted to a numeric value.

Description

The atoi and atol functions convert the initial portion of a string to its decimal int or long int value, respectively. The atoi and atol functions do not account for overflows resulting from the conversion. The string to be converted has the following format: [white-spaces][+|-]digits

The function call atol (str) is equivalent to strtol (str, (char**)NULL, 10), and the function call atoi (str) is equivalent to (int) strtol(str, (char**)NULL, 10), except, in both cases, for the behavior on error.

Return Value

n

The converted value.

atoq, atoll

atoq, atoll — Convert strings of ASCII characters to the appropriate numeric values. atoll is a synonym for atoq.

Format

#include <stdlib.h>
__int64 atoq (const char *nptr);
__int64 atoll (const char *nptr);

Argument

nptr

A pointer to the character string to be converted to a numeric value.

Description

The atoq (or atoll) function converts the initial portion of a string to its decimal __int64 value. This function does not account for overflows resulting from the conversion. The string to be converted has the following format:
[white-spaces][+|-]digits

The function call atoq (str) is equivalent to strtoq (str, (char**)NULL, 10), except for the behavior on error.

Return Value

n

The converted value.

basename

basename — Returns the last component of a pathname.

Format

#include <libgen.h>
char *basename (char *path);

Function Variants

The basename function has variants named _basename32 and _basename64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Argument

path

A UNIX style pathname from which the base pathname is extracted.

Description

The basename function takes the UNIX style pathname pointed to by path and returns a pointer to the pathname's final component, deleting any trailing slash (/) characters.

If path consists entirely of the slash (/) character, the function returns a pointer to the string "/".

If path is a NULL pointer or points to an empty string, the function returns a pointer to the string ".".

The basename function can modify the string pointed to by path.

Return Values

x

A pointer to the final component of path.

"/"

If path consists entirely of the '/' character.

"."

If path is a NULL pointer or points to an empty string.

bcmp

bcmp — Compares byte strings.

Format

#include <strings.h>
void bcmp (const void *string1, const void *string2, size_t length);

Arguments

string1, string2

The byte strings to be compared.

length

The length (in bytes) of the strings.

Description

The bcmp function compares the byte string in string1 against the byte string in string2.

Unlike the string functions, there is no checking for null bytes. Zero-length strings are always identical.

Note that bcmp is equivalent to memcmp, which is defined by the ANSI C Standard. Therefore, using memcmp is recommended for portable programs.

Return Values

0

The strings are identical.

Nonzero

The strings are not identical.

bcopy

bcopy — Copies byte strings.

Format

#include <strings.h>
void bcopy (const void *source, void *destination, size_t length);

Arguments

source

Pointer to the source string.

destination

Pointer to the destination string.

length

The length (in bytes) of the string.

Description

The bcopy function operates on variable-length strings of bytes. It copies the value of the length argument, in bytes, from the string in the source argument to the string in the destination argument.

Unlike the string functions, there is no checking for null bytes. If the length argument is 0 (zero), no bytes are copied.

Note that bcopy is equivalent to memcpy, which is defined by the ANSI C Standard. Therefore, using memcpy is recommended for portable programs.

box

box — Draws a box around the window using the character vert as the character for drawing the vertical lines of the rectangle, and hor for drawing the horizontal lines of the rectangle.

Format

#include <curses.h>
int box (WINDOW *win, char vert, char hor);

Arguments

win

The address of the window.

vert

The character for the vertical edges of the window.

hor

The character for the horizontal edges of the window.

Description

The box function copies boxes drawn on subwindows onto the underlying window. Use caution when using functions such as overlay and overwrite with boxed subwindows. Such functions copy the box onto the underlying window.

Return Values

OK

Indicates success.

ERR

Indicates an error.

brk

brk — Determines the lowest virtual address that is not used with the program.

Format

#include <stdlib.h>
void *brk (unsigned long int addr);

Argument

addr

The lowest address, which the function rounds up to the next multiple of the page size. This rounded address is called the break address.

Description

An address that is greater than or equal to the break address and less than the stack pointer is considered to be outside the program's address space. Attempts to reference it will cause access violations.

When a program is executed, the break address is set to the highest location defined by the program and data storage areas. Consequently, brk is needed only by programs that have growing data areas.

Return Values

n

The new break address.

(void *)( -1)

Indicates that the program is requesting too much memory. ecrrno and vaxc$errno are updated.

Restriction

Unlike other C library implementations, the C RTL memory allocation functions (such as malloc) do not rely on brk or sbrk to manage the program heap space. Consequently, on OpenVMS systems, calling brk or sbrk can interfere with memory allocation routines. The brk and sbrk functions are provided only for compatibility purposes.

bsearch

bsearch — Performs a binary search. It searches an array of sorted objects for a specified object.

Format

#include <stdlib.h>
void *bsearch (const void *key, const void *base, size_t nmemb,
size_t size, int (*compar) (const void *, const void *));

Function Variants

The bsearch function has variants named _bsearch32 and _bsearch64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

key

A pointer to the object to be sought in the array. This pointer should be of type pointer-to-object and cast to type pointer-to-void.

base

A pointer to the initial member of the array. This pointer should be of type pointer-to-object and cast to type pointer-to-void.

nmemb

The number of objects in the array.

size

The size of an object, in bytes.

compar

A pointer to the comparison function.

Description

The array must first be sorted in increasing order according to the specified comparison function pointed to by compar.

Two arguments are passed to the comparison function pointed to by compar. The two arguments point to the objects being compared. Depending on whether the first argument is less than, equal to, or greater than the second argument, the comparison function must return an integer less than, equal to, or greater than 0.

It is not necessary for the comparison function (compar) to compare every byte in the array. Therefore, the objects in the array can contain arbitrary data in addition to the data being compared.

Since it is declared as type pointer-to-void, the value returned must be cast or assigned into type pointer-to-object.

Return Values

x

A pointer to the matching member of the array or a null pointer if no match is found.

NULL

Indicates that the key cannot be found in the array.

Example

#include <stdio.h>
#include <stdlib.h>

#define SSIZE 30

extern int compare();  /* prototype for comparison function */

int array[SSIZE] = {30, 1, 29, 2, 28, 3, 27, 4, 26, 5,
                    24, 6, 23, 7, 22, 8, 21, 9, 20, 10,
                    19, 11, 18, 12, 17, 13, 16, 14, 15, 25};

 /*  This program takes an unsorted array, sorts it using qsort, */
 /*  and then calls bsearch for each element in the array,       */
 /*  making sure that bsearch returns the correct element.       */

main()
{
    int i;
    int failure = FALSE;
    int *rkey;

    qsort(array, SSIZE, sizeof (array[0]), &compare);

    /* search for each element */
    for (i = 0; i < SSIZE - 1; i++) {
        /* search array element i */
        rkey = bsearch((array + i), array, SSIZE,
                        sizeof(array[0]), &compare);
        /* check for successful search */
        if (&array[i] != rkey) {
            printf("Not in array, array element %d\n", i);
            failure = TRUE;
            break;
        }
    }
    if (!failure)
        printf("All elements successfully found!\n");
}

 /*  Simple comparison routine.  */
 /*                              */
 /*  Returns:  = 0 if a == b     */
 /*            < 0 if a < b      */
 /*            > 0 if a > b      */

int compare(int *a, int *b)
{
    return (*a - *b);
}
This example program outputs the following:
All elements successfully found!

btowc

btowc — Converts a one-byte multibyte character to a wide character in the initial shift state.

Format

#include <wchar.h>
wint_t btowc (int c);

Argument

c

The character to be converted to a wide-character representation.

Description

The btowc function determines whether (unsigned char) c is a valid one-byte multibyte character in the initial shift state, and if so, returns a wide-character representation of that character.

Return Values

x

The wide-character representation of unsigned char c.

WEOF

Indicates an error. The c argument has the value EOF or does not constitute a valid one-byte multibyte character in the initial shift state.

bzero

bzero — Copies null characters into byte strings.

Format

#include <strings.h>
void bzero (void *string, size_t length);

Arguments

string

Specifies the byte string into which you want to copy null characters.

length

Specifies the length (in bytes) of the string.

Description

The bzero function copies null characters ('\0') into the byte string pointed to by string for length bytes. If length is 0 (zero), then no bytes are copied.

cabs

cabs — Returns the absolute value of a complex number.

Format

#include <math.h>
double cabs (cabs_t z);
float cabsf (cabsf_t z); 
long double cabsl (cabsl_t z);

Argument

z

A structure of type cabs_t, cabsf_t, or cabsl_t. These types are defined in the <math.h> header file as follows: 
typedef struct {double x,y;} cabs_t;

typedef struct { float x, y; } cabsf_t; 
typedef struct { long double x, y; } cabsl_t;

Description

The cabs functions return the absolute value of a complex number by computing the Euclidean distance between its two points as the square root of their respective squares:
sqrt(x2 + y2)

On overflow, the return value is undefined.

The cabs, cabsf, and cabsl functions are equivalent to the hypot, hypotf, and hypotl functions, respectively.

cacos

cacos — Returns the complex arc cosine of its argument.

Format

#include <complex.h>
double complex cacos (double complex z);
float complex cacosf (float complex z);
long double complex cacosl (long double complex z);

Argument

z

A complex value.

Description

The cacos functions compute the complex arc cosine of z, with branch cuts outside the interval [-1, +1] along the real axis.

Return Values

n

The complex arc cosine value, in the range of a strip mathematically unbounded along the imaginary axis and in the interval [0, π] along the real axis.

cacosh

cacosh — Returns the complex arc hyperbolic cosine of its argument.

Format

#include <complex.h>
double complex cacosh (double complex z);
float complex cacoshf (float complex z);
long double complex cacoshl (long double complex z);

Argument

z

A complex value.

Description

The cacosh functions compute the complex arc hyperbolic cosine of z, with a branch cut at values less than 1 along the real axis.

Return Values

n

The complex arc hyperbolic cosine value, in the range of a half-strip of non-negative values along the real axis and in the interval [-i π, +i π] along the imaginary axis.

calloc

calloc — Allocates an area of zeroed memory. This function is AST-reentrant.

Format

#include <stdlib.h>
void *calloc (size_t number, size_t size);

Function Variants

The calloc function has variants named _calloc32 and _calloc64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

number

The number of items to be allocated.

size

The size of each item.

Description

The calloc function initializes the items to 0. The maximum amount of memory allocated at once is limited to 0xFFFFD000.

See also malloc and realloc.

Return Values

x

The address of the first byte, which is aligned on a quadword boundary (Alpha only) or an octaword boundary (Integrity servers only).

NULL

Indicates an inability to allocate the space.

carg

carg — Returns the phase angle of its complex argument.

Format

#include <complex.h>
double carg (double complex z);
float cargf (float complex z);
long double cargl (long double complex z);

Argument

z

A complex value.

Description

The carg functions compute the argument (also called phase angle) of z, with a branch cut along the negative real axis.

Return Values

n

The value of the argument of z, in the interval [- π, + π].

casin

casin — Returns the complex arc sine of its argument.

Format

#include <complex.h>
double complex casin (double complex z);
float complex casinf (float complex z);
long double complex casinl (long double complex z);

Argument

z

A complex value.

Description

The casin functions compute the complex arc sine of z, with branch cuts outside the interval [-1, +1] along the real axis.

Return Values

n

The complex arc sine value, in the range of a strip mathematically unbounded along the imaginary axis and in the interval [- π/2, + π/2] along the real axis.

casinh

casinh — Returns the complex arc hyperbolic sine of its argument.

Format

#include <complex.h>
double complex casinh (double complex z);
float complex casinhf (float complex z);
long double complex casinhl (long double complex z);

Argument

z

A complex value.

Description

The casinh functions compute the complex arc hyperbolic sine of z, with branch cuts outside the interval [-i, +i] along the imaginary axis.

Return Values

n

The complex arc hyperbolic sine value, in the range of a strip mathematically unbounded along the real axis and in the interval [-i π/2, +i π/2] along the imaginary axis.

catan

catan — Returns the complex arc tangent of its argument.

Format

#include <complex.h>
double complex catan (double complex z);
float complex catanf (float complex z);
long double complex catanl (long double complex z);

Argument

z

A complex value.

Description

The catan functions compute the complex arc tangent of z, with branch cuts outside the interval [-i, +i] along the imaginary axis.

Return Values

n

The complex arc tangent value, in the range of a strip mathematically unbounded along the imaginary axis and in the interval [- π/2, + π/2] along the real axis.

catanh

catanh — Returns the complex arc hyperbolic tangent of its argument.

Format

#include <complex.h>
double complex catanh (double complex z);
float complex catanhf (float complex z);
long double complex catanhl (long double complex z);

Argument

z

A complex value.

Description

The catanh functions compute the complex arc hyperbolic tangent of z, with branch cuts outside the interval [-1, +1] along the imaginary axis.

Return Values

n

The complex arc hyperbolic tangent value, in the range of a strip mathematically unbounded along the real axis and in the interval [-i π/2, +i π/2] along the imaginary axis.

catclose

catclose — Closes a message catalog.

Format

#include <nl_types.h>
int catclose (nl_catd catd);

Argument

catd

A message catalog descriptor. This is returned by a successful call to catopen.

Description

The catclose function closes the message catalog referenced by catd and frees the catalog file descriptor.

Return Values

0

Indicates that the catalog was successfully closed.

-1
Indicates that an error occurred. The function sets errno to the following value:

  • EBADF – The catalog descriptor is not valid.

catgets

catgets — Retrieves a message from a message catalog.

Format

#include <nl_types.h>
char *catgets (nl_catd catd, int set_id, int msg_id, const char *s);

Function Variants

The catgets function has variants named _catgets32 and _catgets64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

catd

A message catalog descriptor. This is returned by a successful call to catopen.

set_id

An integer set identifier.

msg_id

An integer message identifier.

s

A pointer to a default message string that is returned by the function if the message cannot be retrieved.

Description

The catgets function retrieves a message identified by set_id and msg_id, in the message catalog catd. The message is stored in a message buffer in the nl_catd structure, which is overwritten by subsequent calls to catgets. If a message string needs to be preserved, it should be copied to another location by the program.

Return Values

x

Pointer to the retrieved message.

s
Pointer to the default message string. Indicates that the function is not able to retrieve the requested message from the catalog. This condition can arise if the requested pair (set_d, msg_id) does not represent an existing message from the open catalog, or it indicates that an error occurred. If an error occurred, the function sets errno to one of the following values:

  • EBADF – The catalog descriptor is not valid.

  • EVMSRR – An OpenVMS I/O read error; the OpenVMS error code can be found in vaxc$errno.

Example

#include <nl_types.h>
#include <locale.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <unixio.h>

 /* This test makes use of all the message catalog routines. catopen  */
 /* opens the catalog ready for reading, then each of the three       */
 /* messages in the catalog are extracted in turn using catgets and   */
 /* printed out. catclose closes the catalog after use.               */
 /* The catalog source file used to create the catalog is as follows: */
 /* $ This is a message file
 * $
 * $quote "
 * $ another comment line
 * $set 1
 * 1 "First set, first message"
 * 2 "second message - This long message uses a backslash \
 * for continuation."
 * $set 2
 * 1 "Second set, first message"                                      */

char *default_msg = "this is the first message.";

main()
{
  nl_catd catalog;
  int msg1,
      msg2,
      retval;

  char *cat = "sys$disk:[]catgets_example.cat"; /*Force local catalog*/

  char *msgtxt;

  char string[128];

  /* Create the message test catalog */

  system("gencat catgets_example.msgx catgets_example.cat") ;

  if ((catalog = catopen(cat, 0)) == (nl_catd) - 1) {
      perror("catopen");
      exit(EXIT_FAILURE);
  }

  msgtxt = catgets(catalog, 1, 1, default_msg);
  printf("%s\n", msgtxt);

  msgtxt = catgets(catalog, 1, 2, default_msg);
  printf("%s\n", msgtxt);

  msgtxt = catgets(catalog, 2, 1, default_msg);
  printf("%s\n", msgtxt);

  if ((retval = catclose(catalog)) == -1) {
      perror("catclose");
      exit(EXIT_FAILURE);
  }

  delete("catgets_example.cat;") ;  /* Remove the test catalog */
}
Running the example program produces the following result: 
First set, first message
second message - This long message uses a backslash for
                                                continuation.
Second set, first message

catopen

catopen — Opens a message catalog.

Format

#include <nl_types.h>
nl_catd catopen (const char *name, int oflag);

Arguments

name

The name of the message catalog to open.

oflag

An object of type int that determines whether the locale set for the LC_MESSAGES category in the current program's locale or the logical name LANG is used to search for the catalog file.

Description

The catopen function opens the message catalog identified by name.

If name contains a colon (:), a square opening bracket ([), or an angle bracket (<), or is defined as a logical name, then it is assumed that name is the complete file specification of the catalog.

If it does not include these characters, catopen assumes that name is a logical name pointing to an existing catalog file. If name is not a logical name, then the logical name NLSPATH is used to define the file specification of the message catalog. NLSPATH is defined in the user's process. If the NLSPATH logical name is not defined, or no message catalog can be opened in any of the components specified by the NLSPATH, then the SYS$NLSPATH logical name is used to search for a message catalog file.

Both NLSPATH and SYS$NLSPATH are comma-separated lists of templates. The catopen function uses each template to construct a file specification. For example, NLSPATH could be defined as:
DEFINE NLSPATH SYS$SYSROOT:[SYS$I18N.MSG]%N.CAT,SYS$COMMON:[SYSMSG]%N.CAT

In this example, catopen first searches the directory SYS$SYSROOT:[SYS$I18N.MSG] for the named catalog. If the named catalog is not found there, the directory SYS$COMMON:[SYSMSG] is searched. The catalog name is constructed by substituting %N with the name passed to catopen, and adding the .cat suffix. %N is known as a substitution field. The following substitution fields are valid:

Field

Meaning

%N

Substitute the name passed to catopen

%L?

Substitute the locale name.

The period (.) and at-sign (@) characters in the locale name are replaced by an underscore (_) character.

For example, the "zh_CN.dechanzi@radical" locale name results in a substitution of ZH_CN_DECHANZI_RADICAL.

%l?

Substitute the language part of the locale name. For example, the language part of the en_GB.ISO8859-1 locale name is en.

%t?

Substitute the territory part of the locale name. For example, the territory part of the en_GB.ISO8859-1 locale is GB.

%c?

Substitute the codeset name from the locale name. For example, the codeset name of the en_GB.ISO8859-1 locale name is ISO8859-1.

If the oflag argument is set to NL_CAT_LOCALE, then the current locale as defined for the LC_MESSAGES category is used to determine the substitution for the %L, %l, %t, and %c substitution fields. If the oflag argument is set to 0, then the value of the LANG environment variable is used as a locale name to determine the substitution for these fields. Note that using NL_CAT_LOCALE conforms to the XPG4 specification while a value of 0 (zero) exists for the purpose of preserving XPG3 compatibility. Note also, that catopen uses the value of the LANG environment variable without checking whether the program's locale can be set using this value. That is, catopen does not check whether this value can serve as a valid locale argument in the setlocale call.

If the substitution value is not defined, an empty string is substituted.

A leading comma or two adjacent commas (,,) is equivalent to specifying %N. For example, 
DEFINE NLSPATH ",%N.CAT,SYS$COMMON:[SYSMSG.%L]%N.CAT"
In this example, catopen searches in the following locations in the order shown:

  1. name (in the current directory)

  2. name.cat (in the current directory)

  3. SYS$COMMON:[SYSMSG. locale_name] name.cat

Return Values

x

A message catalog file descriptor. Indicates the call was successful. This descriptor is used in calls to catgets and catclose.

(nl_catd) -1
Indicates an error occurred. The function sets errno to one of the following values:

  • EACCES – Insufficient privilege or file protection violation, or file currently locked by another user.

  • EMFILE – Process channel count exceeded.

  • ENAMETOOLONG – The full file specification for message catalog is too long

  • ENOENT – Unable to find the requested message catalog.

  • ENOMEM – Insufficient memory available.

  • ENOTDIR – Part of the name argument is not a valid directory.

  • EVMSERR – An error occurred that does not match any errno value. Check the value of vaxc$errno.

cbrt

cbrt — Returns the rounded cube root of y.

Format

#include <math.h>
double cbrt (double y);
float cbrtf (float y);
long double cbrtl (long double y);

Argument

y

A real number.

ccos

ccos — Returns the complex cosine of its argument.

Format

#include <complex.h>
double complex ccos (double complex z);
float complex ccosf (float complex z);
long double complex ccosl (long double complex z);

Argument

z

A complex value.

Description

The ccos functions return the complex cosine of z.

Return Values

x

The complex cosine value.

ccosh

ccosh — Returns the complex hyperbolic cosine of its argument.

Format

#include <complex.h>
double complex ccosh (double complex z);
float complex ccoshf (float complex z);
long double complex ccoshl (long double complex z);

Argument

z

A complex value.

Description

The ccosh functions return the complex hyperbolic cosine of z.

Return Values

x

The complex hyperbolic cosine value.

ceil

ceil — Returns the smallest integer that is greater than or equal to its argument.

Format

#include <math.h>
double ceil (double x);
float ceilf (float x);
long double ceill (long double x);

Argument

x

A real value.

Return Value

n

The smallest integer greater than or equal to the function argument.

cexp

cexp — Returns the complex exponent of its argument.

Format

#include <complex.h>
double complex cexp (double complex z);
float complex cexpf (float complex z);
long double complex cexpl (long double complex z);

Argument

z

A complex value.

Description

The cexp functions compute the complex exponential value of z, defined as e** z, where e is the constant used as a base for natural logarithms.

Return Values

x

The complex exponential value of the argument.

cfree

cfree — Makes available for reallocation the area allocated by a previous calloc, malloc, or realloc call. This function is AST-reentrant.

Format

#include <stdlib.h>
void cfree (void *ptr);

Argument

ptr

The address returned by a previous call to malloc, calloc, or realloc.

Description

The contents of the deallocated area are unchanged.

In VSI C for OpenVMS systems, the free and cfree functions are equivalent. Some other C implementations use free with malloc or realloc, and cfree with calloc. However, since the ANSI C standard does not include cfree, using free may be preferable.

See also free.

chdir

chdir — Changes the default directory.

Format

#include <unistd.h>
int chdir (const char *dir_spec); (ISO POSIX-1)
int chdir (const char *dir_spec, ...); (VSI C Extension)

Arguments

dir_spec

A null-terminated character string naming a directory in either an OpenVMS or UNIX style specification.

. . .

This argument is an VSI C extension available when not defining any of the standards-related feature-test macros (see Section 1.4) and not compiling in strict ANSI C mode (/STANDARD=ANSI89). The argument is an optional flag of type int that is significant only when calling chdir from USER mode.

If the value of the flag is 1, the new directory is effective across images. If the value is not 1, the original default directory is restored when the image exits.

Description

The chdir function changes the default directory. The change can be permanent or temporary. Permanent means that the new directory remains as the default directory after the image exits. Temporary means that on image exit, the default is set to whatever it was before the execution of the image.

There are two ways of making the change permanent:

  • Call chdir from USER mode with the second argument set to 1.

  • Call chdir from SUPERVISOR or EXECUTIVE mode, regardless of the value of the second argument.

Otherwise, the change is temporary.

Return Values

0

Indicates that the directory is successfully changed to the given name.

-1

Indicates that the change attempt has failed.

chmod

chmod — Changes the file protection of a file.

Format

#include <stat.h>
int chmod (const char *file_spec, mode_tmode);

Arguments

file_spec

The name of an OpenVMS or UNIX style file specification.

mode

A file protection. Modes are constructed by performing a bitwise OR on any of the values shown in Table 34.
Table 34. File Protection Values and Their Meanings

Value

Privilege

0400

OWNER:READ

0200

OWNER:WRITE

0100

OWNER:EXECUTE

0040

GROUP:READ

0020

GROUP:WRITE

0010

GROUP:EXECUTE

0004

WORLD:READ

0002

WORLD:WRITE

0001

WORLD:EXECUTE

When you supply a mode value of 0, the chmod function gives the file the user's default file protection.

The system is given the same privileges as the owner. A WRITE privilege also implies a DELETE privilege.

Description

You must have a WRITE privilege for the file specified to change the mode.

The C RTL does not support the S_ISVTX bit. Setting the S_ISVTX mode has no effect.

Return Values

0

Indicates that the mode is successfully changed.

-1

Indicates that the change attempt has failed.

chown

chown — Changes the user ID and group ID of the specified file.

Format

#include <unistd.h>
int chown (const char *file_spec, uid_t owner, gid_t group);

Arguments

file_spec

The address of an ASCII filename.

owner

The new user ID of the file.

group

The new group ID of the file.

Return Values

0

Indicates success.

-1

Indicates failure.

cimag

cimag — Returns the imaginary part of its complex argument.

Format

#include <complex.h>
double cimag (double complex z);
float cimagf (float complex z);
long double cimagl (long double complex z);

Argument

z

A complex value.

Description

The cimag functions return the imaginary part of z as a real number.

Return Values

x

The imaginary part value.

[w]clear

[w]clear — Erase the contents of the specified window and reset the cursor to coordinates (0,0). The clear function acts on the stdscr window.

Format

#include <curses.h>
int clear();
int wclear (WINDOW *win);

Argument

win

A pointer to the window.

Return Values

OK

Indicates success.

ERR

Indicates an error.

clearerr

clearerr — Resets the error and end-of-file indicators for a file (so that ferror and feof will not return a nonzero value).

Format

#include <stdio.h>
void clearerr (FILE *file_ptr);

Argument

file_ptr

A file pointer.

clearerr_unlocked

clearerr_unlocked — Same as the clearerr function, except used only within a scope protected by flockfile and funlockfile.

Format

#include <stdio.h>
void clearerr_unlocked (FILE *file_ptr);

Argument

file_ptr

A file pointer.

Description

The reentrant version of the clearerr function is locked against multiple threads calling it simultaneously. This incurs overhead to ensure integrity of the stream. The unlocked version of this call, clearerr_unlocked can be used to avoid the overhead. The clearerr_unlocked macro is functionally identical to the clearerr macro, except that it is not required to be implemented in a thread-safe manner. The clearerr_unlocked function can be safely used only within a scope that is protected by the flockfile and funlockfile functions used as a pair. The caller must ensure that the stream is locked before clearerr_unlocked is used.

See also flockfile, ftrylockfile, and funlockfile.

clearok

clearok — Sets the clear flag for the window.

Format

#include <curses.h>
clearok (WINDOW *win, bool boolf);

Arguments

win

The entire size of the terminal screen. You can use the windows stdscr and curscr with clearok.

boolf

A Boolean value of TRUE or FALSE. If the argument is TRUE, this forces a clear screen to be printed on the next call to refresh, or stops the screen from being cleared if boolf is FALSE.

The type bool is defined in the <curses.h> header file as follows: 
#define bool int

Description

Unlike the clear function, the clearok function does not alter the contents of the window. If the win argument is curscr, the next call to refresh causes a clear screen, even if the window passed to refresh is not a window the size of the entire terminal screen.

clock

clock — Determines the CPU time (in 10-millisecond units) used since the beginning of the process. The time reported is the sum of the user and system times of the calling process and any terminated child processes for which the calling process has executed wait or system.

Format

#include <time.h>
clock_t clock (void);

Description

The value returned by the clock function must be divided by the value of the CLK_TCK, as defined in the standard header file <time.h>, to obtain the time in seconds.

The type clock_t is defined in the <time.h> header file as follows: 
typedef long int clock_t;

Only the accumulated times for child processes running a C main program or a program that calls VAXC$CRTL_INIT or DECC$CRTL_INIT are included.

A typical usage of the clock function is to call it after a program does its initial setup, and then again after the program executes the code to be timed. Then subtract the two values to give elapsed CPU time.

Return Values

n

The processor time used.

-1

Indicates that the processor time used is not available.

clock_getres

clock_getres — Gets the resolution for the specified clock.

Format

#include <time.h>
int clock_getres (clockid_t clock_id, struct timespec *res);

Arguments

clock_id

The clock type used to obtain the resolution. The CLOCK_REALTIME clock is supported and represents the TIME-OF-DAY clock for the system.

res

A pointer to the timespec data structure that receives the value of the clock's resolution.

Description

The clock_getres function obtains the resolution value for the specified clock. Clock resolutions are implementation-dependent and cannot be set by a process.

If the res argument is not NULL, the resolution of the specified clock is stored in the location pointed to by res.

If res is NULL, the clock resolution is not stored.

If the time argument ( tp) of clock_settime is not a multiple of res, then the value is truncated to a multiple of res.

On success, the function returns 0.

On failure, the function returns -1 and sets errno to indicate the error.

See also clock_gettime, clock_settime, time, and ctime.

Return Values

0

Indicates success.

-1
Indicates failure; errno is set to the following value:

  • EINVAL– The clock_id argument does not specify a known clock.

clock_gettime

clock_gettime — Returns the current time (in seconds and nanoseconds) for the specified clock.

Format

#include <time.h>
int clock_gettime (clockid_t clock_id, struct timespec *tp);

Arguments

clock_id

The clock type used to obtain the time for the clock that is set. The CLOCK_REALTIME clock is supported and represents the TIME-OF-DAY clock for the system. CLOCK_MONOTONIC, CLOCK_MONOTONIC_COARSE, and CLOCK_MONOTONIC_RAW are also supported.

tp

A pointer to a timespec data structure.

Description

The clock_gettime function returns the current tp value for the specified clock, clock_id.

On success, the function returns 0.

On failure, the function returns -1 and sets errno to indicate the error.

See also clock_getres, clock_settime, time, and ctime.

Return Values

0

Indicates success.

-1
Indicates failure; errno is set to the following value:

  • EINVAL– The clock_id argument does not specify a known clock, or the tp argument specifies a nanosecond value less than 0 or greater than or equal to 1 billion.

clock_settime

clock_settime — Sets the specified clock.

Format

#include <time.h>
int clock_settime (clockid_t clock_id, const struct timespec *tp);

Arguments

clock_id

The clock type used for the clock that is to be set. The CLOCK_REALTIME clock is supported and represents the TIME-OF-DAY clock for the system.

tp

A pointer to a timespec data structure.

Description

The clock_settime function sets the specified clock, clock_id, to the value specified by tp. Time values that are between two consecutive non-negative integer multiples of the resolution of the specified clock are truncated down to the smaller multiple of the resolution.

A clock can be systemwide (that is, visible to all processes) or per-process (measuring time that is meaningful only within a process).

The CLOCK_REALTIME clock, defined in <time.h>, represents the real time clock for the system. For this clock, the values specified by clock_settime and returned by clock_gettime represent the amount of time elapsed, in seconds and nanoseconds, since the Epoch. The Epoch is defined as 00:00:00:00 January 1, 1970 Greenwich Mean Time (GMT).

You must have OPER, LOG_IO, and SYSPRV privileges to use the clock_settime function.

On success, the function returns 0.

On failure, the function returns -1 and sets errno to indicate the error.

See also clock_getres, clock_gettime, time, and ctime.

Return Values

0

Indicates success.

-1
Indicates failure; errno is set to the following value:

  • EINVAL– The clock_id argument does not specify a known clock, or the tp argument is outside the range for the given clock_id or specifies a nanosecond value less than 0 or greater than or equal to 1 billion.

  • EPERM– The requesting process does not have the appropriate privilege to set the specified clock.

clog

clog — Returns the complex natural (base e) logarithm of its argument.

Format

#include <complex.h>
double complex clog (double complex z);
float complex clogf (float complex z);
long double complex clogl (long double complex z);

Argument

z

A complex value.

Description

The clog functions return the complex natural (base e) logarithm of z, with a branch cut along the negative real axis.

Return Values

x

The complex natural logarithm value in the range of a strip mathematically unbounded along the real axis and in the interval [-i π, +i π] along the imaginary axis.

close

close — Closes the file associated with a file descriptor.

Format

#include <unistd.h>
int close (int file_desc);

Argument

file_desc

A file descriptor.

Description

The close function tries to write buffered data by using an implicit call to fflush. If the write fails (because the disk is full or the user's quota was exceeded, for example), close continues executing. It closes the OpenVMS channel, deallocates any buffers, and releases the memory associated with the file descriptor (or FILE pointer). Any buffered data is lost, and the file descriptor (or FILE pointer) no longer refers to the file.

If your program needs to recover from errors when flushing buffered data, it should make an explicit call to fsync (or fflush) before calling close.

Return Values

0

Indicates that the file is properly closed.

-1

Indicates that the file descriptor is undefined or an error occurred while the file was being closed (for example, if the buffered data cannot be written out).

Example

#include
<unistd.h>int fd;
    .
    .
    .
fd = open ("student.dat", 1);
    .
    .
    .
close(fd);

closedir

closedir — Closes directories.

Format

#include <dirent.h>
int closedir (DIR *dir_pointer);

Argument

dir_pointer

Pointer to the dir structure of an open directory.

Description

The closedir function closes a directory stream and frees the structure associated with the dir_pointer argument. Upon return, the value of dir_pointer does not necessarily point to an accessible object of the type DIR.

The type DIR, which is defined in the <dirent.h> header file, represents a directory stream that is an ordered sequence of all the directory entries in a particular directory. Directory entries represent files. You can remove files from or add files to a directory asynchronously to the operation of the readdir function.

Note

An open directory must always be closed with the closedir function to ensure that the next attempt to open the directory is successful.

Example

The following example shows how to search a directory for the entry name, using the opendir, readdir, and closedir functions:
#include <dirent.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define FOUND     1
#define NOT_FOUND 0

static int dir_example(const char *name, unsigned int unix_style)
{
    DIR *dir_pointer;
    struct dirent *dp;

    if ( unix_style )
        dir_pointer = opendir(".");
    else
        dir_pointer = opendir(getenv("PATH"));

    if ( !dir_pointer ) {
        perror("opendir");
        return NOT_FOUND;
    }

    /* Note, that if opendir() was called with UNIX style file  */
    /* spec like ".", readdir() will return only a single       */
    /* version of each file in the directory. In this case the  */
    /* name returned in d_name member of the dirent structure   */
    /* will contain only file name and file extension fields,   */
    /* both lowercased like "foo.bar".                          */

    /* If opendir() was called with OpenVMS style file spec,    */
    /* readdir() will return every version of each file in the  */
    /* directory. In this case the name returned in d_name      */
    /* member of the dirent structure will contain file name,   */
    /* file extension and file version fields. All in upper     */
    /* case, like "FOO.BAR;1".                                  */

    for ( dp = readdir(dir_pointer);
          dp && strcmp(dp->d_name, name);
          dp = readdir(dir_pointer) )
        ;

    closedir(dir_pointer);

    if ( dp != NULL )
        return FOUND;
    else
        return NOT_FOUND;
}

int main(void)
{
   char *filename = "foo.bar";
   FILE *fp;

   remove(filename);

   if ( !(fp = fopen(filename, "w")) ) {
        perror("fopen");
        return (EXIT_FAILURE);
   }

   if ( dir_example( "FOO.BAR;1", 0 ) == FOUND )
        puts("OpenVMS style: found");
   else
        puts("OpenVMS style: not found");

   if ( dir_example( "foo.bar", 1 ) == FOUND )
        puts("UNIX style: found");
   else
        puts("UNIX style: not found");

   fclose(fp);
   remove(filename);
   return( EXIT_SUCCESS );
}

Return Values

0

Indicates success.

-1

Indicates an error and is further specified in the global errno.

[w]clrattr

[w]clrattr — Deactivate the video display attribute attr within the window. The clrattr function acts on the stdscr window.

Format

#include <curses.h>
int clrattr (int attr);
int wclrattr (WINDOW *win, int attr);

Arguments

win

A pointer to the window.

attr

Video display attributes that can be blinking, boldface, reverse video, and underlining; they are represented by the defined constants _BLINK, _BOLD, _REVERSE, and _UNDERLINE. To clear multiple attributes, separate them with a bitwise OR operator ( |) as follows:
clrattr(_BLINK | _UNDERLINE);

Description

These functions are specific to VSI C for OpenVMS systems and are not portable.

Return Values

OK

Indicates success.

ERR

Indicates an error.

[w]clrtobot

[w]clrtobot — Erase the contents of the window from the current position of the cursor to the bottom of the window. The clrtobot function acts on the stdscr window.

Format

#include <curses.h>
int clrtobot();
int wclrtobot (WINDOW *win);

Argument

win

A pointer to the window.

Return Values

OK

Indicates success.

ERR

Indicates an error.

[w]clrtoeol

[w]clrtoeol — Erase the contents of the window from the current cursor position to the end of the line on the specified window. The clrtoeol function acts on the stdscr window.

Format

#include <curses.h>
int clrtoeol();
int wclrtoeol (WINDOW *win);

Argument

win

A pointer to the window.

Return Values

OK

Indicates success.

ERR

Indicates an error.

confstr

confstr — Determines the current value of a specified system variable defined by a string value.

Format

#include <unistd.h>
size_t confstr (int name, char *buf, size_t len);

Arguments

name

The system variable setting. Valid values for the name argument are the _CS_X names defined in the <unistd.h> header file.

buf

Pointer to the buffer where the confstr function copies the name value.

len

The size of the buffer storing the name value.

Description

The confstr function allows an application to determine the current setting of certain system parameters, limits, or options that are defined by a string value. The function is mainly used by applications to find the system default value for the PATH environment variable.

If the following conditions are true, then the confstr function copies that value into a len-byte buffer pointed to by buf:

  • The len argument can be 0 (zero).

  • The name argument has a system-defined value.

  • The buf argument is not a NULL pointer.

If the returned string is longer than len bytes, including the terminating null, then the confstr function truncates the string to len - 1 bytes and adds a terminating null to the result. The application can detect that the string was truncated by comparing the value returned by the confstr function with the value of the len argument.

The <limits.h> header file contains system-defined limits. The <unistd.h> header file contains system-defined environmental variables.

Also, confstr supports the following three HP-UX symbolic constants, which are added to header file <unistd.h>:

  • _CS_MACHINE_IDENT

  • _CS_PARTITION_IDENT

  • _CS_MACHINE_SERIAL

Example

To find out how big a buffer is needed to store the string value of name, enter: confstr(_CS_PATH, NULL, (size_t) 0)

The confstr function returns the size of the buffer necessary.

Return Values

0
Indicates an error. When the specified name value:

  • Is invalid, errno is set to EINVAL.

  • Does not have a system-defined value, errno is not set.

n
The size of the buffer needed to hold the value.

  • When the value of the name argument is system-defined, confstr returns the size of the buffer needed to hold the entire value. If this return value is greater than the len value, the string returned as the buf value is truncated.

  • When the value of the len argument is set to 0 or the buf value is NULL, confstr returns the size of the buffer needed to hold the entire system-defined value. The string value is not copied.

conj

conj — Returns the complex conjugate of its argument.

Format

#include <complex.h>
double complex conj (double complex z);
float complex conjf (float complex z);
long double complex conjl (long double complex z);

Argument

z

A complex value.

Description

The conj functions return the complex conjugate of z, by reversing the sign of its imaginary part.

Return Values

x

The complex conjugate value.

copysign

copysign — Returns x with the same sign as y.

Format

#include <math.h>
double copysign (double x, double y);
float copysignf (float x, float y); 
long double copysignl (long double x, long double y);

Arguments

x

A real value.

y

A real value.

Description

The copysign functions return x with the same sign as y. IEEE 754 requires copysign(x,NaN), copysignf(x,NaN), and copysignl(x,NaN) to return + x or - x.

Return Value

x

The value of x with the same sign as y.

cos

cos — Returns the cosine of its radian argument.

Format

#include <math.h>
double cos (double x);
float cosf (float x);
long double cosl (long double x);
double cosd (double x);
float cosdf (float x);
long double cosdl (long double x);

Argument

x

A radian expressed as a real value.

Description

The cos functions return the cosine of their argument, measured in radians.

The cosd functions return the cosine of their argument, measured in degrees.

|x| = Infinity is an invalid argument.

Return Values

x

The cosine of the argument.

HUGE_VAL

Indicates that the argument is too large; errno is set to ERANGE.

cosh

cosh — Returns the hyperbolic cosine of its radian argument.

Format

#include <math.h>
double cosh (double x);
float coshf (float x);
long double coshl (long double x);

Argument

x

A radian expressed as a real number.

Description

The cosh functions return the hyperbolic cosine of x and are defined as (e** x + e**( - x))/2.

Return Values

x

The hyperbolic cosine of the argument.

HUGE_VAL

Indicates that the argument is too large; errno is set to ERANGE.

cot

cot — Returns the cotangent of its radian argument.

Format

#include <math.h>
double cot (double x);
float cotf (float x);
long double cotl (long double x);
double cotd (double x);
float cotdf (float x);
long double cotdl (long double x);

Argument

x

A radian expressed as a real number.

Description

The cot functions return the cotangent of their argument, measured in radians.

The cotd functions return the cotangent of their argument, measured in degrees.

x = 0 is an invalid argument.

Return Values

x

The cotangent of the argument.

HUGE_VAL

Indicates that the argument is zero; errno is set to ERANGE.

cpow

cpow — Returns the complex power function x** y.

Format

#include <complex.h>
double complex cpow (double complex x, double complex y);
float complex cpowf (float complex x, float complex y);
long double complex cpowl (long double complex x, long double complex y);

Argument

x

A complex value.

y

A complex value.

Description

The cpow functions return the complex power function x** y, with a branch cut for the first parameter along the negative real axis.

Return Values

x

The complex power function value.

cproj

cproj — Returns a projection of its argument onto the Riemann sphere.

Format

#include <complex.h>
double complex cproj (double complex z);
float complex cprojf (float complex z);
long double complex cprojl (long double complex z);

Argument

z

A complex value.

Description

The cproj functions compute and return a projection of z onto the Riemann sphere: z projects to z, except that all complex infinities (even those with one infinite part and one NaN part) project to positive infinity on the real axis. If z has an infinite part, then cproj(z) is equivalent to:

INFINITY + I * copysign(0.0, cimag(z))

Return Values

x

The value of the projection onto the Riemann sphere.

creal

creal — Returns the real part of its complex argument.

Format

#include <complex.h>
double creal (double complex z);
float crealf (float complex z);
long double creall (long double complex z);

Argument

z

A complex value.

Description

The creal functions return the real part of z.

Return Values

x

The real part value.

creat

creat — Creates a new file.

Format

#include <fcntl.h>
int creat (const char *file_spec, mode_t mode); (ISO POSIX-1)
int creat (const char *file_spec, mode_t mode, ...); (VSI C Extension)

Arguments

file_spec

A null-terminated string containing any valid file specification.

mode

An unsigned value that specifies the file-protection mode. The compiler performs a bitwise AND operation on the mode and the complement of the current protection mode.

You can construct modes by using the bitwise OR operator (|) to create mode combinations. The modes are:

0400

OWNER:READ

0200

OWNER:WRITE

0100

OWNER:EXECUTE

0040

GROUP:READ

0020

GROUP:WRITE

0010

GROUP:EXECUTE

0004

WORLD:READ

0002

WORLD:WRITE

0001

WORLD:EXECUTE

The system is given the same privileges as the owner. A WRITE privilege implies a DELETE privilege.

Note

To create files with OpenVMS RMS default protections using the UNIX system-call functions umask, mkdir, creat, and open, call mkdir, creat, and open with a file-protection mode argument of 0777 in a program that never specifically calls umask. These default protections include correctly establishing protections based on ACLs, previous versions of files, and so on.

In programs that do vfork/ exec calls, the new process image inherits whether umask has ever been called or not from the calling process image. The umask setting and whether the umask function has ever been called are both inherited attributes.

. . .

An optional argument list of character strings of the following form:
"keyword = value", . . . ,"keyword = value"
Or in the case of "acc" or "err", this form:
"keyword"

Here, keyword is an RMS field in the file access block (FAB) or record access block (RAB); value is valid for assignment to that field. Some fields permit you to specify more than one value. In these cases, the values are separated by commas.

The RMS callback keywords "acc" and "err" are the only keywords that do not take values. Instead, they are followed by a pointer to the callback routine to be used, followed by a pointer to a user-specified value to be used as the first argument of the callback routine. For example, to set up an access callback routine called acc_callback whose first argument is a pointer to the integer variable first_arg in a call to open, you can use the following statement:
open("file.dat", O_RDONLY, 0 ,"acc", acc_callback, &first_arg)
The second and third arguments to the callback routine must be pointers to a FAB and RAB, respectively, and the routine must have a return type of int. If the callback returns a value less than 0, the open, creat, or fopen fails. The error callback can correct the error condition and return a status greater than or equal to 0 to continue the creat call. Assuming the previous open statement, the function prototype for acc_callback would be similar to the following statement:
#include <rms.h>
int acc_callback(int *first_arg, struct FAB *fab, struct RAB *rab);

FAB and RAB are defined in the <rms.h> header file, and the actual pointers passed to the routine are pointers to the RAB and FAB being used to open the file file.dat.

If an access callback routine is established, then it will be called in the open-type routine immediately before the call to the RMS function sys$create or sys$open. If an error callback routine is established and an error status is returned from the sys$create or sys$open function, then the callback routine will be invoked immediately after the status is checked and the error value is discovered.

Note

Any manipulation of the RAB or FAB in a callback function could lead to serious problems in later calls to the C RTL I/O functions.

Table 35 describes the RMS keywords and values.
Table 35. RMS Valid Keywords and Values

Keyword

Value

Description

“acc”

callback

Access callback routine.

“alq = n”

decimal

Allocation quantity.

“bls = n”

decimal

Block size.

“ctx = bin”

string

No translation of ' \n' to the terminal. Use this for writing binary data to files.

“ctx = cvt”

string

Negates a previous setting of “ctx=nocvt”. This is the default.

“ctx = nocvt”

string

No conversion of Fortran carriage-control bytes.

“ctx = rec”

string

Forces record mode access.

“ctx = stm”

string

Forces stream mode access.

“ctx = xplct”

string

Causes records to be written only when explicitly specified by a call to fflush, close, or fclose.

“deq = n”

decimal

Default extension quantity.

“dna = filespec”

string

Default file-name string.

“err”

callback

Error callback routine.

“fop = val, val , …”

File-processing options:

ctg

Contiguous.

cbt

Contiguous-best-try.

dfw

Deferred write; only applicable to files opened for shared access.

dlt

Delete file on close.

tef

Truncate at end-of-file.

cif

Create if nonexistent.

sup

Supersede.

scf

Submit as command file on close.

spl

Spool to system printer on close.

tmd

Temporary delete.

tmp

Temporary (no file directory).

nef

Not end-of-file.

rck

Read check compare operation.

wck

Write check compare operation.

mxv

Maximize version number.

rwo

Rewind file on open.

pos

Current position.

rwc

Rewind file on close.

sqo

File can only be processed in a sequential manner.

“fsz = n”

decimal

Fixed header size.

“gbc = n”

decimal

The requested number of global buffers for a file.

“mbc = n”

decimal

Multiblock count.

“mbf = n”

decimal

Multibuffer count.

“mrs = n”

decimal

Maximum record size.

“pmt=usr-prmpt”

string

Prompts for terminal input. Any RMS input from a terminal device will be preceded by “usr-prmpt”when this option and “rop=pmt” are specified.

“rat = val, val …”

Record attributes:

cr

Carriage-return control.

blk

Disallow records to span block boundaries.

ftn

Fortran print control.

none

Explicitly forces no carriage control.

prn

Print file format.

“rfm = val”

Record format:

fix

Fixed-length record format.

stm

RMS stream record format.

stmlf

Stream format with line-feed terminator.

stmcr

Stream format with carriage-return terminator.

var

Variable-length record format.

vfc

Variable-length record with fixed control.

udf

Undefined.

“rop = val, val …”

Record-processing operations:

asy

Asynchronous I/O.

cco

Cancels Ctrl/O (used with Terminal I/O).

cvt

Capitalizes characters on a read from the terminal.

eof

Positions the record stream to the end-of-file for the connect operation only.

nlk

Do not lock record.

pmt

Enables use of the prompt specified by “pmt=usr-prmpt”on input from the terminal.

pta

Eliminates any information in the type-ahead buffer on a read from the terminal.

rea

Locks record for a read operation for this process, while allowing other accessors to read the record.

rlk

Locks record for write.

rne

Suppresses echoing of input data on the screen as it is entered on the keyboard.

rnf

Indicates that Ctrl/U, Ctrl/R, and DELETE are not to be considered control commands on terminal input, but are to be passed to the application program.

rrl

Reads regardless of lock.

syncsts

Returns a success status of RMS$_SYNCH if the requested service completes its task immediately.

tmo

Timeout I/O.

tpt

Allows put/write services using sequential record access mode to occur at any point in the file, truncating the file at that point.

ulk

Prohibits RMS from automatically unlocking records.

wat

Wait until record is available, if currently locked by another stream.

rah

Read ahead.

wbh

Write behind.

“rtv=n”

decimal

The number of retrieval pointers that RMS has to maintain in memory (0 to 127,255).

“shr = val, val, …”

File sharing options:

del

Allows users to delete.

get

Allows users to read.

mse

Allows multistream connects.

nil

Prohibits file sharing.

put

Allows users to write.

upd

Allows users to update.

upi

Allows one or more writers.

nql

No query locking (file level).

“tmo = n”

decimal

I/O timeout value.

In addition to these options, any option that takes a key value (such as “fop” or “rat”) can be negated by prefixing the value with “no”. For example, specify “fop=notmp” to clear the “tmp” bit in the “fop” field.

Notes

  • While these options provide much flexibility and functionality, many of them can also cause severe problems if not used correctly.

  • You cannot share the default VSI C for OpenVMS stream file I/O. If you wish to share files, you must specify “ctx=rec” to force record access mode. You must also specify the appropriate “shr” options depending on the type of access you want.

  • If you intend to share a file opened for append, you must specify appropriate share and record-locking options, to allow other accessors to read the record. The reason for doing this: the file is positioned at the end-of-file by reading records in a loop until end-of-file is reached.

For more information on these options, see the VSI OpenVMS Record Management Services Reference Manual.

Description

The C RTL opens the new file for reading and writing, and returns the corresponding file descriptor.

If the file exists:

  • A version number one greater than any existing version is assigned to the newly created file.

  • By default, the new file inherits certain attributes from the existing version of the file unless those attributes are specified in the creat call. The following attributes are inherited:

    • Record format (FAB$B_RFM)

    • Maximum record size (FAB$W_MRS)

    • Carriage control (FAB$B_RAT)

    • File protection

  • When a new version of a file is created, and the named file already exists as a symbolic link, the file to which the symbolic link refers is created.

If the file did not previously exist:

  • It is given the file protection that results from performing a bitwise AND on the mode argument and the complement of the current protection mask.

  • It defaults to stream format with line-feed record separator and implied carriage-return attributes.

See also open, close, read, write, and lseek in this section.

Return Values

n

A file descriptor.

-1

Indicates errors, including protection violations, undefined directories, and conflicting file attributes.

[no]crmode

[no]crmode — In the UNIX system environment, the crmode and nocrmode functions set and unset the terminal from cbreak mode. In cbreak mode, a single input character can be processed without pressing Return. This mode of single-character input is only supported with the Curses input routine getch.

Format

#include <curses.h>
crmode()
nocrmode()

Example

/* Program to demonstrate the use of crmod() and curses */

#include <curses.h>

main()
{
    WINDOW *win1;
    char vert = '.',
         hor = '.',
         str[80];

    /*  Initialize standard screen, turn echo off.  */
    initscr();
    noecho();

    /*  Define a user window.  */
    win1 = newwin(22, 78, 1, 1);

    /*  Turn on reverse video and draw a box on border.  */
    setattr(_REVERSE);
    box(stdscr, vert, hor);
    mvwaddstr(win1, 2, 2, "Test cbreak input");
    refresh();
    wrefresh(win1);

    /*  Set cbreak, do some input, and output it.  */
    crmode();
    getch();
    nocrmode(); /* Turn off cbreak. */
    mvwaddstr(win1, 5, 5, str);
    mvwaddstr(win1, 7, 7, "Type something to clear the screen");
    wrefresh(win1);

    /*  Get another character, then delete the window.  */
    getch();
    wclear(win1);
    touchwin(stdscr);
    endwin();
}

In this example, the first call to getch returns as soon as one character is entered, because crmode was called before getch was called. The second time getch is called, it waits until the Return key is pressed before processing the character entered, because nocrmode was called before getch was called the second time.

crypt

crypt — The password encryption function.

Format

#include <unistd.h>
#include <stdlib.h>
char *crypt (const char *key, const char *salt;)

Function Variants

The crypt function has variants named _crypt32 and _crypt64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Argument

key

A user's typed password.

salt

A 2-character string.

Description

The crypt function generates an encoded version of a password. It is based on the NBS Data Encryption Standard, with variations intended to frustrate use of hardware implementations of the DES for key search.

The first argument to crypt is normally a user's typed password. The second is a 2-character string chosen from the set [a-zA-Z0-9./]. The salt string is used to perturb the DES algorithm in one of 4096 different ways, after which the password is used as the key to encrypt repeatedly a constant string. The returned value points to the encrypted password, in the same alphabet as the salt. The first two characters are the salt itself.

The return value from crypt points to a static data area whose content is overwritten by each call.

See also encrypt and setkey.

Return Value

pointer

Pointer to the encrypted password.

csin

csin — Returns the complex sine of its argument.

Format

#include <complex.h>
double complex csin (double complex z);
float complex csinf (float complex z);
long double complex csinl (long double complex z);

Argument

z

A complex value.

Description

The csin functions compute the complex sine value of z.

Return Values

x

The complex sine value.

csinh

csinh — Returns the complex hyperbolic sine of its argument.

Format

#include <complex.h>
double complex csinh (double complex z);
float complex csinhf (float complex z);
long double complex csinhl (long double complex z);

Argument

z

A complex value.

Description

The csinh functions compute the complex hyperbolic sine of z.

Return Values

x

The complex hyperbolic sine value.

csqrt

csqrt — Returns the complex square root of its argument.

Format

#include <complex.h>
double complex csqrt (double complex z);
float complex csqrtf (float complex z);
long double complex csqrtl (long double complex z);

Argument

z

A complex value.

Description

The csqrt functions compute the complex square root of z, with a branch cut along the negative real axis.

Return Values

x

The complex square root value in the range of the right half-plane (including the imaginary axis).

ctan

ctan — Returns the complex tangent of its argument.

Format

#include <complex.h>
double complex ctan (double complex z);
float complex ctanf (float complex z);
long double complex ctanl (long double complex z);

Argument

z

A complex value.

Description

The ctan functions compute the complex tangent value of z.

Return Values

x

The complex tangent value.

ctanh

ctanh — Returns the complex hyperbolic tangent of its argument.

Format

#include <complex.h>
double complex ctanh (double complex z);
float complex ctanhf (float complex z);
long double complex ctanhl (long double complex z);

Argument

z

A complex value.

Description

The ctanh functions compute the complex hyperbolic tangent value of z.

Return Values

x

The complex hyperbolic tangent value.

ctermid

ctermid — Returns a character string giving the equivalence string of SYS$COMMAND. This is the name of the controlling terminal.

Format

#include <stdio.h>
char *ctermid (char *str);

Function Variants

The ctermid function has variants named _ctermid32 and _ctermid64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Argument

str

Must be a pointer to an array of characters. If this argument is NULL, the filename is stored internally and might be overwritten by the next ctermid call. Otherwise, the filename is stored beginning at the location indicated by the argument. The argument must point to a storage area of length L_ctermid (defined by the <stdio.h> header file).

Return Value

pointer

Points to a character string.

ctime, ctime_r

ctime, ctime_r — Converts a time in seconds, since 00:00:00 January 1, 1970, to an ASCII string in the form generated by the asctime function.

Format

#include <time.h>
char *ctime (const time_t *bintim);
char *ctime_r (const time_t *bintim, char *buffer); (ISO POSIX-1)

Function Variants

Compiling with the _DECC_V4_SOURCE and _VMS_V6_SOURCE feature-test macros defined enables a local-time-based entry point to this function that is equivalent to the behavior before OpenVMS Version 7.0.

Arguments

bintim

A pointer to a variable that specifies the time value (in seconds) to be converted.

buffer

A pointer to a character array that is at least 26 bytes long. This array is used to store the generated date-and-time string.

Description

The ctime and ctime_r functions convert the time pointed to by bintim into a 26-character string, and return a pointer to the string.

The difference between the ctime_r and ctime functions is that the former puts its result into a user-specified buffer. The latter puts its result into thread-specific static memory allocated by the C RTL, which can be overwritten by subsequent calls to ctime or asctime; you must make a copy if you want to save it.

On success, ctime returns a pointer to the string; ctime_r returns its second argument. On failure, these functions return the NULL pointer.

The type time_t is defined in the <time.h> header file as follows:
typedef long int time_t
The ctime function behaves as if it called tzset.

Note

Generally speaking, UTC-based time functions can affect in-memory time-zone information, which is processwide data. However, if the system time zone remains the same during the execution of the application (which is the common case) and the cache of timezone files is enabled (which is the default), then the _r variant of the time functions asctime_r, ctime_r, gmtime_r, and localtime_r, is both thread-safe and AST-reentrant.

If, however, the system time zone can change during the execution of the application or the cache of timezone files is not enabled, then both variants of the UTC-based time functions belong to the third class of functions, which are neither thread-safe nor AST-reentrant.

Return Values

x

A pointer to the 26-character ASCII string, if successful.

NULL

Indicates failure.

cuserid

cuserid — Returns a pointer to a character string containing the name of the user initiating the current process.

Format

#include <unistd.h> (X/Open, POSIX-1)
#include <stdio.h> (X/Open)
char *cuserid (char *str);

Function Variants

The cuserid function has variants named _cuserid32 and _cuserid64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Argument

str

If this argument is NULL, the user name is stored internally. If the argument is not NULL, it points to a storage area of length L_cuserid (defined by the <stdio.h> header file), and the name is written into that storage. If the user name is a null string, the function returns NULL.

Return Values

pointer

Points to a string.

NULL

If the user name is a null string.

DECC$CRTL_INIT

DECC$CRTL_INIT — Allows you to call the C RTL from other languages or to use the C RTL when your main function is not in C. It initializes the run-time environment and establishes both an exit and condition handler. VAXC$CRTL_INIT is a synonym for DECC$CRTL_INIT. Either name invokes the same routine.

Format

#include <signal.h>
void DECC$CRTL_INIT(void);

Description

The following example shows a Pascal program that calls the C RTL using the DECC$CRTL_INIT function: 
$ PASCAL EXAMPLE1
$ LINK EXAMPLE1
$ TY EXAMPLE1.PAS
PROGRAM TESTC(input, output);
PROCEDURE DECC$CRTL_INIT; extern;
BEGIN
   DECC$CRTL_INIT;
END

A shareable image need only call this function if it contains an VSI C function for signal handling, environment variables, I/O, exit handling, a default file protection mask, or if it is a child process that should inherit context.

Although many of the initialization activities are performed only once, DECC$CRTL_INIT can safely be called multiple times.

At least one frame in the current call stack must have that handler established for OpenVMS exceptions to get mapped to UNIX signals.

decc$feature_get

decc$feature_get — Calls decc$feature_get_value with a character-string feature name, rather than an index.

Format

#include <unixlib.h>
int decc$feature_get (const char *name, int mode);

Argument

name

Pointer to a character string passed as a name in the list of supported features.

mode

An integer indicating which feature value to return. The values for mode are:
  • _ _FEATURE_MODE_DEFVAL - Default value
  • _ _FEATURE_MODE_CURVAL - Current value
  • _ _FEATURE_MODE_MINVAL - Minimum value
  • _ _FEATURE_MODE_MAXVAL - Maximum value
  • _ _FEATURE_MODE_INIT_STATE - Initialization state

Description

The decc$feature_get function allows you to call the decc$feature_get_value function with a character-string feature name, rather than an index into an internal C RTL table.

On error, -1 is returned and errno is set to indicate the error.

See also decc$feature_get_value, decc$feature_get_index, decc$feature_get_name, decc$feature_set, decc$feature_set_value, decc$feature_show, and decc$feature_show_all.

Return Values

n

An integer corresponding to the specified name and mode arguments.

-1

Indicates an error; errno is set.

decc$feature_get_index

decc$feature_get_index — Returns an index for accessing feature values.

Format

#include <unixlib.h>
int decc$feature_get_index (char *name);

Argument

name

Pointer to a character string passed as a name in the list of supported features.

Description

The decc$feature_get_index function looks up the string passed as name in the list of supported features. If the name is found, decc$feature_get_index returns a (nonnegative) index that can be used to set or retrieve the values for the feature. The comparison for name is case insensitive.

On error, -1 is returned and errno is set to indicate the error.

See also decc$feature_get, decc$feature_get_value, decc$feature_get_name, decc$feature_set, decc$feature_set_value, decc$feature_show, and decc$feature_show_all.

Return Values

n

A nonnegative index that can be used to set or retrieve the specified values for the feature.

-1

Indicates an error; errno is set.

decc$feature_get_name

decc$feature_get_name — Returns a feature name.

Format

#include <unixlib.h>
char *decc$feature_get_name (int index);

Argument

index

An integer value from 0 to the highest allocated feature.

Description

The decc$feature_get_name function returns a pointer to a null-terminated string containing the name of the feature for the entry specified by index. The index value can be 0 to the highest allocated feature. If there is no feature corresponding to the index value, then the function returns a NULL pointer.

On error, NULL is returned and errno is set to indicate the error.

See also decc$feature_get, decc$feature_get_index, decc$feature_get_value, decc$feature_set, decc$feature_set_value, decc$feature_show, and decc$feature_show_all.

Return Values

x

Pointer to a null-terminated string containing the name of the feature for the entry specified by index.

NULL

Indicates an error; errno is set.

decc$feature_get_value

decc$feature_get_value — Returns a feature value specified by the index and mode arguments.

Format

#include <unixlib.h>
int decc$feature_get_value (int index, int mode);

Arguments

index

An integer value from 0 to the highest allocated feature.

mode

An integer indicating which feature value to return. The values for mode are:
  • _ _FEATURE_MODE_DEFVAL - Default value
  • _ _FEATURE_MODE_CURVAL - Current value
  • _ _FEATURE_MODE_MINVAL - Minimum value
  • _ _FEATURE_MODE_MAXVAL - Maximum value
  • _ _FEATURE_MODE_INIT_STATE - Initialization state

Description

The decc$feature_get_value function retrieves a value for the feature specified by index. The mode determines which value is returned.

The default value is what is used if not set by a logical name or overridden by a call to decc$feature_set_value.

If mode = 4, then the initialization state is returned. Values for the initialization state are:
  • 0 not initialized
  • 1 set by logical name
  • 2 forced by decc$feature_set_value
  • -1 – initialized to default value

On error, -1 is returned and errno is set to indicate the error.

See also decc$feature_get, decc$feature_get_index, decc$feature_get_name, decc$feature_set, decc$feature_set_value, decc$feature_show, and decc$feature_show_all.

Return Values

n

An integer corresponding to the specified index and mode arguments.

-1

Indicates an error; errno is set.

decc$feature_set

decc$feature_set — Calls decc$feature_set_value with a character-string feature name, rather than an index.

Format

#include <unixlib.h>
int decc$feature_set (const char *name, int mode, int value);

Argument

name

Pointer to a character string passed as a name in the list of supported features.

mode

An integer indicating which feature value to return. The values for mode are:
  • _ _FEATURE_MODE_DEFVAL - Default value
  • _ _FEATURE_MODE_CURVAL - Current value
  • _ _FEATURE_MODE_MINVAL - Minimum value
  • _ _FEATURE_MODE_MAXVAL - Maximum value
  • _ _FEATURE_MODE_INIT_STATE - Initialization state

value

The feature value to be set.

Description

The decc$feature_set function allows you to call the decc$feature_set_value function with a character-string feature name, rather than an index into an internal C RTL table.

If successful, the function returns the previous value.

On error, -1 is returned and errno is set to indicate the error.

See also decc$feature_set_value, decc$feature_get, decc$feature_get_index, decc$feature_get_name, decc$feature_get_value. decc$feature_show, and decc$feature_show_all.

Return Values

n

The previous feature value.

-1

Indicates an error; errno is set.

decc$feature_set_value

decc$feature_set_value — Sets the default value or the current value for the feature specified by index.

Format

#include <unixlib.h>
int decc$feature_set_value (int index, int mode, int value);

Arguments

index

An integer value from 0 to the highest allocated feature.

mode

An integer indicating whether to set the default or current feature value. The values for mode are:
  • 0 default value
  • 1 current value

value

The feature value to be set.

Description

The decc$feature_set_value function sets the default value or the current value (as determined by the mode argument) for the feature specified by index.

If this function is successful, it returns the previous value.

On error, -1 is returned and errno is set to indicate the error.

See also decc$feature_get, decc$feature_get_index, decc$feature_get_name, decc$feature_get_value, decc$feature_set, decc$feature_show, and decc$feature_show_all.

Return Values

n

The previous feature value.

-1

Indicates an error; errno is set.

decc$feature_show

decc$feature_show — Displays all feature values for the specified feature name.

Format

#include <unixlib.h>
int decc$feature_show (const char *name);

Argument

name

Pointer to a character string passed as a name in the list of supported features.

Description

The decc$feature_show function displays to stdout all values for the specified feature name. For example:
--------- C RTL Feature Name ---------   Cur  Def  Min  Max  Ini
DECC$V62_RECORD_GENERATION                0    0    0    1    -1

On error, -1 is returned and errno is set to indicate the error.

See also decc$feature_get, decc$feature_get_index, decc$feature_get_name, decc$feature_get_value, decc$feature_set, decc$feature_set_value, and decc$feature_show_all.

Return Values

0

Indicates success.

-1

Indicates an error; errno is set.

decc$feature_show_all

decc$feature_show_all — Displays all feature values for all feature names.

Format

#include <unixlib.h>
int decc$feature_show_all (void);

Description

The decc$feature_show_all function displays to stdout all values for all feature names.

On error, -1 is returned and errno is set to indicate the error.

See also decc$feature_get, decc$feature_get_index, decc$feature_get_name, decc$feature_get_value, decc$feature_set, decc$feature_set_value, and decc$feature_show.

Return Values

0

Indicates success.

-1

Indicates an error; errno is set.

decc$fix_time

decc$fix_time — Converts OpenVMS binary system times to UNIX binary times.

Format

#include <unixlib.h>
unsigned int decc$fix_time (void *vms_time);

Argument

vms_time

The address of a quadword containing an OpenVMS binary time: 
unsigned int quadword[2];
unsigned int *vms_time = quadword;

Description

The decc$fix_time routine converts an OpenVMS binary system time (a 64-bit quadword containing the number of 100-nanosecond ticks since 00:00 November 17, 1858) to a UNIX binary time (a longword containing the number of seconds since 00:00 January 1, 1970). This routine is useful for converting binary times returned by OpenVMS system services and RMS services to the format used by some C RTL routines, such as ctime and localtime.

Return Values

x

A longword containing the number of seconds since 00:00 January 1, 1970.

(unsigned int)(-1)

Indicates an error. Be aware, that a return value of (unsigned int)(-1) can also represent a valid date of Sun Feb 7 06:28:15 2106.

Example

#include <unixlib.h>
#include <stdio.h>
#include <starlet.h>  /* OpenVMS specific SYS$ routines)  */

main()
{
unsigned int current_vms_time[2]; /*quadword for OpenVMS time*/
unsigned int number_of_seconds;   /* number of seconds     */

/* first get the current system time */
sys$gettim(&current_vms_time[0]);

/* fix the time */
number_of_seconds = decc$fix_time(&current_vms_time[0]);

printf("Number of seconds since 00:00 January 1, 1970 = %d",
        number_of_seconds);
}

This example shows how to use the decc$fix_time routine in VSI C. It also shows the use of the SYS$GETTIM system service.

decc$from_vms

decc$from_vms — Converts OpenVMS file specifications to UNIX style file specifications.

Format

#include <unixlib.h>
int decc$from_vms (const char *vms_filespec, int action_routine, int wild_flag);

Arguments

vms_filespec

The address of a null-terminated string containing a name in OpenVMS file specification format.

action_routine

The address of a routine that takes as its only argument a null-terminated string containing the translation of the given OpenVMS filename to a valid UNIX style filename.

If the action_routine returns a nonzero value (TRUE), file translation continues. If it returns a zero value (FALSE), no further file translation takes place.

wild_flag

Either 0 or 1, passed by value. If a 0 is specified, wildcards found in vms_filespec are not expanded. Otherwise, wildcards are expanded and each one is passed to action_routine. Only expanded filenames that correspond to existing UNIX style files are included.

Description

The decc$from_vms routine converts the given OpenVMS file specification into the equivalent UNIX style file specification. It allows you to specify OpenVMS wildcards, which are translated into a list of corresponding existing files in UNIX style file specification format.

Return Value

x

The number of filenames that result from the specified OpenVMS file specification.

Example

/* This example must be run as a foreign command        */
/* and be supplied with an OpenVMS file specification.  */

#include <unixlib.h>
#include <stdio.h>

int main(int argc, char *argv[])
{
    int number_found;           /* number of files found */
    int print_name();           /* name printer          */

    printf("Translating: %s\n", argv[1]);
    number_found = decc$from_vms(argv[1], print_name, 1);
    printf("\n%d files found", number_found);
}

/* print the name on each line */
print_name(char *name)
{
    printf("\n%s", name);
    /* will continue as long as success status is returned */
    return (1);
}

This example shows how to use the decc$from_vms routine in VSI C. It produces a simple form of the ls command that lists existing files that match an OpenVMS file specification supplied on the command line. The matching files are displayed in UNIX style file specification format.

decc$match_wild

decc$match_wild — Matches a string to a pattern.

Format

#include <unixlib.h>
int decc$match_wild (char *test_string, char *string_pattern);

Arguments

test_string

The address of a null-terminated string.

string_pattern

The address of a string containing the pattern to be matched. This pattern can contain wildcards (such as asterisks (*), question marks (?), and percent signs (%) as well as regular expressions (such as the range [a-z]).

Description

The decc$match_wild routine determines whether the specified test string is a member of the set of strings specified by the pattern.

Return Values

1 (TRUE)

The string matches the pattern.

0 (FALSE)

The string does not match the pattern.

Example

/* Define as a foreign command and then provide */
/* two arguments: test_string, string_pattern.  */

#include <unixlib.h>
#include <stdio.h>
int main(int argc, char *argv[])
{
    if (decc$match_wild(argv[1], argv[2]))
        printf("\n%s matches %s", argv[1], argv[2]);
    else
        printf("\n%s does not match %s", argv[1], argv[2]);
}

decc$record_read

decc$record_read — Reads a record from a file.

Format

#include <stdio.h>
int decc$record_read (FILE *fp, void *buffer, int nbytes);

Arguments

fp

A file pointer. The specified file pointer must refer to a file currently opened for reading.

buffer

The address of contiguous storage in which the input data is placed.

nbytes

The maximum number of bytes involved in the read operation.

Description

The decc$record_read function is specific to OpenVMS systems and should not be used when writing portable applications.

This function is equivalent to the read function, except that the first argument is a file pointer, not a file descriptor.

Return Values

x

The number of characters read.

-1

Indicates a read error, including physical input errors, illegal buffer addresses, protection violations, undefined file descriptors, and so forth.

decc$record_write

decc$record_write — Writes a record to a file.

Format

#include <stdio.h>
int decc$record_write (FILE *fp, void *buffer, int nbytes);

Arguments

fp

A file pointer. The specified file pointer must refer to a file currently opened for writing or updating.

buffer

The address of contiguous storage from which the output data is taken.

nbytes

The maximum number of bytes involved in the write operation.

Description

The decc$record_write function is specific to OpenVMS systems and should not be used when writing portable applications.

This function is equivalent to the write function, except that the first argument is a file pointer, not a file descriptor.

Return Values

x

The number of bytes written.

-1

Indicates errors, including undefined file descriptors, illegal buffer addresses, and physical I/O errors.

decc$set_child_default_dir

decc$set_child_default_dir — Sets the default directory for a child process spawned by a function from the exec family of functions.

Format

#include <unixlib.h>
int decc$set_child_default_dir (const char *default_dir);

Argument

default_dir

The default directory specification for child processes, or NULL.

Description

By default, child processes created by one of the exec family of functions inherit the default (working) directory of their parent process.

The decc$set_child_default_dir function lets you set the default directory for a child process. After calling decc$set_child_default_dir, newly spawned child processes have their default directory set to default_dir as they begin execution. The default_dir argument must represent a valid directory specification, or results of the call are unpredictable (subsequent calls to the child process might fail without notification). Both OpenVMS and UNIX style file specifications are supported for this function call.

You can reestablish the default behavior by specifying default_dir as NULL. Subsequently, newly created child processes will inherit their parent's working directory.

Return Values

0

Successful completion. The new inherited default directory was established.

-1
Indicates failure. No new default directory was established for child processes. The function sets errno to one of the following values:

  • ENOMEM– Insufficient memory

  • ENAMETOOLONG– default_dir is too long to issue the required SET DEFAULT command.

decc$set_child_standard_streams

decc$set_child_standard_streams — For a child spawned by a function from the exec family of functions, associates specified file descriptors with a child's standard streams: stdin, stdout, and stderr.

Format

#include <unixlib.h>
int decc$set_child_standard_streams (int fd1, int fd2, int fd3);

Arguments

fd1

The file associated with this file descriptor in the parent process is associated with file descriptor number 0 ( stdin) in the child process. If -1 is specified, the file associated with the parent's file descriptor number 0 is used (the default).

fd2

The file associated with this file descriptor in the parent process is associated with file descriptor number 1 (stdout) in the child process. If -1 is specified, the file associated with the parent's file descriptor number 1 is used (the default).

fd3

The file associated with this file descriptor in the parent process is associated with file descriptor number 2 (stderr) in the child process. If -1 is specified, the file associated with the parent's file descriptor number 2 is used (the default).

Description

The decc$set_child_standard_streams function allows mapping of specified file descriptors to the child's stdin/stdout/stderr streams, thereby compensating, to a certain degree, the lack of a real fork function on OpenVMS systems.

On UNIX systems, the code between fork and exec is executed in the context of the child process:
parent:
  create pipes p1, p2 and p3
  fork
child:

  map stdin to p1  like dup2(p1, stdin);
  map stdout to p2 like dup2(p2, stdout);
  map stderr to p3 like dup2(p3, stderr);

  exec (child reads from stdin and writes to stdout and stderr)
  exit
parent:
  communicates with the child using pipes
On OpenVMS systems, the same task could be achieved as follows: 
parent:
  create pipes p1, p2 and p3
  decc$set_child_standard_streams(p1, p2, p3);
  vfork
  exec (child reads from stdin and writes to stdout and stderr)
parent:
  communicates with the child using pipes
Once established through the call to decc$set_child_standard_streams, the mapping of the child's standard streams remains in effect until explicitly disabled by one of the following calls:
decc$set_child_standard_streams(-1, -1, -1);
Or:
decc$set_child_standard_streams(0, 1, 2);
Usually, the child process inherits all its parent's open file descriptors. However, if file descriptor number n was specified in the call to decc$set_child_standard_streams, it is not inherited by the child process as file descriptor number n; instead, it becomes one of the child's standard streams.

Notes

  • Standard streams can be redirected only to pipes.

  • If the parent process redefines the DCL DEFINE command, this redefinition is not in effect in a subprocess with user-defined channels. The subprocess always sees the standard DCL DEFINE command.

  • It is the responsibility of the parent process to consume all the output written by the child process to stdout and stderr. Depending on how the subprocess writes to stdout and stderr—in wait or nowait mode—the subprocess might be placed in LEF state waiting for the reader. For example, DCL writes to SYS$OUTPUT and SYS$ERROR in a wait mode, so a child process executing a DCL command procedure will wait until all the output is read by the parent process.

    Recommendation: Read the pipes associated with the child process' stdout and stderr in a loop until an EOF message is received, or declare write attention ASTs on these mailboxes.

  • The amount of data written to SYS$OUTPUT depends on the verification status of the process (SET VERIFY/NOVERIFY command); the subprocess inherits the verification status of the parent process. It is the caller's responsibility to set the verification status of the parent process to match the expected amount of data written to SYS$OUTPUT by the subprocess.

  • Some applications, like DTM, define SYS$ERROR as SYS$OUTPUT. If stderr is not redefined by the caller, it is set in the subprocess as the parent's SYS$ERROR, which in this case translates to the parent's SYS$OUTPUT.

    If the caller redefines stdout to a pipe and does not redefine stderr, output sent to stderr goes to the pipe associated with stdout, and the amount of data written to this mailbox may be more than expected. Although redefinition of any subset of standard channels is supported, it is always safe to explicitly redefine all of them (or at least stdout and stderr) to avoid this situation.

  • For a child process executing a DCL command procedure, SYS$COMMAND is set to the pipe specified for the child's stdin so that the parent process can feed the child requesting data from SYS$COMMAND through the pipe. For DCL command procedures, it is impossible to pass data from the parent to the child by means of the child's SYS$INPUT because for a command procedure, DCL defines SYS$INPUT as the command file itself.

Return Values

x

The number of file descriptors set for the child. This number does not include file descriptors specified as -1 in the call.

-1

Indicates that an invalid file descriptor was specified; errno is set to EBADF.

Example

parent.c
========

#include <stdio.h>
#include <string.h>
#include <unistd.h>

int decc$set_child_standard_streams(int, int, int);

main()
{
    int fdin[2], fdout[2], fderr[2];
    char msg[] = "parent writing to child's stdin";
    char buf[80];
    int nbytes;

    pipe(fdin);
    pipe(fdout);
    pipe(fderr);

    if ( vfork() == 0 ) {
        decc$set_child_standard_streams(fdin[0], fdout[1], fderr[1]);
      execl( "child", "child" );
    }
    else {
        write(fdin[1], msg, sizeof(msg));
        nbytes = read(fdout[0], buf, sizeof(buf));
        buf[nbytes] = '\0';
        puts(buf);
        nbytes = read(fderr[0], buf, sizeof(buf));
        buf[nbytes] = '\0';
        puts(buf);
    }
}

child.c
=======

#include <stdio.h>
#include <unistd.h>

main()
{
    char msg[] = "child writing to stderr";
    char buf[80];
    int nbytes;

    nbytes = read(0, buf, sizeof(buf));
    write(1, buf, nbytes);
    write(2, msg, sizeof(msg));
}

child.com
=========

$ read sys$command s
$ write sys$output s
$ write sys$error "child writing to stderr"
This example program returns the following for both child.c and child.com: 
$ run parent
parent writing to child's stdin
child writing to stderr

Note that in order to activate child.com, you must explicitly specify execl("child.com", ...) in the parent.c program.

decc$set_reentrancy

decc$set_reentrancy — Controls the type of reentrancy that reentrant C RTL routines will exhibit.

Format

#include <reentrancy.h>
int decc$set_reentrancy (int type);

Argument

type

The type of reentrancy desired. Use one of the following values:

  • C$C_MULTITHREAD — Designed to be used in conjunction with the DECthreads product. It performs DECthreads locking and never disables ASTs. DECthreads must be available on your system to use this form of reentrancy.

  • C$C_AST — Uses the _ _TESTBITSSI (Integrity servers, Alpha) built-in function to perform simple locking around critical sections of RTL code, and it may additionally disable asynchronous system traps (ASTs) in locked regions of code. This type of locking should be used when AST code contains calls to C RTL I/O routines, or when the user application disables ASTs.

  • C$C_TOLERANT — Uses the _ _TESTBITSSI (Integrity servers, Alpha) built-in function to perform simple locking around critical sections of RTL code, but ASTs are not disabled. This type of locking should be used when ASTs are used and must be delivered immediately. TOLERANT is the default reentrancy type.

  • C$C_NONE — Gives optimal performance in the C RTL, but does absolutely no locking around critical sections of RTL code. It should only be used in a single-threaded environment when there is no chance that the thread of execution will be interrupted by an AST that would call the C RTL.

The reentrancy type can be raised but never lowered. The ordering of reentrancy types from low to high is C$C_NONE, C$C_TOLERANT, C$C_AST and C$C_ MULTITHREAD. For example, once an application is set to multithread, a call to set the reentrancy to AST is ignored. A call to decc$set_reentrancy that attempts to lower the reentrancy type returns a value of -1.

Description

Use the decc$set_reentrancy function to change the type of reentrancy exhibited by reentrant routines.

decc$set_reentrancy must be called exclusively at the non-AST level.

In an application using DECthreads, DECthreads automatically sets the reentrancy to multithread.

Return Value

type

The type of reentrancy used before this call.

-1

The reentrancy was set to a lower type.

decc$to_vms

decc$to_vms — Converts UNIX style file specifications to OpenVMS file specifications.

Format

#include <unixlib.h>
int decc$to_vms (const char *unix_style_filespec, int (*action_routine)(char *OpenVMS_style_filespec, int type_of_file), int allow_wild, int no_directory);

Arguments

unix_style_filespec

The address of a null-terminated string containing a name in UNIX style file specification format.

action_routine

The address of a routine called by decc$to_vms that accepts the following arguments:

  • A pointer to a null-terminated string that is the result of the translation to OpenVMS format.

  • An integer that has one of the following values:

    Value

    Translation

    0 (DECC$K_FOREIGN)

    A file on a remote system that is not running the OpenVMS or VAXELN operating system.

    1 (DECC$K_FILE)

    The translation is a file.

    2 (DECC$K_DIRECTORY)

    The OpenVMS translation of the UNIX style filename is a directory.

    These values can be defined symbolically with the symbols DECC$K_FOREIGN, DECC$K_FILE, and DECC$K_DIRECTORY. See the example for more information.

If action_routine returns a nonzero value (TRUE), file translation continues. If it returns a 0 value (FALSE), no further file translation takes place.

allow_wild

Either 0 or 1, passed by value. If a 0 is specified, wildcards found in unix_style_filespec are not expanded. Otherwise, wildcards are expanded and each one is passed to action_routine. Only expanded filenames that correspond to existing OpenVMS files are included.

no_directory

An integer that has one of the following values:

Value

Translation

0

Directory allowed.

1

Prevent expansion of the string as a directory name.

2

Forced to be a directory name.

Description

The decc$to_vms function converts the given UNIX style file specification into the equivalent OpenVMS file specification (in all uppercase letters). It allows you to specify UNIX style wildcards, which are translated into a list of corresponding OpenVMS files.

See Section 1.5 for descriptions of the following feature logicals that can affect the behavior of decc$to_vms:
  • DECC$DISABLE_TO_VMS_LOGNAME_TRANSLATION
  • DECC$NO_ROOTED_SEARCH_LISTS

Return Value

x

The number of filenames that result from the specified UNIX style file specification.

Example

/* Translate "UNIX" wildcard file names to OpenVMS names.*/
/* Define as a foreign command and provide the name as   */
/* an argument.                                          */

#include <unixlib.h>
#include <stdio.h>
int print_name(char *, int);
int main(int argc, char *argv[])
{
    int number_found;           /* number of files found */

    printf("Translating: %s\n", argv[1]);

    number_found = decc$to_vms(argv[1], print_name, 1, 0);
    printf("%d files found\n", number_found);
}

/* action routine that prints name and type on each line */

int print_name(char *name, int type)
{
    if (type == DECC$K_DIRECTORY)
        printf("directory: %s\n", name);
    else if (type == DECC$K_FOREIGN)
        printf("remote non-VMS: %s\n", name);
    else
        printf("file:        %s\n", name);

/* Translation continues as long as success status is returned */
    return (1);
}

This example shows how to use the decc$to_vms routine in VSI C. It takes a UNIX style file specification argument and displays, in OpenVMS file specification format, the name of each existing file that matches it.

decc$translate_vms

decc$translate_vms — Translates OpenVMS file specifications to UNIX style file specifications.

Format

#include <unixlib.h>
char *decc$translate_vms (const char *vms_filespec);

Argument

vms_filespec

The address of a null-terminated string containing a name in OpenVMS file specification format.

Description

The decc$translate_vms function translates the given OpenVMS file specification into the equivalent UNIX style file specification, whether or not the file exists. The translated name string is stored in a thread-specific memory, which is overwritten by each call to decc$translate_vms from the same thread.

This function differs from the decc$from_vms function, which does the conversion for existing files only.

Return Values

x

The address of a null-terminated string containing a name in UNIX style file specification format.

0

Indicates that the filename is null or syntactically incorrect.

-1

Indicates that the file specification contains an ellipsis (for example, [. . .]a.dat), but is otherwise correct. You cannot translate the OpenVMS ellipsis syntax into a valid UNIX style file specification.

Example

/* Demonstrate translation of a "UNIX" name to OpenVMS  */
/* form, define a foreign command, and pass the name as */
/* the argument.                                        */

#include <unixlib.h>
#include <stdio.h>

int main(int argc, char *argv[])
{
    char *ptr;                      /* translation result */

    ptr = decc$translate_vms( argv[1] );

    if ((int) ptr == 0 || (int) ptr == -1)

        printf( "could not translate %s\n", argv[1]);
    else
        printf( "%s is translated to %s\n", argv[1], ptr );
}

decc$validate_wchar

decc$validate_wchar — Confirms that its argument is a valid wide character in the current program's locale.

Format

#include <unistd.h>
int decc$validate_wchar (wchar_t wc);

Argument

wc

Wide character to be validated.

Description

The decc$validate_wchar function provides a convenient way to verify whether a specified argument of wchar_t type is a valid wide character in the current program's locale.

One reason to call decc$validate_wchar is that the isw* wide-character classification functions and macros do not validate their argument before dereferencing the classmask array describing character properties. Passing an isw* function a value that exceeds the maximum wide-character value for the current program's locale can result in an attempt to access memory beyond the allocated classmask array.

A standard way to validate a wide character is to call the wctomb function, but this way is less convenient because it requires declaring a multibyte character array of sufficient size and passing it to wctomb.

Return Values

1

Indicates that the specified wide character is a valid wide character in the current program's locale.

0

Indicates that the specified wide character is not a valid wide character in the current program's locale. errno is not set.

decc$write_eof_to_mbx

decc$write_eof_to_mbx — Writes an end-of-file message to the mailbox.

Format

#include <unistd.h>
int decc$write_eof_to_mbx (int fd);

Argument

fd

File descriptor associated with the mailbox.

Description

The decc$write_eof_to_mbx function writes end-of-file message to the mailbox.

For a mailbox that is not a pipe, the write function called with an nbytes argument value of 0 sends an end-of-file message to the mailbox. For a pipe, however, the only way to write an end-of-file message to the mailbox is to close the pipe.

If the child's standard input is redirected to a pipe through a call to the decc$set_child_standard_streams function, the parent process can call decc$write_eof_to_mbx for this pipe to send an EOF message to the child. It has the same effect as if the child read the data from a terminal, and Ctrl/Z was pressed.

After a call to decc$write_eof_to_mbx, the pipe can be reused for communication with another child, for example. This is the purpose of decc$write_eof_to_mbx: to allow reuse of the pipe instead of having to close it just to send an end-of-file message.

Return Values

0

Indicates success.

-1

Indicates failure; errno and vaxc$errno are set according to the failure status returned by SYS$QIOW.

Example

/*      decc$write_eof_to_mbx_example.c         */

#include <errno.h>
#include <stdio.h>
#include <string.h>

#include <fcntl.h>
#include <unistd.h>
#include <unixio.h>

#include <descrip.h>
#include <ssdef.h>
#include <starlet.h>


int decc$write_eof_to_mbx( int );

main()
{
  int status, nbytes, failed = 0;
  int fd, fd2[2];
  short int channel;
  $DESCRIPTOR(mbxname_dsc, "TEST_MBX");
  char c;

  /* first try a mailbox created by SYS$CREMBX        */

status = sys$crembx(0, &channel, 0, 0, 0, 0, &mbxname_dsc, 0, 0);
if ( status != SS$_NORMAL ) {
     printf("sys$crembx failed: %s\n",strerror(EVMSERR, status));
     failed = 1;
  }

 if ( (fd = open(mbxname_dsc.dsc$a_pointer, O_RDWR, 0)) == -1) {
      perror("? open mailbox");
      failed = 1;
  }

  if ( decc$write_eof_to_mbx(fd) == -1 ) {
      perror("?  decc$write_eof_to_mbx to mailbox");
      failed = 1;
  }

  if ( (nbytes = read(fd, &c, 1)) != 0 || errno != 0 ) {
      perror("? read mailbox");
      printf("? nbytes = %d\n", nbytes);
      failed = 1;
  }

  if ( close(fd) == -1 ) {
      perror("? close mailbox");
      failed = 1;
  }

  /* Now do the same thing with a pipe                */

  errno = 0;           /* Clear errno for consistency */

  if ( pipe(fd2) == -1 ) {
      perror("? opening pipe");
      failed = 1;
  }

  if ( decc$write_eof_to_mbx(fd2[1]) == -1 ) {
      perror("? decc$write_eof_to_mbx to pipe");
      failed = 1;
  }

  if ( (nbytes = read(fd2[0], &c, 1)) != 0 || errno != 0 ) {
      perror("? read pipe");
      printf("? nbytes = %d\n", nbytes);
      failed = 1;
  }

  /* Close both file descriptors involved with the pipe    */

  if ( close(fd2[0]) == -1 ) {
      perror("close(fd2[0])");
      failed = 1;
  }

  if ( close(fd2[1]) == -1 ) {
      perror("close(fd2[1])");
      failed = 1;
  }

  if ( failed )
      puts("?Example program failed");
  else
      puts("Example ran to completion");
}
This example program produces the following result:
Example ran to completion

[w]delch

[w]delch — Delete the character on the specified window at the current position of the cursor. The delch function operates on the stdscr window.

Format

#include <curses.h>
int delch();
int wdelch (WINDOW *win);

Argument

win

A pointer to the window.

Description

All of the characters to the right of the cursor on the same line are shifted to the left, and a blank character is appended to the end of the line.

Return Values

OK

Indicates success.

ERR

Indicates an error.

delete

delete — Deletes a file.

Format

#include <unixio.h>
int delete (const char *file_spec);

Argument

file_spec

A pointer to the string that is an OpenVMS or UNIX style file specification. The file specification can include a wildcard in its version number (but not in any other part of the file spec). So, for example, files of the form filename. txt;* can be deleted.

Description

If you specify a directory in the filename and it is a search list that contains an error, VSI C for OpenVMS systems interprets it as a file error.

When delete is used to delete a symbolic link, the link itself is deleted, not the file to which it refers.

The remove and delete functions are functionally equivalent in the C RTL.

See also remove.

Note

The delete routine is not available to C++ programmers because it conflicts with the C++ reserved word delete. C++ programmers should use the ANSI/ISO C standard function remove instead.

Return Values

0

Indicates success.

nonzero value

Indicates that the operation has failed.

[w]deleteln

[w]deleteln — Delete the line at the current position of the cursor. The deleteln function acts on the stdscr window.

Format

#include <curses.h>
int deleteln();
int wdeleteln (WINDOW *win);

Argument

win

A pointer to the window.

Description

Every line below the deleted line moves up, and the bottom line becomes blank. The current ( y, x) coordinates of the cursor remain unchanged.

Return Values

OK

Indicates success.

ERR

Indicates an error.

delwin

delwin — Deletes the specified window from memory.

Format

#include <curses.h>
int delwin (WINDOW *win);

Argument

win

A pointer to the window.

Description

If the window being deleted contains a subwindow, the subwindow is invalidated. Delete subwindows before deleting their parent. The delwin function refreshes all windows covered by the deleted window.

Return Values

OK

Indicates success.

ERR

Indicates an error.

difftime

difftime — Computes the difference, in seconds, between the two times specified by the time1 and time2 arguments.

Format

#include <time.h>
double difftime (time_t time2, time_t time1);

Arguments

time2

A time value of type time_t.

time1

A time value of type time_t.

Description

The type time_t is defined in the <time.h> header file as follows:
typedef unsigned long int time_t

Return Value

n

time2 - time1 in seconds expressed as a double.

dirname

dirname — Reports the parent directory name of a file pathname.

Format

#include <libgen.h>
char *dirname (char *path);

Function Variants

The dirname function has variants named _dirname32 and _dirname64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Argument

path

The file pathname.

Description

The dirname function takes a pointer to a character string that contains a UNIX pathname and returns a pointer to a string that is a pathname of the parent directory of that file. Trailing slash (/) characters in the path are not counted as part of the path.

This function returns a pointer to the string "."(dot), when the path argument:

  • Does not contain a slash (/).

  • Is a NULL pointer.

  • Points to an empty string.

The dirname function can modify the string pointed to by the path argument.

The dirname and basename functions together yield a complete pathname. The expression dirname( path) obtains the pathname of the directory where basename (path) is found.

See also basename.

Return Values

x

A pointer to a string that is the parent directory of the path argument.

"."
The path argument:

  • Does not contain a slash (/).

  • Is a NULL pointer.

  • Points to an empty string.

Example

Using the dirname function, the following example reads a pathname, changes the current working directory to the parent directory, and opens a file.
    char path [MAXPATHLEN], *pathcopy;
    int fd;

    fgets(path, MAXPATHLEN, stdin);
    pathcopy = strdup(path);
    chdir(dirname(pathcopy));
    fd = open(basename(path), O_RDONLY);

div

div — Returns the quotient and the remainder after the division of its arguments.

Format

#include <stdlib.h>
div_t div (int numer, int denom);

Arguments

numer

A numerator of type int.

denom

A denominator of type int.

Description

The type div_t is defined in the standard header file <stdlib.h> as follows:
typedef struct
        {
             int   quot, rem;
        } div_t;

dlclose

dlclose — Deallocates the address space for a shared library.

Format

#include <dlfcn.h>
void dlclose (void *handle);

Argument

handle

Pointer to the shared library.

Description

The dlclose function deallocates the address space allocated by the C RTL for the handle.

There is no way on OpenVMS systems to unload a shareable image dynamically loaded by the LIB$FIND_IMAGE_SYMBOL routine, which is the routine called by the dlsym function. In other words, there is no way on OpenVMS systems to release the address space occupied by the shareable image brought into memory by dlsym.

dlerror

dlerror — Returns a string describing the last error that occurred from a call to dlopen, dlclose, or dlsym.

Format

#include <dlfcn.h>
char *dlerror (void);

Return Value

x

A string describing the last error that occurred from a call to dlopen, dlclose, or dlsym.

dlopen

dlopen — Provides an interface to the dynamic library loader to allow shareable images to be loaded and called at run time.

Format

#include <dlfcn.h>
void *dlopen (char *pathname, int mode);

Arguments

pathname

The name of the shareable image. This name is saved for subsequent use by the dlsym function.

mode

This argument is ignored on OpenVMS systems.

Description

The dlopen function provides an interface to the dynamic library loader to allow shareable images to be loaded and called at run time.

This function does not load a shareable image but rather saves its pathname argument for subsequent use by the dlsym function. dlsym is the function that actually loads the shareable image through a call to LIB$FIND_IMAGE_SYMBOL.

The pathname argument of the dlopen function must be the name of the shareable image. This name is passed as-is by the dlsym function to the LIB$FIND_IMAGE_SYMBOL routine as the filename argument. No image-name argument is specified in the call to LIB$FIND_IMAGE_SYMBOL, so default file specification of SYS$SHARE:.EXE is applied to the image name.

The dlopen function returns a handle that is used by a dlsym or dlclose call. If an error occurs, a NULL pointer is returned.

Return Values

x

A handle to be used by a dlsym or dlclose call.

NULL

Indicates an error.

dlsym

dlsym — Returns the address of the symbol name found in a shareable image.

Format

#include <dlfcn.h>
void *dlsym (void *handle, char *name);

Arguments

handle

Pointer to the shareable image.

name

Pointer to the symbol name.

Description

The dlsym function returns the address of the symbol name found in the shareable image corresponding to handle. If the symbol is not found, a NULL pointer is returned.

As of OpenVMS Version 7.3-2, library symbols containing lowercase characters can be loaded using the dlsym function. More generally, the functions that dynamically load libraries (dlopen, dlsym, dlclose, dlerror) are enhanced to provide the following capabilities:

  • Support for libraries with mixed-case symbol names

  • Ability to pass a full file path to dlopen

  • Validation of the specified library name

Return Values

x

Address of the symbol name found.

NULL

Indicates that the symbol was not found.

drand48

drand48 — Generates uniformly distributed pseudo-random-number sequences. Returns 48-bit, nonnegative, double-precision floating-point values.

Format

#include <stdlib.h>
double drand48 (void);

Description

The drand48 function generates pseudorandom numbers using the linear congruential algorithm and 48-bit integer arithmetic.

It returns nonnegative, double-precision, floating-point values uniformly distributed over the range of y values such that 0.0 ≤ y < 1.0.

Before you call drand48, use either srand48, seed48, or lcong48 to initialize the random-number generator. You must initialize prior to invoking the drand48 function because it stores the last 48-bit X i generated into an internal buffer. (Although it is not recommended, constant default initializer values are supplied automatically if the drand48, lrand48, or mrand48 functions are called without first calling an initialization function.)

The drand48 function works by generating a sequence of 48-bit integer values, X i, according to the linear congruential formula:
       Xn+1 = (aXn+c)mod m        n >= 0
The argument m equals 2 48, so 48-bit integer arithmetic is performed. Unless you invoke lcong48, the multiplier value a and the addend value c are: 
     a = 5DEECE66D16 = 2736731631558
     c = B16 = 138

The values returned by drand48 are computed by first generating the next 48-bit X i in the sequence. Then the appropriate bits, according to the type of returned data item, are copied from the high-order (most significant) bits of X i and transformed into the returned value.

See also srand48, seed48, lcong48, lrand48, and mrand48.

Return Value

n

A nonnegative, double-precision, floating-point value.

dup, dup2

dup, dup2 — Allocate a new descriptor that refers to a file specified by a file descriptor returned by open, creat, or pipe.

Format

#include <unistd.h>
int dup (int file_desc1);
int dup2 (int file_desc1, int file_desc2);

Arguments

file_desc1

The file descriptor being duplicated.

file_desc2

The new file descriptor to be assigned to the file designated by file_desc1.

Description

The dup function causes a previously unallocated descriptor to refer to its argument, while the dup2 function causes its second argument to refer to the same file as its first argument.

The argument file_desc1 is invalid if it does not describe an open file; file_desc2 is invalid if the new file descriptor cannot be allocated. If file_desc2 is connected to an open file, that file is closed.

Return Values

n

The new file descriptor.

-1

Indicates that an invalid argument was passed to the function.

[no]echo

[no]echo — Set the terminal so that characters may or may not be echoed on the terminal screen. This mode of single-character input is only supported with Curses.

Format

#include <curses.h>
void echo (void);
void noecho (void);

Description

The noecho function may be helpful when accepting input from the terminal screen with wgetch and wgetstr; it prevents the input characters from being written onto the screen.

ecvt

ecvt — Converts its argument to a null-terminated string of ASCII digits and returns the address of the string. The string is stored in a thread-specific memory location created by the C RTL.

Format

#include <stdlib.h>
char *ecvt (double value, int ndigits, int *decpt, int *sign);

Arguments

value

An object of type double that is converted to a null-terminated string of ASCII digits.

ndigits

The number of ASCII digits to be used in the converted string.

decpt

The position of the decimal point relative to the first character in the returned string. A negative int value means that the decimal point is decpt number of spaces to the left of the returned digits (the spaces being filled with zeros). A 0 value means that the decimal point is immediately to the left of the first digit in the returned string.

sign

An integer value that indicates whether the value argument is positive or negative. If value is negative, the function places a nonzero value at the address specified by sign. Otherwise, the function assigns 0 to the address specified by sign.

Description

The ecvt function converts value to a null-terminated string of length ndigits, and returns a pointer to it. The resulting low-order digit is rounded to the correct digit for outputting ndigits digits in C E-format. The decpt argument is assigned the position of the decimal point relative to the first character in the string.

Repeated calls to the ecvt function overwrite any existing string.

The ecvt, fcvt, and gcvt functions represent the following special values specified in the IEEE Standard for floating-point arithmetic:

Value

Representation

Quiet NaN

NaNQ

Signalling NaN

NaNS

+Infinity

Infinity

-Infinity

-Infinity

The sign associated with each of these values is stored into the sign argument. In IEEE floating-point representation, a value of 0 (zero) can be positive or negative, as set by the sign argument.

See also gcvt and fcvt.

Return Value

x

The value of the converted string.

encrypt

encrypt — Encrypts a string using the key generated by the setkey function.

Format

#include <unistd.h>
#include <stdlib.h>
void encrypt (char *block[64], int edflag);

Argument

block

A character array of length 64 containing 0s and 1s.

edflag

An integer. If edflag is 0, the argument is encrypted; if nonzero, it is decrypted.

Description

The encrypt function encrypts a string using the key generated by the setkey function.

The first argument to encrypt is a character array of length 64 containing 0s and 1s. The argument array is modified in place to a similar array representing the bits of the argument after having been subjected to the DES algorithm using the key set by setkey.

The second argument, edflag, determines whether the first argument is encrypted or decrypted: if edflag is 0, the first argument array is encrypted; if nonzero, it is decrypted.

No value is returned.

See also crypt and setkey.

Return Value

pointer

Pointer to the encrypted password.

endgrent

endgrent — Closes the group database when processing is complete.

Format

#include <grp.h>
void endgrent (void);

Description

The endgrent function closes the group database.

This function is always successful. No value is returned, and errno is not set.

endpwent

endpwent — Closes the user database and any private stream used by getpwent.

Format

#include <pwd.h>
void endpwent (void);

Description

The endpwent function closes the user database and any private stream used by getpwent.

No value is returned. If an I/O error occurred, the function sets errno to EIO.

See also getpwent, getpwuid, getpwnam, and setpwent.

endwin

endwin — Clears the terminal screen and frees any virtual memory allocated to Curses data structures.

Format

#include <curses.h>
void endwin (void);

Description

A program that calls Curses functions must call the endwin function before exiting to restore the previous environment of the terminal screen.

erand48

erand48 — Generates uniformly distributed pseudorandom-number sequences. Returns 48-bit nonnegative, double-precision, floating-point values.

Format

#include <stdlib.h>
double erand48 (unsigned short int xsubi[3]);

Argument

xsubi

An array of three short ints, which form a 48-bit integer when concatenated together.

Description

The erand48 function generates pseudorandom numbers using the linear congruential algorithm and 48-bit integer arithmetic.

It returns nonnegative, double-precision, floating-point values uniformly distributed over the range of y values, such that 0.0 ≤ y < 1.0.

The erand48 function works by generating a sequence of 48-bit integer values, X i, according to the linear congruential formula: 
       Xn+1 = (aXn+c)mod m        n >= 0
The argument m equals 2 48, so 48-bit integer arithmetic is performed. Unless you invoke the lcong48 function, the multiplier value a and the addend value c are: 
      a = 5DEECE66D16 = 2736731631558
      c = B16 = 138

The erand48 function requires that the calling program pass an array as the xsubi argument. For the first call, the array must be initialized to the value of the pseudorandom-number sequence. Unlike the drand48 function, it is not necessary to call an initialization function prior to the first call.

By using different arguments, the erand48 function allows separate modules of a large program to generate several independent sequences of pseudorandom numbers; for example, the sequence of numbers that one module generates does not depend upon how many times the function is called by other modules.

Return Value

n

A nonnegative, double-precision, floating-point value.

[w]erase

[w]erase — Erases the window by painting it with blanks. The erase function acts on the stdscr window.

Format

#include <curses.h>
int erase();
int werase (WINDOW *win);

Argument

win

A pointer to the window.

Description

Both the erase and werase functions leave the cursor at the current position on the terminal screen after completion; they do not return the cursor to the home coordinates of (0,0).

Return Values

OK

Indicates success.

ERR

Indicates an error.

erf

erf — Returns the error function of its argument.

Format

#include <math.h>
double erf (double x);
float erff (float x);
long double erfl (long double x);
double erfc (double x);
float erfcf (float x);
long double erfcl (long double x);

Argument

x

A radian expressed as a real number.

Description

The erf functions return the error function of x, where erf( x), erff(x), and erfl(x) equal 2/sqrt(π) times the area under the curve e**(-t**2) between 0 and x.

The erfc functions return (1.0 -erf(x)). The erfcfunction can result in an underflow as x gets large.

Return Values

x

The value of the error function (erf) or complementary error function (erfc).

NaN

x is NaN; errno is set to EDOM.

0

Underflow occurred; errno is set to ERANGE.

execl

execl — Passes the name of an image to be activated in a child process. This function is nonreentrant.

Format

#include <unistd.h>
int execl (const char *file_spec, const char *arg0, ..., (char *)0);
(ISO POSIX-1)
int execl (char *file_spec, ...); (Compatibility)

Arguments

file_spec

The full file specification of a new image to be activated in the child process.

arg0, ...

A sequence of pointers to null-terminated character strings.

If the POSIX-1 format is used, at least one argument must be present and must point to a string that is the same as the new process filename (or its last component). (This pointer can also be the NULL pointer, but then execle would accomplish nothing.) The last pointer must be the NULL pointer. This is also the convention if the compatibility format is used.

Description

To understand how the exec functions operate, consider how the OpenVMS system calls any VSI C program, as shown in the following syntax: 
int main (int argc, char *argv[], char *envp[]);

The identifier argc is the argument count; argv is an array of argument strings. The first member of the array (argv[0]) contains the name of the image. The arguments are placed in subsequent elements of the array. The last element of the array is always the NULL pointer.

An exec function calls a child process in the same way that the run-time system calls any other VSI C program. The exec functions pass the name of the image to be activated in the child; this value is placed in argv[0]. However, the functions differ in the way they pass arguments and environment information to the child:

  • Arguments can be passed in separate character strings (execl, execle, and execlp) or in an array of character strings (execv, execve, and execvp).

  • The environment can be explicitly passed in an array (execle and execve) or taken from the parent's environment (execl, execv, execlp, and execvp).

If vfork was called before invoking an exec function, then when the exec function completes, control is returned to the parent process at the point of the vfork call. If vfork was not called, the exec function waits until the child has completed execution and then exits the parent process. See vfork and Chapter 5 for more information.

Return Value

-1

Indicates failure.

execle

execle — Passes the name of an image to be activated in a child process. This function is nonreentrant.

Format

#include <unistd.h>
int execle (char *file_spec, char *arg0, ..., (char *)0,
char *envp[ ]); (ISO POSIX-1)
int execle (char *file_spec, ...); (Compatibility)

Arguments

file_spec

The full file specification of a new image to be activated in the child process.

arg0, ...

A sequence of pointers to null-terminated character strings.

If the POSIX-1 format is used, at least one argument must be present and must point to a string that is the same as the new process filename (or its last component). (This pointer can also be the NULL pointer, but then execle would accomplish nothing.) The last pointer must be the NULL pointer. This is also the convention if the compatibility format is used.

envp

An array of strings that specifies the program's environment. Each string in envp has the following form:
name = value
The name can be one of the following names and the value is a null-terminated string to be associated with the name:

  • HOME—Your login directory

  • TERM—The type of terminal being used

  • PATH—The default device and directory

  • USER—The name of the user who initiated the process

The last element in envp must be the NULL pointer.

When the operating system executes the program, it places a copy of the current environment vector ( envp) in the external variable environ.

Description

See execl for a description of how the exec functions operate.

Return Value

-1

Indicates failure.

execlp

execlp — Passes the name of an image to be activated in a child process. This function is nonreentrant.

Format

#include <unistd.h>
int execlp (const char *file_name, const char *arg0, ..., (char *)0);
(ISO POSIX-1)
int execlp (char *file_name, ...); (Compatibility)

Arguments

file_name

The filename of a new image to be activated in the child process. The device and directory specification for the file is obtained by searching the VAXC$PATH environment name.

argn

A sequence of pointers to null-terminated character strings. By convention, at least one argument must be present and must point to a string that is the same as the new process filename (or its last component).

. . .

A sequence of pointers to strings. At least one pointer must exist to terminate the list. This pointer must be the NULL pointer.

Description

See execl for a description of how the exec functions operate.

Return Value

-1

Indicates failure.

execv

execv — Passes the name of an image to be activated in a child process. This function is nonreentrant.

Format

#include <unistd.h>
int execv (char *file_spec, char *argv[]);

Arguments

file_spec

The full file specification of a new image to be activated in the child process.

argv

An array of pointers to null-terminated character strings. These strings constitute the argument list available to the new process. By convention, argv[0] must point to a string that is the same as the new process filename (or its last component). argv is terminated by a NULL pointer.

Description

See execl for a description of how the exec functions operate.

Return Value

-1

Indicates failure.

execve

execve — Passes the name of an image to be activated in a child process. This function is nonreentrant.

Format

#include <unistd.h>
int execve (const char *file_spec, char *argv[], char *envp[]);

Arguments

file_spec

The full file specification of a new image to be activated in the child process.

argv

An array of pointers to null-terminated character strings. These strings constitute the argument list available to the new process. By convention, argv[0] must point to a string that is the same as the new process filename (or its last component). argv is terminated by a NULL pointer.

envp

An array of strings that specifies the program's environment. Each string in envp has the following form:
name = value
The name can be one of the following names and the value is a null-terminated string to be associated with the name:

  • HOME—Your login directory

  • TERM—The type of terminal being used

  • PATH—The default device and directory

  • USER—The name of the user who initiated the process

The last element in envp must be the NULL pointer.

When the operating system executes the program, it places a copy of the current environment vector ( envp) in the external variable environ.

Description

See execl for a description of how the exec functions operate.

Return Value

-1

Indicates failure.

execvp

execvp — Passes the name of an image to be activated in a child process. This function is nonreentrant.

Format

#include <unistd.h>
int execvp (const char *file_name, char *argv[]);

Arguments

file_name

The filename of a new image to be activated in the child process. The device and directory specification for the file is obtained by searching the environment name VAXC$PATH.

argv

An array of pointers to null-terminated character strings. These strings constitute the argument list available to the new process. By convention, argv[0] must point to a string that is the same as the new process filename (or its last component). argv is terminated by a NULL pointer.

Description

See execl for a description of how the exec functions operate.

Return Value

-1

Indicates failure.

exit, _exit

exit, _exit — Terminate execution of the program from which they are called. These functions are nonreentrant.

Format

#include <stdlib.h>
void exit (int status);
#include <unistd.h>
void _exit (int status);

Argument

status

For non-POSIX behavior, a status value of EXIT_SUCCESS (1), EXIT_FAILURE (2), or a number from 3 to 255, as follows:

  • A status value of 0, 1 or EXIT_SUCCESS is translated to the OpenVMS SS$_NORMAL status code to return the OpenVMS success value.

  • A status value of 2 or EXIT_FAILURE is translated to an error-level exit status. The status value is passed to the parent process.

  • Any other status value is left the same.

For POSIX behavior:

  • A status value of 0 is translated to the OpenVMS SS$_NORMAL status code to return the OpenVMS success value.

  • Any other status is returned to the parent process as an OpenVMS message symbol with facility set to C, severity set to success, and with the status in the message number field. For more information on the format of message symbols, see "message code" in the VSI OpenVMS Command Definition, Librarian, and Message Utilities Manual.

To get POSIX behavior, include <unistd.h> and compile with the _POSIX_EXIT feature-test macro set (either with /DEFINE=_POSIX_EXIT, or with #define _POSIX_EXIT at the top of your file, before any file inclusions). This behavior is available only on OpenVMS Version 7.0 and higher systems.

Description

If the process was invoked by DCL, the status is interpreted by DCL, and a message is displayed.

If the process was a child process created using vfork or an exec function, then the child process exits and control returns to the parent. The two functions are identical; the _exit function is retained for reasons of compatibility with VAX C.

The exit and _exit functions make use of the $EXIT system service. If your process is being invoked by the RUN command using any of the hibernation and scheduled wakeup qualifiers, the process might not correctly return to hibernation state when an exit or _exit call is made.

The C compiler command-line qualifier /[NO]MAIN=POSIX_EXIT can be used to direct the compiler to call __posix_exit instead of exit when returning from main. The default is /NOMAIN.

Beginning with OpenVMS Version 8.3, C RTL contains a fix for the problem in which a call to _exit after a failed execl really exits but must not.

In the OpenVMS implementation of vfork, a child process is not actually started as it is started on most UNIX systems. However, the C RTL creates some internal data structures intended to mimic child-process functionality (called the "child context").

A bug occurred whereby after a vfork while in the child context, a call to an exec function justifiably fails, then calls _exit. On UNIX systems, after the failed exec call, the child process continues to execute. A subsequent call to _exit terminates the child. In the OpenVMS implementation, after the failed exec call, the child context terminates. A subsequent call to _exit terminates the parent. The C RTL fix is enabled by a feature logical switch, DECC$EXIT_AFTER_FAILED_EXEC. Enabling this feature logical allows the child context to continue execution.

With DECC$EXIT_AFTER_FAILED_EXEC disabled or not defined, the current behavior remains the default.

Note

EXIT_SUCCESS and EXIT_FAILURE are portable across any ANSI C compiler to indicate success or failure. On OpenVMS systems, they are mapped to OpenVMS condition codes with the severity set to success or failure, respectively. Values in the range of 3 to 255 can be used by a child process to communicate a small amount of data to the parent. The parent retrieves this data using the wait, wait3, wait4, or waitpid functions.

exp

exp — Returns the base e raised to the power of the argument.

Format

#include <math.h>
double exp (double x);
float expf (float x);
long double expl (long double x);
double expm1 (double x);
float expm1f (float x);
long double expm1l (long double x);

Argument

x

A real value.

Description

The exp functions compute the value of the exponential function, defined as e** x, where e is the constant used as a base for natural logarithms.

The expm1 functions compute exp( x) - 1 accurately, even for tiny x.

If an overflow occurs, the exp functions return the largest possible floating-point value and set errno to ERANGE. The constant HUGE_VAL is defined in the <math.h> header file to be the largest possible floating-point value.

Return Values

x

The exponential value of the argument.

HUGE_VAL

Overflow occurred; errno is set to ERANGE.

0

Underflow occurred; errno is set to ERANGE.

NaN

x is NaN; errno is set to EDOM.

exp2

exp2 — Returns the value of 2 raised to the power of the argument.

Format

#include <math.h>
double exp2 (double x);
float exp2f (float x);
long double exp2l (long double x);

Argument

x

A real value.

Description

The exp2 functions compute the base-2 exponential of x.

If an overflow occurs, the exp functions return the largest possible floating-point value and set errno to ERANGE. The constant HUGE_VAL is defined in the <math.h> header file to be the largest possible floating-point value.

Return Values

n

2** x.

HUGE_VAL

Overflow occurred; errno is set to ERANGE.

1

x is +0 or -0; errno is set to ERANGE.

0

x is -Inf or underflow occurred; errno is set to ERANGE.

x

x is +Inf; errno is set to ERANGE.

NaN

x is NaN; errno is set to EDOM.

fabs

fabs — Returns the absolute value of its argument.

Format

#include <math.h>
double fabs (double x);
float fabsf (float x);
long double fabsl (long double x);

Argument

x

A real value.

Return Value

x

The absolute value of the argument.

fchmod

fchmod — Changes file access permissions.

Format

#include <stat.h>
int fchmod (int fildes, mode_t mode);

Arguments

fildes

An open file descriptor.

mode

The bit pattern that determines the access permissions.

Description

The fchmod function is equivalent to the chmod function, except that the file whose permissions are changed is specified by a file descriptor (fildes) rather than a filename.

Return Values

0

Indicates that the mode is successfully changed.

-1

Indicates that the change attempt has failed.

fchown

fchown — Changes the owner and group of a file.

Format

#include <unistd.h>
int fchown (int fildes, uid_t owner, gid_t group);

Arguments

fildes

An open file descriptor.

owner

A user ID corresponding to the new owner of the file.

group

A group ID corresponding to the group of the file.

Description

The fchown function has the same effect as chown except that the file whose owner and group are to be changed is specified by the file descriptor fildes.

Return Values

0

Indicates success.

-1

Indicates failure. The function sets errno to one of the following values:

The fchown function will fail if:

  • EBADF– The fildes argument is not an open file descriptor.

  • EPERM– The effective user ID does not match the owner of the file, or the process does not have appropriate privilege.

  • EROFS– The file referred to by fildes resides on a read-only file system.

The fchown function may fail if:

  • EINVAL– The owner or group ID is not a value supported by the implementation.

  • EIO– A physical I/O error has occurred.

  • EINTR– The fchown function was interrupted by a signal that was intercepted.

fclose

fclose — Closes a file by flushing any buffers associated with the file control block and freeing the file control block and buffers previously associated with the file pointer.

Format

#include <stdio.h>
int fclose (FILE *file_ptr);

Argument

file_ptr

A pointer to the file to be closed.

Description

When a program terminates normally, the fclose function is automatically called for all open files.

The fclose function tries to write buffered data by using an implicit call to fflush.

If the write fails (because the disk is full or the user's quota is exceeded, for example), fclose continues executing. It closes the OpenVMS channel, deallocates any buffers, and releases the memory associated with the file descriptor (or FILE pointer). Any buffered data is lost, and the file descriptor (or FILE pointer) no longer refers to the file.

If your program needs to recover from errors when flushing buffered data, it should make an explicit call to fsync (or fflush) before calling fclose.

Return Values

0

Indicates success.

EOF

Indicates that the file control block is not associated with an open file.

fcntl

fcntl — Performs controlling operations on an open file.

Format

#include <sys/types.h>
#include <unistd.h>
#include <fcntl.h>
int fcntl (int file_desc, int request [,int arg]);
int fcntl (int file_desc, int request [,struct flock *arg]);

Arguments

file_desc

An open file descriptor obtained from a successful open, fcntl, or pipe function.

request

The operation to be performed.

arg

A variable that depends on the value of the request argument.

For a request of F_DUPFD, F_SETFD, or F_SETFL, specify arg as an int.

For a request of F_GETFD and F_GETFL, do not specify arg.

For a request of F_GETLK, F_SETLK, or F_SETLKW specify arg as a pointer to a flock structure.

Description

The fcntl function performs controlling operations on the open file specified by the file_desc argument.

The values for the request argument are defined in the header file <fcntl.h>, and include the following:

F_DUPFD

Returns a new file descriptor that is the lowest numbered available (that is, not already open) file descriptor greater than or equal to the third argument (arg) taken as an integer of type int.

The new file descriptor refers to the same file as the original file descriptor (file_desc). The FD_CLOEXEC flag associated with the new file descriptor is cleared to keep the file open across calls to one of the exec functions.

The following two calls are equivalent:
fid = dup(file_desc);
fid = fcntl(file_desc, F_DUPFD, 0);
Consider the following call: 
fid = dup2(file_desc, arg);
It is similar (but not equivalent) to: 
close(arg);
fid = fcntl(file_desc, F_DUPFD, arg);

F_GETFD

Gets the value of the close-on-exec flag associated with the file descriptor file_desc. File descriptor flags are associated with a single file descriptor and do not affect other file descriptors that refer to the same file. The arg argument should not be specified.

F_SETFD

Sets the close-on-exec flag associated with file_desc to the value of the third argument, taken as type int.

If the third argument is 0, the file remains open across the exec functions, which means that a child process spawned by the exec function inherits this file descriptor from the parent.

If the third argument is FD_CLOEXEC, the file is closed on successful execution of the next exec function, which means that the child process spawned by the exec function will not inherit this file descriptor from the parent.

F_GETFL

Gets the file status flags and file access modes, defined in <fcntl.h>, for the file description associated with file_desc. The file access modes can be extracted from the return value using the mask O_ACCMODE, which is defined in <fcntl.h>. File status flags and file access modes are associated with the file description and do not affect other file descriptors that refer to the same file with different open file descriptions.

The status flags and access modes supported are O_RDWR, O_RDONLY, O_WRONLY, O_APPEND, O_SYNC, O_DSYNC, and O_NONBLOCK.

F_SETFL

Sets the file status flags, defined in <fcntl.h>, for the file description associated with file_desc from the corresponding bits in the third argument, arg, taken as type int. Bits corresponding to the file access mode and the file creation flags, as defined in <fcntl.h>, that are set in arg are ignored. If any bits in arg other than those mentioned here are changed by the application, the result is unspecified.

Note: The status flags supported are O_APPEND, O_SYNC, O_DSYNC, and O_NONBLOCK. Support for the file status flags is not standard-compliant. The X/Open standard states that "File status flags and file access modes are associated with the file description and do not affect other file descriptors that refer to the same file with different open file descriptions." However, because the append bit is stored in the FCB, all file descriptors using the same FCB are using the same append flag, so that setting this flag with fcntl(F_SETFL) will affect all files sharing the FCB; that is, all files duplicated from the same file descriptor.

Record Locking Requests

F_GETLK

Gets the first lock that blocks the lock description pointed to by the arg parameter, taken as a pointer to type struct flock. The information retrieved overwrites the information passed to the fcntl function in the flock structure. If no lock is found that would prevent this lock from being created, then the structure is left unchanged except for the lock type, which is set to F_UNLCK.

F_SETLK

Sets or clears a file segment lock according to the lock description pointed to by arg, taken as a pointer to type struct flock. F_SETLK is used to establish shared locks (F_RDLCK), or exclusive locks (F_WRLCK), as well as remove either type of lock (F_UNLCK). If a shared (read) or exclusive (write) lock cannot beset, the fcntl function returns immediately with a value of -1.

An unlock (F_UNLCK) request in which the l_len of the flock structure is nonzero and the offset of the last byte of the requested segment is the maximum value for an object of type off_t, when the process has an existing lock in which l_len is 0 and which includes the last byte of the requested segment, is treated as a request to unlock from the start of the requested segment with an l_len equal to 0. Otherwise, an unlock (F_UNLCK) request attempts to unlock only the requested file.

F_SETLKW

Same as F_SETLK except that if a shared or exclusive lock is blocked by other locks, the process will wait until it is unblocked. If a signal is received while fcntl is waiting for a region, the function is interrupted, -1 is returned, and errno is set to EINTR.

File Locking

The C RTL supports byte-range file locking using the F_GETLK, F_SETLK, and F_SETLKW commands of the fcntl function, as defined in the X/Open specification. Byte-range file locking is supported across OpenVMS clusters. You can only use offsets that fit into 32-bit unsigned integers.

When a shared lock is set on a segment of a file, other processes on the cluster are able to set shared locks on that segment or a portion of it. A shared lock prevents any other process from setting an exclusive lock on any portion of the protected area. A request for a shared lock fails if the file descriptor was not opened with read access.

An exclusive lock prevents any other process on the cluster from setting a shared lock or an exclusive lock on any portion of the protected area. A request for an exclusive lock fails if the file descriptor was not opened with write access.

The flock structure describes the type (l_type), starting offset (l_whence), relative offset (l_start), size (l_len) and process ID (l_pid) of the segment of the file to be affected.

The value of l_whence is set to SEEK_SET, SEEK_CUR or SEEK_END, to indicate that the relative offset l_start bytes is measured from the start of the file, from the current position, or from the end of the file, respectively. The value of l_len is the number of consecutive bytes to be locked. The l_len value may be negative (where the definition of off_t permits negative values of l_len). The l_pid field is only used with F_GETLK to return the process ID of the process holding a blocking lock. After a successful F_GETLK request, the value of l_whence becomes SEEK_SET.

If l_len is positive, the area affected starts at l_start and ends at l_start + l_len - 1. If l_len is negative, the area affected starts at l_start+ l_len and ends at l_start - 1. Locks may start and extend beyond the current end of a file, but may not be negative relative to the beginning of the file. If l_len is set to 0 (zero), a lock may be set to always extend to the largest possible value of the file offset for that file. If such a lock also has l_start set to 0 (zero) and l_whence is set to SEEK_SET, the whole file is locked.

Changing or unlocking a portion from the middle of a larger locked segment leaves a smaller segment at either end. Locking a segment that is already locked by the calling process causes the old lock type to be removed and the new lock type to take effect.

All locks associated with a file for a given process are removed when a file descriptor for that file is closed by that process or the process holding that file descriptor terminates. Locks are not inherited by a child process.

If the request argument is F_SETLKW, the lock is blocked by some lock from another process, and putting the calling process to sleep to wait for that lock to become free would cause a deadlock, then the application will hang.

Return Values

n
Upon successful completion, the value returned depends on the value of the request argument as follows:

  • F_DUPFD– Returns a new file descriptor.

  • F_GETFD– Returns FD_CLOEXEC or 0.

  • F_SETFD, F_GETLK, F_SETLK, F_UNLCK – Return a value other than -1.

-1
Indicates that an error occurred. The function sets errno to one of the following values:

  • EACCES– The request argument is F_SETLK; the type of lock (l_type) is a shared (F_RDLCK) or exclusive (F_WRLCK) lock, and the segment of a file to be locked is already exclusive-locked by another process; or the type is an exclusive (F_WRLCK) lock and the some portion of the segment of a file to be locked is already shared-locked or exclusive-locked by another process.

  • EBADF – The file_desc argument is not a valid open file descriptor and the arg argument is negative or greater than or equal to the per-process limit.

    The request parameter is F_SETLK or F_SETLKW, the type of lock (l_type) is a shared lock (F_RDLCK), and file_desc is not a valid file descriptor open for reading.

    The type of lock ( l_type) is an exclusive lock (F_WRLCK), and file_desc is not a valid file descriptor open for writing.

  • EFAULT– The arg argument is an invalid address.

  • EINVAL – The request argument is F_DUPFD and arg is negative or greater than or equal to OPEN_MAX.

    Either the OPEN_MAX value or the per-process soft descriptor limit is checked.

    An illegal value was provided for the request argument.

    The request argument is F_GETLK, F_SETLK, or F_SETLKW and the data pointed to by arg is invalid, or file_desc refers to a file that does not support locking.

  • EMFILE– The request argument is F_DUPFD and too many or OPEN_MAX file descriptors are currently open in the calling process, or no file descriptors greater than or equal to arg are available.

    Either the OPEN_MAX value or the per-process soft descriptor limit is checked.

  • EOVERFLOW– One of the values to be returned cannot be represented correctly.

    The request argument is F_GETLK, F_SETLK, or F_SETLKW and the smallest or, if l_len is nonzero, the largest offset of any byte in the requested segment cannot be represented correctly in an object of type off_t.

  • EINTR– The request argument is F_SETLKW, and the function was interrupted by a signal.

  • ENOLCK– The request argument is F_SETLK or F_SETLKW, and satisfying the lock or unlock request would exceed the configurable system limit of NLOCK_RECORD.

  • ENOMEM– The system was unable to allocate memory for the requested file descriptor.

Example

The following code sample shows how to set the close-on-exec flag using the fcntl function:
#include <unistd.h>
#include <fcntl.h>
...
    int flags;


    flags = fcntl(fd, F_GETFD);
    if (flags == -1)
        /* Handle error */;
    flags |= FD_CLOEXEC;
    if (fcntl(fd, F_SETFD, flags) == -1)
        /* Handle error */;"

fcvt

fcvt — Converts its argument to a null-terminated string of ASCII digits and returns the address of the string. The string is stored in a thread-specific location created by the C RTL.

Format

#include <stdlib.h>
char *fcvt (double value, int ndigits, int *decpt, int *sign);

Arguments

value

An object of type double that is converted to a null-terminated string of ASCII digits.

ndigits

The number of ASCII digits after the decimal point to be used in the converted string.

decpt

The position of the decimal point relative to the first character in the returned string. The returned string does not contain the actual decimal point. A negative int value means that the decimal point is decpt number of spaces to the left of the returned digits (the spaces are filled with zeros). A 0 value means that the decimal point is immediately to the left of the first digit in the returned string.

sign

An integer value that indicates whether the value argument is positive or negative. If value is negative, the fcvt function places a nonzero value at the address specified by sign. Otherwise, the functions assign 0 to the address specified by sign.

Description

The fcvt function converts value to a null-terminated string and returns a pointer to it. The resulting low-order digit is rounded to the correct digit for outputting ndigits digits in C F-format. The decpt argument is assigned the position of the decimal point relative to the first character in the string.

In C F-format, ndigits is the number of digits desired after the decimal point. Very large numbers produce a very long string of digits before the decimal point, and ndigit of digits after the decimal point. For large numbers, it is preferable to use the gcvt or ecvt function so that E-format is used.

Repeated calls to the fcvt function overwrite any existing string.

The ecvt, fcvt, and gcvt functions represent the following special values specified in the IEEE Standard for floating-point arithmetic:

Value

Representation

Quiet NaN

NaNQ

Signalling NaN

NaNS

+Infinity

Infinity

-Infinity

-Infinity

The sign associated with each of these values is stored into the sign argument. In IEEE floating-point representation, a value of 0 (zero) can be positive or negative, as set by the sign argument.

See also gcvt and ecvt.

Return Value

x

A pointer to the converted string.

fdim

fdim — Determines the positive difference between its arguments.

Format

#include <math.h>
double fdim (double x, double y);
float fdimf (float x, float y);
long double fdiml (long double x, long double y);

Argument

x

A real value.

y

A real value.

Description

The fdim functions determine the positive difference between their arguments. If x is greater than y, x - y is returned. If x is less than or equal to y, +0 is returned.

Return Values

n

Upon success, the positive difference value.

HUGE_VAL

If x - y is positive and overflows; errno is set to ERANGE.

0

If x - y is positive and underflows; errno is set to ERANGE.

NaN

x or y is NaN; errno is set to EDOM.

fdopen

fdopen — Associates a file pointer with a file descriptor returned by an open, creat, dup, dup2, or pipe function.

Format

#include <stdio.h>
FILE *fdopen (int file_desc, char *a_mode);

Arguments

file_desc

The file descriptor returned by open, creat, dup, dup2, or pipe.

a_mode

The access mode indicator. See the fopen function for a description. Note that the access mode specified must agree with the mode used to originally open the file. This includes binary/text access mode ("b" mode on fdopen and the "ctx=bin" option on creat or open).

Description

The fdopen function allows you to access a file, originally opened by one of the UNIX I/O functions, with Standard I/O functions. Ordinarily, a file can be accessed by either a file descriptor or by a file pointer, but not both, depending on the way you open it. For more information, see Chapters 1 and 2.

Return Values

pointer

Indicates that the operation has succeeded.

NULL

Indicates that an error has occurred.

feof

feof — Tests a file to see if the end-of-file has been reached.

Format

#include <stdio.h>
int feof (FILE *file_ptr);

Argument

file_ptr

A file pointer.

Return Values

nonzero integer

Indicates that the end-of-file has been reached.

0

Indicates that the end-of-file has not been reached.

feof_unlocked

feof_unlocked — Same as feof, except used only within a scope protected by flockfile and funlockfile.

Format

#include <stdio.h>
int feof_unlocked (FILE *file_ptr);

Argument

file_ptr

A file pointer.

Description

The reentrant version of the feof function is locked against multiple threads calling it simultaneously. This incurs overhead to ensure integrity of the stream. The unlocked version of this call, feof_unlocked can be used to avoid the overhead. The feof_unlocked function is functionally identical to the feof function, except that it is not required to be implemented in a thread-safe manner. The feof_unlocked function can be safely used only within a scope that is protected by the flockfile and funlockfile functions used as a pair. The caller must ensure that the stream is locked before feof_unlocked is used.

See also flockfile, ftrylockfile, and funlockfile.

Return Values

nonzero integer

Indicates end-of-file has been reached.

0

Indicates end-of-file has not been reached.

ferror

ferror — Returns a nonzero integer if an error occurred while reading or writing a file.

Format

#include <stdio.h>
int ferror (FILE *file_ptr);

Argument

file_ptr

A file pointer.

Description

A call to ferror continues to return a nonzero integer until the file is closed or until clearerr is called.

Return Values

0

Indicates success.

nonzero integer

Indicates that an error has occurred.

ferror_unlocked

ferror_unlocked — Same as ferror, except used only within a scope protected by flockfile and funlockfile.

Format

#include <stdio.h>
int ferror_unlocked (FILE *file_ptr);

Argument

file_ptr

A file pointer.

Description

The reentrant version of the ferror function is locked against multiple threads calling it simultaneously. This incurs overhead to ensure integrity of the stream. The unlocked version of this call, ferror_unlocked can be used to avoid the overhead. The ferror_unlocked function is functionally identical to the ferror function, except that it is not required to be implemented in a thread-safe manner. The ferror_unlocked function can be safely used only within a scope that is protected by the flockfile and funlockfile functions used as a pair. The caller must ensure that the stream is locked before ferror_unlocked is used.

See also flockfile, ftrylockfile, and funlockfile.

Return Values

0

Indicates success.

nonzero integer

Indicates that an error has occurred.

fflush

fflush — Writes out any buffered information for the specified file.

Format

#include <stdio.h>
int fflush (FILE *file_ptr);

Argument

file_ptr

A file pointer. If this argument is a NULL pointer, all buffers associated with all currently open files are flushed.

Description

The output files are normally buffered only if they are not directed to a terminal, except for stderr, which is not buffered by default.

The fflush function flushes the C RTL buffers. However, RMS has its own buffers. The fflush function does not guarantee that the file will be written to disk. See the description of fsync for a way to flush buffers to disk.

If the file pointed to by file_ptr was opened in record mode and if there is unwritten data in the buffer, then fflush always generates a record.

Return Values

0

Indicates that the operation is successful.

EOF

Indicates that the buffered data cannot be written to the file, or that the file control block is not associated with an output file.

ffs

ffs — Finds the index of the first bit set in a string.

Format

#include <strings.h>
int ffs (int integer);

Argument

integer

The integer to be examined for the first bit set.

Description

The ffs function finds the first bit set (beginning with the least significant bit) and returns the index of that bit. Bits are numbered starting at 1 (the least significant bit).

Return Values

x

The index of the first bit set.

0

If index is 0.

fgetc

fgetc — Returns the next character from a specified file.

Format

#include <stdio.h>
int fgetc (FILE *file_ptr);

Argument

file_ptr

A pointer to the file to be accessed.

Description

The fgetc function returns the next character from the specified file.

Compiling with the _ _UNIX_PUTC macro defined enables an optimization that uses a faster, inlined version of this function.

See also the fgetc_unlocked function and the getc macro.

Return Values

x

The returned character.

EOF

Indicates the end-of-file or an error.

fgetc_unlocked

fgetc_unlocked — Same as the fgetc function, except used only within a scope protected by flockfile and funlockfile.

Format

#include <stdio.h>
int fgetc_unlocked (FILE *file_ptr);

Argument

file_ptr

A file pointer.

Description

The reentrant version of the fgetc function is locked against multiple threads calling it simultaneously. This incurs overhead to ensure integrity of the stream. The unlocked version of this call, fgetc_unlocked can be used to avoid the overhead. The fgetc_unlocked function is functionally identical to the fgetc function, except that fgetc_unlocked can be safely used only within a scope that is protected by the flockfile and funlockfile functions used as a pair. The caller must ensure that the stream is locked before fgetc_unlocked is used.

Compiling with the _ _UNIX_PUTC macro defined enables an optimization that uses a faster, inlined version of this function.

See also getc_unlocked, flockfile, ftrylockfile, and funlockfile.

Return Values

n

The returned character.

EOF

Indicates the end-of-file or an error.

fgetname

fgetname — Returns the file specification associated with a file pointer.

Format

#include <stdio.h>
char *fgetname (FILE *file_ptr, char *buffer, ...);

Function Variants

The fgetname function has variants named _fgetname32 and _fgetname64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

file_ptr

A file pointer.

buffer

A pointer to a character string that is large enough to hold the file specification.

. . .

An optional additional argument that can be either 1 or 0.If you specify 1, the fgetname function returns the file specification in OpenVMS format. If you specify 0, fgetname returns the file specification in UNIX style format. If you do not specify this argument, fgetname returns the filename according to your current command language interpreter. For more information about UNIX style file specifications, see Section 1.3.3.

Description

The fgetname function places the file specification at the address given in the buffer. The buffer should be an array large enough to contain a fully qualified file specification (the maximum length is 256 characters).

Return Values

n

The address of the buffer.

0

Indicates an error.

Restriction

The fgetname function is specific to the C RTL and is not portable.

fgetpos

fgetpos — Stores the current file position for a given file.

Format

#include <stdio.h>
int fgetpos (FILE *stream, fpos_t *pos);

Arguments

stream

A file pointer.

pos

A pointer to an implementation-defined structure. The fgetpos function fills this structure with information that can be used on subsequent calls to fsetpos.

Description

The fgetpos function stores the current value of the file position indicator for the stream pointed to by stream into the object pointed to by pos.

Return Values

0

Indicates successful completion.

-1

Indicates that there are errors.

Example

#include <stdio.h>
#include <stdlib.h>

main()
{
    FILE *fp;
    int stat,
        i;
    int character;
    char ch,
         c_ptr[130],
         d_ptr[130];
    fpos_t posit;

    /* Open a file for writing.  */

    if ((fp = fopen("file.dat", "w+")) == NULL) {
        perror("open");
        exit(1);
    }

   /* Get the beginning position in the file.  */

    if (fgetpos(fp, &posit) != 0)
        perror("fgetpos");

    /* Write some data to the file. */

    if (fprintf(fp, "this is a test\n") == 0) {
        perror("fprintf");
        exit(1);
    }

    /* Set the file position back to the beginning. */

    if (fsetpos(fp, &posit) != 0)
        perror("fsetpos");

    fgets(c_ptr, 130, fp);
    puts(c_ptr);        /* Should be "this is a test."  */

    /* Close the file. */

    if (fclose(fp) != 0) {
        perror("close");
        exit(1);
    }

}

fgets

fgets — Reads a line from the specified file, up to one less than the specified maximum number of characters or up to and including the new-line character, whichever comes first. The function stores the string in str.

Format

#include <stdio.h>
char *fgets (char *str, int maxchar, FILE *file_ptr);

Function Variants

The fgets function has variants named _fgets32 and _fgets64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

str

A pointer to a character string that is large enough to hold the information fetched from the file.

maxchar

The maximum number of characters to fetch.

file_ptr

A file pointer.

Description

The fgets function terminates the line with a null character (\0). Unlike gets, fgets places the new-line character that terminates the input line into the user buffer if more than maxchar characters have not already been fetched.

When the file pointed to by file_ptr is opened in record mode, fgets treats the end of a record the same as a new-line character, so it reads up to and including a new-line character or to the end of the record.

Return Values

x

Pointer to str.

NULL

Indicates the end-of-file or an error. The contents of str are undefined if a read error occurs.

Example

#include <stdio.h>
#include <stdlib.h>
#include <unixio.h>

main()
{
    FILE *fp;
    char c_ptr[130];

    /* Create a dummy data file  */

    if ((fp = fopen("file.dat", "w+")) == NULL) {
        perror("open");
        exit(1);
    }

    fprintf(fp, "this is a test\n") ;
    fclose(fp) ;

    /* Open a file with some data -"this is a test"   */

    if ((fp = fopen("file.dat", "r+")) == NULL) {
       perror("open error") ;
        exit(1);
    }

    fgets(c_ptr, 130, fp);
    puts(c_ptr);        /* Display what fgets got.  */
    fclose(fp);

    delete("file.dat") ;
}

fgetwc

fgetwc — Reads the next character from a specified file, and converts it to a wide-character code.

Format

#include <wchar.h>
wint_t fgetwc (FILE *file_ptr);

Argument

file_ptr

A pointer to the file to be accessed.

Description

Upon successful completion, the fgetwc function returns the wide-character code read from the file pointed to by file_ptr and converted to type wint_t. If the file is at end-of-file, the end-of-file indicator is set, and WEOF is returned. If an I/O read error occurred, then the error indicator is set, and WEOF is returned.

Applications can use ferror or feof to distinguish between an error condition and an end-of-file condition.

Return Values

x

The wide-character code of the character read.

WEOF
Indicates the end-of-file or an error. If a read error occurs, the function sets errno to one of the following:

  • EALREADY – An operation is already in progress on the same file.

  • EBADF – The file descriptor is not valid.

  • EILSEQ – Invalid character detected.

fgetws

fgetws — Reads a line of wide characters from a specified file.

Format

#include <wchar.h>
wchar_t *fgetws (wchar_t *wstr, int maxchar, FILE *file_ptr);

Function Variants

The fgetws function has variants named _fgetws32 and _fgetws64 for use with 32-bit and64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

wstr

A pointer to a wide-character string large enough to hold the information fetched from the file.

maxchar

The maximum number of wide characters to fetch.

file_ptr

A file pointer.

Description

The fgetws function reads wide characters from the specified file and stores them in the array pointed to by wstr. The function reads up to maxchar-1 characters or until the new-line character is read, converted, and transferred to wstr, or until an end-of-file condition is encountered. The function terminates the line with a null wide character. fgetws places the new-line that terminates the input line into the user buffer, unless maxchar characters have already been fetched.

Return Values

x

Pointer to wstr.

NULL

Indicates the end-of-file or an error. The contents of wstr are undefined if a read error occurs. If a read error occurs, the function sets errno. For a list of possible errno values, see fgetwc.

Example

#include <stdlib.h>
#include <stdio.h>
#include <locale.h>
#include <wchar.h>

main()
{
    wchar_t wstr[80],
           *ret;
    FILE *fp;

    /* Create a dummy data file  */

    if ((fp = fopen("file.dat", "w+")) == NULL) {
        perror("open");
        exit(1);
    }

    fprintf(fp, "this is a test\n") ;
    fclose(fp) ;

   /* Open a test file containing : "this is a test" */

    if ((fp = fopen("file.dat", "r")) == (FILE *) NULL) {
        perror("File open error");
        exit(EXIT_FAILURE);
    }

    ret = fgetws(wstr, 80, fp);
    if (ret == (wchar_t *) NULL) {
        perror("fgetws failure");
        exit(EXIT_FAILURE);
    }

    fputws(wstr, stdout);
    fclose(fp);
    delete("file.dat");
}

fileno

fileno — Returns the file descriptor associated with the specified file pointer.

Format

#include <stdio.h>
int fileno (FILE *file_ptr);

Argument

file_ptr

A file pointer.

Description

If you are using version 5.2 or lower of the C compiler, undefine the fileno macro:
#if defined(fileno)
#undef fileno
#endif

Return Values

x

Integer file descriptor.

-1

Indicates an error.

finite

finite — Returns the integer value 1 (TRUE) when its argument is a finite number, or 0 (FALSE) if not.

Format

#include <math.h>
int finite (double x);
int finitef (float x);
int double finitel (long double x);

Argument

x

A real value.

Description

The finite functions return 1 when -Infinity <x < +Infinity. They return 0 when | x| = Infinity, or x is a NaN.

flockfile

flockfile — Locks a stdio stream.

Format

#include <stdio.h>
void flockfile (FILE *file_ptr);

Argument

file_ptr

A file pointer.

Description

The flockfile function locks a stdio stream so that a thread can have exclusive use of that stream for multiple I/O operations. Use the flockfile function for a thread that wants to ensure that the output of several printf functions, for example, is not garbled by another thread also trying to use printf.

File pointers passed are assumed to be valid; flockfile will perform locking even on invalid file pointers. Also, the funlockfile function will not fail if the calling thread does not own a lock on the file pointer passed.

Matching flockfile and funlockfile calls can be nested. If the stream has been locked recursively, it will remain locked until the last matching funlockfile is called.

All C RTL file-pointer I/O functions lock their file pointers as if calling flockfile and funlockfile.

See also ftrylockfile and funlockfile.

floor

floor — Returns the largest integer less than or equal to the argument.

Format

#include <math.h>
double floor (double x);
float floorf (float x);
long double floorl (long double x);

Argument

x

A real value.

Return Value

n

The largest integer less than or equal to the argument.

fma

fma — Computes (x * y) + z, rounded as one ternary operation.

Format

#include <math.h>
double fma (double x, double y, double z);
float fmaf (float x, float y, float z);
long double fmal (long double x, long double y, long double z);

Argument

x,y,z

Real values.

Description

The fma functions compute (x * y) + z, rounded as one ternary operation: the value is computed as if to infinite precision and rounded once to the result format, according to the rounding mode characterized by the value of FLT_ROUNDS.

Return Values

n

Upon success, ( x * y) + z, rounded as one ternary operation.

NaN

x or y is NaN; errno is set to EDOM.

fmax

fmax — Returns the maximum numeric value of its arguments.

Format

#include <math.h>
double fmax (double x, double y);
float fmaxf (float x, float y);
long double fmaxl (long double x, long doubley);

Argument

x

A real value.

y

A real value.

Description

The fmax functions determine the maximum numeric value of their arguments. NaN arguments are treated as missing data: if one argument is a NaN and the other numeric, then the numeric value is returned.

Return Values

n

Upon success, the maximum numeric value of the arguments. If just one argument is a NaN, the other argument is returned.

NaN

Both x and y are NaNs.

fmin

fmin — Returns the minimum numeric value of its arguments.

Format

#include <math.h>
double fmin (double x, double y);
float fminf (float x, float y);
long double fminl (long double x, long double y);

Argument

x

A real value.

y

A real value.

Description

The fmin functions determine the minimum numeric value of their arguments. NaN arguments are treated as missing data: if one argument is a NaN and the other numeric, then the numeric value is returned.

Return Values

n

Upon success, the minimum numeric value of the arguments. If just one argument is a NaN, the other argument is returned.

NaN

Both x and y are NaNs.

fmod

fmod — Computes the floating-point remainder.

Format

#include <math.h>
double fmod (double x, double y);
float fmodf (float x, float y);
long double fmodl (long double x, long double y);

Arguments

x

A real value.

y

A real value.

Description

The fmod functions return the floating-point remainder of the first argument divided by the second. If the second argument is 0, the function returns 0.

Return Values

x

The value f, which has the same sign as the argument x, such that x == i * y + f for some integer i, where the magnitude of f is less than the magnitude of y.

0

Indicates that y is 0.

fopen

fopen — Opens a file by returning the address of a FILE structure.

Format

#include <stdio.h>
FILE *fopen (const char *file_spec, const char *a_mode); (ANSI C)
FILE *fopen (const char *file_spec, const char *a_mode, ...);
(VSI C Extension)

Arguments

file_spec

A character string containing a valid file specification.

a_mode

The access mode indicator. Use one of the following character strings: "r", "w", "a", "e" "r+ , "w+", "rb", "r+b ", "rb+", "wb", "w+b", "wb+", "ab", "a+b", "ab+", or "a+".

These access modes have the following effects:

  • "r" opens an existing file for reading.

  • "w" creates a new file, if necessary, and opens the file for writing. If the file exists, it creates a new file with the same name and a higher version number.

  • "a" opens the file for append access. An existing file is positioned at the end-of-file, and data is written there. If the file does not exist, the C RTL creates it.

  • "e" opens the file with the O_CLOEXEC flag.

The update access modes allow a file to be opened for both reading and writing. When used with existing files, "r+" and "a+" differ only in the initial positioning within the file. The modes are:

  • "r+" opens an existing file for read update access. It is opened for reading, positioned first at the beginning-of-file, but writing is also allowed.

  • "w+" opens a new file for write update access.

  • "a+" opens a file for append update access. The file is first positioned at the end-of-file (writing). If the file does not exist, the C RTL creates it.

  • "b" means binary access mode. In this case, no conversion of carriage-control information is attempted.

. . .

Optional file attribute arguments. The file attribute arguments are the same as those used in the creat function. For more information, see the creat function.

Description

If a version of the file exists, a new file created with fopen inherits certain attributes from the existing file unless those attributes are specified in the fopen call. The following attributes are inherited:
  • Record format
  • Maximum record size
  • Carriage control
  • File protection

If you specify a directory in the filename and it is a search list that contains an error, VSI C for OpenVMS systems interprets it as a file open error.

The file control block can be freed with the fclose function, or by default on normal program termination.

Return Values

x

File pointer.

NULL
Indicates an error. The constant NULL is defined in the <stdio.h> header file to be the NULL pointer value. The function returns NULL to signal the following errors:

  • File protection violations

  • Attempts to open a nonexistent file for read access

  • Failure to open the specified file

fp_class

fp_class — Determines the class of IEEE floating-point values.

Format

#include <math.h>
int fp_class (double x);
int fp_classf (float x);
int fp_classl (long double x);

Argument

x

An IEEE floating-point number.

Description

The fp_class functions determine the class of the specified IEEE floating-point number, returning a constant from the <fp_class.h> header file. They never cause an exception, even for signaling NaNs (Not-a-Number). These functions implement the recommended class(x) function in the appendix of the IEEE 754-1985 standard for binary floating-point arithmetic. The constants in <fp_class.h> refer to the following classes of values:

FP_SNAN

Signaling NaN (Not-a-Number)

FP_QNAN

Quiet NaN

FP_POS_INF

+Infinity

FP_NEG_INF

-Infinity

FP_POS_NORM

positive normalized

FP_NEG_NORM

negative normalized

FP_POS_DENORM

positive denormalized

FP_NEG_DENORM

negative denormalized

FP_POS_ZERO

+0.0 (positive zero)

FP_NEG_ZERO

-0.0 (negative zero)

Return Value

x

A constant from the <fp_class.h> header file.

fpathconf

fpathconf — Retrieves file implementation characteristics.

Format

#include <unistd.h>
long int fpathconf (int filedes, int name);

Arguments

filedes

An open file descriptor.

name

The configuration attribute to query. If this attribute is not applicable to the file specified by the filesdes argument, fpathconf returns an error.

Description

The fpathconf function allows an application to retrieve the characteristics of operations supported by the file system underlying the file named by the filesdes argument. Read, write, or execute permission of the named file is not required, but you must be able to search all directories in the path leading to the file.

Symbolic values for the name argument are defined in the <unistd.h> header file as follows:

_PC_LINK_MAX

The maximum number of links to the file. If the filedes argument refers to a directory, the value returned applies to the directory itself.

_PC_MAX_CANON

The maximum number of bytes in a canonical input line. This is applicable only to terminal devices.

_PC_MAX_INPUT

The number of types allowed in an input queue. This is applicable only to terminal devices.

_PC_NAME_MAX

Maximum number of bytes in a filename (not including a terminating null). The byte range value is between 13 and 255. This is applicable only to a directory file. The value returned applies to filenames within the directory.

_PC_PATH_MAX

Maximum number of bytes in a pathname (not including a terminating null). The value is never larger than 65,535. This is applicable only to a directory file. The value returned is the maximum length of a relative pathname when the specified directory is the working directory.

_PC_PIPE_BUF

Maximum number of bytes guaranteed to be written atomically. This is applicable only to a FIFO. The value returned applies to the referenced object. If the path argument refers to a directory, the value returned applies to any FIFO that exists or can be created within the directory.

_PC_CHOWN_RESTRICTED

The value returned applies to any files (other than directories) that exist or can be created within the directory. This is applicable only to a directory file.

_PC_NO_TRUNC

Returns 1 if supplying a component name longer than allowed by NAME_MAX causes an error. Returns 0 (zero) if long component names are truncated. This is applicable only to a directory file.

_PC_VDISABLE

This is always 0 (zero); no disabling character is defined. This is applicable only to a terminal device.

Return Values

x

The resultant value for the configuration attribute specified in the name argument.

-1
Indicates an error; errno is set to one of the following values:

  • EINVAL– The name argument specifies an unknown or inapplicable characteristic.

  • EBADF– The filedes argument is not a valid file descriptor.

fpclassify

fpclassify — Classifies the real floating-point type.

Format

#include <math.h>
int fpclassify (real-floating x);

Argument

x

Value to classify.

Description

The fpclassify macro classifies its argument value as NaN, infinite, normal, subnormal, zero, or into another implementation-defined category.

First, an argument represented in a format wider than its semantic type is converted to its semantic type. Then classification is based on the type of the argument.

Return Value

The fpclassify macro returns the value of the number classification macro appropriate to the value of its argument.

fprintf

fprintf — Performs formatted output to a specified file.

Format

#include <stdio.h>
int fprintf (FILE *file_ptr, const char *format_spec, ...);

Arguments

file_ptr

A pointer to the file to which the output is directed.

format_spec

A pointer to a character string that contains the format specification. For more information on format specifications and conversion characters, see Chapter 2.

. . .

Optional expressions whose resultant types correspond to conversion specifications given in the format specification.

If no conversion specifications are given, the output sources can be omitted. Otherwise, the function calls must have exactly as many output sources as there are conversion specifications, and the conversion specifications must match the types of the output sources.

Conversion specifications are matched to output sources in left-to-right order. Any excess output sources are ignored.

Example

An example of a conversion specification follows: 
#include <stdio.h>

main()
{
   int  temp = 4, temp2 = 17;

   fprintf(stdout, "The answers are %d, and %d.", temp, temp2);
}
This example outputs the following to the stdout file: 
The answers are 4, and 17.

For a complete description of the format specification and the output source, see Chapter 2.

Return Values

x

The number of bytes written, excluding the null terminator.

Negative value
Indicates an error. The function sets errno to one of the following:

  • EILSEQ – Invalid character detected.

  • EINVAL – Insufficient arguments.

  • ENOMEM – Not enough memory available for conversion.

  • ERANGE – Floating-point calculations overflow.

  • EVMSERR – Nontranslatable OpenVMS error. vaxc$errno contains the OpenVMS error code. This might indicate that conversion to a numeric value failed because of overflow.

The function can also set errno to the following as a result of errors returned from the I/O subsystem:

  • EBADF – The file descriptor is not valid.

  • EIO – I/O error.

  • ENOSPC – No free space on the device containing the file.

  • ENXIO – Device does not exist.

  • EPIPE – Broken pipe.

  • ESPIPE – Illegal seek in a file opened for append.

  • EVMSERR – Nontranslatable OpenVMS error. vaxc$errno contains the OpenVMS error code. This indicates that an I/O error occurred for which there is no equivalent C error code.

fputc

fputc — Writes a character to a specified file.

Format

#include <stdio.h>
int fputc (int character, FILE *file_ptr);

Arguments

character

An object of type int.

file_ptr

A file pointer.

Description

The fputc function writes a single character to the specified file and returns the character.

Compiling with the _ _UNIX_PUTC macro defined enables an optimization that uses a faster, inlined version of this function.

See also the fputc_unlocked function and the putc macro.

Return Values

x

The character written to the file. Indicates success.

EOF

Indicates an output error.

fputc_unlocked

fputc_unlocked — Same as the fputc function, except used only within a scope protected by flockfile and funlockfile.

Format

#include <stdio.h>
int fputc_unlocked (int character, FILE *file_ptr);

Arguments

character

The character to be written. An object of type int.

file_ptr

A file pointer.

Description

See the putc_unlocked macro.

Compiling with the _ _UNIX_PUTC macro defined enables an optimization that uses a faster, inlined version of this function.

See also flockfile, ftrylockfile, and funlockfile.

Return Values

n

The returned character.

EOF

Indicates the end-of-file or an error.

fputs

fputs — Writes a character string to a file without copying the string's null terminator (\0).

Format

#include <stdio.h>
int fputs (const char *str, FILE *file_ptr);

Arguments

str

A pointer to a character string.

file_ptr

A file pointer.

Description

Unlike puts, the fputs function does not append a new-line character to the output string.

See also puts.

Return Values

Nonnegative value

Indicates success.

EOF

Indicates an error.

fputwc

fputwc — Converts a wide character to its corresponding multibyte value, and writes the result to a specified file.

Format

#include <wchar.h>
wint_t fputwc (wint_t wc, FILE *file_ptr);

Arguments

wc

An object of type wint_t.

file_ptr

A file pointer.

Description

The fputwc function writes a wide character to a file and returns the character.

See also putwc.

Return Values

x

The character written to the file. Indicates success.

WEOF

Indicates an output error. The function sets errno to the following:

  • EILSEQ – Invalid wide-character code detected.

The function can also set errno to the following as a result of errors returned from the I/O subsystem:

  • EBADF – The file descriptor is not valid.

  • EIO – I/O error.

  • ENOSPC – No free space on the device containing the file.

  • ENXIO – Device does not exist.

  • EPIPE – Broken pipe.

  • ESPIPE – Illegal seek in a file opened for append.

  • EVMSERR – Nontranslatable OpenVMS error. vaxc$errno contains the OpenVMS error code. This indicates that an I/O error occurred for which there is no equivalent C error code.

fputws

fputws — Writes a wide-character string to a file without copying the null-terminating character.

Format

#include <wchar.h>
int fputws (const wchar_t *wstr, FILE *file_ptr);

Arguments

wstr

A pointer to a wide-character string.

file_ptr

A file pointer.

Description

The fputws function converts the specified wide-character string to a multibyte character string and writes it to the specified file. The function does not append a terminating null byte corresponding to the null wide-character to the output string.

Return Values

Nonnegative value

Indicates success.

-1

Indicates an error. The function sets errno. For a list of the values, see fputwc.

fread

fread — Reads a specified number of items from the file.

Format

#include <stdio.h>
size_t fread (void *ptr, size_t size_of_item, size_t number_items,
FILE *file_ptr);

Arguments

ptr

A pointer to the location, within memory, where you place the information being read. The type of the object pointed to is determined by the type of the item being read.

size_of_item

The size of the items being read, in bytes.

number_items

The number of items to be read.

file_ptr

A pointer that indicates the file from which the items are to be read.

Description

The type size_t is defined in the header file <stdio.h> as follows: 
typedef unsigned int size_t

The reading begins at the current location in the file. The items read are placed in storage beginning at the location given by the first argument. You must also specify the size of an item, in bytes.

If the file pointed to by file_ptr was opened in record mode, fread will read size_of_item multiplied by number_items bytes from the file. That is, it does not necessarily read number_items records.

Return Values

n

The number of bytes read divided by size_of_item.

0

Indicates the end-of-file or an error.

free

free — Makes available for reallocation the area allocated by a previous calloc, malloc, or realloc call.

Format

#include <stdlib.h>
void free (void *ptr);

Argument

ptr

The address returned by a previous call to malloc, calloc, or realloc. If ptr is a NULL pointer, no action occurs.

Description

The ANSI C standard defines free as not returning a value; therefore, the function prototype for free is declared with a return type of void. However, since a free can fail, and since previous versions of the C RTL have declared free to return an int, the implementation of free does return 0 on success and -1 on failure.

freeifaddrs

freeifaddrs — Frees network interface addresses.

Format

#include <ifaddrs.h>
void freeifaddrs(struct ifaddrs *ifp);

Argument

ifp

A pointer to the linked list of ifaddrs structures to be freed.

Description

The freeifaddrs function frees the dynamically allocated data returned by the getifaddrs function. ifp is the address returned by a previous call to getifaddrs. If ifp is a NULL pointer, no action occurs.

freopen

freopen — Substitutes the file named by a file specification for the open file addressed by a file pointer. The latter file is closed.

Format

#include <stdio.h>
FILE *freopen (const char *file_spec, const char *a_mode,
FILE *file_ptr, ...);

Arguments

file_spec

A pointer to a string that contains a valid OpenVMS or UNIX style file specification. After the function call, the given file pointer is associated with this file.

a_mode

The access mode indicator. See the fopen function for a description.

file_ptr

A file pointer.

. . .

Optional file attribute arguments. The file attribute arguments are the same as those used in the creat function.

Description

The freopen function is typically used to associate one of the predefined names stdin, stdout, or stderr with a file. For more information about these predefined names, see Chapter 2.

Return Values

file_ptr

The file pointer, if freopen is successful.

NULL

Indicates an error.

frexp

frexp — Calculates the fractional and exponent parts of a floating-point value.

Format

#include <math.h>
double frexp (double value, int *eptr);
float frexpf (float value, int *eptr);
long double frexpl (long double value, int *eptr);

Arguments

value

A floating-point number of type double, float, or long double.

eptr

A pointer to an int where frexp places the exponent.

Description

The frexp functions break the floating-point number (value) into a normalized fraction and an integral power of 2, as follows:
value = fraction * (2exp)

The fractional part is returned as the return value. The exponent is placed in the integer variable pointed to by eptr.

Example

#include <math.h>

main ()
{
   double val = 16.0, fraction;
   int exp;

   fraction = frexp(val, &exp);
   printf("fraction = %f\n",fraction);
   printf("exp = %d\n",exp);

}
In this example, 
frexp
converts the value 16 to .5 * 2 5. The example produces the following output: 
fraction = 0.500000
exp = 5

|value| = Infinity or NaN is an invalid argument.

Return Values

x

The fractional part of value.

0

Both parts of the result are 0.

NaN

If value is NaN, NaN is returned, errno is set to EDOM, and the value of * eptr is unspecified.

value

If |value | = Infinity, value is returned, errno is set to EDOM, and the value of * eptr is unspecified.

fscanf

fscanf — Performs formatted input from a specified file, interpreting it according to the format specification.

Format

#include <stdio.h>
int fscanf (FILE *file_ptr, const char *format_spec, ...);

Arguments

file_ptr

A pointer to the file that provides input text.

format_spec

A pointer to a character string that contains the format specification. For more information on conversion characters, see Chapter 2.

. . .

Optional expressions whose results correspond to conversion specifications given in the format specification.

If no conversion specifications are given, you can omit the input pointers. Otherwise, the function calls must have exactly as many input pointers as there are conversion specifications, and the conversion specifications must match the types of the input pointers.

Conversion specifications are matched to input sources in left-to-right order. Excess input pointers, if any, are ignored.

Description

An example of a conversion specification follows:
#include <stdio.h>

main ()
{
   int   temp, temp2;

   fscanf(stdin, "%d %d", &temp, &temp2);
   printf("The answers are %d, and %d.", temp, temp2);
}
Consider a file, designated by stdin, with the following contents:
4 17
The example conversion specification produces the following result:
The answers are 4, and 17.

For a complete description of the format specification and the input pointers, see Chapter 2.

Return Values

x

The number of successfully matched and assigned input items.

EOF

Indicates that the end-of-file was encountered or a read error occurred. If a read error occurs, the function sets errno to one of the following:

  • EILSEQ – Invalid character detected.

  • EVMSERR – Nontranslatable OpenVMS error. vaxc$errno contains the OpenVMS error code. This can indicate that conversion to a numeric value failed due to overflow.

The function can also set errno to the following as a result of errors returned from the I/O subsystem:

  • EBADF – The file descriptor is not valid.

  • EIO – I/O error.

  • ENXIO – Device does not exist.

  • EPIPE – Broken pipe.

  • EVMSERR – Nontranslatable OpenVMS error. vaxc$errno contains the OpenVMS error code. This indicates that an I/O error occurred for which there is no equivalent C error code.

fseek

fseek — Positions the file to the specified byte offset in the file.

Format

#include <stdio.h>
int fseek (FILE *file_ptr, long int offset, int direction);

Arguments

file_ptr

A file pointer.

offset

The offset, specified in bytes.

direction

An integer indicating the position to which the offset is added to calculate the new position. The new position is the beginning of the file if direction is SEEK_SET, the current value of the file position indicator if direction is SEEK_CUR, or end-of-file if direction is SEEK_END.

Description

The fseek function can position a fixed-length record-access file with no carriage control or a stream-access file on any byte offset, but can position all other files only on record boundaries.

The available Standard I/O functions position a variable-length or VFC record file at its first byte, at the end-of-file, or on a record boundary. Therefore, the arguments given to fseek must specify any of the following:

  • The beginning or end of the file

  • A 0 offset from the current position (an arbitrary record boundary)

  • The position returned by a previous, valid ftell call

See the fgetpos and fsetpos functions for a portable way to seek to arbitrary locations with these types of record files.

Caution

If, while accessing a stream file, you seek beyond the end-of-file and then write to the file, the fseek function creates a hole by filling the skipped bytes with zeros.

In general, for record files, fseek should only be directed to an absolute position that was returned by a previous valid call to ftell, or to the beginning or end of a file. If a call to fseek does not satisfy these conditions, the results are unpredictable.

See also open, creat, dup, dup2, and lseek.

Return Values

0

Indicates successful seeks.

-1

Indicates improper seeks.

fseeko

fseeko — Positions the file to the specified byte offset in the file. Equivalent to fseek.

Format

#include <stdio.h>
int fseeko (FILE *file_ptr, off_t offset, int direction);

Arguments

file_ptr

A file pointer.

offset

The offset, specified in bytes. The off_t data type is either a 32-bit or 64-bit integer. The 64-bit interface allows for file sizes greater than 2 GB, and can be selected at compile time by defining the _LARGEFILE feature-test macro as follows:
CC/DEFINE=_LARGEFILE

direction

An integer indicating the position to which the offset is added to calculate the new position. The new position is the beginning of the file if direction is SEEK_SET, the current value of the file position indicator if direction is SEEK_CUR, or end-of-file if direction is SEEK_END.

Description

The fseeko function is identical to the fseek function, except that the offset argument is of type off_t instead of long int.

fsetpos

fsetpos — Sets the file position indicator for a given file.

Format

#include <stdio.h>
int fsetpos (FILE *stream, const fpos_t *pos);

Arguments

stream

A file pointer.

pos

A pointer to an implementation-defined structure. The fgetpos function fills this structure with information that can be used on subsequent calls to fsetpos.

Description

Call the fgetpos function before using the fsetpos function.

Return Values

0

Indicates success.

-1

Indicates an error.

fstat

fstat — Accesses information about the file specified by the file descriptor.

Format

#include <stat.h>
int fstat (int file_desc, struct stat *buffer);

Function Variants

Compiling with the _DECC_V4_SOURCE and _VMS_V6_SOURCE feature-test macros defined enables a local-time-based entry point to the fstat function that is equivalent to the behavior before OpenVMS Version 7.0.

Arguments

file_desc

A file descriptor.

buffer

A pointer to a structure of type stat_t, which is defined in the <stat.h> header file. The argument receives information about that particular file. The members of the structure pointed to by buffer are:

Member

Type

Definition

st_dev

 
dev_t

Pointer to a physical device name

st_ino[3]

 
ino_t

Three words to receive the file ID

st_mode

 
mode_t

File “mode” (prot, dir, …)

st_nlink

 
nlink_t

For UNIX system compatibility only

st_uid

 
uid_t

Owner user ID

st_gid

 
gid_t

Group member: from st_uid

st_rdev

 
dev_t

UNIX system compatibility – always 0

st_size

 
off_t

File size, in bytes. For st_size to report a correct value, you need to flush both the CRTL and RMS buffers.

st_atime

 
time_t

File access time; always the same as st_mtime

st_mtime

 
time_t

Last modification time

st_ctime

 
time_t

File creation time

st_fab_rfm

 
char

Record format

st_fab_rat

 
char

Record attributes

st_fab_fsz

 
char

Fixed header size

st_fab_mrs

 
unsigned

Record size

The types dev_t, ino_t, off_t, mode_t, nlink_t, uid_t, gid_t, and time_t,are defined in the <stat.h> header file. However, when compiling for compatibility (/DEFINE=_DECC_V4_SOURCE), only dev_t, ino_t, and off_t are defined.

The off_t data type is either a 32-bit or 64-bit integer. The 64-bit interface allows for file sizes greater than 2 GB,and can be selected at compile time by defining the _LARGEFILE feature-test macro as follows:
CC/DEFINE=_LARGEFILE

As of OpenVMS Version 7.0, times are given in seconds since the Epoch (00:00:00 GMT, January 1, 1970).

The st_mode structure member is the status information mode and is defined in the <stat.h> header file. The st_mode bits follow:

Bits

Constant

Definition

0170000

S_IFMT

Type of file

0040000

S_IFDIR

Directory

0020000

S_IFCHR

Character special

0060000

S_IFBLK

Block special

0100000

S_IFREG

Regular

0030000

S_IFMPC

Multiplexed char special

0070000

S_IFMPB

Multiplexed block special

0004000

S_ISUID

Set user ID on execution

0002000

S_ISGID

Set group ID on execution

0001000

S_ISVTX

Save swapped text even after use

0000400

S_IREAD

Read permission, owner

0000200

S_IWRITE

Write permission, owner

0000100

S_IEXEC

Execute/search permission, owner

Description

The fstat function does not work on remote network files.

Be aware that for the stat_t structure member st_size to report a correct value, you need to flush both the C RTL and RMS buffers.

Note

(Integrity servers, Alpha) On OpenVMS Alpha and Integrity server systems, the stat, fstat, utime, and utimes functions have been enhanced to take advantage of the new file-system support for POSIX compliant file timestamps.

This support is available only on ODS-5 devices on OpenVMS Alpha and Integrity servers systems beginning with a version of OpenVMS Alpha after Version 7.3.

Before this change, the stat and fstat functions were setting the values of the st_ctime, st_mtime, and st_atime fields based on the following file attributes:
  • st_ctime - ATR$C_CREDATE (file creation time)
  • st_mtime - ATR$C_REVDATE (file revision time)
  • st_atime - was always set to st_mtime because no support for file access time was available

Also, for the file-modification time, utime and utimes were modifying the ATR$C_REVDATE file attribute, and ignoring the file-access-time argument.

After the change, for a file on an ODS-5 device, the stat and fstat functions set the values of the st_ctime, st_mtime, and st_atime fields based on the following new file attributes:
  • st_ctime - ATR$C_ATTDATE (last attribute modification time)
  • st_mtime - ATR$C_MODDATE (last data modification time)
  • st_atime - ATR$C_ACCDATE (last access time)

If ATR$C_ACCDATE is zero, as on an ODS-2 device, the stat and fstat functions set st_atime to st_mtime.

For the file-modification time, the utime and utimes functions modify both the ATR$C_REVDATE and ATR$C_MODDATE file attributes. For the file-access time, these functions modify the ATR$C_ACCDATE file attribute. Setting the ATR$C_MODDATE and ATR$C_ACCDATE file attributes on an ODS-2 device has no effect.

For compatibility, the old behavior of stat, fstat, utime, and utimes remains the default, regardless of the kind of device.

The new behavior must be explicitly enabled at run time by defining the DECC$EFS_FILE_TIMESTAMPS logical name to "ENABLE" before invoking the application. Setting this logical does not affect the behavior of stat, fstat, utime and utimes for files on an ODS-2 device.

Return Values

0

Indicates successful completion.

-1

Indicates an error other than a protection violation.

-2

Indicates a protection violation.

fstatvfs

fstatvfs — Gets information about a device containing the specified file.

Format

#include <statvfs.h>
int fstatvfs (int filedes, struct statvfs *buffer);

Arguments

filedes

File descriptor obtained from a successful open or fcntl function call.

buffer

Pointer to a statvfs structure to hold the returned information.

Description

The fstatvfs function returns descriptive information about the device containing the specified file. Read, write, or execute permission of the specified file is not required. The returned information is in the format of a statvfs structure, which is defined in the <statvfs.h> header file and contains the following members:
  • unsigned long f_bsize - Preferred block size.
  • unsigned long f_frsize - Fundamental block size.
  • fsblkcnt_t f_blocks - Total number of blocks in units of f_frsize.
  • fsblkcnt_t f_bfree - Total number of free blocks. If f_bfree would assume a meaningless value due to the misreporting of free block count by $GETDVI for a DFS disk, then f_bfree is set to the maximum block count.
  • fsblkcnt_t f_bavail - Number of free blocks available. Set to the unused portion of the caller's disk quota.
  • fsfilcnt_t f_files - Total file (inode) count.
  • fsfilcnt_t f_ffree - Free file (inode) count. For OpenVMS systems, this value is calculated as freeblocks/clustersize.
  • fsfilcnt_t f_favail - Free file (inode) count nonprivileged. Set to f_ffree.
  • unsigned long f_fsid - File system identifier. This identifier is based on the allocation-class device name. This gives a unique value based on device, as long as the device is locally mounted.
  • unsigned long f_flag - Bit mask representing one or more of the following flags:

  • ST_RONLY - The volume is read-only.

  • ST_NOSUID - The volume has protected subsystems enabled.


  • unsigned long f_namemax - Maximum length of a filename.
  • char f_basetype[64] - Device-type name.
  • char f_fstr[64] - Logical volume name.
  • char __reserved[64] - Media type name.

Upon successful completion, fstatvfs returns 0 (zero). Otherwise, it returns -1 and sets errno to indicate the error.

See also statvfs.

Return Value

0

Successful completion.

-1
Indicates an error. errno is set to one of the following:

  • EBADF - The file descriptor parameter contains an invalid value.

  • EIO - An I/O error occurred while reading the device.

  • EINTR - A signal was intercepted during execution of the function.

  • EOVERFLOW - One of the values to be returned cannot be represented correctly in the structure pointed to by buffer.

fsync

fsync — Flushes data all the way to the disk.

Format

#include <unistd.h>
int fsync (int fd);

Argument

fd

A file descriptor corresponding to an open file.

Description

The fsync function behaves much like the fflush function. The primary difference between the two is that fsync flushes data all the way to the disk while fflush flushes data only as far as the underlying RMS buffers. Also, with fflush, you can flush all buffers at once; with fsync you cannot.

Return Values

0

Indicates successful completion.

-1

Indicates an error.

ftell

ftell — Returns the current byte offset to the specified stream file.

Format

#include <stdio.h>
long int ftell (FILE *file_ptr);

Argument

file_ptr

A file pointer.

Description

The ftell function measures the byte offset from the beginning of the file.

For variable-length files, VFC files, or any file with carriage-control attributes, if the file is opened in record mode, then ftell returns the starting position of the current record, not the current byte offset.

When using record files, the ftell function ignores any characters that have been pushed back using either ungetc or ungetwc. This behavior does not occur if stream files are being used.

For a portable way to measure the exact offset for any type of file, see the fgetpos function.

Return Values

n

The current offset.

EOF

Indicates an error.

ftello

ftellos — Returns the current byte offset to the specified stream file. This function is equivalent to ftell.

Format

#include <stdio.h>
off_t ftello (FILE *file_ptr);

Argument

file_ptr

A file pointer.

Description

The ftello function is identical to the ftell function, except that the return value is of type off_t instead of long int.

The off_t data type is either a 64-bit or 32-bit integer. The 64-bit interface allows for file sizes greater than 2 GB, and can be selected at compile time by defining the _LARGEFILE feature-test macro as follows:
CC/DEFINE=_LARGEFILE

ftime

ftime — Returns the elapsed time since 00:00:00, January 1, 1970, in the structure pointed at by timeptr.

Format

#include <timeb.h>
int ftime (struct timeb *timeptr);

Function Variants

Compiling with the _DECC_V4_SOURCE and _VMS_V6_SOURCE feature-test macros defined enables a local-time-based entry point to the ftime function that is equivalent to the behavior before OpenVMS Version 7.0.

Argument

timeptr

A pointer to the structure timeb_t.

Description

The typedef timeb_t refers to the following structure defined in the <timeb.h> header file:
typedef struct timeb
   {
      time_t         time;
      unsigned short millitm;
      short          timezone;
      short          dstflag;
   };

The member time gives the time in seconds.

The member millitm gives the fractional time in milliseconds.

After a call to ftime, the timezone and dstflag members of the timeb structure have the values of the global variables timezone and dstflag, respectively. See the description of the tzset function for timezone and dstflag global variables.

Return Values

0

Successful execution. The timeb_t structure is filled in.

-1

Indicates an error. Failure might indicate that the system's time-differential factor (that is, the difference between the system time and UTC time) is not set correctly.

If the value of the SYS$TIMEZONE_DIFFERENTIAL logical is wrong, the function fails with errno set to EINVAL.

ftok

ftok — Generates a standard interprocess communication key that is usable in subsequent calls to semget.

Format

#include <ipc.h>
key_t ftok (const char *path_name, int project_id);

Argument

path_name

the pathname of an existing file that is accessible to the process.

project_id

a value that uniquely identifies a project.

Description

The ftok function returns a key, based on the path_name and project_id parameters, that is usable in subsequent calls to the semget function. The ftok function returns the same key for all paths that name the same file, when called with the same project_id parameter. Different keys are returned for the same file if different project_id parameters are used, or if paths are used that name different files existing on the same file system at the same time. If a file named by path_name is removed and recreated with the same name, the ftok function may return a different key than the original one.

Only the low order 8 bits of project_id are significant. The behavior of ftok is unspecified if these bits are 0.

For maximum portability, project_id must be a single-byte character.

Upon successful completion, the ftok function returns a key. Otherwise, it returns the value (key_t)-1 and sets errno to indicate the error.

Return Values

n

Upon successful completion, the ftok function returns a key.

(key_t) -1
Indicates an error. The function sets errno to:

  • EACCESS– Search permission is denied for a component of the path_name parameter.

ftruncate

ftruncate — Truncates a file to a specified length.

Format

#include <unistd.h>
int ftruncate (int filedes, off_t length);

Arguments

filedes

The descriptor of a file that must be open for writing.

length

The new length of the file, in bytes. The off_t data type is either a 32-bit or 64-bit integer. The 64-bit interface allows for file sizes greater than 2 GB, and can be selected at compile time by defining the _LARGEFILE feature-test macro as follows:
CC/DEFINE=_LARGEFILE

Description

The ftruncate function truncates a file at the specified position. For record files, the position must be a record boundary. Also, the files must be local, regular files.

If the file was previously larger than length, extra data is lost. If the file was previously shorter than length, bytes between the old and new lengths are read as zeros.

Return Values

0

Indicates success.

-1

An error occurred; errno is set to indicate the error.

ftrylockfile

ftrylockfile — Acquires ownership of a stdio (FILE*) object.

Format

#include <stdio.h>
int ftrylockfile (FILE *file_ptr);

Argument

file_ptr

A file pointer.

Description

The ftrylockfile function is used by a thread to acquire ownership of a stdio (FILE*) object, if the object is available. The ftrylockfile function is a non-blocking version of flockfile.

The ftrylockfile function returns zero for success and nonzero to indicate that the lock cannot be acquired.

See also flockfile and funlockfile.

Return Values

0

Indicates success.

nonzero

Indicates the lock cannot be acquired.

ftw

ftw — Walks a file tree.

Format

#include <ftw.h>
int ftw (const char *path, int(*function)(const char *,
const struct stat *, int), int depth);

Arguments

path

The directory hierarchy to be searched.

function

The function to be invoked for each file in the directory hierarchy.

depth

The maximum number of directory streams or file descriptors, or both, available for use by ftw. This argument should be in the range of 1 to OPEN_MAX.

Description

The ftw function recursively searches the directory hierarchy that descends from the directory specified by the path argument. The path argument can be specified in OpenVMS style or UNIX style.

For each file in the hierarchy, ftw calls the function specified by the function argument, passes it a pointer to a null-terminated character string containing the name of the file, a pointer to a stat structure containing information about the file, and an integer.

The integer identifies the file type. Possible values, defined in <ftw.h> are:

FTW_F

Regular file.

FTW_D

Directory.

FTW_DNR

Directory that cannot be read.

FTW_NS

A file on which stat could not successfully be executed.

If the integer is FTW_DNR, then the files and subdirectories contained in that directory are not processed.

If the integer is FTW_NS, then the stat structure contents are meaningless. For example, a file in a directory for which you have read permission but not execute (search) permission can cause the function argument to pass FTW_NS.

The ftw function finishes processing a directory before processing any of its files or subdirectories.

The ftw function continues the search until:

  • The directory hierarchy specified by the path argument is completed.

  • An invocation of the function specified by the function argument returns a nonzero value.

  • An error (such as an I/O error) is detected within the ftw function.

Because the ftw function is recursive, it is possible for it to terminate with a memory fault because of stack overflow when applied to very deep file structures.

The ftw function uses the malloc function to allocate dynamic storage during its operation. If ftw is forcibly terminated, as with a call to longjmp from the function pointed to by the function argument, ftw has no chance to free that storage. It remains allocated.

A safe way to handle interrupts is to store the fact that an interrupt has occurred, and arrange to have the function specified by the function argument return a nonzero value the next time it is called.

Notes

  • The ftw function is reentrant; make sure that the function supplied as argument function is also reentrant.

  • The C RTL supports a standard-compliant definition of the stat structure and associated definitions. To use them, compile your application with the _USE_STD_STAT feature-test macro defined. See the <stat.h> header file on your system for more information.

  • The ftw function supports UNIX style path name specifications. For more information about UNIX style directory specifications, see Section 1.3.3.

See also malloc, longjump, and stat.

Return Values

0

Indicates success.

x

Indicates that the function specified by the function argument stops its search, and returns the value that was returned by the function.

-1

Indicates an error; errno is set to one of the following values:

  • EACCES– Search permission is denied for any component of the path argument or read permission is denied for the path argument.

  • ENAMETOOLONG– The length of the path string exceeds PATH_MAX, or a pathname component is longer than NAME_MAX while [_POSIX_NO_TRUNC] is in effect.

  • ENOENT– The path argument points to the name of a file that does not exist or points to an empty string.

  • ENOMEM– There is insufficient memory for this operation.

Also, if the function pointed to by the function argument encounters an error, errno can be set accordingly.

funlockfile

funlockfile — Unlocks a stdio stream.

Format

#include <stdio.h>
void funlockfile (FILE *file_ptr);

Argument

file_ptr

A file pointer.

Description

The funlockfile function unlocks a stdio stream, causing the thread that had been holding the lock to relinquish exclusive use of the stream.

File pointers passed are assumed to be valid; flockfile will perform locking even on invalid file pointers. Also, the funlockfile function will not fail if the calling thread does not own a lock on the file pointer passed.

Matching flockfile and funlockfile calls can be nested. If the stream has been locked recursively, it will remain locked until the last matching funlockfile is called.

All C RTL file-pointer I/O functions lock their file pointers as if calling flockfile and funlockfile.

See also flockfile and ftrylockfile.

fwait

fwait — Waits for I/O on a specific file to complete.

Format

#include <stdio.h>
int fwait (FILE *fp);

Argument

fp

A file pointer corresponding to an open file.

Description

The fwait function is used primarily to wait for completion of pending asynchronous I/O.

Return Values

0

Indicates successful completion.

-1

Indicates an error.

fwide

fwide — Determines and sets the orientation of a stream.

Format

#include <wchar.h>
int fwide (FILE *stream, int mode);

Arguments

stream

A file pointer.

mode

A value that specifies the desired orientation of the stream.

Description

The fwide function determines the orientation of the stream pointed to by stream and sets the orientation of a nonoriented stream according to the mode argument in the following way:

If the mode argument is:

Then the fwide function:

greater than zero

makes the stream wide-oriented.

less than zero

makes the stream byte-oriented.

zero

does not alter the orientation of the stream.

If the orientation of the stream has already been set, fwide does not alter it. Because no error status is defined for fwide, the calling application should check errno if fwide returns a 0.

Return Values

> 0

After the call, the stream is wide-oriented.

< 0

After the call, the stream is byte-oriented.

0

After the call, the stream has no orientation or a stream argument is invalid; the function sets errno.

fwprintf

fwprintf — Writes output to the stream under control of the wide-character format string.

Format

#include <wchar.h>
int fwprintf (FILE *stream, const wchar_t *format, ...);

Arguments

stream

A file pointer.

format

A pointer to a wide-character string containing the format specifications. For more information about format and conversion specifications and their corresponding arguments, see Chapter 2.

. . .

Optional expressions whose resultant types correspond to conversion specifications given in the format specification.

If no conversion specifications are given, the output sources can be omitted. Otherwise, the function calls must have exactly as many output sources as there are conversion specifications, and the conversion specifications must match the types of the output sources.

Conversion specifications are matched to output sources in left-to-right order. Any excess output sources are ignored.

Description

The fwprintf function writes output to the stream pointed to by stream under control of the wide-character string pointed to by format, which specifies how to convert subsequent arguments to output. If there are insufficient arguments for the format, the behavior is undefined. If the format is exhausted while arguments remain, the excess arguments are evaluated, but are otherwise ignored. The fwprintf function returns when it encounters the end of the format string.

The format argument is composed of zero or more directives that include:

  • Ordinary wide characters (not the percent sign (%))

  • Conversion specifications

Return Values

n

The number of wide characters written.

Negative value

Indicates an error. The function sets errno to one of the following:

  • EILSEQ – Invalid character detected.

  • EINVAL – Insufficient arguments.

  • ENOMEM – Not enough memory available for conversion.

  • ERANGE – Floating-point calculations overflow.

  • EVMSERR – Nontranslatable OpenVMS error. vaxc$errno contains the OpenVMS error code. This might indicate that conversion to a numeric value failed because of overflow.

The function can also set errno to the following as a result of errors returned from the I/O subsystem:

  • EBADF – The file descriptor is not valid.

  • EIO – I/O error.

  • ENOSPC – No free space on the device containing the file.

  • ENXIO – Device does not exist.

  • EPIPE – Broken pipe.

  • ESPIPE – Illegal seek in a file opened for append.

  • EVMSERR – Nontranslatable OpenVMS error. vaxc$errno contains the OpenVMS error code. This indicates that an I/O error occurred for which there is no equivalent C error code.

Example

The following example shows how to print a date and time in the form "Sunday, July 3, 10:02", followed by π to five decimal places:
#include <math.h>
#include <stdio.h>
#include <wchar.h>
/*...*/
wchar_t *weekday, *month; /* pointers to wide-character strings */
int day, hours, min;
fwprintf(stdout, L"%ls, %ls %d, %.2d:%.2d\n",
   weekday, month, day, hour, min);
fwprintf(stdout, L"pi = %.5f\n", 4 * atan(1.0));

fwrite

fwrite — Writes a specified number of items to the file.

Format

#include <stdio.h>
size_t fwrite (const void *ptr, size_t size_of_item, size_t number_items,
FILE *file_ptr);

Arguments

ptr

A pointer to the memory location from which information is being written. The type of the object pointed to is determined by the type of the item being written.

size_of_item

The size, in bytes, of the items being written.

number_items

The number of items to be written.

file_ptr

A file pointer that indicates the file to which the items are being written.

Description

The type size_t is defined in the header file <stdio.h> as follows:
typedef unsigned int size_t

The writing begins at the current location in the file. The items are written from storage beginning at the location given by the first argument. You must also specify the size of an item, in bytes.

If the file pointed to by file_ptr is a record file, the fwrite function outputs at least number_items records, each of length size_of_item.

Return Value

x

The number of items written. The number of records written depends upon the maximum record size of the file.

fwscanf

fwscanf — Reads input from the stream under control of the wide-character format string.

Format

#include <wchar.h>
int fwscanf (FILE *stream, const wchar_t *format, ...);

Arguments

stream

A file pointer.

format

A pointer to a wide-character string containing the format specification. For more information about format and conversion specifications and their corresponding arguments, see Chapter 2.

. . .

Optional expressions whose results correspond to conversion specifications given in the format specification. For more information about format and conversion specifications and their corresponding arguments, see Chapter 2.

If no conversion specifications are given, you can omit the input pointers. Otherwise, the function calls must have exactly as many input pointers as there are conversion specifications, and the conversion specifications must match the types of the input pointers.

Conversion specifications are matched to input sources in left-to-right order. Excess input pointers, if any, are ignored.

Description

The fwscanf function reads input from the stream pointed to by stream under the control of the wide-character string pointed to by format. If there are insufficient arguments for the format, the behavior is undefined. If the format is exhausted while arguments remain, the excess arguments are evaluated, but otherwise ignored.

The format is composed of zero or more directives that include:

  • One or more white-space wide characters.

  • An ordinary wide character (neither a percent (%)) nor a white-space wide character).

  • Conversion specifications.

Each conversion specification is introduced by the wide character %.

If the stream pointed to by the stream argument has no orientation, fwscanf makes the stream wide-oriented.

Return Values

n

The number of input items assigned, sometimes fewer than provided for, or even zero, in the event of an early matching failure.

EOF

Indicates an error; input failure occurs before any conversion.

gcvt

gcvt — Converts its argument to a null-terminated string of ASCII digits and returns the address of the string.

Format

#include <stdlib.h>
char *gcvt (double value, int ndigit, char *buffer);

Function Variants

The gcvt function has variants named _gcvt32 and _gcvt64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

value

An object of type double that is converted to a null-terminated string of ASCII digits.

ndigit

The number of ASCII digits to use in the converted string. If ndigit is less than 6, the value of 6 is used.

buffer

A storage location to hold the converted string.

Description

The gcvt function places the converted string in a buffer and returns the address of the buffer. If possible, gcvt produces ndigit significant digits in F-format, or if not possible, in E-format. Trailing zeros are suppressed.

The ecvt, fcvt, and gcvt functions represent the following special values specified in the IEEE Standard for floating-point arithmetic:

Value

Representation

Quiet NaN

NaNQ

Signalling NaN

NaNS

+Infinity

Infinity

-Infinity

-Infinity

The sign associated with each of these values is stored into the sign argument. In IEEE floating-point representation, a value of 0 (zero) can be positive or negative, as set by the sign argument.

See also fcvt and ecvt.

Return Value

x

The address of the buffer.

getc

getc — Returns the next character from a specified file.

Format

#include <stdio.h>
int getc (FILE *file_ptr);

Argument

file_ptr

A pointer to the file to be accessed.

Description

The getc macro returns the next byte from the input stream specified by the file_ptr parameter and moves the file pointer, if defined, ahead one byte in the input stream.

Since getc is a macro, a file pointer argument with side effects (for example, getc (*f++)) might be evaluated incorrectly. In such a case, use the fgetc function instead. See the fgetc function.

See also getc_unlocked.

Return Values

n

The returned character.

EOF

Indicates the end-of-file or an error.

getc_unlocked

getc_unlocked — Same as getc, except used only within a scope protected by flockfile and funlockfile.

Format

#include <stdio.h>
int getc_unlocked (FILE *file_ptr);

Argument

file_ptr

A file pointer.

Description

The reentrant version of the getc macro is locked against multiple threads calling it simultaneously. This incurs overhead to ensure integrity of the stream. The unlocked version of this call, getc_unlocked can be used to avoid the overhead. The getc_unlocked macro is functionally identical to the getc macro, except that it is not required to be implemented in a thread-safe manner. The getc_unlocked macro can be safely used only within a scope that is protected by the flockfile and funlockfile functions used as a pair. The caller must ensure that the stream is locked before getc_unlocked is used.

Since getc_unlocked is a macro, a file pointer argument with side effects might be evaluated incorrectly. In such a case, use the fgetc_unlocked function instead.

See also flockfile, ftrylockfile, and funlockfile.

Return Values

n

The returned character.

EOF

Indicates the end-of-file or an error.

[w]getch

[w]getch — Get a character from the terminal screen and echo it on the specified window. The getch function echoes the character on the stdscr window.

Format

#include <curses.h>
char getch();
char wgetch (WINDOW *win);

Argument

win

A pointer to the window.

Description

The getch and wgetch functions refresh the specified window before fetching a character. For more information, see the scrollok function.

Return Values

x

The returned character.

ERR

Indicates that the function makes the screen scroll illegally.

getchar

getchar — Reads a single character from the standard input (stdin).

Format

#include <stdio.h>
int getchar (void);

Description

The getchar function is identical to fgetc(stdin).

See also getchar_unlocked.

Return Values

x

The next character from stdin, converted to int.

EOF

Indicates the end-of-file or an error.

getchar_unlocked

getchar_unlocked — Same as getchar, except used only within a scope protected by flockfile and funlockfile.

Format

#include <stdio.h>
int getchar_unlocked (void);

Description

The reentrant version of the getchar function is locked against multiple threads calling it simultaneously. This incurs overhead to ensure integrity of the input stream. The unlocked version of this call, getchar_unlocked can be used to avoid the overhead. The getchar_unlocked function is functionally identical to the getchar function, except that it is not required to be implemented in a thread-safe manner. The getchar_unlocked function can be safely used only within a scope that is protected by the flockfile and funlockfile functions used as a pair. The caller must ensure that the stream is locked before getchar_unlocked is used.

See also flockfile, ftrylockfile, and funlockfile.

Return Values

x

The next character from stdin, converted to int.

EOF

Indicates the end-of-file or an error.

getclock

getclock — Gets the current value of the systemwide clock.

Format

#include <timers.h>
int getclock (int clktyp, struct timespec *tp);

Arguments

clktyp

The type of systemwide clock.

tp

Pointer to a timespec structure space where the current value of the systemwide clock is stored.

Description

The getclock function sets the current value of the clock specified by clktyp into the location pointed to by tp.

The clktyp argument is given as a symbolic constant name, as defined in the <timers.h> header file. Only the TIMEOFDAY symbolic constant, which specifies the normal time-of-day clock to access for systemwide time, is supported.

For the clock specified by TIMEOFDAY, the value returned by this function is the elapsed time since the Epoch. The Epoch is referenced to 00:00:00 UTC (Coordinated Universal Time) 1 Jan 1970.

The getclock function returns a timespec structure, which is defined in the <timers.h> header file as follows:
 struct  timespec {

  unsigned long  tv_sec   /* Elapsed time in seconds since the Epoch*/
  long           tv_nsec  /* Elapsed time as a fraction of a second */
                          /* since the Epoch (in nanoseconds)       */

 };

Return Values

0

Indicates success.

-1
Indicates an error; errno is set to one of the following values:

  • EINVAL– The clktyp argument does not specify a known systemwide clock.

    Or, the value of SYS$TIMEZONE_DIFFERENTIAL logical is wrong.

  • EIO– An error occurred when the systemwide clock specified by the clktyp argument was accessed.

getcwd

getcwd — Returns a pointer to the file specification for the current working directory.

Format

#include <unistd.h>
char *getcwd (char *buffer, size_t size); (ISO POSIX-1)
char *getcwd (char *buffer, unsigned int size, ...); (VSI C Extension)

Function Variants

The getcwd function has variants named _getcwd32 and _getcwd64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

buffer

Pointer to a character string large enough to hold the directory specification.

If buffer is a NULL pointer, getcwd obtains size bytes of space using malloc. In this case, you can use the pointer returned by getcwd as the argument in a subsequent call to free.

size

The length of the directory specification to be returned.

. . .

An optional argument that can be either 1 or 0. If you specify 1, the directory specification is returned in OpenVMS format. If you specify 0, the directory specification (pathname) is returned in UNIX style format. If you omit this argument, getcwd returns the filename according to your current command-language interpreter (CLI). For more information about UNIX style directory specifications, see Section 1.3.3.

Return Values

x

A pointer to the file specification.

NULL

Indicates an error.

get[w]delim

get[w]delim — Read characters from an input stream until the specified delimiter character is encountered.

Format

#include <stdio.h>
ssize_t getdelim (char **lineptr, size_t *n, int delimiter, FILE *stream);
ssize_t getwdelim (wchar_t **lineptr, size_t *n, wint_t delimiter,
FILE *stream);

Function Variants

The getdelim function has variants named _getdelim32 and _getdelim64 for use with 32-bit and 64-bit pointer sizes, respectively.

The getwdelim function has variants named _getwdelim32 and _getwdelim64 for use with 32-bit and 64-bit pointer sizes, respectively.

Arguments

lineptr

A pointer to the initial buffer or to a null pointer.

n

A pointer to the size of the initial buffer.

delimiter

The delimiter character.

stream

Valid input stream.

Description

The getdelim and getwdelim functions work like getline and getwline, respectively, except that a line delimiter other than newline can be specified as the delimiter argument. As with getline and getwline a delimiter character is not added if one was not present in the input before end of file was reached.

Return Value

n

On success, getdelim and getwdelim return the number of characters read, including the delimiter character, but not including the terminating null byte.

getdtablesize

getdtablesize — Gets the total number of file descriptors that a process can have open simultaneously.

Format

#include <unistd.h>
int getdtablesize (void);

Description

The getdtablesize function returns the total number of file descriptors that a process can have open simultaneously. Each process is limited to a fixed number of open file descriptors.

The number of file descriptors that a process can have open is the minimum of the following:

  • C RTL open file limit – 65535 on OpenVMS Alpha and Integrity servers.

  • SYSGEN CHANNELCNT parameter – permanent I/O channel count.

  • Process open file quota FILLM parameter – number of open files that can be opened by a process at one time.

Return Values

x

The number of file descriptors that a process can have open simultaneously.

-1

Indicates an error.

getegid

getegid — With POSIX IDs disabled, this function is equivalent to getgid and returns the group number from the user identification code (UIC). With POSIX IDs enabled, this function returns the effective group ID of the calling process.

Format

#include <unistd.h>
gid_t getegid (void);

Description

The getegid function can be used with POSIX style identifiers (IDs) or with UIC-based identifiers.

POSIX style IDs are supported on OpenVMS Version 7.3-2 and higher.

With POSIX style IDs disabled, the getegid and getgid functions are equivalent and return the group number from the current UIC. For example, if the UIC is [313,031], 313 is the group number.

With POSIX style IDs enabled, getegid returns the effective group ID of the calling process, and getgid returns the real group ID of the calling process. The real group ID is specified at login time. The effective group ID is more transient, and determines additional access permission during execution of a set-group-ID process. It is for such processes that the getgid function is most useful.

The getegid function is always successful; no return value is reserved to indicate an error.

To enable/disable POSIX style IDs, see Section 1.6.

See also geteuid and getuid.

Return Value

x

The effective group ID (POSIX IDs enabled), or the group number from the UIC (POSIX IDs disabled).

getenv

getenv — Searches the environment array for the current process and returns the value associated with a specified environment name.

Format

#include <stdlib.h>
char *getenv (const char *name);

Argument

name

One of the following values:

  • HOME—Your login directory

  • TERM—The type of terminal being used

  • PATH—The default device and directory

  • *.?)

    USER—The name of the user who initiated the process

  • Logical name or command-language interpreter (CLI) symbolic name

  • An environment variable set with setenv or putenv

The case of the specified name is important.

Description

In certain situations, the getenv function attempts to perform a logical name translation on the user-specified argument:

  1. If the argument to getenv does not match any of the environment strings present in your environment array, getenv attempts to translate your argument as a logical name by searching the logical name tables indicated by the LNM$FILE_DEV logical, as is done for file processing.

    getenv first does a case-sensitive lookup. If that fails, it does a case-insensitive lookup. In most instances, logical names are defined in uppercase, but getenv can also find logical names that include lowercase letters.

    getenv does not perform iterative logical name translation.

  2. If the logical name is a search list with multiple equivalence values, the returned value points to the first equivalence value. For example:
    $ DEFINE A B,C
ptr = getenv("A");

    A returns a pointer to " B".

  3. If no logical name exists, getenv attempts to translate the argument string as a CLI symbol. If it succeeds, it returns the translated symbol text. If it fails, the return value is NULL.

    getenv does not perform iterative CLI translation.

If your CLI is the DEC/Shell, the function does not attempt a logical name translation since Shell environment symbols are implemented as DCL symbols.

Notes

  • In OpenVMS Version 7.1, a cache of OpenVMS environment variables (that is, logical names and DCL symbols) was added to the getenv function to avoid the library making repeated calls to translate a logical name or to obtain the value of a DCL symbol. By default, the cache is disabled. If your application does not need to track changes in OpenVMS environment variables that can occur during its execution, the cache can be enabled by enabling the DECC$ENABLE_GETENV_CACHE logical before invoking the application.

  • Do not use the setenv, getenv, and putenv functions to manipulate symbols and logicals. Instead use the OpenVMS library calls lib$set_logical, lib$get_logical, lib$set_symbol, and lib$get_symbol. The * env functions deliberately provide UNIX behavior, and are not a substitute for these OpenVMS runtime library calls.

    OpenVMS DCL symbols, not logical names, are the closest analog to environment variables on UNIX systems. While getenv is a mechanism to retrieve either a logical name or a symbol, it maintains an internal cache of values for use with setenv and subsequent getenv calls. The setenv function does not write or create DCL symbols or OpenVMS logical names.

    This is consistent with UNIX behavior. On UNIX systems, setenv does not change or create any symbols that will be visible in the shell after the program exits.

Return Values

x

Pointer to an array containing the translated symbol. An equivalence name is returned at index zero.

NULL

Indicates that the translation failed.

geteuid

geteuid — With POSIX IDs disabled, this function is equivalent to getuid and returns the member number (in OpenVMS terms) from the user identification code (UIC). With POSIX IDs enabled, this function returns the effective user ID.

Format

#include <unistd.h>
uid_t geteuid (void);

Description

The geteuid function can be used with POSIX style identifiers (IDs) or with UIC-based identifiers.

POSIX style IDs are supported on OpenVMS Version 7.3-2 and higher.

With POSIX style IDs disabled (the default), the geteuid and getuid functions are equivalent and return the member number from the current UIC as follows:

  • For programs compiled with the _VMS_V6_SOURCE feature-test macro or programs that do not include the <unistd.h> header file, the getuid and geteuid functions return the member number of the OpenVMS UIC. For example, if the UIC is [313,31], then the member number, 31, is returned.

  • For programs compiled without the _VMS_V6_SOURCE feature-test macro that do include the <unistd.h> header file, the full UIC is returned in decimal after converting the octal representation to decimal. For example, if the UIC is [313, 31] then 13303833 is returned. (13303833 = 25 + 203 * 65536; Octal 31 = 25 decimal; Octal 313 = 203 decimal.)

With POSIX style IDs enabled, geteuid returns the effective user ID of the calling process, and getuid returns the real user ID of the calling process.

To enable/disable POSIX style IDs, see Section 1.6.

See also getegid and getgid.

Return Value

x

The effective user ID (POSIX IDs enabled), or the member number from the current UIC or the full UIC (POSIX IDs disabled).

getgid

getgid — With POSIX IDs disabled, this function is equivalent to getegid and returns the group number from the user identification code (UIC). With POSIX IDs enabled, this function returns the real group ID.

Format

#include <unistd.h>
gid_t getgid (void);

Description

The getgid function can be used with POSIX style identifiers or with UIC-based identifiers.

POSIX style IDs are supported on OpenVMS Version 7.3-2 and higher.

With POSIX style IDs disabled (the default), the getegid and getgid functions are equivalent and return the group number from the current UIC. For example, if the UIC is [313,031], 313 is the group number.

With POSIX style IDs enabled, getegid returns the effective group ID of the calling process, and getgid returns the real group ID of the calling process. The real group ID is specified at login time. The effective group ID is more transient, and determines additional access permission during execution of a set-group-ID process. It is for such processes that the getgid function is most useful.

To enable/disable POSIX style IDs, see Section 1.6.

See also geteuid and getuid.

Return Value

x

The real group ID (POSIX IDs enabled), or the group number from the current UIC (POSIX IDs disabled).

getgrent

getgrent — Gets a group database entry.

Format

#include <grp.h>
struct group *getgrent (void);

Description

The getgrent function returns the next group in the sequential search, returning a pointer to a structure containing the broken-out fields of an entry in the group database.

When first called, getgrent returns a pointer to a group structure containing the first entry in the group database. Thereafter, it returns a pointer to the next group structure in the group database, so successive calls can be used to search the entire database.

If an end-of-file or an error is encountered on reading, getgrent returns a NULL pointer and sets errno.

Return Values

x

Pointer to a group structure, if successful.

NULL
Indicates that an error occurred. The function sets errno to one of the following values:

  • EACCES– The user process does not have appropriate privileges enabled to access the user authorization file.

  • EINTR– A signal was intercepted during the operation.

  • EIO– Indicates that an I/O error occurred.

  • EMFILE– OPEN_MAX file descriptors are currently open in the calling process.

  • ENFILE– The maximum allowable number of files is currently open in the system.

getgrent_r

getgrent_r — Gets a group database entry (reentrant).

Format

#include <grp.h>
int getgrent_r(struct group *grp, char *buffer, size_t bufsize,
struct group **result);

Function Variant

The getgrent_r function has a variant named __getgrent_r64 for use with 64-bit pointers. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

grp

The storage area to hold the retrieved group structure.

buffer

A pointer to a temporary buffer that the function can use during the operation to store the longest group entry in the database.

bufsize

The length of the temporary buffer (in characters).

result

A pointer to the retrieved group structure.

Description

The getgrent_r function is the reentrant version of getgrent. The getgrent_r function returns a pointer to a structure containing the broken-out fields of a record in the group database.

When first called, getgrent_r returns a pointer to a group structure containing the first entry in the group database. Thereafter, it returns a pointer to the next group structure in the group database, so successive calls can be used to search the entire database.

It updates the group structure pointed to by grp and stores a pointer to that structure at the location pointed to by result. Storage referenced by the group structure is allocated from the memory provided with the buffer argument, which is bufsize characters in size. The maximum size needed for this buffer can be determined with the _SC_GETGR_R_SIZE_MAX parameter of the sysconf function.

If the requested entry is not found or an error is encountered, a NULL pointer is returned at the location pointed to by result.

Return Values

0

On success, result is a pointer to the struct group.

x

On error, the function returns an error value, and result is NULL.

getgrgid

getgrgid — Gets a group database entry for a group ID.

Format

#include <types.h>
#include <grp.h>
struct group *getgrgid (gid_t gid);

Argument

gid

The group ID of the group for which the group database entry is to be retrieved.

Description

The getgrgid function searches the group database for an entry with a matching gid and returns a pointer to the group structure containing the matching entry.

Return Values

x

Pointer to a valid group structure containing a matching entry.

NULL

An error occurred.

Note: The return value points to a static area that is overwritten by subsequent calls to getgrent, getgrgid, or getgrnam.

On error, the function sets errno to one of the following values:

  • EACCES– The user process does not have appropriate privileges enabled to access the user authorization file.

  • EIO – An I/O error has occurred.

  • EINTR– A signal was intercepted during getgrgid.

  • EMFILE– OPEN_MAX file descriptors are currently open in the calling process.

  • ENFILE– The maximum allowable number of files is currently open in the system.

Applications checking for error situations must set errno to 0 before calling getgrgid. If errno is set on return, an error has occurred.

getgrgid_r

getgrgid_r — Gets a group database entry for a group ID.

Format

#include <types.h>
#include <grp.h>
int getgrgid_r (gid_t gid, struct group *grp, char *buffer, size_t bufsize,
struct group **result);

Arguments

gid

The group ID of the group for which the group database entry is to be retrieved.

grp

The storage area to hold the retrieved group structure.

buffer

The working buffer that is able to hold the longest group entry in the database.

bufsize

The length, in characters, of buffer.

result

Upon successful return, result points to the retrieved group structure.

Upon unsuccessful return, result is set to NULL.

Description

The getgrgid_r function updates the group structure pointed to by grp and stores a pointer to that structure at the location pointed to by result. The structure contains an entry from the group database with a matching gid. Storage referenced by the group structure is allocated from the memory provided with the buffer argument, which is bufsize characters in size. The maximum size needed for this buffer can be determined with the _SC_GETGR_R_SIZE_MAX parameter of the sysconf function. On error or if the requested entry is not found, a NULL pointer is returned at the location pointed to by result.

Return Values

0

Successful completion.

x
On error, the function sets the return value to one of the following:

  • EACCES– The user process does not have appropriate privileges enabled to access theuser authorization file.

  • EIO – An I/O error has occurred.

  • EINTR– A signal was intercepted during getgrgid.

  • EMFILE– OPEN_MAX file descriptors are currently open in the calling process.

  • ENFILE– The maximum allowable number of files is currently open in the system.

  • ERANGE– Insufficient storage was supplied through the buffer and bufsize arguments to contain the data to be referenced by the resulting group structure.

getgrnam

getgrnam — Gets a group database entry for a name.

Format

#include <types.h>
#include <grp.h>
struct group *getgrnam (const char *name);

Argument

name

The group name of the group for which the group database entry is to be retrieved.

Description

The getgrnam function searches the group database for an entry with a matching name, and returns a pointer to the group structure containing the matching entry.

Return Values

x

Pointer to a valid group structure containing a matching entry.

NULL

Indicates an error.

Note: The return value points to a static area which is overwritten by subsequent calls to getgrent, getgrgid, or getgrnam.

On error, the function sets the return value to one of the following:

  • EACCES– The user process does not have appropriate privileges enabled to access theuser authorization file.

  • EIO – An I/O error has occurred.

  • EINTR– A signal was intercepted during getgrnam.

  • EMFILE– OPEN_MAX file descriptors are currently open in the calling process.

  • ENFILE– The maximum allowable number of files is currently open in the system.

Applications wishing to check for error situations should set errno to 0 before calling getgrnam. If errno is set on return, an error occurred.

getgrnam_r

getgrnam_r — Gets a group database entry for a name.

Format

#include <types.h>
#include <grp.h>
int getgrnam_r (const char *name, struct group *grp, char *buffer,
size_t bufsize, struct group **result);

Arguments

name

The group name of the group for which the group database entry is to be retrieved.

grp

The storage area to hold the retrieved group structure.

buffer

The working buffer that is able to hold the longest group entry in the database.

bufsize

The length, in characters, of buffer.

result

Upon successful return, result points to the retrieved group structure.

Upon unsuccessful return, result is set to NULL.

Description

The getgrnam_r function updates the group structure pointed to by grp and stores a pointer to that structure at the location pointed to by result. The structure contains an entry from the group database with a matching name. Storage referenced by the group structure is allocated from the memory provided with the buffer argument, which is bufsize characters in size. The maximum size needed for this buffer can be determined with the _SC_GETGR_R_SIZE_MAX parameter of the sysconf function. On error or if the requested entry is not found, a NULL pointer is returned at the location pointed to by result.

Return Values

0

Successful completion.

x
On error, the function sets the return value to one of the following:

  • EACCES– The user process does not have appropriate privileges enabled to access the user authorization file.

  • EIO – An I/O error has occurred.

  • EINTR– A signal was intercepted during getgrnam.

  • EMFILE– OPEN_MAX file descriptors are currently open in the calling process.

  • ENFILE– The maximum allowable number of files is currently open in the system.

  • ERANGE– Insufficient storage was supplied through the buffer and bufsize arguments to contain the data to be referenced by the resulting group structure.

getgroups

getgroups — Gets the current supplementary group IDs of the calling process.

Format

#include <unistd.h>
int getgroups (int gidsetsize, gid_t grouplist[]);

Arguments

gidsetsize

Indicates the number of entries that can be stored in the array pointed to by the grouplist parameter.

grouplist

Points to the array in which the supplementary group IDs of the process are stored. The effective group ID of the process is not returned by the getgroups function if it is not also a supplementary group ID of the calling process.

Description

The getgroups function gets the current supplementary group IDs of the calling process. The list is stored in the array pointed to by the grouplist parameter. The gidsetsize parameter indicates the number of entries that can be stored in this array.

The getgroups function never returns more IDs than the value indicated by the sysconf parameter _SC_NGROUPS_MAX.

See also getgid and setsid.

Return Value

n

The number of elements stored in the array pointed to by the grouplist parameter.

-1
Indicates failure. errno might be set to one of the following values:

  • EFAULT– The gidsetsize and grouplist parameters specify an array that is partially or completely outside of the allocated address space of the process.

  • EINVAL– The gidsetsize parameter is nonzero and smaller than the number of supplementary group IDs.

getifaddrs

getifaddrs — Gets interface addresses.

Format

#include <sys/socket.h>
#include <ifaddrs.h>
int getifaddrs(struct ifaddrs **ifap);

Function Variants

The getifaddrs function has variants named _getifaddrs32 and _getifaddrs64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

ifap

The address of a location where the function can store a pointer to a linked list of ifaddrs structures that contain the data related to the network interfaces on the local machine.

Description

The getifaddrs function creates a linked list of structures describing the network interfaces, one for each network interface on the host machine. The getifaddrs function stores a reference to a linked list of the network interfaces on the local machine in the memory referenced by ifap. The list consists of ifaddrs structures, as defined in the include file <ifaddrs.h>. The ifaddrs structure contains the following entries:
     struct    ifaddrs  *ifa_next;       /* Pointer to next struct */
     char               *ifa_name;       /* Interface name */
     u_int               ifa_flags;      /* Interface flags */
     struct    sockaddr *ifa_addr;       /* Interface address */
     struct    sockaddr *ifa_netmask;    /* Interface netmask */
     struct    sockaddr *ifa_broadaddr;  /* Interface broadcast address */
     struct    sockaddr *ifa_dstaddr;    /* P2P interface destination */
     void               *ifa_data;       /* unused */

The data returned by getifaddrs is dynamically allocated and should be freed using freeifaddrs when no longer needed.

Return Values

0

Successful completion.

-1

Indicates an error. errno contains the error.

getitimer

getitimer — Returns the value of interval timers.

Format

#include <time.h>
int getitimer (int which, struct itimerval *value);

Arguments

which

The type of interval timer. The C RTL supports only ITIMER_REAL.

value

Pointer to an itimerval structure whose members specify a timer interval and the time left to the end of the interval.

Description

The getitimer function returns the current value for the timer specified by the which argument in the structure pointed to by value.

A timer value is defined by the itimerval structure:
       struct itimerval {
               struct  timeval it_interval;
               struct  timeval it_value;
       };
The following table lists the values for the itimerval structure members:

itimerval Member Value

Meaning

it_interval = 0

Disables a timer after its next expiration and assumes it_value is nonzero.

it_interval = nonzero

Specifies a value used in reloading it_value when the timer expires.

it_value = 0

Disables a timer.

it_value = nonzero

Indicates the time to the next timer expiration.

Time values smaller than the resolution of the system clock are rounded up to this resolution.

The C RTL provides each process with one interval timer, defined in the <time.h> header file as ITIMER_REAL. This timer decrements in real time and delivers a SIGALRM signal when the timer expires.

Return Values

0

Indicates success.

-1

Indicates an error; errno is set to EINVAL (The value argument specified a time that was too large to handle.)

get[w]line

get[w]line — Read characters from an input stream.

Format

#include <stdio.h>
ssize_t getline (char **lineptr, size_t *n, FILE *stream);
ssize_t getwline (wchar_t **lineptr, size_t *n, FILE *stream);

Function Variants

The getline function has variants named _getline32 and _getline64 for use with 32-bit and 64-bit pointer sizes, respectively.

The getwline function has variants named _getwline32 and _getwline64 for use with 32-bit and 64-bit pointer sizes, respectively.

Arguments

lineptr

A pointer to the initial buffer or to a null pointer.

n

A pointer to the size of the initial buffer.

stream

Valid input stream.

Description

The getline and getwline read an entire line from stream, storing the address of the buffer, which contains the text into *lineptr. The buffer is null-terminated and includes the newline characterqa if one was found.

If *lineptr is NULL, then getline will allocate a buffer for storing the line, which should be freed by the user program. (In this case, the value in n is ignored.)

Alternatively, before calling getline, *lineptr can contain a pointer to a malloc allocated buffer n bytes in size. If the buffer is not large enough to hold the line, getline resizes it with realloc, updating *lineptr and n as necessary.

Return Value

n

On success, getline and getwline return the number of characters read, including the delimiter character, but not including the terminating null byte.

getlogin

getlogin — Gets the login name.

Format

#include <unistd.h>
char *getlogin (void);
int *getlogin_r (char *name, size_t namesize);

Description

The getlogin function returns the login name of the user associated with the current session. If getlogin returns a non-null pointer, then that pointer points to the name that the user logged in under, even if there are several login names with the same user ID.

The getlogin_r function is the reentrant version of getlogin. Upon successful completion, getlogin_r returns 0 and puts the name associated by the login activity with the controlling terminal of the current process in the character array pointed to by name. The array is namesize characters long and should have space for the name and the terminating null character. The maximum size of the login name is LOGIN_NAME_MAX.

If getlogin_r is successful, name points to the name the user used at login, even if there are several login names with the same user ID.

Return Values

x

Upon successful completion, getlogin returns a pointer to a null-terminated string in a static buffer.

0

Indicates successful completion of getlogin_r.

NULL

Indicates an error; errno is set.

getname

getname — Returns the file specification associated with a file descriptor.

Format

#include <unixio.h>
char *getname (int file_desc, char *buffer, ...);

Function Variants

The getname function has variants named _getname32 and _getname64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

file_desc

A file descriptor.

buffer

A pointer to a character string that is large enough to hold the file specification.

. . .

An optional argument that can be either 1 or 0. If you specify 1, the getname function returns the file specification in OpenVMS format. If you specify 0, the getname function returns the file specification in UNIX style format. If you omit this argument, the getname function returns the filename according to your current command-language interpreter (CLI). For more information about UNIX style file specifications, see Section 1.3.3.

Description

The getname function places the file specification into the area pointed to by buffer and returns that address. The area pointed to by buffer should be an array large enough to contain a fully qualified file specification (the maximum length is 256 characters).

Return Values

x

The address passed in the buffer argument.

0

Indicates an error.

getopt

getopt — A command-line parser that can be used by applications that follow UNIX command-line conventions.

Format

#include <unistd.h> (X/Open, POSIX-1)
#include <stdio.h> (X/Open, POSIX-2)
int getopt (int argc, char * const argv[], const char *optstring);
extern char *optarg;
extern int optind, opterr, optopt;

Arguments

argc

The argument count as passed to main.

argv

The argument array as passed to main.

optstring

A string of recognized option characters. If a character is followed by a colon, the option takes an argument.

Description

The variable optind is the index of the next element of the argv vector to be processed. It is initialized to 1 by the system, and it is updated by getopt when it finishes with each element of argv. When an element of argv contains multiple option characters, it is unspecified how getopt determines which options have already been processed.

The getopt function returns the next option character (if one is found) from argv that matches a character in optstring, if there is one that matches. If the option takes an argument, getopt sets the variable optarg to point to the option-argument as follows:

  • If the option was the last character in the string pointed to by an element of argv, then optarg contains the next element of argv, and optind is incremented by 2. If the resulting value of optind is not less than argc, getopt returns an error, indicating a missing option-argument.

  • Otherwise, optarg points to the string following the option character in that element of argv, and optind is incremented by 1.

If one of the following is true, getopt returns -1 without changing optind:
  • argv[optind] is a NULL pointer
  • * argv[optind] is not the character –
  • argv[optind] points to the string "–"

If argv[optind] points to the string "– –" getopt returns -1 after incrementing optind.

If getopt encounters an option character not contained in optstring, the question-mark character (?) is returned.

If getopt detects a missing argument, the colon character (:) is returned if the first character of optstring is a colon; otherwise, a question-mark character is returned.

In either of the previous two cases, getopt sets the variable optopt to the option character that caused the error. If the application has not set the variable opterr to 0 and the first character of optstring is not a colon, getopt also prints a diagnostic message to stderr.

Return Values

x

The next option character specified on the command line.

A colon is returned if getopt detects a missing argument and the first character of optstring is a colon.

A question mark is returned if getopt encounters an option character not in optstring or detects a missing argument and the first character of optstring is not a colon.

-1

When all command-line options are parsed.

Example

The following example shows how you might process the arguments for a utility that can take the mutually exclusive options a and b and the options f and o, both of which require arguments:
#include <unistd.h>

int main (int argc, char *argv[ ])
{
         int c;
         int bflg, aflg, errflg;
         char *ifile;
         char *ofile;
         extern char *optarg;
         extern int optind, optopt;
         .
         .
         .
         while ((c = getopt(argc, argv, ":abf:o:)) != -1) {

                switch (c) {
                case 'a':
                        if (bflg)
                                errflg++;
                        else
                                aflg++;
                        break;
                case 'b':
                        if (aflg)
                               errflg++;
                        else {
                               bflg++;
                               bproc();
                        }

                        break;
                case 'f':
                        ifile = optarg;
                        break;
                case 'o':
                        ofile = optarg;
                        break;
                case ':':      /* -f or -o without operand */
                        fprintf (stderr,
                         "Option -%c requires an operand\n"' optopt);
                        errflg++;
                        break;
                case '?':
                        fprintf (stderr,
                                "Unrecognized option -%c\n"' optopt);
                        errflg++;
                }
         }
         if (errflg) {
                fprintf (stderr, "usage: ...");
                exit(2);
         }
         for ( ; optind < argc; optind++)  {
                if (access(argv[optind], R_OK)) {
         .
         .
         .
}
This sample code accepts any of the following as equivalent:
cmd -ao arg path path
cmd -a -o arg path path
cmd -o arg -a path path
cmd -a -o arg – path path
cmd -a -oarg path path
cmd -aoarg path path

getpagesize

getpagesize — Gets the system page size.

Format

#include <unistd.h>
int getpagesize (void);

Description

The getpagesize function returns the number of bytes in a page. The system page size is useful for specifying arguments to memory management system calls.

The page size is a system page size and is not necessarily the same as the underlying hardware page size.

Return Value

x

Always indicates success. Returns the number of bytes in a page.

getpgid

getpgid — Gets the process group ID for a process.

Format

#include <unistd.h>
pid_t getpgid (pid_t pid);

Argument

pid

The process ID for which the group ID is being requested.

Description

The getpgid function returns the process group ID of the process specified by pid. If pid is 0, the getpgid function returns the process group ID of the calling process.

This function requires that long (32-bit) UID/GID support be enabled. See Section 1.4.8 for more information.

Return Values

x

The process group ID of the session leader of the specified process.

(pid_t ) -1
Indicates an error. The function sets errno to one of the following values:

  • EPERM – The process specified by pid is not in the same session as the calling process, and the implementation does not allow access to the process group ID of that process from the calling process.

  • ESRCH– There is no process with a process ID of pid.

  • EINVAL– The value of pid is invalid.

getpgrp

getpgrp — Gets the process group ID of the calling process.

Format

#include <unistd.h>
pid_t getpgrp (void);

Description

The getpgrp function returns the process group ID of the calling process.

The getpgrp function is always successful, and no return value is reserved to indicate an error.

This function requires that long (32-bit) UID/GID support be enabled. See Section 1.4.8 for more information.

Return Values

x

The process group ID of the calling process.

getpid

getpid — Returns the process ID of the current process.

Format

#include <unistd.h>
pid_t getpid (void);

Return Value

x

The process ID of the current process.

getppid

getppid — Returns the parent process ID of the calling process.

Format

#include <unistd.h>
pid_t getppid (void);

Return Values

x

The parent process ID.

0

Indicates that the calling process does not have a parent process.

getpwent

getpwent — Accesses user entry information in the user database, returning a pointer to a passwd structure.

Format

#include <pwd.h>
struct passwd *getpwent (void);

Function Variants

The getpwent function has variants named __32_getpwent and __64_getpwent for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Description

The getpwent function returns a pointer to a structure containing fields whose values are derived from an entry in the user database. Entries in the database are accessed sequentially by getpwent. When first called, getpwent returns a pointer to a passwd structure containing the first entry in the user database. Thereafter, it returns a pointer to a passwd structure containing the next entry in the user database. Successive calls can be used to search the entire user database.

The passwd structure is defined in the <pwd.h> header file as follows:

pw_name

The name of the user.

pw_uid

The ID of the user.

pw_gid

The group ID of the principle group of the user.

pw_dir

The home directory of the user.

pw_shell

The initial program for the user.

If an end-of-file or an error is encountered on reading, getpwent returns a NULL pointer.

Because getpwent accesses the user authorization file (SYSUAF) directly, the process must have appropriate privileges enabled or the function will fail.

Notes

All information generated by the getpwent function is stored in a per-thread static area and is overwritten on subsequent calls to the function.

Password file entries that are too long are ignored.

Return Values

x

Pointer to a passwd structure, if successful.

NULL
Indicates an end-of-file or error occurred. The function sets errno to one of the following values:

  • EIO– Indicates that an I/O error occurred or the user does not have appropriate privileges enabled to access the user authorization file (SYSUAF).

  • EMFILE– OPEN_MAX file descriptors are currently open in the calling process.

  • ENFILE– The maximum allowable number of files is currently open in the system.

getpwnam, getpwnam_r

getpwnam, getpwnam_r — The getpwnam function returns information about a user database entry for the specified name. The getpwnam_r function is a reentrant version of getpwnam.

Format

#include <pwd.h>
struct passwd *getpwnam (const char *name); (ISO POSIX-1)
struct passwd *getpwnam (const char *name, ...); (VSI C Extension)
int getpwnam_r (const char *name, struct passwd *pwd, char *buffer,
size_t bufsize, struct passwd **result (ISO POSIX-1),
int getpwnam_r (const char *name, struct passwd *pwd, char *buffer,
size_t bufsize, struct passwd **result, ...); (VSI C Extension),

Function Variants

The getpwnam and getpwnam_r functions have variants named __32_getpwnam, _getpwnam_r32 and __64_getpwnam, _getpwnam_r64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

name

The name of the user for which the attributes are to be read.

pwd

The address of a passwd structure into which the function writes its results.

buffer

A working buffer for the result argument that is able to hold the largest entry in the passwd structure. Storage referenced by the passwd structure is allocated from the memory provided with the buffer argument, which is bufsize characters in length.

bufsize

The length of the character array that buffer points to.

result

Upon successful return, is set to pwd. Upon unsuccessful return, the result is set to NULL.

. . .

An optional argument that can be either 1 or 0. If you specify 1, the directory specification is returned in OpenVMS format. If you specify 0, the directory specification (pathname) is returned in UNIX style format. If you omit this argument, the function returns the directory specification according to your current command-language interpreter. For more information about UNIX style directory specifications, see Section 1.3.3.

Description

The getpwnam function searches the user database for an entry with the specified name. The function returns the first user entry in the database with the pw_name member of the passwd structure that matches the name argument.

The passwd structure is defined in the <pwd.h> header file as follows:

pw_name

The user's login name.

pw_uid

The numerical user ID.

pw_gid

The numerical group ID.

pw_dir

The home directory of the user.

pw_shell

The initial program for the user.


Note

All information generated by the getpwnam function is stored in a per-thread static area and is overwritten on subsequent calls to the function.

The getpwnam_r function is the reentrant version of getpwnam. The getpwnam_r function updates the passwd structure pointed to by pwd and stores a pointer to that structure at the location pointed to by result. The structure will contain an entry from the user database that matches the specified name. Storage referenced by the structure is allocated from the memory provided with the buffer argument, which is bufsize characters in length. The maximum size needed for this buffer can be determined with the _SC_GETPW_R_SIZE_MAX parameter of the sysconf function. On error or if the requested entry is not found, a NULL pointer is returned at the location pointed to by result.

Applications wishing to check for error situations should set errno to 0 before calling getpwnam. If getpwnam returns a NULL pointer and errno is nonzero, an error occurred.

Return Values

x

getpwnam returns a pointer to a valid passwd structure, if a matching entry is found.

NULL
getpwnam returns NULL if an error occurred or the specified entry was not found. errno is set to indicate the error. The getpwnam function may fail if:

  • EIO– An I/O error has occurred.

  • EINTR– A signal was intercepted during getpwnam.

  • EMFILE– OPEN_MAX file descriptors are currently open in the calling process.

  • ENFILE– The maximum allowable number of files is currently open in the system.

0

When successful, getpwnam_r returns 0 and stores a pointer to the updated passwd structure at the location pointed to by result.

0
When unsuccessful (on error or if the requested entry is not found), getpwnam_r returns 0 and stores a NULL pointer at the location pointed to by result. The getpwnam_r function may fail if:

  • ERANGE– Insufficient storage was supplied through buffer and bufsize to contain the data to be referenced by the resulting passwd structure.

Example

When building a sample program with /def=_USE_STD_STAT, you can observe the following:
  • When the DECC$POSIX_STYLE_UID logical is enabled:

    • For a system, that supports POSIX style identifiers:

      - getpwnam_r API reads information from the TCP/IP proxy database and fills UID and GID with values from the TCP/IP proxy database.

      - getgrgid_r API returns gr_name and gr_mem from the right's database associated with GID returned by getpwnam_r API.

    • System with no support for POSIX style identifiers, getpwnam_r fills GID and UID with SYSGEN parameters as "DEFUID" and "DEFGID".

  • When the DECC$POSIX_STYLE_UID logical is not defined:

    getpwnam function returns information about a user database entry for the specified name, which is specified in SYSUAF.DAT


#include <unistd>  // getuid()
#include <pwd>     // getpwuid_r()
#include <grp>
#include <errno.h>
#include <stdio.h>
#include <string.h>

main()
{

struct passwd pwd2;
const unsigned int PWD_BUFF_SIZE = 1024; const unsigned int GRP_BUFF_SIZE = 1024;

struct passwd *p_passwd;
struct passwd *result;
struct group *grpresult;
struct group grp;
char pwdBuffer[PWD_BUFF_SIZE],*name;
char grpBuffer[GRP_BUFF_SIZE];
char buf[PWD_BUFF_SIZE];

gid_t gid;
uid_t uid;

int status;
p_passwd = getpwnam("user1");
uid=p_passwd->pw_uid;
gid=p_passwd->pw_gid;

printf("User id is %u\n", uid);
printf("Group id is %u\n", gid);

status = getpwnam_r("user1", &pwd2, pwdBuffer, PWD_BUFF_SIZE, &result);

gid = pwd2.pw_gid;

status = getgrgid_r(gid, &grp, grpBuffer, GRP_BUFF_SIZE, &grpresult);

gid=grp.gr_gid; name=grp.gr_name;

strcpy(name,grp.gr_name);

printf("Group id is %u\n", gid);
printf("Group name is %s\n", name);

}
Running the example program with /def=_USE_STD_STAT produces the following result:

  • When the DECC$POSIX_STYLE_UID logical is NOT enabled, prints uid as 11010118 (result of 65536*168+ 70) and gid as 168 with group name as RTL.

  • When the DECC$POSIX_STYLE_UID logical is enabled and POSIX style identifiers are supported, prints uid as 70, gid as 168 with group name as FOR_POSIX_TEST (retrieved from TCP/IP proxy database).

  • When the DECC$POSIX_STYLE_UID logical is enabled, but POSIX style identifiers are not supported, prints uid as DEFUID, gid as DEFGID with group name as invalid buffer.

getpwuid, getpwuid_r

getpwuid, getpwuid_r — The getpwuid function returns information about a user database entry for the specified uid. The getpwuid_r function is a reentrant version of getpwuid.

Format

#include <pwd.h>
struct passwd *getpwuid (uid_t uid); (ISO POSIX-1)
struct passwd *getpwuid (uid_t uid, . . .); (VSI C Extension)
int getpwuid_r (uid_t uid, struct passwd *pwd, char *buffer,
size_t bufsize, struct passwd **result); (ISO POSIX-1)
int getpwuid_r (uid_t uid, struct passwd *pwd, char *buffer,
size_t bufsize, struct passwd **result, ...); (VSI C Extension)

Function Variants

The getpwuid and getpwuid_r functions have variants named __32_getpwuid, _getpwuid_r32 and __64_getpwuid, _getpwuid_r64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

uid

The user ID (UID) for which the attributes are to be read.

pwd

The location where the retrieved passwd structure is to be placed.

buffer

A working buffer for the result argument that is able to hold the entry in the passwd structure. Storage referenced by the passwd structure is allocated from the memory provided with the buffer argument, which is bufsize characters in size.

bufsize

The length of the character array that buffer points to.

result

Upon successful return, result is set to pwd. Upon unsuccessful return, result is set to NULL.

. . .

An optional argument that can be either 1 or 0. If you specify 1, the directory specification is returned in OpenVMS format. If you specify 0, the directory specification (pathname) is returned in UNIX style format. If you omit this argument, the function returns the directory specification according to your current command-language interpreter. For more information about UNIX style directory specifications, see Section 1.3.3.

Description

The getpwuid function searches the user database for an entry with the specified uid. The function returns the first user entry in the database with a pw_uid member of the passwd structure that matches the uid argument.

The passwd structure is defined in the <pwd.h> header file as follows:

pw_name

The user's login name.

pw_uid

The numerical user ID.

pw_gid

The numerical group ID.

pw_dir

The home directory of the user.

pw_shell

The initial program for the user.


Note

All information generated by the getpwuid function is stored in a per-thread static area and is overwritten on subsequent calls to the function.

The getpwuid_r function is the reentrant version of getpwuid. The getpwuid_r function updates the passwd structure pointed to by pwd and stores a pointer to that structure at the location pointed to by result. The structure will contain an entry from the user database with a matching uid. Storage referenced by the structure is allocated from the memory provided with the buffer argument, which is bufsize characters in size. The maximum size needed for this buffer can be determined with the _SC_GETPW_R_SIZE_MAX parameter of the sysconf function. On error or if the requested entry is not found, a NULL pointer is returned at the location pointed to by result.

Applications wishing to check for error situations should set errno to 0 before calling getpwuid. If getpwuid returns a NULL pointer and errno is nonzero, an error occurred.

See also getuid to know how UIC is represented.

Return Values

x

getpwuid returns a pointer to a valid passwd structure, if a matching entry is found.

NULL
getpwuid returns NULL if an error occurred or a matching entry was not found. errno is set to indicate the error. The getpwuid function may fail if:

  • EIO– An I/O error has occurred.

  • EINTR– A signal was intercepted during getpwnam.

  • EMFILE– OPEN_MAX file descriptors are currently open in the calling process.

  • ENFILE– The maximum allowable number of files is currently open in the system.

0

When successful, getpwuid_r returns 0 and stores a pointer to the updated passwd structure at the location pointed to by result.

0
When unsuccessful (on error or if the requested entry is not found), getpwuid_r returns 0 and stores a NULL pointer at the location pointed to by result. The getpwuid_r function may fail if:

  • ERANGE– Insufficient storage was supplied through buffer and bufsize to contain the data to be referenced by the resulting passwd structure.

getrusage

getrusage — Gets information about resource utilization.

Format

#include <sys/resource.h>
int getrusage(int who, struct rusage *r_usage);

Arguments

who

The process which you want to get the resource usage for.

r_usage

A pointer to an object of type struct rusage in which the function can store the resource usage information.

Description

The getrusage function provides measures of the resources used by the current process or its terminated and waited-for child processes.

If the value of the who argument is RUSAGE_SELF, information is returned about resources used by the current process. If the value of the who argument is RUSAGE_CHILDREN, information is returned about resources used by the terminated and waited-for children of the current process. If the child is never waited for, the resource information for the child process is discarded and not included in the resource information provided by getrusage.

Currently, only getting elapsed user time (ru_utime) and maximum resident memory (ru_maxrss) is supported.

Return Values

0

Successful completion.

-1

Indicated an error. errno contains the error.

gets

gets — Reads a line from the standard input (stdin).

Format

#include <stdio.h>
char *gets (char *str);

Function Variants

The gets function has variants named _gets32 and _gets64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Argument

str

A pointer to a character string that is large enough to hold the information fetched from stdin.

Description

The new-line character ( \n) that ends the line is replaced by the function with an ASCII null character ( \0).

When stdin is opened in record mode, gets treats the end of a record the same as a new-line character and, therefore, reads up to and including a new-line character or to the end of the record.

Return Values

x

A pointer to the str argument.

NULL

Indicates that an error has occurred or that the end-of-file was encountered before a new-line character was encountered. The contents of str are undefined if a read error occurs.

getsid

getsid — Gets the process group ID of the session leader.

Format

#include <unistd.h>
pid_t getsid (pid_t pid);

Argument

pid

The process ID of the process whose session leader process group ID is being requested.

Description

The getsid function obtains the process group ID of the process that is the session leader of the process specified by pid. If pid is (pid_t) 0, it specifies the calling process.

This function requires that long (32-bit) UID/GID support be enabled. See Section 1.4.8 for more information.

Return Values

x

The process group ID of the session leader of the specified process.

(pid_t ) -1
Indicates an error. The function sets errno to one of the following values:

  • EPERM – The process specified by pid is not in the same session as the calling process, and the implementation does not allow access to the process group ID of the session leader of that process from the calling process.

  • ESRCH– There is no process with a process ID of pid.

[w]getstr

[w]getstr — Get a string from the terminal screen, store it in the variable str, and echo it on the specified window. The getstr function works on the stdscr window.

Format

#include <curses.h>
int getstr (char *str);
int wgetstr (WINDOW *win, char *str);

Arguments

win

A pointer to the window.

str

Must be large enough to hold the character string fetched from the window.

Description

The getstr and wgetstr functions refresh the specified window before fetching a string. The new-line terminator is stripped from the fetched string. For more information, see the scrollok function.

Return Values

OK

Indicates success.

ERR

Indicates that the function makes the screen scroll illegally.

gettimeofday

gettimeofday — Gets the date and time.

Format

#include <time.h>
int gettimeofday (struct timeval *tp, void *tzp);

Arguments

tp

Pointer to a timeval structure, defined in the <time.h> header file.

tzp

A NULL pointer. If this argument is not a NULL pointer, it is ignored.

Description

The gettimeofday function gets the current time (expressed as seconds and microseconds) since 00::00 Coordinated Universal Time, January 1, 1970. The current time is stored in the timeval structure pointed to by the tp argument.

The tzp argument is intended to hold time-zone information set by the kernel. However, because the OpenVMS kernel does not set time-zone information, the tzp argument should be NULL. If it is not NULL, it is ignored. This function is supported for compatibility with BSD programs.

If the value of the SYS$TIMEZONE_DIFFERENTIAL logical is wrong, the function fails with errno set to EINVAL.

Return Values

0

Indicates success.

-1

An error occurred. errno is set to indicate the error.

getuid

getuid — With POSIX IDs disabled, this function is equivalent to geteuid and returns the member number (in OpenVMS terms) from the user identification code (UIC). With POSIX IDs enabled, returns the real user ID.

Format

#include <unistd.h>
uid_t getuid (void);

Description

The getuid function can be used with POSIX style identifiers or with UIC-based identifiers.

POSIX style IDs are supported on OpenVMS Version 7.3-2 and higher.

With POSIX style IDs disabled (the default), the geteuid and getuid functions are equivalent and return the member number from the current UIC as follows:

  • For programs compiled with the _VMS_V6_SOURCE feature-test macro or programs that do not include the <unistd.h> header file, the getuid and geteuid functions return the member number of the OpenVMS UIC. For example, if the UIC is [313,31], then the member number, 31, is returned.

  • For programs compiled without the _VMS_V6_SOURCE feature-test macro that do include the <unistd.h> header file, the full UIC is returned in decimal after converting the octal representation to decimal. For example, if the UIC is [313, 31] then 13303833 is returned. (13303833 = 25 + 203 * 65536; Octal 31 = 25 decimal; Octal 313 = 203 decimal.)

With POSIX style IDs enabled, geteuid returns the effective user ID of the calling process, and getuid returns the real user ID of the calling process.

To enable/disable POSIX style IDs, see Section 1.6.

See also getegid and getgid.

Return Value

x

The real user ID (POSIX IDs enabled), or the member number from the current UIC or the full UIC (POSIX IDs disabled).

getw

getw — Returns characters from a specified file.

Format

#include <stdio.h>
int getw (FILE *file_ptr);

Argument

file_ptr

A pointer to the file to be accessed.

Description

The getw function returns the next four characters from the specified input file as an int.

Return Values

x

The next four characters, in an int.

EOF

Indicates that the end-of-file was encountered during the retrieval of any of the four characters and all four characters were lost. Since EOF is an acceptable integer, use feof and ferror to check the success of the function.

getwc

getwc — Reads the next character from a specified file, and converts it to a wide-character code.

Format

#include <wchar.h>
wint_t getwc (FILE *file_ptr);

Argument

file_ptr

A pointer to the file to be accessed.

Description

Since getwc is implemented as a macro, a file pointer argument with side effects (for example getwc (*f++)) might be evaluated incorrectly. In such a case, use the fgetwc function instead. See the fgetwc function.

Return Values

n

The returned character.

WEOF

Indicates the end-of-file or an error. If an error occurs, the function sets errno. For a list of the values set by this function, see fgetwc.

getwchar

getwchar — Reads a single wide character from the standard input (stdin).

Format

#include <wchar.h>
wint_t getwchar (void);

Description

The getwchar function is identical to fgetwc(stdin).

Return Values

x

The next character from stdin, converted to wint_t.

WEOF

Indicates the end-of-file or an error. If an error occurs, the function sets errno. For a list of the values set by this function, see fgetwc.

getyx

getyx — Puts the (y, x) coordinates of the current cursor position on win in the variables y and x.

Format

#include <curses.h>
getyx (WINDOW *win, int y, int x);

Arguments

win

Must be a pointer to the window.

y

Must be a valid lvalue.

x

Must be a valid lvalue.

glob

glob — Returns a list of existing files for a user supplied pathname (with optional wildcards).

Format

#include <glob.h>
int glob (const char *pattern, int flags, int (*errfunc)(const char *epath,
int eerrno), glob_t *pglob);

Function Variants

The glob function has variants named _glob32 and _glob64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

pattern

The pattern string to match with accessible files and pathnames. This pattern can have wildcards.

flags

Controls the customizable behavior of the glob function.

errfunc

An optional function that, if specified, is called when the glob function detects an error condition, or if not specified, is NULL.

epath

First argument of the optional errfunc function, epath is the pathname that failed because a directory could not be opened or read.

eerrno

Second argument of the optional errfunc function, eerrno is the errno value from a failure specified by the epath argument as set by the opendir, readdir, or stat functions.

pglob

Pointer to a glob_t structure that returns the matching accessible existing filenames. The structure is allocated by the caller. The array of structures containing the located filenames that match the pattern argument are stored by the glob function into the structure. The last entry is a NULL pointer.

The structure type glob_t is defined in the <glob.h> header file and includes at least the following members:
size_t   gl_pathc    //Count of paths matched by pattern.
char **  gl_pathv    //Pointer to a list of matched pathnames.
size_t   gl_offs     //Slots to reserve at the beginning of gl_pathv.

Description

The glob function constructs a list of accessible files that match the pattern argument.

The glob function operates in one of two modes: UNIX mode or OpenVMS mode.

You can select UNIX mode explicitly by enabling the feature logical DECC$GLOB_UNIX_STYLE, which is disabled by default.

The glob function defaults to OpenVMS mode unless one of the following conditions is met (in which case glob uses UNIX mode):

  • The DECC$GLOB_UNIX_STYLE is enabled.

  • The DECC$FILENAME_UNIX_ONLY feature logical is enabled.

  • The glob function checks the specified pattern for pathname indications, such as directory delimiters, and determines it to be a UNIX style pathname.

OpenVMS mode

This mode allows an OpenVMS programmer to give an OpenVMS style pattern to the glob function and get expected OpenVMS style output. The OpenVMS style pattern is what a user would expect from DCL commands or as input to the SYS$PARSE and SYS$SEARCH system routines.

In this mode, you can use any of the expected OpenVMS wildcards (see the OpenVMS documentation for additional information).

OpenVMS mode does not support the UNIX wildcard ?, or [] pattern matching. OpenVMS users expect [] to be available as directory delimiters.

Some additional behavior differences between OpenVMS mode and UNIX mode:

  • OpenVMS mode outputs full file specifications, not relative ones, as in UNIX mode.

  • The GLOB_MARK flag is ignored in OpenVMS mode because it is not meaningful to append a slash (/) to a directory on OpenVMS.

For example:
Sample pattern input      Sample output

[.SUBDIR1]A.TXT           DEV:[DIR.SUBDIR1]A.TXT;1
[.SUB*]%.*                DEV:[DIR.SUBDIR1]A.TXT;1

UNIX mode

You can enable this mode explicitly with:
$ DEFINE DECC$GLOB_UNIX_STYLE ENABLE

UNIX mode is also enabled if the DECC$FILENAME_UNIX_ONLY feature logical is set, or if the glob function determines that the specified pattern looks like a UNIX style pathname.

In UNIX mode, the glob function follows the X/Open specification where possible.

For example: 
Sample pattern input      Sample output

./a/b/c                   ./a/b/c
./?/b/*                   ./a/b/c
[a-c]                     c

Standard Description

The glob function matches all accessible pathnames against this pattern and develops a list of all pathnames that match. To have access to a pathname, the glob function requires search permission on every component of a pathname except the last, and read permission on each directory of any filename component of the pattern argument.

The glob function stores the number of matched pathnames and a pointer to a list of pointers to pathnames in the pglob argument. The pathnames are sorted, based on the setting of the LC_COLLATE category in the current locale. The first pointer after the last pathname is NULL. If the pattern does not match any pathnames, the returned number of matched pathnames is 0.

It is the caller's responsibility to create the structure pointed to by the pglob argument. The glob function allocates other space as needed. The globfree function frees any space associated with the pglob argument as a result of a previous call to the glob function.

The flags argument is used to control the behavior of the glob function. The flags value is the bitwise inclusive OR (|) of any of the following constants, which are defined in the <glob.h> header file:

GLOB_APPEND

Appends pathnames located with this call to any pathnames previously located.

GLOB_DOOFFS

Uses the gl_offs structure to specify the number of NULL pointers to add to the beginning of the gl_pathv component of the pglob argument.

GLOB_ERR

Causes the glob function to return when it encounters a directory that it cannot open or read. If the GLOB_ERR flag is not set, the glob function continues to find matches if it encounters a directory that it cannot open or read.

GLOB_MARK

Specifies that each pathname that is a directory should have a slash (/) appended. GLOB_MARK is ignored in OpenVMS mode because it is not meaningful to append a slash to a directory on OpenVMS systems.

GLOB_NOCHECK

If the pattern argument does not match any pathname, then the glob function returns a list consisting only of the pattern argument, and the number of matched pathnames is 1.

GLOB_NOESCAPE

If the GLOB_NOESCAPE flag is set, a backslash ( \) cannot be used to escape meta characters.

The GLOB_APPEND flag can be used to append a new set of pathnames to those found in a previous call to the glob function. The following rules apply when two or more calls to the glob function are made with the same value of the pglob argument, and without intervening calls to the globfree function:

  • If the application sets the GLOB_DOOFFS flag in the first call to the glob function, then it is also set in the second call, and the value of the gl_offs field of the pglob argument is not modified between the calls.

  • If the application did not set the GLOB_DOOFFS flag in the first call to the glob function, then it is not set in the second call.

  • After the second call, pglob -> gl_pathvpoints to a list containing the following:

    • Zero or more NULLs, as specified by the GLOB_DOOFFS flag and pglob -> gl_offs.

    • Pointers to the pathnames that were in the pglob -> gl_pathv list before the call, in the same order as after the first call to the glob function.

    • Pointers to the new pathnames generated by the second call, in the specified order.

  • The count returned in the pglob -> gl_offs argument is the total number of pathnames from the two calls.

  • The application should not modify the pglob -> gl_pathc or pglob -> gl_pathv fields between the two calls.

On successful completion, the glob function returns a value of 0 (zero). The pglob -> gl_pathc field returns the number of matched pathnames and the pglob -> gl_pathv field contains a pointer to a NULL-terminated list of matched and sorted pathnames. If the number of matched pathnames in the pglob -> gl_pathc argument is 0 (zero), the pointer in the pglob -> gl_pathv argument is undefined.

If the glob function terminates because of an error, the function returns one of the nonzero constants GLOB_ABORTED, GLOB_NOMATCH, or GLOB_NOSPACE, defined in the <glob.h> header file. In this case, the pglob argument values are still set as defined above.

If, during the search, a directory is encountered that cannot be opened or read and the errfunc argument value is not NULL, the glob function calls errfunc with the two arguments epath and eerno:
  • epath—The pathname that failed because a directory could not be opened or read.
  • eerno—The errno value from a failure specified by the epath argument as set by the opendir, readdir, or stat functions.

If errfunc is called and returns nonzero, or if the GLOB_ERR flag is set in flags, the glob function stops the scan and returns GLOB_ABORTED after setting the pglob argument to reflect the pathnames already scanned. If GLOB_ERR is not set and either errfunc is NULL or errfunc returns zero, the error is ignored.

No errno values are returned.

See also globfree, readdir, and stat.

Return Values

0

Successful completion.

GLOB_ABORTED

The scan was stopped because GLOB_ERROR was set or errfunc returned a nonzero value.

GLOB_NOMATCH

The pattern does not match any existing pathname, and GLOB_NOCHECK was not set in flags.

GLOB_NOSPACE

An attempt to allocate memory failed.

globfree

globfree — Frees any space associated with the pglob argument resulting from a previous call to the glob function.

Format

#include <glob.h>
void globfree (glob_t *pglob);

Function Variants

The globfree function has variants named _globfree32 and _globfree64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Argument

pglob

Pointer to a previously allocated glob_t structure.

Description

The globfree function frees any space associated with the pglob argument resulting from a previous call to the glob function. The globfree function returns no value.

gmtime, gmtime_r

gmtime, gmtime_r — Converts time units to the broken-down UTC time.

Format

#include <time.h>
struct tm *gmtime (const time_t *timer);
struct tm *gmtime_r (const time_t *timer, struct tm *result); (ISO POSIX-1)

Function Variants

Compiling with the _DECC_V4_SOURCE and _VMS_V6_SOURCE feature-test macros defined enables a local-time-based entry point to the gmtime_r function that is equivalent to the behavior before OpenVMS Version 7.0.

Arguments

timer

Points to a variable that specifies a time value in seconds since the Epoch.

result

A pointer to a tm structure where the result is stored.

The tm structure is defined in the <time.h> header, and is also shown in Table 36 in the description of localtime.

Description

The gmtime and gmtime_r functions convert the time (in seconds since the Epoch) pointed to by timer into a broken-down time, expressed as Coordinated Universal Time (UTC), and store it in a tm structure.

The difference between the gmtime_r and gmtime functions is that the former puts the result into a user-specified tm structure where the result is stored. The latter puts the result into thread-specific static memory allocated by the C RTL, and which is overwritten by subsequent calls to gmtime; you must make a copy if you want to save it.

On success, gmtime returns a pointer to the tm structure; gmtime_r returns its second argument. On failure, these functions return the NULL pointer.

Note

Generally speaking, UTC-based time functions can affect in-memory time-zone information, which is processwide data. However, if the system time zone remains the same during the execution of the application (which is the common case) and the cache of timezone files is enabled (which is the default), then the _r variant of the time functions asctime_r, ctime_r, gmtime_r and localtime_r, is both thread-safe and AST-reentrant.

If, however, the system time zone can change during the execution of the application or the cache of timezone files is not enabled, then both variants of the UTC-based time functions belong to the third class of functions, which are neither thread-safe nor AST-reentrant.

Return Values

x

Pointer to a tm structure.

NULL
Indicates an error; errno is set to the following value:

  • EINVAL– The timer argument is NULL.

gsignal

gsignal — Generates a specified software signal, which invokes the action routine established by a signal, ssignal, or sigvec function.

Format

#include <signal.h>
int gsignal (int sig [, int sigcode]);

Arguments

sig

The signal to be generated.

sigcode

An optional signal code. For example, signal SIGFPE—the arithmetic trap signal—has 10 different codes, each representing a different type of arithmetic trap.

The signal codes can be represented by mnemonics or numbers. The arithmetic trap codes are represented by the numbers 1 to 10, but the SIGILL codes are represented by the numbers 0 to 2. The code values are defined in the <signal.h> header file. See Table 4.4 for a list of signal mnemonics,codes, and corresponding OpenVMS exceptions.

Description

Calling the gsignal function has one of the following results:

  • If gsignal specifies a sig argument that is outside the range defined in the <signal.h> header file, then gsignal returns 0 and sets errno to EINVAL.

  • If signal, ssignal, or sigvec establishes SIG_DFL (default action) for the signal, then gsignal does not return. The image is exited with the OpenVMS error code corresponding to the signal.

  • If signal, ssignal, or sigvec establishes SIG_IGN (ignore signal) as the action for the signal, then gsignal returns its argument, sig.

  • signal, ssignal, or sigvec must be used to establish an action routine for the signal. That function is called and its return value is returned by gsignal.

See Chapter 4 for more information.

See also raise, signal, ssignal, and sigvec.

Return Values

0

Indicates a sig argument that is outside the range defined in the <signal.h> header file; errno is set to EINVAL.

sig

Indicates that SIG_IGN (ignore signal) has been established as the action for the signal.

x

Indicates that signal, ssignal,or sigvec has established an action function for the signal. That function is called, and its return value is returned by gsignal.

hypot

hypot — Returns the length of the hypotenuse of a right triangle.

Format

#include <math.h>
double hypot (double x, double y);
float hypotf (float x, float y);
long double hypotl (long double x, long double y);

Arguments

x

A real value.

y

A real value.

Description

The hypot functions return the length of the hypotenuse of a right triangle, where x and y represent the perpendicular sides of the triangle. The length is calculated as:
sqrt(x2 + y2)

On overflow, the return value is undefined, and errno is set to ERANGE.

Return Values

x

The length of the hypotenuse.

HUGE_VAL

Overflow occurred; errno is set to ERANGE.

0

Underflow occurred; errno is set to ERANGE.

NaN

x or y is NaN; errno is set to EDOM.

iconv

iconv — Converts characters coded in one codeset to characters coded in another codeset.

Format

#include <iconv.h>
size_t iconv (iconv_t cd, const char **inbuf,size_t *inbytesleft,
char **outbuf, size_t *outbytesleft);

Arguments

cd

A conversion descriptor. This is returned by a successful call to iconv_open.

inbuf

A pointer to a variable that points to the first character in the input buffer.

inbytesleft

Initially, this argument is a pointer to a variable that indicates the number of bytes to the end of the input buffer ( inbuf). When the conversion is completed, the variable indicates the number of bytes in inbuf not converted.

outbuf

A pointer to a variable that points to the first available byte in the output buffer. The output buffer contains the converted characters.

outbytesleft

Initially, this argument is a pointer to a variable that indicates the number of bytes to the end of the output buffer (outbuf). When the conversion is completed, the variable indicates the number of bytes left in outbuf.

Description

The iconv function converts characters in the buffer pointed to by inbuf to characters in another code set. The resulting characters are stored in the buffer pointed to by outbuf. The conversion type is specified by the conversion descriptor cd. This descriptor is returned from a successful call to iconv_open.

If an invalid character is found in the input buffer, the conversion stops after the last successful conversion. The variable pointed to by inbytesleft is updated to reflect the number of bytes in the input buffer that are not converted. The variable pointed to by outbytesleft is updated to reflect the number of bytes remaining in the output buffer.

Return Values

x

Number of nonidentical conversions performed. Indicates successful conversion. In most cases, 0 is returned.

size_t -1
Indicates an error condition. The function sets errno to one of the following:

  • EBADF – The cd argument is not a valid conversion descriptor.

  • EILSEQ – The conversion stops when an invalid character detected.

  • E2BIG – The conversion stops because of insufficient space in the output buffer.

  • EINVAL – The conversion stops because of an incomplete character at the end of the input buffer.

iconv_close

iconv_close — Deallocates a specified conversion descriptor and the resources allocated to the descriptor.

Format

#include <iconv.h>
int iconv_close (iconv_t cd);

Argument

cd

The conversion descriptor to be deallocated. A conversion descriptor is returned by a successful call to iconv_open.

Return Values

0

Indicates that the conversion descriptor was successfully deallocated.

-1
Indicates an error occurred. The function sets errno to one of the following:

  • EBADF – The cd argument is not a valid conversion descriptor.

  • EVMSERR – Nontranslatable OpenVMS error occur. vaxc$errno contains the VMS error code.

iconv_open

iconv_open — Allocates a conversion descriptor for a specified codeset conversion.

Format

#include <iconv.h>
iconv_t iconv_open (const char *tocode, const char *fromcode);

Arguments

tocode

The name of the codeset to which characters are converted.

fromcode

The name of the source codeset. See Chapter 11 for information on obtaining a list of currently available codesets or for details on adding new codesets.

Return Values

x

A conversion descriptor. Indicates the call was successful. This descriptor is used in subsequent calls to iconv

iconv_t-1
Indicates an error occurred. The function sets errno to one of the following:

  • EMFILE – The process does not have enough I/O channels to open a file.

  • ENOMEM – Insufficient space is available.

  • EINVAL – The conversion specified by fromcode and tocode is not supported.

  • EVMSERR – Nontranslatable OpenVMS error occur. vaxc$errno contains the OpenVMS error code. A value of SS$_BADCHKSUM in vaxc$errno indicates that a conversion table file was found, but its contents is corrupted. A value of SS$_IDMISMATCH in vaxc$errno indicates that the conversion table file version does not match the version of the C Run-Time Library.

Example

#include <stdio.h>
#include <iconv.h>
#include <errno.h>


int main()
{
  /* Declare variables to be used                      */

  char fromcodeset[30];
  char tocodeset[30];
  int iconv_opened;
  iconv_t iconv_struct;       /* Iconv descriptor      */

  /* Initialize variables                              */

  sprintf(fromcodeset, "DECHANYU");
  sprintf(tocodeset, "EUCTW");
  iconv_opened = FALSE;

  /* Attempt to create a conversion descriptor for the */
  /* codesets specified. If the return value from      */
  /* iconv_open is -1 then an error has occurred.      */
  /*  Check the value of errno.                        */

  if ((iconv_struct = iconv_open(tocodeset, fromcodeset))
     == (iconv_t) - 1) {

      /* Check the value of errno                      */

      switch (errno) {
      case EMFILE:
      case ENFILE:
          printf("Too many iconv conversion files open\n");
          break;

      case ENOMEM:
          printf("Not enough memory\n");
          break;

      case EINVAL:
          printf("Unsupported conversion\n");
          break;

      default:
          printf("Unexpected error from iconv_open\n");
          break;
     }
  }
  else

      /* Successfully allocated a conversion descriptor   */

      iconv_opened = TRUE;

  /*  Was a conversion descriptor allocated               */

   if (iconv_opened) {

      /* Attempt to deallocate the conversion descriptor. */
      /* If iconv_close returns -1 then an error has      */
      /* occurred.                                        */

      if (iconv_close(iconv_struct) == -1) {

          /* An error occurred. Check the value of errno  */

          switch (errno) {
          case EBADF:
              printf("Conversion descriptor is invalid\n");
              break;
          default:
              printf("Unexpected error from iconv_close\n");
              break;
          }
      }
  }
  return (EXIT_FAILURE);
}

ilogb

ilogb — Returns the exponent part of its argument.

Format

#include <math.h>
int ilogb (double x);
int ilogbf (float x);
int ilogbl (long double x);

Argument

x

A real value.

Description

The ilogb functions return the exponent part of their argument x. Formally, the return value is the integral part of logr |x| as a signed integral value, for nonzero x, where r is the radix of the machine's floating-point arithmetic, which is the value of FLT_RADIX defined in <float.h>.

Return Values

n

Upon success, the exponent part of x as a signed integer value. These functions are equivalent to calling the corresponding logb function and casting the returned value to type int.

[w]inch

[w]inch — Return the character at the current cursor position on the specified window without making changes to the window. The inch function acts on the stdscr window.

Format

#include <curses.h>
char inch();
char winch (WINDOW *win);

Argument

win

A pointer to the window.

Return Values

x

The returned character.

ERR

Indicates an input error.

index

index — Searches for a character in a string.

Format

#include <strings.h>
char *index (const char *s, int c);

Function Variants

The index function has variants named _index32 and _index64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

s

The string to search.

c

The character to search for.

Description

The index function is identical to the strchr function, and is provided for compatibility with some UNIX implementations.

initscr

initscr — Initializes the terminal-type data and all screen functions. You must call initscr before using any of the curses functions.

Format

#include <curses.h>
void initscr (void);

Description

The OpenVMS Curses version of the initscr function clears the screen before doing the initialization. The BSD-based Curses version does not.

initstate

initstate — Initializes random-number generators.

Format

#include <stdlib.h>
char *initstate (unsigned int seed, char *state, int size);

Arguments

seed

An initial seed value.

state

Pointer to an array of state information.

size

The size of the state information array.

Description

The initstate function initializes random-number generators. It lets you initialize, for future use, a state array passed as an argument. The size, in bytes, of the state array is used by the initstate function to decide how sophisticated a random-number generator to use; the larger the state array, the more random the numbers.

Values for the amount of state information are 8, 32, 64, 128, and 256 bytes. Amounts less than 8 bytes generate an error, while other amounts are rounded down to the nearest known value.

The seed argument specifies a starting point for the random-number sequence and provides for restarting at the same point. The initstate function returns a pointer to the previous state information array.

Once you initialize a state, the setstate function allows rapid switching between states. The array defined by the state argument is used for further random-number generation until the initstate function is called or the setstate function is called again. The setstate function returns a pointer to the previous state array.

After initialization, you can restart a state array at a different point in one of two ways:

  • Use the initstate function with the desired seed argument, state array, and size of the array.

  • Use the setstate function with the desired state, followed by the srandom function with the desired seed. The advantage of using both functions is that you do not have to save the state array size once you initialize it.

See also setstate, srandom, and random.

Return Values

x

A pointer to the previous state array information.

0

Indicates an error. Call made with less than 8 bytes of state information. Further specified in the global errno.

[w]insch

[w]insch — Insert a character at the current cursor position in the specified window. The insch function acts on the stdscr window.

Format

#include <curses.h>
int insch (char ch);
int winsch (WINDOW *win, char ch);

Arguments

win

A pointer to the window.

ch

The character to be inserted.

Description

After the character is inserted, each character on the line shifts to the right, and the last character in the line is deleted. For more information, see the scrollok function.

Return Values

OK

Indicates success.

ERR

Indicates that the function makes the screen scroll illegally.

[w]insertln

[w]insertln — Insert a line above the line containing the current cursor position. The insertln function acts on the stdscr window.

Format

#include <curses.h>
int insertln();
int winsertln (WINDOW *win);

Argument

win

A pointer to the window.

Description

The current line and every line below it shifts down, and the bottom line disappears. The inserted line is blank and the current (y, x) coordinates remain the same. For more information, see the scrollokfunction.

Return Values

OK

Indicates success.

ERR

Indicates that the function makes the screen scroll illegally.

[w]insstr

[w]insstr — Insert a string at the current cursor position in the specified window. The insstr function acts on the stdscr window.

Format

#include <curses.h>
int insstr (char *str);
int winsstr (WINDOW *win, char *str);

Arguments

win

A pointer to the window.

str

A pointer to the string to be inserted.

Description

Each character after the string shifts to the right, and the last character disappears. These functions are specific to VSI C for OpenVMS systems and are not portable.

Return Values

OK

Indicates success.

ERR

Indicates that the function makes the screen scroll illegally. For more information, see the scrollok function.

isalnum

isalnum — Indicates if a character is classed either as alphabetic or as a digit in the program's current locale.

Format

#include <ctype.h>
int isalnum (int character);

Argument

character

An object of type int. The value of character must be representable as an unsigned char or must equal the value of the macro EOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If alphanumeric.

0

If not alphanumeric.

isalpha

isalpha — Indicates if a character is classed as an alphabetic character in the program's current locale.

Format

#include <ctype.h>
int isalpha (int character);

Argument

character

An object of type int. The value of character must be representable as an unsigned char or must equal the value of the macro EOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If alphabetic.

0

If not alphabetic.

isapipe

isapipe — Indicates if a specified file descriptor is associated with a pipe.

Format

#include <unixio.h>
int isapipe (int file_desc);

Argument

file_desc

A file descriptor.

Description

For more information about pipes, see Chapter 5.

Return Values

1

Indicates an association with a pipe.

0

Indicates no association with a pipe.

-1

Indicates an error (for example, if the file descriptor is not associated with an open file).

isascii

isascii — Indicates if a character is an ASCII character.

Format

#include <ctype.h>
int isascii (int character);

Argument

character

An object of type char.

Return Values

nonzero

If ASCII.

0

If not ASCII.

isatty

isatty — Indicates if a specified file descriptor is associated with a terminal.

Format

#include <unistd.h>
int isatty (int file_desc);

Argument

file_desc

A file descriptor.

Return Values

1

If the file descriptor is associated with a terminal.

0

Indicates an error (for example, if the file descriptor is not associated with an open file) and errno is set to indicate the error.

isblank

isblank — Checks if a character is blank.

Format

#include <ctype.h>
int isblank (int c);

Argument

c

Character to be checked.

Description

The isblank function tests for any character that is a standard blank character or is one of a locale-specific set of characters for which isspace is true and that is used to separate words within a line of text.

The standard blank characters are the space character (' ') and the horizontal tab character ('\t').

In the "C" locale, isblank returns true only for the standard blank characters.

See also iswblank.

Return Values

nonzero

If a blank character.

0

If not a blank character.

iscntrl

iscntrl — Indicates if a character is classed as a control character in the program's current locale.

Format

#include <ctype.h>
int iscntrl (int character);

Argument

character

An object of type int. The value of character must be representable as an unsigned char or must equal the value of the macro EOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If a control character.

0

If not a control character.

isdigit

isdigit — Indicates if a character is classed as a digit in the program's current locale.

Format

#include <ctype.h>
int isdigit (int character);

Argument

character

An object of type int. The value of character must be representable as an unsigned char or must equal the value of the macro EOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If a decimal digit.

0

If not a decimal digit.

isgraph

isgraph — Indicates if a character is classed as a graphic character in the program's current locale.

Format

#include <ctype.h>
int isgraph (int character);

Argument

character

An object of type int. The value of character must be representable as an unsigned char or must equal the value of the macro EOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If a graphic character.

0

If not a graphic character.

isgreater

isgreater — Determines whether x is greater than y.

Format

#include <math.h>
int isgreater (x, y);

Arguments

x, y

Values to be compared.

Description

The function fails if one of the arguments is NaN. This causes an exception. To avoid this, C99 defines the macro isgreater (x,y), which determines (x) > (y) without an exception if x or y is NaN.

The macro is guaranteed to evaluate the arguments only once. The arguments must be of real floating-point type.

Note

Do not pass integer values as arguments to this macro because the arguments will not be promoted to real floating-point types.

Return Values

The isgreater (x,y) macro returns the result of the relational comparison. It returns 0 if either argument is a NaN.

isgreaterequal

isgreaterequal — Determines whether x is greater than or equal to y.

Format

#include <math.h>
int isgreaterequal (x, y);

Arguments

x, y

Values to be compared.

Description

The function fails if one of the arguments is NaN. This causes an exception. To avoid this, C99 defines the macro isgreaterequal (x, y), which determines (x) >= (y) without an exception if x or y is NaN.

The macro is guaranteed to evaluate the arguments only once. The arguments must be of real floating-point type.

Note

Do not pass integer values as arguments to this macro because the arguments will not be promoted to real floating-point types.

Return Values

The isgreaterequal (x, y) macro returns the result of the relational comparison. It returns 0 if either argument is a NaN.

isless

isless — Determines whether x is less than y.

Format

#include <math.h>
int isless (x, y);

Arguments

x, y

Values to be compared.

Description

The function fails if one of the arguments is NaN. This causes an exception. To avoid this, C99 defines the macro isless (x, y), which determines (x) < (y) without an exception if x or y is NaN.

The macro is guaranteed to evaluate the arguments only once. The arguments must be of real floating-point type.

Note

Do not pass integer values as arguments to this macro because the arguments will not be promoted to real floating-point types.

Return Values

The isless (x, y) macro returns the result of the relational comparison. It returns 0 if either argument is a NaN.

islessequal

islessequal — Determines whether x is less than or equal to y.

Format

#include <math.h>
int islessequal (x, y);

Arguments

x, y

Values to be compared.

Description

The function fails if one of the arguments is NaN. This causes an exception. To avoid this, C99 defines the macro islessequal (x, y), which determines (x) <= (y) without an exception if x or y is NaN.

The macro is guaranteed to evaluate the arguments only once. The arguments must be of real floating-point type.

Note

Do not pass integer values as arguments to this macro because the arguments will not be promoted to real floating-point types.

Return Values

The islessequal (x, y) macro returns the result of the relational comparison. It returns 0 if either argument is a NaN.

islessgreater

islessgreater — Determines whether x is less than or greater than y.

Format

#include <math.h>
int islessgreater (x, y);

Arguments

x, y

Values to be compared.

Description

The function fails if one of the arguments is NaN. This causes an exception. To avoid this, C99 defines the macro islessgreater (x, y), which determines (x) < (y) || (x) > (y) without an exception if x or y is NaN.

Note

The islessgreater (x, y) macro is not equivalent to x!=y because that expression is true if x or y is NaN.

The macro is guaranteed to evaluate the arguments only once. The arguments must be of real floating-point type.

Note

Do not pass integer values as arguments to this macro because the arguments will not be promoted to real floating-point types.

Return Values

The islessgreater (x, y) macro returns the result of the relational comparison. It returns 0 if either argument is a NaN.

islower

islower — Indicates if a character is classed as a lowercase character in the program's current locale.

Format

#include <ctype.h>
int islower (int character);

Argument

character

An object of type int. The value of character must be representable as an unsigned char or must equal the value of the macro EOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If a lowercase alphabetic character.

0

If not a lowercase alphabetic character.

isnan

isnan — Tests for a NaN. Returns 1 if the argument is NaN; 0 if not.

Format

#include <math.h>
int isnan (double x);
int isnanf (float x);
int isnanl (long double x);

Argument

x

A real value.

Description

The isnan functions return the integer value 1 (TRUE) if x is NaN (the IEEE floating point reserved not-a-number value); otherwise, they return the value 0 (FALSE).

isprint

isprint — Indicates if a character is classed as a printing character in the program's current locale.

Format

#include <ctype.h>
int isprint (int character);

Argument

character

An object of type int. The value of character must be representable as an unsigned char or must equal the value of the macro EOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If a printing character.

0

If not a printing character.

ispunct

ispunct — Indicates if a character is classed as a punctuation character in the program's current locale.

Format

#include <ctype.h>
int ispunct (int character);

Argument

character

An object of type int. The value of character must be representable as an unsigned char or must equal the value of the macro EOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If a punctuation character.

0

If not a punctuation character.

isspace

isspace — Indicates if a character is classed as white space in the program's current locale; that is, if it is an ASCII space, tab (horizontal or vertical), carriage-return, form-feed, or new-line character.

Format

#include <ctype.h>
int isspace (int character);

Argument

character

An object of type int. The value of character must be representable as an unsigned char or must equal the value of the macro EOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If a white-space character.

0

If not a white-space character.

isunordered

isunordered — Determines whether x or y are unordered values.

Format

#include <math.h>
int isunordered (x, y);

Arguments

x, y

Values to check whether they are unordered.

Description

The function fails if one of the arguments is NaN. This causes an exception. To avoid this, C99 defines the macro isunordered (x, y), which determines whether the arguments are unordered, that is, whether at least one of the arguments is a NaN.

The macro is guaranteed to evaluate the arguments only once. The arguments must be of real floating-point type.

Note

Do not pass integer values as arguments to this macro because the arguments will not be promoted to real floating-point types.

Return Values

1

If either x or y is NaN.

0

Otherwise.

isupper

isupper — Indicates if a character is classed as an uppercase character in the program's current locale.

Format

#include <ctype.h>
int isupper (int character);

Argument

character

An object of type int. The value of character must be representable as an unsigned char or must equal the value of the macro EOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If an uppercase alphabetic character.

0

If not an uppercase alphabetic character.

iswalnum

iswalnum — Indicates if a wide character is classed either as alphabetic or as a digit in the program's current locale.

Format

#include <wctype.h> (ISO C)
#include <wchar.h> (XPG4)
int iswalnum (wint_t wc);

Argument

wc

An object of type wint_t. The value of character must be representable as a wchar_t in the current locale, or must equal the value of the macro WEOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If alphanumeric.

0

If not alphanumeric.

iswalpha

iswalpha — Indicates if a wide character is classed as an alphabetic character in the program's current locale.

Format

#include <wctype.h> (ISO C)
#include <wchar.h> (XPG4)
int iswalpha (wint_t wc);

Argument

wc

An object of type wint_t. The value of wc must be representable as a wchar_t in the current locale, or must equal the value of the macro WEOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If alphabetic.

0

If not alphabetic.

iswblank

iswblank — Checks if a wide character is blank.

Format

#include <wctype.h>
int iswblank (wint_t wc);

Argument

wc

Wide character to be checked.

Description

The iswblank function tests for any wide character that is a standard blank wide character or is one of a locale-specific set of wide characters for which iswspace is true and that is used to separate words within a line of text.

The standard blank wide characters are the space character (L' ') and the horizontal tab character (L'\t').

In the "C" locale, iswblank returns true only for the standard blank characters.

See also isblank.

Return Values

nonzero

If a blank character.

0

If not a blank character.

iswcntrl

iswcntrl — Indicates if a wide character is classed as a control character in the program's current locale.

Format

#include <wctype.h> (ISO C)
#include <wchar.h> (XPG4)
int iswcntrl (wint_t wc);

Argument

wc

An object of type wint_t. The value of wc must be representable as a wchar_t in the current locale, or must equal the value of the macro WEOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If a control character.

0

If not a control character.

iswctype

iswctype — Indicates if a wide character has a specified property.

Format

#include <wctype.h> (ISO C)
#include <wchar.h> (XPG4)
int iswctype (wint_t wc, wctype_t wc_prop);

Arguments

wc

An object of type wint_t. The value of wc must be representable as a valid wide-character code in the current locale, or must equal the value of the macro WEOF. If it has any other value, the behavior is undefined.

wc_prop

A valid property name in the current locale. This is set up by calling the wctype function.

Description

The iswctype function tests whether wc has the character-class property wc_prop. Set wc_prop by calling the wctype function.

See also wctype.

Return Values

nonzero

If the character has the property wc_prop.

0

If the character does not have the property wc_prop.

Example

#include <locale.h>
#include <wchar.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

/* This test will set up the "upper" character class using      */
/* wctype() and then verify whether the characters 'a' and 'A'  */
/* are members of this class                                    */

#include <stdlib.h>

main()
{

    wchar_t w_char1,
            w_char2;
    wctype_t ret_val;

    char *char1 = "a";
    char *char2 = "A";

    ret_val = wctype("upper");

    /* Convert char1 to wide-character format - w_char1 */

    if (mbtowc(&w_char1, char1, 1) == -1) {
       perror("mbtowc");
        exit(EXIT_FAILURE);
    }

    if (iswctype((wint_t) w_char1, ret_val))
        printf("[%C] is a member of the character class upper\n",
                w_char1);
    else
     printf("[%C] is not a member of the character class upper\n",
              w_char1);

    /* Convert char2 to wide-character format - w_char2 */

    if (mbtowc(&w_char2, char2, 1) == -1) {
        perror("mbtowc");
        exit(EXIT_FAILURE);
    }

    if (iswctype((wint_t) w_char2, ret_val))
        printf("[%C] is a member of the character class upper\n",
                w_char2);
    else
     printf("[%C] is not a member of the character class upper\n",
                w_char2);
}
Running the example program produces the following result:
[a] is not a member of the character class upper
[A] is a member of the character class upper

iswdigit

iswdigit — Indicates if a wide character is classed as a digit in the program's current locale.

Format

#include <wctype.h> (ISO C)
#include <wchar.h> (XPG4)
int iswdigit (wint_t wc);

Argument

wc

An object of type wint_t. The value of wc must be representable as a wchar_t in the current locale, or must equal the value of the macro WEOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If a decimal digit.

0

If not a decimal digit.

iswgraph

iswgraph — Indicates if a wide character is classed as a graphic character in the program's current locale.

Format

#include <wctype.h> (ISO C)
#include <wchar.h> (XPG4)
int iswgraph (wint_t wc);

Argument

wc

An object of type wint_t. The value of wc must be representable as a wchar_t in the current locale, or must equal the value of the macro WEOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If a graphic character.

0

If not a graphic character.

iswlower

iswlower — Indicates if a wide character is classed as a lowercase character in the program's current locale.

Format

#include <wctype.h> (ISO C)
#include <wchar.h> (XPG4)
int iswlower (wint_t wc);

Argument

wc

An object of type wint_t. The value of wc must be representable as a wchar_t in the current locale, or must equal the value of the macro WEOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If a lowercase character.

0

If not a lowercase character.

iswprint

iswprint — Indicates if a wide character is classed as a printing character in the program's current locale.

Format

#include <wctype.h> (ISO C)
#include <wchar.h> (XPG4)
int iswprint (wint_t wc);

Argument

wc

An object of type wint_t. The value of wc must be representable as a wchar_t in the current locale, or must equal the value of the macro WEOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If a printing character.

0

If not a printing character.

iswpunct

iswpunct — Indicates if a wide character is classed as a punctuation character in the program's current locale.

Format

#include <wctype.h> (ISO C)
#include <wchar.h> (XPG4)
int iswpunct (wint_t wc);

Argument

wc

An object of type wint_t. The value of wc must be representable as a wchar_t in the current locale, or must equal the value of the macro WEOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If a punctuation character.

0

If not a punctuation character.

iswspace

iswspace — Indicates if a wide character is classed as a space character in the program's current locale.

Format

#include <wctype.h> (ISO C)
#include <wchar.h> (XPG4)
int iswspace (wint_t wc);

Argument

wc

An object of type wint_t. The value of wc must be representable as a wchar_t in the current locale, or must equal the value of the macro WEOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If a white-space character.

0

If not a white-space character.

iswupper

iswupper — Indicates if a wide character is classed as an uppercase character in the program's current locale.

Format

#include <wctype.h> (ISO C)
#include <wchar.h> (XPG4)
int iswupper (wint_t wc);

Argument

wc

An object of type wint_t. The value of wc must be representable as a wchar_t in the current locale, or must equal the value of the macro WEOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If an uppercase character.

0

If not an uppercase character.

iswxdigit

iswxdigit — Indicates if a wide character is a hexadecimal digit (0 to 9, A to F, or a to f) in the program's current locale.

Format

#include <wctype.h> (ISO C)
#include <wchar.h> (XPG4)
 int iswxdigit (wint_t wc);

Argument

wc

An object of type wint_t. The value of wc must be representable as a wchar_t in the current locale, or must equal the value of the macro WEOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If a hexadecimal digit.

0

If not a hexadecimal digit.

isxdigit

isxdigit — Indicates if a character is a hexadecimal digit (0 to 9, A to F, or a to f) in the program's current locale.

Format

#include <ctype.h>
int isxdigit (int character);

Argument

character

An object of type int. The value of character must be representable as an unsigned char in the current locale, or must equal the value of the macro EOF. If it has any other value, the behavior is undefined.

Return Values

nonzero

If a hexadecimal digit.

0

If not a hexadecimal digit.

j0, j1, jn

j0, j1, jn — Compute Bessel functions of the first kind.

Format

#include <math.h>
double j0 (double x);
float j0f (float x);
long double j0l (long double x);
double j1 (double x);
float j1f (float x);
long double j1l (long double x);
double jn (int n, double x);
float jnf (int n, float x);
long double jnl (int n, long double x);

Arguments

x

A real value.

n

An integer.

Description

The j0 functions return the value of the Bessel function of the first kind of order 0.

The j1 functions return the value of the Bessel function of the first kind of order 1.

The jn functions return the value of the Bessel function of the first kind of order n.

The j1 and jn functions can result in an underflow as x gets small. The largest value of x for which this occurs is a function of n.

Return Values

x

The relevant Bessel value of x of the first kind.

0

The value of the x argument is too large, or underflow occurred; errno is set to ERANGE.

NaN

x is NaN; errno is set to EDOM.

jrand48

jrand48 — Generates uniformly distributed pseudorandom-number sequences. Returns 48-bit signed, long integers.

Format

#include <stdlib.h>
long int jrand48 (unsigned short int xsubi[3]);

Argument

xsubi

An array of three short ints that form a 48-bit integer when concatenated together.

Description

The jrand48 function generates pseudorandom numbers using the linear congruential algorithm and 48-bit integer arithmetic.

The function returns signed long integers uniformly distributed over the range of y values, such that -2 31 ≤ y < 2 31.

The function works by generating a sequence of 48-bit integer values, X i, according to the linear congruential formula:
       Xn+1 = (aXn+c)mod m        n >= 0
The argument m equals 2 48, so 48-bit integer arithmetic is performed. Unless you invoke the lcong48 function, the multiplier value a and the addend value c are:
      a = 5DEECE66D16 = 2736731631558
      c = B16 = 138

The jrand48 function requires that the calling program pass an array as the xsubi argument, which for the first call must be initialized to the initial value of the pseudorandom-number sequence. Unlike the drand48 function, it is not necessary to call an initialization function prior to the first call.

By using different arguments, jrand48 allows separate modules of a large program to generate several independent sequences of pseudorandom numbers. For example, the sequence of numbers that one module generates does not depend upon how many times the function is called by other modules.

Return Value

n

Signed, long integers uniformly distributed over the range -2 31 ≤ y < 2 31.

kill

kill — Sends a signal to the process specified by a process ID.

Format

#include <signal.h>
int kill (int pid, int sig);

Arguments

pid

The process ID.

sig

The signal code.

Description

The kill function is restricted to C and C++ programs that include the main function.

The kill function sends a signal to a process, as if the process had called raise. If the signal is not trapped or ignored by the target program, the program exits.

OpenVMS VAX and Alpha implement different rules about what process you are allowed to send signals to. A program always has privileges to send a signal to a child started with vfork/exec. For other processes, the results are determined by the OpenVMS security model for your system.

Because of an OpenVMS restriction, the kill function cannot deliver a signal to a target process that runs an image installed with privileges.

Unless you have system privileges, the sending and receiving processes must have the same user identification code (UIC).

On OpenVMS systems before Version 7.0, kill treats a signal value of 0 as if SIGKILL were specified.

For OpenVMS Version 7.0 and higher systems, if you include <stdlib.h> and compile with the _POSIX_EXIT feature-test macro set, then:

  • If the signal value is 0, kill validates the process ID but does not send any signals.

  • If the process ID is not valid, kill returns -1 and sets errno to ESRCH.

Return Values

0

Indicates that kill was successfully queued.

-1

Indicates errors. The receiving process may have a different UIC and you are not a system user, or the receiving process does not exist.

l64a

l64a — Converts a long integer to a character string.

Format

#include <stdlib.h>
char *l64a (long l);

Argument

l

A long integer that is to be converted to a character string.

Description

The a64l and l64a functions are used to maintain numbers stored in base-64 ASCII characters:

  • a64l converts a character string to a long integer.

  • l64a converts a long integer to a character string.

Each character used to store a long integer represents a numeric value from 0 through 63. Up to six characters can be used to represent a long integer.

The characters are translated as follows:

  • A period (.) represents 0.

  • A slash (/) represents 1.

  • The numbers 0 through 9 represent 2 through 11.

  • Uppercase letters A through Z represent 12 through 37.

  • Lowercase letters a through z represent 38 through 63.

The l64a function takes a long integer and returns a pointer to a corresponding base-64 notation of the least significant 32 bits.

The value returned by l64a is a pointer to a thread-specific buffer whose contents are overwritten on subsequent calls from the same

See also a64l.

Return Value

x

Upon successful completion, a pointer to the corresponding base-64 ASCII character-string notation. If the l parameter is 0, l64a returns a pointer to an empty string.

labs

labs — Returns the absolute value of an integer as a long int.

Format

#include <stdlib.h>
long int labs (long int j);

Argument

j

A value of type long int.

lchown

lchown — Changes the user and group ownership of the specified file.

Format

#include <unistd.h>
int lchown (const char *file_path, uid_t file_owner, gid_t file_group);

Arguments

file_path

The name of the file for which you want to change the owner and group IDs.

file_owner

The new user ID for the file.

file_group

The new group ID for the file.

Description

The lchown function changes the owner and/or group of the specified file ( file_path). If the file is a symbolic link, the owner of the symbolic link is modified (in contrast to chown which would modify the file that the symbolic link points to).

See also symlink, unlink, readlink, realpath, and lstat.

Return Values

0

Successful completion.

-1

Indicates an error. errno is set to any errno value returned by chown.

lcong48

lcong48 — Initializes a 48-bit uniformly distributed pseudorandom-number sequence.

Format

#include <stdlib.h>
void lcong48 (unsigned short int param[7]);

Argument

param

An array that in turn specifies the initial X i, the multiplier value a, and the addend value c.

Description

The lcong48 function generates pseudorandom numbers using the linear congruential algorithm and 48-bit integer arithmetic.

You can use lcong48 to initialize the random number generator before you call any of the following functions:
  • drand48
  • lrand48
  • mrand48
The lcong48 function specifies the initial X i value, the multiplier value a, and the addend value c.The param array elements specify the following:

param[0-2]

X i

param[3-5]

Multiplier a value

param[6]

16-bit addend c value

After lcong48 has been called, a subsequent call to either srand48 or seed48 restores the standard a and c as specified previously.

The lcong48 function does not return a value.

See also drand48, lrand48, mrand48, srand48, and seed48.

ldexp

ldexp — Returns its first argument multiplied by 2 raised to the power of its second argument; that is, x(2 n).

Format

#include <math.h>
double ldexp (double x, int n);
float ldexp (float x, int n);
long double ldexp (long double x, int n);

Arguments

x

A base value of type double, float, or long double that is to be multiplied by 2 n.

n

The integer exponent value to which 2 is raised.

Return Values

x(2 n)

The first argument multiplied by 2 raised to the power of the second argument.

0

Underflow occurred; errno is set to ERANGE.

HUGE_VAL

Overflow occurred; errno is set to ERANGE.

NaN

x is NaN; errno is set to EDOM.

ldiv

ldiv — Returns the quotient and the remainder after the division of its arguments.

Format

#include <stdlib.h>
ldiv_t ldiv (long int numer, long int denom);

Arguments

numer

A numerator of type long int.

denom

A denominator of type long int.

Description

The type ldiv_t is defined in the <stdlib.h> header file as follows:
typedef struct
        {
             long   quot, rem;
        } ldiv_t;

See also div.

leaveok

leaveok — Signals Curses to leave the cursor at the current coordinates after an update to the window.

Format

#include <curses.h>
leaveok (WINDOW *win, bool boolf);

Arguments

win

A pointer to the window.

boolf

A Boolean TRUE or FALSE value. If boolf is TRUE, the cursor remains in place after the last update and the coordinate setting on win changes accordingly. If boolf is FALSE, the cursor moves to the currently specified ( y, x) coordinates of win.

Description

The leaveok function defaults to moving the cursor to the current coordinates of win. The bool type is defined in the <curses.h> header file as follows:
#define bool int

lgamma

lgamma — Computes the logarithm of the gamma function.

Format

#include <math.h>
double lgamma (double x);
float lgammaf (float x);
long double lgammal (long double x);

Argument

x

A real number. x cannot be 0, a negative integer, or Infinity.

Description

The lgamma functions return the logarithm of the absolute value of gamma of x, or ln(|G( x)|), where G is the gamma function.

The sign of gamma of x is returned in the external integer variable signgam. The x argument cannot be 0, a negative integer, or Infinity.

Return Values

x

The logarithmic gamma of the x argument.

-HUGE_VAL

The x argument is a negative integer; errno is set to ERANGE.

NaN

The x argument is NaN; errno is set to EDOM.

0

Underflow occurred; errno is set to ERANGE.

HUGE_VAL

Overflow occurred; errno is set to ERANGE.

llrint

llrint — Rounds to the nearest integer value, using the current rounding direction, and casts to long long integer.

Format

#include <math.h>
long long int llrint (double x);
long long int llrintf (float x);
long long int llrintl (long double x);

Argument

x

Value to round.

Description

The llrint functions round x to the nearest integer value, using the current rounding direction, and return it as a value of type long long int.

If the rounded value is outside the range of the return type, the numeric result is unspecified and a domain error or range error may occur.

See also lrint for an equivalent function that returns a long int.

Return Value

n

On success, the function returns the rounded integer value.

llround

llround — Rounds to the nearest integer value, rounding halfway cases away from zero, regardless of the current rounding direction, and casts to long long integer.

Format

#include <math.h>
long long int llround (double x);
long long int llroundf (float x);
long long int llroundl (long double x);

Argument

x

Value to round.

Description

The llround functions round x to the nearest integer value, rounding halfway cases away from zero, regardless of the current rounding direction, and return it as a value of type long long int.

If the rounded value is outside the range of the return type, the numeric result is unspecified and a domain error or range error may occur.

See also lround for an equivalent function that returns a long int.

Return Value

n

On success, the function returns the rounded integer value.

localeconv

localeconv — Sets the members of a structure of type struct lconv with values appropriate for formatting numeric quantities according to the rules of the current locale.

Format

#include <locale.h>
struct lconv *localeconv (void);

Description

The localeconv function returns a pointer to the lconv structure defined in the <locale.h> header file. This structure should not be modified by the program. It is overwritten by calls to localeconv, or by calls to the setlocale function that change the LC_NUMERIC, LC_MONETARY, or LC_ALL categories.

The members of the structure are:

Member

Description

char *decimal_point

The radix character.

char *thousands_sep

The character used to separate groups of digits.

char *grouping

The string that defines how digits are grouped in nonmonetary values.

char *int_curr_symbol

The international currency symbol.

char *currency_symbol

The local currency symbol.

char *mon_decimal_point

The radix character used to format monetary values.

char *mon_thousands_sep

The character used to separate groups of digits in monetary values.

char *mon_grouping

The string that defines how digits are grouped in a monetary value.

char *positive_sign

The string used to indicate a nonnegative monetary value.

char *negative_sign

The string used to indicate a negative monetary value.

char int_frac_digits

The number of digits displayed after the radix character in a monetary value formatted with the international currency symbol.

char frac_digits

The number of digits displayed after the radix character in a monetary value.

char p_cs_precedes

For positive monetary values, this is set to 1 if the local or international currency symbol precedes the number, and it is set to 0 if the symbol succeeds the number.

char p_sep_by_space

For positive monetary values, this is set to 0 if there is no space between the currency symbol and the number. It is set to 1 if there is a space, and it is set to 2 if there is a space between the symbol and the sign string.

char n_cs_precedes

For negative monetary values, this is set to 1 if the local or international currency symbol precedes the number, and it is set to 0 if the symbol succeeds the number.

char n_sep_by_space

For negative monetary values, this is set to 0 if there is no space between the currency symbol and the number. It is set to 1 if there is a space, and it is set to 2 if there is a space between the symbol and the sign string.

char p_sign_posn

An integer used to indicate where the positive_sign string should be placed for a nonnegative monetary quantity.

char n_sign_posn

An integer used to indicate where the negative_sign string should be placed for a negative monetary quantity.

Members of the structure of type char* are pointers to strings, any of which (except decimal_point) can point to "", indicating that the associated value is not available in the current locale or is zero length. Members of the structure of type char are positive numbers, any of which can be CHAR_MAX, indicating that the associated value is not available in the current locale. CHAR_MAX is defined in the <limits.h> header file.

Be aware that the value of the CHAR_MAX macro in the <limits.h> header depends on whether the program is compiled with the /UNSIGNED_CHAR qualifier:

  • Use the CHAR_MAX macro as an indicator of a nonavailable value in the current locale only if the program is compiled without /UNSIGNED_CHAR (/NOUNSIGNED_CHAR is the default).

  • If the program is compiled with /UNSIGNED_CHAR, use the SCHAR_MAX macro instead of the CHAR_MAX macro.

In /NOUNSIGNED_CHAR mode, the values of CHAR_MAX and SCHAR_MAX are the same; therefore, comparison with SCHAR_MAX gives correct results regardless of the /[NO]UNSIGNED_CHAR mode used.

The members grouping and mon_grouping point to a string that defines the size of each group of digits when formatting a number. Each group size is separated by a semicolon (;). For example, if grouping points to the string 5;3 and the thousands_sep character is a comma (,), the number 123450000 would be formatted as 1,234,50000.

The elements of grouping and mon_grouping are interpreted as follows:

Value

Interpretation

CHAR_MAX

No further grouping is performed.

0

The previous element is to be used repeatedly for the remainder of the digits.

other

The integer value is the number of digits that comprise the current group. The next element is examined to determine the size of the next group of digits before the current group.

The values of p_sign_posn and n_sign_posn are interpreted as follows:

Value

Interpretation

0

Parentheses surround the number and currency symbol.

1

The sign string precedes the number and currency symbol.

2

The sign string succeeds the number and currency symbol.

3

The sign string immediately precedes the number and currency symbol.

4

The sign string immediately succeeds the number and currency symbol.

Return Value

x

Pointer to the lconv structure.

Example

#include <stdlib.h>
#include <stdio.h>
#include <limits.h>
#include <locale.h>
#include <string.h>

/* The following test program will set up the British English   */
/* locale, and then extract the International Currency symbol   */
/* and the International Fractional Digits fields for this      */
/* locale and print them.                                       */

int main()
{
    /* Declare variables                                        */

    char *return_val;
    struct lconv *lconv_ptr;

    /* Load a locale                                            */

    return_val = (char *) setlocale(LC_ALL, "en_GB.iso8859-1");

    /* Did the locale load successfully?                        */

    if (return_val == NULL) {

        /* It failed to load the locale                         */
       printf("ERROR : The locale is unknown");
        exit(EXIT_FAILURE);
    }

    /*  Get the lconv structure from the locale                 */

    lconv_ptr = (struct lconv *) localeconv();

    /* Compare the international currency symbol string with an */
    /* empty string. If they are equal, then the international  */
    /* currency symbol is not defined in the locale.            */

    if (strcmp(lconv_ptr->int_curr_symbol, "")) {
        printf("International Currency Symbol = %s\n",
               lconv_ptr->int_curr_symbol);
    }
    else {
        printf("International Currency Symbol =");
        printf("[Not available in this locale]\n");
    }

    /* Compare International Fractional Digits with CHAR_MAX.   */
    /* If they are equal, then International Fractional Digits  */
    /* are not defined in this locale.                          */

    if ((unsigned char) (lconv_ptr->int_frac_digits) != CHAR_MAX) {
        printf("International Fractional Digits = %d\n",
               lconv_ptr->int_frac_digits);
    }
    else {
        printf("International Fractional Digits =");
        printf("[Not available in this locale]\n");
    }
}
Running the example program produces the following result:
International Currency Symbol = GBP
International Fractional Digits = 2

localtime, localtime_r

localtime, localtime_r — Convert a time value to broken-down local time.

Format

#include <time.h>
struct tm *localtime (const time_t *timer);
struct tm *localtime_r (const time_t *timer, struct tm *result);
(ISO POSIX-1)

Function Variants

Compiling with the _DECC_V4_SOURCE and _VMS_V6_SOURCE feature-test macros defined enables a local-time-based entry point to the localtime_r function that is equivalent to the behavior before OpenVMS Version 7.0.

Arguments

timer

A pointer to a time in seconds since the Epoch. You can generate this time by using the time function or you can supply a time.

result

A pointer to a tm structure where the result is stored. The tm structure is defined in the <time.h> header file, and is also shown in Table 36.

Description

The localtime and localtime_r functions convert the time (in seconds since the Epoch) pointed to by timer into a broken-down time, expressed as a local time, and store it in a tm structure.

The difference between the localtime_r and localtime functions is that the former stores the result into a user-specified tm structure. The latter stores the result into thread-specific static memory allocated by the C RTL, and which is overwritten by subsequent calls to localtime; you must make a copy if you want to save it.

On success, localtime returns a pointer to the tm structure; localtime_r returns its second argument. On failure, these functions return the NULL pointer.

The tm structure is defined in the <time.h> header file and described in Table 36.
Table 36. tm Structure

int tm_sec;

Seconds after the minute (0-60)

int tm_min;

Minutes after the hour (0-59)

int tm_hour;

Hours since midnight (0-23)

int tm_mday;

Day of the month (1-31)

int tm_mon;

Months since January (1-11)

int tm_year;

Years since 1900

int tm_wday;

Days since Sunday (0-6)

int tm_yday;

Days since January 1 (0-365)

int tm_isdst;
Daylight Savings Time flag

  • tm_isdst = 0 for Standard Time

  • tm_isdst = 1 for Daylight Time

long tm_gmtoff;?

Seconds east of Greenwich (negative values indicate seconds west of Greenwich)

char * tm_zone;?

Time zone string, for example "GMT"

The type time_t is defined in the <time.h> header file as follows: 
typedef long int time_t

Note

Generally speaking, UTC-based time functions can affect in-memory time-zone information, which is processwide data. However, if the system time zone remains the same during the execution of the application (which is the common case) and the cache of timezone files is enabled (which is the default), then the _r variant of the time functions asctime_r, ctime_r, gmtime_r and localtime_r, is both thread-safe and AST-reentrant.

If, however, the system time zone can change during the execution of the application or the cache of timezone files is not enabled, then both variants of the UTC-based time functions belong to the third class of functions, which are neither thread-safe nor AST-reentrant.

Return Values

x

Pointer to a tm structure.

NULL

Indicates failure.

log, log2, log10

log, log2, log10 — Return the logarithm of their arguments.

Format

#include <math.h>
double log (double x);
float logf (float x);
long double logl (long double x);
double log2 (double x);
float log2f (float x);
long double log2l (long double x);
double log10 (double x);
float log10f (float x);
long double log10l (long double x);

Argument

x

A real number.

Description

The log functions compute the natural (base e) logarithm of x.

The log2 functions compute the base 2 logarithm of x.

The log10 functions compute the common (base 10) logarithm of x.

Return Values

x

The logarithm of the argument (in the appropriate base).

-HUGE_VAL

x is 0 (errno is set to ERANGE), or x is negative (errno is set to EDOM).

NaN

x is NaN; errno is set to EDOM.

log1p

log1p — Computes ln(1+ y) accurately.

Format

#include <math.h>
double log1p (double y);
float log1pf (float y);
long double log1pl (long double y);

Argument

y

A real number greater than -1.

Description

The log1p functions compute ln(1+ y) accurately, even for tiny y.

Return Values

x

The natural logarithm of (1+ y).

-HUGE_VAL

y is less than -1 (errno is set to EDOM), or y = -1 (errno is set to ERANGE).

NaN

y is NaN; errno is set to EDOM.

logb

logb — Returns the radix-independent exponent of the argument.

Format

#include <math.h>
double logb (double x);
float logbf (float x);
long double logbl (long double x);

Argument

x

A nonzero, real number.

Description

The logb functions return the exponent of x, which is the integral part of log 2| x|, as a signed floating-point value, for nonzero x.

Return Values

x

The exponent of x.

-HUGE_VAL

x = 0.0; errno is set to EDOM.

+Infinity

x is +Infinity or -Infinity.

NaN

y is NaN; errno is set to EDOM.

longjmp

longjmp — Provides a way to transfer control from a nested series of function invocations back to a predefined point without returning normally; that is, by not using a series of return statements. The longjmp function restores the context of the environment buffer.

Format

#include <setjmp.h>
void longjmp (jmp_buf env, int value);

Arguments

env

The environment buffer, which must be an array of integers long enough to hold the register context of the calling function. The type jmp_buf is defined in the <setjmp.h> header file. The contents of the general-purpose registers, including the program counter (PC), are stored in the buffer.

value

Passed from longjmp to setjmp, and then becomes the subsequent return value of the setjmp call. If value is passed as 0, it is converted to 1.

Description

When setjmp is first called, it returns the value 0. If longjmp is then called, naming the same environment as the call to setjmp, control is returned to the setjmp call as if it had returned normally a second time. The return value of setjmp in this second return is the value you supply in the longjmp call. To preserve the true value of setjmp, the function calling setjmp must not be called again until the associated longjmp is called.

The setjmp function preserves the hardware general-purpose registers, and the longjmp function restores them. After a longjmp, all variables have their values as of the time of the longjmp except for local automatic variables not marked volatile. These variables have indeterminate values.

The setjmp and longjmp functions rely on the OpenVMS condition-handling facility to effect a nonlocal go to with a signal handler. The longjmp function is implemented by generating a C RTL specified signal and allowing the OpenVMS condition-handling facility to unwind back to the desired destination. The C RTL must be in control of signal handling for any VSI C image.

For VSI C to be in control of signal handling, you must establish all exception handlers through a call to the VAXC$ESTABLISH function (rather than LIB$ESTABLISH). See Section 4.2.5 and the VAXC$ESTABLISH function for more information.

Note

The C RTL provides nonstandard decc$setjmp and decc$fast_longjmp functions for Alpha and Integrity server systems. To use these nonstandard functions instead of the standard ones, a program must be compiled with the _ _FAST_SETJMP or _ _UNIX_SETJMP macros defined.

Unlike the standard longjmp function, the decc$fast_longjmp function does not convert its second argument from 0 to 1. After a call to decc$fast_longjmp, a corresponding setjmp function returns with the exact value of the second argument specified in the decc$fast_longjmp call.

Restrictions

You cannot invoke the longjmp function from an OpenVMS condition handler. However, you may invoke longjmp from a signal handler that has been established for any signal supported by the C RTL, subject to the following nesting restrictions:

  • The longjmp function will not work if invoked from nested signal handlers. The result of the longjmp function, when invoked from a signal handler that has been entered as a result of an exception generated in another signal handler, is undefined.

  • Do not invoke the setjmp function from a signal handler unless the associated longjmp is to be issued before the handling of that signal is completed.

  • Do not invoke the longjmp function from within an exit handler (established with atexit or SYS$DCLEXH). Exit handlers are invoked after image tear-down, so the destination address of the longjmp no longer exists.

  • Invoking longjmp from within a signal handler to return to the main thread of execution might leave your program in an inconsistent state. Possible side effects include the inability to perform I/O or to receive any more UNIX signals.

longname

longname — Returns the full name of the terminal.

Format

#include <curses.h>
void longname (char *termbuf, char *name);

Function Variants

The longname function has variants named _longname32 and _longname64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

termbuf

A string containing the name of the terminal.

name

A character-string buffer with a minimum length of 64 characters.

Description

The terminal name is in a readable format so that you can double-check to be sure that Curses has correctly identified your terminal. The dummy argument termbuf is required for UNIX software compatibility and serves no function in the OpenVMS environment. If portability is a concern, you must write a set of dummy routines to perform the functionality provided by the database termcap in the UNIX system environment.

lrand48

lrand48 — Generates uniformly distributed pseudorandom-number sequences. Returns 48-bit signed long integers.

Format

#include <stdlib.h>
long int lrand48 (void);

Description

The lrand48 function generates pseudorandom numbers using the linear congruential algorithm and 48-bit integer arithmetic.

It returns nonnegative, long integers uniformly distributed over the range of y values such that 0 ≤ y < 231.

Before you call the lrand48 function use either srand48, seed48, or lcong48 to initialize the random-number generator. You must initialize prior to invoking the lrand48 function, because it stores the last 48-bit X i generated into an internal buffer. (Although it is not recommended, constant default initializer values are supplied automatically if the drand48, lrand48, or mrand48 functions are called without first calling an initialization function.)

The function works by generating a sequence of 48-bit integer values, X i, according to the linear congruential formula:
       Xn+1 = (aXn+c)mod m        n >= 0
The argument m equals 2 48, so 48-bit integer arithmetic is performed. Unless you invoke the lcong48 function, the multiplier value a and the addend value c are:
      a = 5DEECE66D16 = 2736731631558
      c = B16 = 138

The value returned by the lrand48 function is computed by first generating the next 48-bit X i in the sequence. Then the appropriate bits, according to the type of data item to be returned, are copied from the high-order (most significant) bits of X i and transformed into the returned value.

See also drand48, lcong48, mrand48, seed48, and srand48.

Return Value

n

Signed nonnegative long integers uniformly distributed over the range 0 ≤ y < 231.

lrint

lrint — Rounds to the nearest integer value, rounding according to the current rounding direction.

Format

#include <math.h>
long lrint (double x);
long lrintf (float x);
long lrintl (long double x);

Argument

x

A real value.

Description

The lrint functions return the rounded integer value of x, rounded according to the current rounding direction.

Return Values

n

Upon success, the rounded integer value.

lround

lround — Rounds to the nearest integer value, rounding halfway cases away from zero regardless of the current rounding direction.

Format

#include <math.h>
long lround (double x);
long lroundf (float x);
long lroundl (long double x);

Argument

x

A real value.

Description

The lround functions return the rounded integer value of x, with halfway cases rounded away from zero regardless of the current rounding direction.

Return Values

n

Upon success, the rounded integer value.

lseek

— Positions a file to an arbitrary byte position and returns the new position.

Format

#include <unistd.h>
off_t lseek (int file_desc, off_t offset, int direction);

Arguments

file_desc

An integer returned by open, creat, dup, or dup2.

offset

The offset, specified in bytes. The off_t data type is either a 32-bit or a 64-bit integer. The 64-bit interface allows for file sizes greater than 2 GB, and can be selected at compile time by defining the _LARGEFILE feature-test macro as follows:
CC/DEFINE=_LARGEFILE

direction

An integer indicating whether the offset is to be measured forward from the beginning of the file (direction=SEEK_SET), forward from the current position (direction=SEEK_CUR), or backward from the end of the file (direction=SEEK_END).

Description

The lseek function can position a fixed-length record-access file with no carriage control or a stream-access file on any byte offset, but can position all other files only on record boundaries.

The available Standard I/O functions position a record file at its first byte, at the end-of-file, or on a record boundary. Therefore, the arguments given to lseek must specify either the beginning or end of the file, a 0 offset from the current position (an arbitrary record boundary), or the position returned by a previous, valid lseek call.

This function returns the new file position as an integer of type off_t which, like the offset argument, is either a 64-bit integer if _LARGEFILE is defined, or a 32-bit integer if not.

For a portable way to position an arbitrary byte location with any type of file, see the fgetpos and fsetpos functions.

Caution

If, while accessing a stream file, you seek beyond the end-of-file and then write to the file, the lseek function creates a hole by filling the skipped bytes with zeros.

In general, for record files, lseek should only be directed to an absolute position that was returned by a previous valid call to lseek or to the beginning or end of a file. If a call to lseek does not satisfy these conditions, the results are unpredictable.

See also open, creat, dup, dup2, and fseek.

Return Values

x

The new file position.

-1

Indicates that the file descriptor is undefined, or a seek was attempted before the beginning of the file.

lstat

lstat — Retrieves information about the specified file.

Format

#include <sys/stat.h>
int lstat (const char *restrict file_path,
struct stat *restrict user_buffer);

Arguments

file_path

The name of the file for which you want to retrieve information.

user_buffer

The stat structure in which information is returned.

Description

The lstat function retrieves information about the specified file (file_path). If the file is a symbolic link, information about the link itself is returned (in contrast to stat, which returns information about the file that the symbolic link points to).

See also symlink, unlink, readlink, realpath, and lchown.

Return Values

0

Successful completion.

-1

Indicates an error. errno is set to any errno value returned by stat.

lwait

lwait — Waits for I/O on a specific file to complete.

Format

#include <stdio.h>
int lwait (int fd);

Argument

fd

A file descriptor corresponding to an open file.

Description

The lwait function is used primarily to wait for completion of pending asynchronous I/O.

Return Values

0

Indicates successful completion.

-1

Indicates an error.

malloc

malloc — Allocates an area of memory. These functions are AST-reentrant.

Format

#include <stdlib.h>
void *malloc (size_t size);

Function Variants

The malloc function has variants named _malloc32 and _malloc64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Argument

size

The total number of bytes to be allocated.

Description

The malloc function allocates a contiguous area of memory whose size, in bytes, is supplied as an argument. The space is not initialized.

Note

The malloc routines call the system routine LIB$VM_MALLOC. Because LIB$VM_MALLOC is designed as a general-purpose routine to allocate memory, it is called upon in a wide array of scenarios to allocate and reallocate blocks efficiently. The most common usage is the management of smaller blocks of memory, and the most important aspect of memory allocation under these circumstances is efficiency.

LIB$VM_MALLOC makes use of its own free space to satisfy requests, once the heap storage is consumed by splitting large blocks and merging adjacent blocks. Memory can still become fragmented, leaving unused blocks. Once heap storage is consumed, LIB$VM_MALLOC manages its own free space and merged blocks to satisfy requests, but varying sizes of memory allocations can cause blocks to be left unused.

Because LIB$VM_MALLOC cannot be made to satisfy all situations in the best possible manner, perform your own memory management if you have special memory usage needs. This assures the best use of memory for your particular application.

The VSI OpenVMS Programming Concepts Manual explains the several memory allocation routines that are available. They are grouped into three levels of hierarchy:

  1. At the highest level are the RTL Heap Management Routines LIB$GET_VM and LIB$FREE_VM, which provide a mechanism for allocating and freeing blocks of memory of arbitrary size. Also at this level are the routines based on the concept of zones, such as LIB$CREATE_VM_ZONE, and so on.

  2. At the next level are the RTL Page Management routines LIB$GET_VM_PAGE and LIB$FREE_VM_PAGE, which allocate a specified number of contiguous pages.

  3. At the lowest level are the Memory Management System Services, such as $CRETVA and $EXPREG, that provide extensive control over address space allocation. At this level, you must manage the allocation precisely.

The maximum amount of memory allocated at once is limited to 0xFFFFD000.

Return Values

x

The address of the first byte, which is aligned on a quadword boundary (Alpha only) or an octaword boundary (Integrity servers only).

NULL

Indicates that the function is unable to allocate enough memory. errno is set to ENOMEM.

mblen

mblen — Determines the number of bytes comprising a multibyte character.

Format

#include <stdlib.h>
int mblen (const char *s, size_t n);

Arguments

s

A pointer to the multibyte character.

n

The maximum number of bytes that comprise the multibyte character.

Description

If the character is n bytes or less, the mblen function returns the number of bytes comprising the multibyte character pointed to by s. If the character is greater than n bytes, the function returns -1 to indicate an error.

This function is affected by the LC_CTYPE category of the program's current locale.

Return Values

x

The number of bytes that comprise the multibyte character, if the next n or fewer bytes form a valid character.

0

If s is NULL or a pointer to the NULL character.

-1

Indicates an error. The function sets errno to EILSEQ – Invalid character detected.

mbrlen

mbrlen — Determines the number of bytes comprising a multibyte character.

Format

#include <wchar.h>
size_t mbrlen (const char *s, size_t n, mbstate_t *ps);

Arguments

s

A pointer to a multibyte character.

n

The maximum number of bytes that comprise the multibyte character.

ps

A pointer to the mbstate_t object. If a NULL pointer is specified, the function uses its internal mbstate_t object. mbstate_t is an opaque datatype intended to keep the conversion state for the state-dependent codesets.

Description

The mbrlen function is equivalent to the call:
    mbrtowc(NULL, s, n, ps != NULL ? ps : &internal)

Where internal is the mbstate_t object for the mbrlen function.

If the multibyte character pointed to by s is of n bytes or less, the function returns the number of bytes comprising the character (including any shift sequences).

If either an encoding error occurs or the next n bytes contribute to an incomplete but potentially valid multibyte character, the function returns -1 or -2, respectively.

See also mbrtowc.

Return Values

x

The number of bytes comprising the multibyte character.

0

Indicates that s is a NULL pointer or a pointer to a null byte.

-1

Indicates an encoding error, in which case the next n or fewer bytes do not contribute to a complete and valid multibyte character. errno is set to EILSEQ; the conversion state is undefined.

-2

Indicates an incomplete but potentially valid multibyte character (all n bytes have been processed).

mbrtowc

mbrtowc — Converts a multibyte character to its wide-character representation.

Format

#include <wchar.h>
size_t mbrtowc (wchar_t *pwc, const char *s, size_t n, mbstate_t *ps);

Arguments

pwc

A pointer to the resulting wide-character code.

s

A pointer to a multibyte character.

n

The maximum number of bytes that comprise the multibyte character.

ps

A pointer to the mbstate_t object. If a NULL pointer is specified, the function uses its internal mbstate_t object. mbstate_t is an opaque datatype intended to keep the conversion state for the state-dependent codesets.

Description

If s is a NULL pointer, mbrtowc is equivalent to the call: 
    mbrtowc(NULL, "", 1, ps)

In this case, the values of pwc and n are ignored.

If s is not a NULL pointer, mbrtowc inspects at most n bytes beginning with the byte pointed to by s to determine the number of bytes needed to complete the next multibyte character (including any shift sequences).

If the function determines that the next multibyte character is completed, it determines the value of the corresponding wide character and then, if pwc is not a NULL pointer, stores that value in the object pointed to by pwc. If the corresponding wide character is the null wide character, the resulting state described is the initial conversion state.

If mbrtowc is called as a counting function, which means that pwc is a NULL pointer and s is neither a NULL pointer nor a pointer to a null byte, the value of the internal mbstate_t object will remain unchanged.

Return Values

x

The number of bytes comprising the multibyte character.

0

The next n or fewer bytes complete the multibyte character that corresponds to the null wide character (which is the value stored if pwc is not a NULL pointer). The wide-character code corresponding to a null byte is zero.

-1

Indicates an encoding error. The next n or fewer bytes do not contribute to a complete and valid multibyte character. errno is set to EILSEQ. The conversion state is undefined.

-2

Indicates an incomplete but potentially valid multibyte character (all n bytes have been processed).

mbstowcs

mbstowcs — Converts a sequence of multibyte characters into a sequence of corresponding wide-character codes.

Format

#include <stdlib.h>
size_t mbstowcs (wchar_t *pwcs, const char *s, size_t n);

Arguments

pwcs

A pointer to the array containing the resulting sequence of wide-character codes.

s

A pointer to the array of multibyte characters.

n

The maximum number of wide-character codes that can be stored in the array pointed to by pwcs.

Description

The mbstowcs function converts a sequence of multibyte characters from the array pointed to by s to a sequence of wide-character codes that are stored into the array pointed to by pwcs, up to a maximum of n codes.

This function is affected by the LC_CTYPE category of the program's current locale. If copying takes place between objects that overlap, the behavior is undefined.

Return Values

x

The number of array elements modified or required, not included any terminating zero code. The array will not be zero-terminated if the value returned is n. If pwcs is the NULL pointer, mbstowcs returns the number of elements required for the wide-character array.

size_t-1

Indicates that an error occurred. The function sets errno to EILSEQ - Invalid character detected.

mbtowc

mbtowc — Converts a multibyte character to its wide-character equivalent.

Format

#include <stdlib.h>
int mbtowc (wchar_t *pwc, const char *s, size_t n);

Arguments

pwc

A pointer to the resulting wide-character code.

s

A pointer to the multibyte character.

n

The maximum number of bytes that comprise the next multibyte character.

Description

If the character is n or fewer bytes, the mbtowc function converts the multibyte character pointed to by s to its wide-character equivalent. If the character is invalid or greater than n bytes, the function returns -1 to indicate an error.

If pwc is a NULL pointer and s is not a null pointer, the function determines the number of bytes that constitute the multibyte character pointed to by s (regardless of the value of n).

This function is affected by the LC_CTYPE category of the program's current locale.

Return Values

x

The number of bytes that comprise the valid character pointed to by s.

0

If s is either a NULL pointer or a pointer to the null byte.

-1

Indicates an error. The function sets errno to EILSEQ – Invalid character detected.

mbsinit

mbsinit — Determines whether an mbstate_t object describes an initial conversion state.

Format

#include <wchar.h>
int mbsinit (const mbstate_t *ps);

Argument

ps

A pointer to the mbstate_t object. mbstate_t is an opaque datatype intended to keep the conversion state for the state-dependent codesets.

Description

If ps is not a NULL pointer, the mbsinit function determines whether the mbstate_t object pointed to by ps describes an initial conversion state. A zero mbstate_t object always describes an initial conversion state.

Return Values

nonzero

The ps argument is a NULL pointer, or the mbstate_t object pointed to by ps describes an initial conversion state.

0

The mbstate_t object pointed to by ps does not describe an initial conversion state.

mbsrtowcs

mbsrtowcs — Converts a sequence of multibyte characters to a sequence of corresponding wide-character codes.

Format

#include <wchar.h>
size_t mbsrtowcs (wchar_t *dst, const char **src, size_t len,
mbstate_t *ps);

Function Variants

The mbsrtowcs function has variants named _mbsrtowcs32 and _mbsrtowcs64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

dst

A pointer to the destination array containing the resulting sequence of wide-character codes.

src

An address of the pointer to an array containing a sequence of multibyte characters to be converted.

len

The maximum number of wide character codes that can be stored in the array pointed to by dst.

ps

A pointer to the mbstate_t object. If a NULL pointer is specified, the function uses its internal mbstate_t object. mbstate_t is an opaque datatype intended to keep the conversion state for the state-dependent codesets.

Description

The mbsrtowcs function converts a sequence of multibyte characters, beginning in the conversion state described by the object pointed to by ps, from the array indirectly pointed to by src, into a sequence of corresponding wide characters.

If dst is not a NULL pointer, the converted characters are stored into the array pointed to by dst. Conversion continues up to and including a terminating null character, which is also stored.

Conversion stops earlier for one of the following reasons:

  • A sequence of bytes is encountered that does not form a valid multibyte character.

  • If dst is not a NULL pointer, when len codes have been stored into the array pointed to by dst.

If dst is not a NULL pointer, the pointer object pointed to by src is assigned either a NULL pointer (if the conversion stopped because of reaching a terminating null wide character), or the address just beyond the last multibyte character converted (if any). If conversion stopped because of reaching a terminating null wide character, the resulting state described is the initial conversion state.

Return Values

n

The number of multibyte characters successfully converted, sequence, not including the terminating null (if any).

-1

Indicates an error. A sequence of bytes that do not form valid multibyte character was encountered. errno is set to EILSEQ; the conversion state is undefined.

memccpy

memccpy — Copies characters sequentially between strings in memory areas.

Format

#include <string.h>
void *memccpy (void *dest, void *source, int c, size_t n);

Function Variants

The memccpy function has variants named _memccpy32 and _memccpy64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

dest

A pointer to the location of a destination string.

source

A pointer to the location of a source string.

c

A character that you want to search for.

n

The number of character you want to copy.

Description

The memccpy function operates on strings in memory areas. A memory area is a group of contiguous characters bound by a count and not terminated by a null character. The function does not check for overflow of the receiving memory area. The memccpy function is defined in the <string.h> header file.

The memccpy function sequentially copies characters from the location pointed to by source into the location pointed to by dest until one of the following occurs:

  • The character specified by c (converted to an unsigned char) is copied.

  • The number of characters specified by n is copied.

Return Values

x

A pointer to the character following the character specified by c in the string pointed to by dest.

NULL

Indicates an error. The character c is not found after scanning n characters in the string.

memchr

memchr — Locates the first occurrence of the specified byte within the initial size bytes of a given object.

Format

#include <string.h>
void *memchr (const void *s1, int c, size_t size);

Function Variants

The memchr function has variants named _memchr32 and _memchr64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

s1

A pointer to the object to be searched.

c

The byte value to be located.

size

The length of the object to be searched.

If size is zero, memchr returns NULL.

Description

Unlike strchr, the memchr function does not stop when it encounters a null character.

Return Values

pointer

A pointer to the first occurrence of the byte.

NULL

Indicates that the specified byte does not occur in the object.

memcmp

memcmp — Compares two objects, byte by byte. The compare operation starts with the first byte in each object.

Format

#include <string.h>
int memcmp (const void *s1, const void *s2, size_t size);

Arguments

s1

A pointer to the first object.

s2

A pointer to the second object.

size

The length of the objects to be compared.

If size is zero, the two objects are considered equal.

Description

The memcmp function uses native byte comparison. The sign of the value returned is determined by the sign of the difference between the values of the first pair of unlike bytes in the objects being compared. Unlike the strcmp function, the memcmp function does not stop when a null character is encountered.

Return Value

x

An integer less than, equal to, or greater than 0, depending on whether the lexical value of the first object is less than, equal to, or greater than that of the second object.

memcpy

memcpy — Copies a specified number of bytes from one object to another.

Format

#include <string.h>
void *memcpy (void *dest, const void *source, size_t size);

Function Variants

The memcpy function has variants named _memcpy32 and _memcpy64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

dest

A pointer to the destination object.

source

A pointer to the source object.

size

The length of the object to be copied.

Description

The memcpy function copies size bytes from the object pointed to by source to the object pointed to by dest; it does not check for the overflow of the receiving memory area (dest). Unlike the strcpy function, the memcpy function does not stop when a null character is encountered.

Return Value

x

The value of dest.

memmove

memmove — Copies a specified number of bytes from one object to another.

Format

#include <string.h>
void *memmove (void *dest, const void *source, size_t size);

Function Variants

The memmove function has variants named _memmove32 and _memmove64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

dest

A pointer to the destination object.

source

A pointer to the source object.

size

The length of the object to be copied.

Description

In VSI C for OpenVMS systems, memmove and memcpy perform the same function. Programs that require portability should use memmove if the area pointed at by dest could overlap the area pointed at by source.

Return Value

x

The value of dest.

Example

#include <string.h>
#include <stdio.h>

main()
{
   char pdest[14] = "hello   there";
   char *psource = "you are there";

   memmove(pdest, psource, 7);
   printf("%s\n", pdest);
}
This example produces the following output:
you are there

mempcpy

mempcpy — Copies a specified number of bytes from one object to another and returns a pointer to the byte following the last written byte.

Format

#include <string.h>
void *mempcpy (void *dest, const void *source, size_t size);

Function Variants

The mempcpy function has variants named _mempcpy32 and _mempcpy64 for use with 32-bit and 64-bit pointer sizes, respectively.

Arguments

dest

A pointer to the destination object.

source

A pointer to the source object.

size

The length of the object to be copied, in bytes.

Description

The mempcpy function, similar to the memcpy function, copies size bytes from the object pointed to by source to the object pointed to by dest; it does not check for the overflow of the receiving memory area (dest). Instead of returning the value of dest, mempcpy returns a pointer to the byte following the last written byte.

Return Value

x

A pointer to the byte following the last written byte.

memset

memset — Sets a specified number of bytes in a given object to a given value.

Format

#include <string.h>
void *memset (void *s, int value, size_t size);

Function Variants

The memset function has variants named _memset32 and _memset64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

s

An array pointer.

value

The value to be placed in s.

size

The number of bytes to be placed in s.

Description

The memset function copies value (converted to an unsigned char) into each of the first size characters of the object pointed to by s.

This function returns s. It does not check for the overflow of the receiving memory area pointed to by s.

Return Value

x

The value of s.

mkdir

mkdir — Creates a directory.

Format

#include <stat.h>
int mkdir (const char *dir_spec, mode_t mode); (ISO POSIX-1)
int mkdir (const char *dir_spec, mode_t mode, ...); (VSI C Extension)

Arguments

dir_spec

A valid OpenVMS or UNIX style directory specification that may contain a device name. For example: 
DBA0:[BAY.WINDOWS]     /*    OpenVMS      */
/dba0/bay/windows      /*   UNIX style    */

This specification cannot contain a node name, filename, file extension, file version, or a wildcard character. The same restriction applies to the UNIX style directory specifications. For more information about the restrictions on UNIX style specifications, see Chapter 1.

mode

A file protection. See the chmod function in this section for information about the specific file protections.

The file protection of the new directory is derived from the mode argument, the process's file protection mask (see the umask function), and the parent-directory default protections.

In a manner consistent with the OpenVMS behavior for creating directories, mkdir never applies delete access to the directory. An application that needs to set delete access should use an explicit call to chmod to set write permission.

See the Description section of this function for more information about how the file protection is set for the newly created directory.

. . .

Represents the following optional arguments. These arguments have fixed position in the argument list, and cannot be arbitrarily placed.
  • unsigned int uic
  • The user identification code (UIC) that identifies the owner of the created directory. If this argument is 0, the C RTL gives the created directory the UIC of the parent directory. If this argument is not specified, the C RTL gives the created directory your UIC. This optional argument is specific to the C RTL and is not portable.
  • unsigned short max_versions
  • The maximum number of file versions to be retained in the created directory. The system automatically purges the directory keeping, at most, max_versions number of every file. If this argument is 0, the C RTL does not place a limit on the maximum number of file versions. If this argument is not specified, the C RTL gives the created directory the default version limit of the parent directory. This optional argument is specific to the C RTL and is not portable.
  • unsigned short r_v_number
  • The volume (device) on which to place the created directory if the device is part of a volume set. If this argument is not specified, the C RTL arbitrarily places the created directory within the volume set. This optional argument is specific to the C RTL and is not portable.

Description

If dir_spec specifies a path that includes directories, which do not exist, intermediate directories are also created. This differs from the behavior of the UNIX system where these intermediate directories must exist and will not be created.

If you do not specify any optional arguments, the C RTL gives the directory your UIC and the default version limit of the parent directory, and arbitrarily places the directory within the volume set. You cannot get the default behavior for the uic or max_versions arguments if you specify any arguments after them.

Note

The way to create files with OpenVMS RMS default protections using the UNIX system-call functions umask, mkdir, creat, and open is to call mkdir, creat, and open with a file-protection mode argument of 0777 in a program that never specifically calls umask. These default protections include correctly establishing protections based on ACLs, previous versions of files, and so on.

In programs that do vfork/exec calls, the new process image inherits whether umask has ever been called or not from the calling process image. The umask setting and whether the umask function has ever been called are both inherited attributes.

The file protection supplied by the mode argument is modified by the process's file protection mask in such a way that the file protection for the new directory is set to the bitwise AND of the mode argument and the complement of the file protection mask.

Default file protections are supplied to the new directory from the parent-directory such that if a protection value bit in the new directory is zero, then the value of this bit is inherited from the parent directory. However, bits in the parent directory's file protection that indicate delete access do not cause corresponding bits to be set in the new directory's file protection.

Return Values

0

Indicates success.

-1

Indicates failure.

Examples

  1. umask (0002); /* turn world write access off */
mkdir ("sys$disk:[.parentdir.childdir]", 0222); /* turn write
                                                   access on */

Parent directory file protection: System:RWD, Owner:RWD, Group:R,
                                                           World:R
    The file protection derived from the combination of the mode argument and the file protection mask set by umask is (0222) & ~(0002), which is 0220. When the parent directory defaults are applied to this protection, the protection for the new directory becomes: 
    File protection:    System:RWD, Owner:RWD, Group:RWD, World:R
  2. umask (0000);
mkdir ("sys$disk:[.parentdir.childdir]", 0444);  /* turn read
                                                    access on */

Parent directory file protection: System:RWD, Owner:RWD,
                                               Group:RWD, World:RWD
    The file protection derived from the combination of the mode argument and the file protection mask set by umask is (0444) & ~(0000), which is 0444. When the parent directory defaults are applied to this protection, the protection for the new directory is:
    File protection:    System:RW, Owner:RW, Group:RW, World:RW

    Note that delete access is not inherited.

mkostemp

mkostemp — Constructs a unique filename, creates and opens the file specifying some flags.

Format

#include <stdlib.h>
int mkostemp (char *template, int flags)

Arguments

template

A pointer to a string that is replaced with a unique filename. The string in the template argument must be a filename with six trailing Xs.

flags

Zero or more of the flags as for the open function.

Description

The mkostemp function is equivalent to mkstemp, with the difference that flags as for open may be specified in flags.

The mkostemp function replaces the six trailing Xs of the string pointed to by template with a unique set of characters, and returns a file descriptor for the file opened using the flags specified in flags.

The string pointed to by template should look like a filename with six trailing Xs. The mkostemp function replaces each X with a character from the portable filename character set, making sure not to duplicate an existing filename.

If the string pointed to by template does not contain six trailing Xs, -1 is returned.

Return Values

x

An open file descriptor.

-1

Indicates an error. The string pointed to by template does not contain six trailing Xs.

mkstemp

mkstemp — Constructs a unique filename, creates and opens the file.

Format

#include <stdlib.h>
int mkstemp (char *template);

Argument

template

A pointer to a string that is replaced with a unique filename. The string in the template argument must be a filename with six trailing Xs.

Description

The mkstemp function replaces the six trailing Xs of the string pointed to by template with a unique set of characters, and returns a file descriptor for the file open for reading and writing.

The string pointed to by template should look like a filename with six trailing Xs. The mkstemp function replaces each X with a character from the portable file-name character set, making sure not to duplicate an existing filename.

If the string pointed to by template does not contain six trailing Xs, -1 is returned.

Return Values

x

An open file descriptor.

-1

Indicates an error. The string pointed to by template does not contain six trailing Xs.

mktemp

mktemp — Creates a unique filename from a template.

Format

#include <stdlib.h>
char *mktemp (char *template);

Function Variants

The mktemp function has variants named _mktemp32 and _mktemp64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Argument

template

A pointer to a buffer containing a user-defined template. You supply the template in the form, namXXXXXX. The six trailing Xs are replaced by a unique series of characters. You may supply the first three characters. Because the template argument is overwritten, do not specify a string literal (const object).

Description

The use of mktemp is not recommended for new applications. See the tmpnam and mkstemp functions for the preferable alternatives.

Return Value

x

A pointer to the template, with the template modified to contain the created filename. If this value is a pointer to a null string, it indicates that a unique filename cannot be created.

mktime

mktime — Converts a local-time structure to a time, in seconds, since the Epoch.

Format

#include <time.h>
time_t mktime (struct tm *timeptr);

Function Variants

Compiling with the _DECC_V4_SOURCE and _VMS_V6_SOURCE feature-test macros defined enables a local-time-based entry point to the mktime function that is equivalent to the behavior before OpenVMS Version 7.0.

Argument

timeptr

A pointer to the local-time structure.

Description

The mktime function converts a local-time structure (struct tm) pointed to by timeptr, to a time in seconds since the Epoch (a time_t variable), in the same manner as the values returned by the time function.

The original values of the tm_wday and tm_yday components of the structure are ignored, and the original values of the other components are not restricted to the ranges defined in <time.h>. Upon successful completion, the tm_wday and tm_yday components of the structure are set appropriately, and the other components are set to represent the specified time, with their values forced to the normal range.

If the local time cannot be encoded, then mktime returns the value (time_t)(-1).

The time_t type is defined in the <time.h> header file as follows:
typedef unsigned long int time_t;

Local time-zone information is set as if mktime called tzset.

If the tm_isdst field in the local-time structure pointed to by timeptr is positive, mktime initially presumes that Daylight Savings Time (DST) is in effect for the specified time.

If tm_isdst is 0, mktime initially presumes that DST is not in effect.

If tm_isdst is negative, mktime attempts to determine whether or not DST is in effect for the specified time.

Return Values

x

The specified calendar time encoded as a value of type time_t.

(time_t)(-1)

If the local time cannot be encoded.

Be aware that a return value of (time_t)(-1) can also represent the valid date: Sun Feb 7 06:28:15 2106.)

mmap

mmap — Maps file system object into virtual memory. This function is reentrant.

Format

#include <types.h>
#include <mman.h>
void mmap (void *addr, size_t len, int prot, int flags, int filedes,
off_t off); (X/Open, POSIX-1)
void mmap (void *addr, size_t len, int prot, int flags, int filedes,
off_t off ...); (VSI C Extension)

Function Variants

The mmap function has variants named _mmap32 and _mmap64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

addr

The starting address of the new region (must be the page boundary).

len

The length, in bytes, of the new region.

prot

Access permission, as defined in the <mman.h> header file. Specify either PROT_NONE, PROT_READ, or PROT_WRITE.

flags

Attributes of the mapped region as the results of a bitwise-inclusive OR operation on any combination of the following:

  • MAP_FILE or MAP_ANONYMOUS

  • MAP_VARIABLE or MAP_FIXED

  • MAP_SHARED or MAP_PRIVATE

filedes

The file that you want to map to the new mapped file region returned by the open function.

off

The offset, specified in bytes. The off_t data type is either a 64-bit or 32-bit integer. The 64-bit interface allows for file sizes greater than 2 GB, and can be selected at compile time by defining the _LARGEFILE feature-test macro as follows:
CC/DEFINE=_LARGEFILE

. . .

An optional integer specifying additional flags for the SYS$CRMPSC system service for MAP_SHARED. This optional argument (VSI C Extension) of the mmap function was introduced in OpenVMS Version 7.2.

Description

The mmap function creates a new mapped file region, a new private region, or a new shared memory region.

Your application must ensure correct synchronization when using mmap in conjunction with any other file access method, such as read and write, and standard input/output.

Before calling mmap, the calling application must also ensure that all bytes in the range [ off, off+ len] are written to the file (using the fsync function, for example). If this requirement is not met, mmap fails with errno set to ENXIO (No such device or address).

The addr and len arguments specify the requested starting address and length, in bytes, for the new region. The address is a multiple of the page size returned by sysconf(_SC_PAGE_SIZE).

If the len argument is not a multiple of the page size returned by sysconf(_SC_PAGE_SIZE), then the result of any reference to an address between the end of the region and the end of the page containing the end of the region is undefined.

The flags argument specifies attributes of the mapped region. Values for flags are constructed by a bitwise-inclusive OR operation on the flags from the following list of symbolic names defined in the <mman.h> header file:

MAP_FILE

Create a mapped file region.

MAP_ANONYMOUS

Create an unnamed memory region.

MAP_VARIABLE

Place region at the computed address.

MAP_FIXED

Place region at fixed address.

MAP_SHARED

Share changes.

MAP_PRIVATE

Changes are private.

The MAP_FILE and MAP_ANONYMOUS flags control whether the region you want to map is a mapped file region or an anonymous shared memory region. One of these flags must be selected.

If MAP_FILE is set in the flags argument:

  • A new mapped file region is created, mapping the file associated with the filedes argument.

  • The off argument specifies the file byte offset where the mapping starts. This offset must be a multiple of the page size returned by sysconf(_SC_PAGE_SIZE).

  • If the end of the mapped file region is beyond the end of the file, the result of any reference to an address in the mapped file region corresponding to an offset beyond the end of the file is unspecified.

If MAP_ANONYMOUS is set in the flags argument:

  • A new memory region is created and initialized to all zeros.

  • The filedes argument is ignored.

The new region is placed at the requested address if the requested address is not null and it is possible to place the region at this address. When the requested address is null or the region cannot be placed at the requested address, the MAP_VARIABLE and MAP_FIXED flags control the placement of the region. One of these flags must be selected.

If MAP_VARIABLE is set in the flags argument:

  • If the requested address is null or if it is not possible for the system to place the region at the requested address, the region is placed at an address selected by the system.

If MAP_FIXED is set in the flags argument:

  • If the requested address is not null, the mmap function succeeds even if the requested address is already part of another region. (If the address is within an existing region, the effect on the pages within that region and within the area of the overlap produced by the two regions is the same as if they were unmapped. In other words, whatever is mapped between addr and addr + len is unmapped.)

  • If the requested address is null and MAP_FIXED is specified, the results are undefined.

The MAP_PRIVATE and MAP_SHARED flags control the visibility of modifications to the mapped file or shared memory region. One of these flags must be selected.

If MAP_SHARED is set in the flags argument:

  • If the region is a mapped region, modifications to the region are visible to other processes that mapped the same region using MAP_SHARED.

  • If the region is a mapped file region, modifications to the region are written to the file. (Note that the modifications are not immediately written to the file because of buffer cache delay; that is, the write to the file does not occur until there is a need to reuse the buffer cache. If the modifications must be written to the file immediately, use the msync function to ensure that this is done.)

If MAP_PRIVATE is set in the flags argument:

  • Modifications to the mapped region by the calling process are not visible to other processes that mapped the same region using either MAP_PRIVATE or MAP_SHARED.

  • Modifications to the mapped region by the calling process are not written to the file.

It is unspecified whether modifications by processes that mapped the region using MAP_SHARED are visible to other processes that mapped the same region using MAP_PRIVATE.

The prot argument specifies access permissions for the mapped region. Specify one of the following:

PROT_NONE

No access

PROT_READ

Read-only

PROT_WRITE

Read/Write access

After the successful completion of the mmap function, you can close the filedes argument without effect on the mapped region or on the contents of the mapped file. Each mapped region creates a file reference, similar to an open file descriptor, that prevents the file data from being deallocated.

Note

The following rules apply to OpenVMS specific file references:

  • Because of the additional file reference, if filedes is not opened for file sharing, mmap reopens it with file sharing enabled.

  • The additional file reference that remains for mapped regions implies that a later open, fopen, or create call to the file that is mapped must specify file sharing.

Modifications made to the file using the write function are visible to mapped regions, and modifications to a mapped region are visible with the read function.

Note

Beginning with OpenVMS Version 7.2, while processing a MAP_SHARED request, the mmap function constructs the flags argument of the SYS$CRMPSC service as a bitwise inclusive OR of those bits it sets by itself to fulfill the MAP_SHARED request and those bits specified by the caller in the optional argument.

By default, for MAP_SHARED the mmap function creates a temporary group global section. The optional mmap argument provides the caller with direct access to the features of the SYS$CRMPSC system service.

Using the optional argument, the caller can create, for example, a system global section (SEC$M_SYSGBL bit) or permanent global section (SEC$M_PERM bit). For example, to create a system permanent global section, the caller can specify (SEC$M_SYSGBL | SEC$M_PERM) in the optional argument.

The mmap function does not check or set any privileges. It is the responsibility of the caller to set appropriate privileges, such as SYSGBL privilege for SEC$M_SYSGBL, and PRMGBL for SEC$M_PERM, before calling mmap with the optional argument.

See also read, write, open, fopen, creat, and sysconf.

Return Values

x

The address where the mapping is placed.

MAP_FAILED
Indicates an error; errno is set to one of the following values:

  • EACCES– The file referred to by filedes is not open for read access, or the file is not open for write access and PROT_WRITE was set for a MAP_SHARED mapping operation.

  • EBADF– The filedes argument is not a valid file descriptor.

  • EINVAL–The flags or prot argument is invalid, or the addr argument or off argument is not a multiple of the page size returned by sysconf(_SC_PAGE_SIZE).

  • ENODEV– The file descriptor filedes refers to an object that cannot be mapped, such as a terminal.

  • ENOMEM– There is not enough address space to map len bytes.

  • ENXIO– The addresses specified by the range [off, off + len] are invalid for filedes.

  • EFAULT– The addr argument is an invalid address.

modf

modf — Decomposes a floating-point number.

Format

#include <math.h>
double modf (double x, double *iptr);
float modff (float x, float *iptr);
long double modfl (long double x, long double *iptr);

Arguments

x

An object of type double, float, or long double.

iptr

A pointer to an object of type double, float, or long double to match the type of x.

Description

The modf functions decompose their first argument x into a positive fractional part f and an integer part i, each of which has the same sign as x.

The functions return f and assign i to the object pointed to by the second argument (iptr).

Return Values

x

The fractional part of the argument x.

NaN

x is NaN; errno is set to EDOM and * iptr is set to NaN.

0

Underflow occurred; errno is set to ERANGE.

[w]move

[w]move — Change the current cursor position on the specified window to the coordinates (y, x). The move function acts on the stdscr window.

Format

#include <curses.h>
int move (int y, int x);
int wmove (WINDOW *win, int y, int x);

Arguments

win

A pointer to the window.

y

A window coordinate.

x

A window coordinate.

Description

For more information, see the scrollok function in this section.

Return Values

OK

Indicates success.

ERR

Indicates that the function makes the screen scroll illegally.

mprotect

mprotect — Modifies access protections of memory mapping. This function is reentrant.

Format

#include <mman.h>
int mprotect (void *addr, size_t len, int prot);

Arguments

addr

The address of the region that you want to modify.

len

The length, in bytes, of the region that you want to modify.

prot

Access permission, as defined in the <mman.h> header file. Specify either PROT_NONE, PROT_READ, or PROT_WRITE.

Description

The mprotect function modifies the access protection of a mapped file or shared memory region.

The addr and len arguments specify the address and length, in bytes, of the region that you want to modify. The len argument must be a multiple of the page size as returned by sysconf(_SC_PAGE_SIZE). If len is not a multiple of the page size as returned by sysconf(_SC_PAGE_SIZE), the length of the region is rounded up to the next multiple of the page size.

The prot argument specifies access permissions for the mapped region. Specify one of the following:

PROT_NONE

No access

PROT_READ

Read-only

PROT_WRITE

Read/Write access

The mprotect function does not modify the access permission of any region that lies outside of the specified region, except that the effect on addresses between the end of the region, and the end of the page containing the end of the region, is unspecified.

If the mprotect function fails under a condition other than that specified by EINVAL, the access protection of some of the pages in the range [addr, addr + len] can change. Suppose the error occurs on some page at an addr2; mprotect can modify protections of all whole pages in the range [ addr, addr2].

See also sysconf.

Return Values

0

Indicates success.

-1
Indicates an error; errno is set to one of the following values:

  • EACCESS– The prot argument specifies a protection that conflicts with the access permission set for the underlying file.

  • EINVAL– The prot argument is invalid, or the addr argument is not a multiple of the page size as returned by sysconf(_SC_PAGE_SIZE).

  • EFAULT– The range [ addr, addr + len] includes an invalid address.

mrand48

mrand48 — Generates uniformly distributed pseudorandom-number sequences. Returns 48-bit signed long integers.

Format

#include <stdlib.h>
long int mrand48 (void);

Description

The mrand48 function generates pseudorandom numbers using the linear congruential algorithm and 48-bit integer arithmetic.

It returns signed long integers uniformly distributed over the range of y values such that -2 31 ≤ y < 2 31.

Before you call the mrand48 function, use either srand48, seed48, or lcong48 to initialize the random-number generator. You must initialize the mrand48 function prior to invoking it, because it stores the last 48-bit Xi generated into an internal buffer. (Although it is not recommended, constant default initializer values are supplied automatically if the drand48, lrand48, or mrand48 functions are called without first calling an initialization function.)

The function works by generating a sequence of 48-bit integer values, Xi, according to the linear congruential formula:
       Xn+1 = (aXn+c)mod m        n >= 0
The argument m equals 2 48, so 48-bit integer arithmetic is performed. Unless you invoke the lcong48 function, the multiplier value a and the addend value care:
      a = 5DEECE66D16 = 2736731631558
      c = B16 = 138

The values returned by the mrand48 function is computed by first generating the next 48-bit Xi in the sequence. Then the appropriate bits, according to the type of returned data item, are copied from the high-order (most significant) bits of Xi and transformed into the returned value.

See also drand48, lrand48, lcong48, seed48, and srand48.

Return Value

n

Returns signed long integers uniformly distributed over the range -2 31 ≤ y < 2 31.

msync

msync — Synchronizes a mapped file.

Format

#include <mman.h>
int msync (void *addr, size_t len, int flags);

Arguments

addr

The address of the region that you want to synchronize.

len

The length, in bytes, of the region that you want to synchronize.

flags

One of the following symbolic constants defined in the <mman.h> header file:

MS_SYNC

Synchronous cache flush

MS_ASYNC

Asynchronous cache flush

MS_INVALIDATE

Invalidate cashed pages

Description

The msync function controls the caching operations of a mapped file region. Use msync to:

  • Ensure that modified pages in the region transfer to the underlying storage device of the file.

  • Control the visibility of modifications with respect to file system operations.

The addr and len arguments specify the region to be synchronized. The len argument must be a multiple of the page size as returned by sysconf(_SC_PAGE_SIZE); otherwise, the length of the region is rounded up to the next multiple of the page size.

If the flags argument is set to:

flags Argument

Then the msync Function...

MS_SYNC

Does not return until the system completes all I/O operations.

MS_ASYNC

Returns after the system schedules all I/O operations.

MS_INVALIDATE

Invalidates all cached copies of the pages. The operating system must obtain new copies of the pages from the file system the next time the application references them.

After a successful call to the msync function with the flags argument set to:

  • MS_SYNC– All previous modifications to the mapped region are visible to processes using the read argument. Previous modifications to the file using the write function are lost.

  • MS_INVALIDATE– All previous modifications to the file using the write function are visible to the mapped region. Previous direct modifications to the mapped region are lost.

See also read, write, and sysconf.

Return Values

0

Indicates success.

-1
Indicates an error; errno is set to one of the following values:

  • EIO– An I/O error occurred while reading from or writing to the file system.

  • ENOMEM– The range specified by [addr, addr + len] is invalid for a process's address space, or the range specifies one or more unmapped pages.

  • EINVAL– The addr argument is not a multiple of the page size as returned by sysconf(_SC_PAGE_SIZE).

  • EFAULT– The range [addr, addr + len] includes an invalid address.

munmap

munmap — Unmaps a mapped region. This function is reentrant.

Format

#include <mman.h>
int munmap (void *addr, size_t len);

Arguments

addr

The address of the region that you want to unmap.

len

The length, in bytes, of that region the you want to unmap.

Description

The munmap function unmaps a mapped file or shared memory region.

The addr and len arguments specify the address and length, in bytes, respectively, of the region to be unmapped.

The len argument must be a multiple of the page size as returned by sysconf(_SC_PAGE_SIZE); otherwise, the length of the region is rounded up to the next multiple of the page size.

The result of using an address that lies in an unmapped region and not in any subsequently mapped region is undefined.

See also sysconf.

Return Values

0

Indicates success.

-1
Indicates an error; errno is set to one of the following values:

  • ENIVAL– The addr argument is not a multiple of the page size as returned by sysconf(_SC_PAGE_SIZE).

  • EFAULT– The range [addr, addr + len] includes an invalid address.

mv[w]addch

mv[w]addch — Move the cursor to coordinates (y, x) and add a character to the specified window.

Format

#include <curses.h>
int mvaddch (int y, int x, char ch);
int mvwaddch (WINDOW *win, int y, int x, char ch);

Arguments

win

A pointer to the window.

y

A window coordinate.

x

A window coordinate.

ch

If this argument is a new-line character (\n), the mvaddch and mvwaddch functions clear the line to the end, and move the cursor to the next line at the same x coordinate. A carriage return ( \r) moves the cursor to the beginning of the specified line. A tab ( \t) moves the cursor to the next tabstop within the window.

Description

This routine performs the same function as mvwaddch, but on the stdscr window.

When mvwaddch is used on a subwindow, it writes the character onto the underlying window as well.

Return Values

OK

Indicates success.

ERR

Indicates that writing the character would cause the screen to scroll illegally. For more information, see the scrollok function.

mv[w]addstr

mv[w]addstr — Move the cursor to coordinates (y, x) and add the specified string, to which str points, to the specified window.

Format

#include <curses.h>
int mvaddstr (int y, int x, char *str);
int mvwaddstr (WINDOW *win, int y, int x, char *str);

Arguments

win

A pointer to the window.

y

A window coordinate.

x

A window coordinate.

str

A pointer to the character string.

Description

This routine performs the same function as mvwaddstr, but on the stdscr window.

When mvwaddstr is used on a subwindow, the string is written onto the underlying window as well.

Return Values

OK

Indicates success.

ERR

Indicates that the function causes the screen to scroll illegally, but it places as much of the string onto the window as possible. For more information, see the scrollok function.

mvcur

mvcur — Moves the terminal's cursor from (lasty, lastx) to (newy, newx).

Format

#include <curses.h>
int mvcur (int lasty, int lastx, int newy, int newx);

Arguments

lasty

The cursor position.

lastx

The cursor position.

newy

The resulting cursor position.

newx

The resulting cursor position.

Description

In VSI C for OpenVMS systems, mvcur and move perform the same function.

See also move.

Return Values

OK

Indicates success.

ERR

Indicates that moving the window placed part or all of the window off the edge of the terminal screen. The terminal screen remains unaltered.

mv[w]delch

mv[w]delch — Move the cursor to coordinates (y, x) and delete the character on the specified window. The mvdelch function acts on the stdscr window.

Format

#include <curses.h>
int mvdelch (int y, int x);
int mvwdelch (WINDOW *win, int y, int x);

Arguments

win

A pointer to the window.

y

A window coordinate.

x

A window coordinate.

Description

Each of the following characters on the same line shifts to the left, and the last character becomes blank.

Return Values

OK

Indicates success.

ERR

Indicates that deleting the character would cause the screen to scroll illegally. For more information, see the scrollok function.

mv[w]getch

mv[w]getch — Move the cursor to coordinates (y, x), get a character from the terminal screen, and echo it on the specified window. The mvgetch function acts on the stdscr window.

Format

#include <curses.h>
int mvgetch (int y, int x);
int mvwgetch (WINDOW *win, int y, int x);

Arguments

win

A pointer to the window.

y

A window coordinate.

x

A window coordinate.

Description

The mvgetch and mvwgetch functions refresh the specified window before fetching the character.

Return Values

x

The returned character.

ERR

Indicates that the function causes the screen to scroll illegally. For more information, see the scrollok function in this section.

mv[w]getstr

mv[w]getstr — Move the cursor to coordinates (y, x), get a string from the terminal screen, store it in the variable str (which must be large enough to contain the string), and echo it on the specified window. The mvgetstr function acts on the stdscr window.

Format

#include <curses.h>
int mvgetstr (int y, int x, char *str);
int mvwgetstr (WINDOW *win, int y, int x, char *str);

Arguments

win

A pointer to the window.

y

A window coordinate.

x

A window coordinate.

str

The string that is displayed.

Description

The mvgetstr and mvwgetstr functions strip the new-line terminator (\n) from the string.

Return Values

OK

Indicates success.

ERR

Indicates that the function causes the screen to scroll illegally.

mv[w]inch

mv[w]inch — Move the cursor to coordinates (y, x) and return the character on the specified window without making changes to the window. The mvinch function acts on the stdscr window.

Format

#include <curses.h>
int mvinch (int y, int x);
int mvwinch (WINDOW *win, int y, int x);

Arguments

win

A pointer to the window.

y

A window coordinate.

x

A window coordinate.

Return Values

x

The returned character.

ERR

Indicates an input error.

mv[w]insch

mv[w]insch — Move the cursor to coordinates (y, x) and insert the character ch into the specified window. The mvinsch function acts on the stdscr window.

Format

#include <curses.h>
int mvinsch (int y, int x, char ch);
int mvwinsch (WINDOW *win, int y, int x, char ch);

Arguments

win

A pointer to the window.

y

A window coordinate.

x

A window coordinate.

ch

The character to be inserted at the window's coordinates.

Description

After the character is inserted, each character on the line shifts to the right, and the last character on the line is deleted.

Return Values

OK

Indicates success.

ERR

Indicates that the function makes the screen scroll illegally. For more information, see the scrollok function in this section.

mv[w]insstr

mv[w]insstr — Move the cursor to coordinates (y, x) and insert the specified string into the specified window. The mvinsstr function acts on the stdscr window.

Format

#include <curses.h>
int mvinsstr (int y, int x, char *str);
int mvwinsstr (WINDOW *win, int y, int x, char *str);

Arguments

win

A pointer to the window.

y

A window coordinate.

x

A window coordinate.

str

The string that is displayed.

Description

Each character after the string shifts to the right, and the last character disappears. The mvinsstr and mvwinsstr functions are specific to VSI C for OpenVMS systems and are not portable.

Return Values

OK

Indicates success.

ERR

Indicates that the function makes the screen scroll illegally. For more information, see the scrollok function.

mvwin

mvwin — Moves the starting position of the window to the specified (y, x) coordinates.

Format

#include <curses.h>
mvwin (WINDOW *win, int y, int x);

Arguments

win

A pointer to the window.

y

A window coordinate.

x

A window coordinate.

Description

When moving subwindows, the mvwin function does not rewrite the contents of the subwindow on the underlying window at the new position. If you write anything to the subwindow after the move, the function also writes to the underlying window.

Return Values

OK

Indicates success.

ERR

Indicates that moving the window put part or all of the window off the edge of the terminal screen. The terminal screen remains unaltered.

nanosleep

nanosleep — High-resolution sleep (REALTIME). Suspends a process (or thread in a threaded program) from execution for the specified timer interval.

Format

#include <time.h>
int nanosleep (const struct timespec *rqtp, struct timespec *rmtp);

Arguments

rqtp

A pointer to the timespec data structure that defines the time interval during which the calling process or thread is suspended.

rmtp

A pointer to the timespec data structure that receives the amount of time remaining in the previously requested interval, or zero if the full interval has elapsed.

Description

The nanosleep function suspends a process or thread until one of the following conditions is met:

  • The time interval specified by the rqtp argument has elapsed.

  • A signal is delivered to the calling process and the action is to invoke a signal-catching function or to terminate the process.

The suspension time may be longer than requested because the argument value is rounded up to an integer multiple of the sleep resolution or because of the scheduling of other activity by the system. Except when interrupted by a signal, the suspension time is not less than the time specified by the rqtp argument (as measured by the system clock, CLOCK_REALTIME).

The use of the nanosleep function has no effect on the action or blockage of any signal.

If the requested time has elapsed, the call was successful and the nanosleep function returns zero.

On failure, the nanosleep function returns -1 and sets errno to indicate the failure. The function fails if it has been interrupted by a signal, or if the rqtp argument specified a nanosecond value less than 0 or greater than or equal to 1 billion.

If the rmtp argument is non-NULL, the timespec structure it references is updated to contain the amount of time remaining in the interval (the requested time minus the time actually slept).

If the rmtp argument is NULL, the remaining time is not returned.

See also clock_getres, clock_gettime, clock_settime, and sleep.

Return Values

0

Indicates success. The requested time has elapsed.

-1
Indicates failure. The function call was unsuccessful or was interrupted by a signal; errno is set to one of the following values:

  • EINTR– The nanosleep function was interrupted by a signal.

  • EINVAL– The rqtp argument specified a nanosecond value less than 0 or greater than or equal to 1 billion.

nearbyint

nearbyint — Rounds to the nearest integer value in floating-point format, using the current rounding direction.

Format

#include <math.h>
double nearbyint (double x);
float nearbyintf (float x);
long double nearbyintl (long double x);

Argument

x

Value to round.

Description

The nearbyint functions round x to an integer value in floating-point format, using the current rounding direction and without raising the "inexact" floating-point exception.

Return Value

n

On success, the function returns the rounded integer value.

newwin

newwin — Creates a new window with numlines lines and numcols columns starting at the coordinates (begin_y, begin_x) on the terminal screen.

Format

#include <curses.h>
WINDOW *newwin (int numlines, int numcols, int begin_y, int begin_x);

Arguments

numlines

If it is 0, the newwin function sets that dimension to LINES ( begin_y). To get a new window of dimensions LINES by COLS, use the following line: 
newwin (0, 0, 0, 0)

numcols

If it is 0, the newwin function sets that dimension to COLS (begin_x). Therefore, to get a new window of dimensions LINES by COLS, use the following line:
newwin (0, 0, 0, 0)

begin_y

A window coordinate.

begin_x

A window coordinate.

Return Values

x

The address of the allocated window.

ERR

Indicates an error.

nextafter

nextafter — Returns the next machine-representable number following x in the direction of y.

Format

#include <math.h>
double nextafter (double x, double y);
float nextafterf (float x, float y);
long double nextafterl (long double x, long double y);

Arguments

x

A real number.

y

A real number.

Description

The nextafter functions return the next machine-representable floating-point number following x in the direction of y. If y is less than x, nextafter returns the largest representable floating-point number less than x.

Return Values

n

The next representable floating-point value following x in the direction of y.

HUGE_VAL

Overflow; errno is set to ERANGE.

NaN

x or y is NaN; errno is set to EDOM.

nexttoward

nexttoward — Equivalent to the nextcafter function, with exceptions noted in the Description.

Format

#include <math.h>
double nexttoward (double x, long double y);
float nexttowardf (float x, long double y);
long double nexttowardl (long double x, long double y);

Arguments

x

A real number.

y

A real number.

Description

The nexttoward functions are equivalent to the corresponding nextafter functions, except that the second parameter has type long double and the functions return y converted to the type of the function if x equals y.

Return Values

n

The next representable floating-point value following x in the direction of y.

y (of the type x)

If x equals y.

HUGE_VAL

Overflow; errno is set to ERANGE.

NaN

x or y is NaN; errno is set to EDOM.

nice

nice — Increases or decreases process priority relative to the process current priority by the amount of the argument. This function is nonreentrant.

Format

#include <unistd.h>
int nice (int increment);

Argument

increment

As a positive argument, decreases priority; as a negative argument, increases priority. Issuing nice(0) restores the base priority. The resulting priority cannot be less than 1, or greater than the process's base priority. If it is, the nice function quietly does nothing.

Description

When a process calls the vfork function, the resulting child inherits the parent's priority.

With the DECC$ALLOW_UNPRIVILEGED_NICE feature logical enabled, the nice function exhibits its legacy behavior of not checking the privilege of the calling process (that is, any user may lower the nice value to increase process priorities). Also, when the caller sets a priority above MAX_PRIORITY, the nice value is set to the base priority.

With DECC$ALLOW_UNPRIVILEGED_NICE disabled, the nice function conforms to the X/Open standard of checking the privilege of the calling process (only users with ALTPRI privilege can lower the nice value to increase process priorities), and when the caller sets a priority above MAX_PRIORITY, the nice value is set to MAX_PRIORITY.

See also vfork.

Return Values

0

Indicates success.

-1

Indicates failure.

nint

nint — Returns the nearest integral value to the argument.

Format

#include <math.h>
double nint (double x);
float nintf (float x,);
long double nintl (long double x);

Argument

x

A real number.

Description

The nint functions return the nearest integral value to x, except halfway cases are rounded to the integral value larger in magnitude. This corresponds to the Fortran generic intrinsic function nint.

Return Values

n

The nearest integral value to x.

NaN

x is NaN; errno is set to EDOM.

[no]nl

[no]nl — The nl and nonl functions are provided only for UNIX software compatibility and have no function in the OpenVMS environment.

Format

#include <curses.h>
void nl (void);
void nonl (void);

nl_langinfo

nl_langinfo — Returns a pointer to a string that contains information obtained from the program's current locale.

Format

#include <langinfo.h>
char *nl_langinfo (nl_item item);

Argument

item

The name of a constant that specifies the information required. These constants are defined in <langinfo.h>.

The following constants are valid:

Constant

Category

Description

D_T_FMT

LC_TIME

String for formatting date and time

D_FMT

LC_TIME

String for formatting date

T_FMT

LC_TIME

String for formatting time

T_FMT_AMPM

LC_TIME

Time format with AM/PM string

AM_STR

LC_TIME

String that represents AM in 12-hour clock notation

PM_STR

LC_TIME

String that represents PM in 12-hour clock notation

DAY_1

LC_TIME

The name of the first day of the week

. . .

DAY_7

LC_TIME

The name of the seventh day of the week

ABDAY_1

LC_TIME

The abbreviated name of the first day of the week

. . .

ABDAY_7

LC_TIME

The abbreviated name of the seventh day of the week

MON_1

LC_TIME

The name of the first month in the year

. . .

MON_12

LC_TIME

The name of the twelfth month in the year

ABMON_1

LC_TIME

The abbreviated name of the first month in the year

. . .

ABMON_12

LC_TIME

The abbreviated name of the twelfth month in the year

ERA

LC_TIME

Era description strings

ERA_D_FMT

LC_TIME

Era date format string

ERA_T_FMT

LC_TIME

Era time format

ERA_D_T_FMT

LC_TIME

Era date and time format

ALT_DIGITS

LC_TIME

Alternative symbols for digits

RADIXCHAR

LC_NUMERIC

The radix character

THOUSEP

LC_NUMERIC

The character used to separate groups of digits in nonmonetary values

YESEXP

LC_MESSAGES

The expression for affirmative responses to yes/no questions

NOEXP

LC_MESSAGES

The expression for negative responses to yes/no questions

CRNCYSTR

LC_MONETARY
The currency symbol. It is preceded by one of the following:

  • A minus (-) if the symbol is to appear before the value

  • A plus (+) if the symbol is to appear after the value

  • A period (.) if the symbol replaces the radix character

CODESET

LC_CTYPE

Codeset name

Description

If the current locale does not have language information defined, the function returns information from the C locale. The program should not modify the string returned by the function. This string might be overwritten by subsequent calls to nl_langinfo.

If the setlocale function is called after a call to nl_langinfo, then the pointer returned by the previous call to nl_langinfo will be unspecified. In this case, the nl_langinfo function should be called again.

Return Value

x

Pointer to the string containing the requested information. If item is invalid, the function returns an empty string.

Example

#include <stdio.h>
#include <locale.h>
#include <langinfo.h>

/* This test sets up the British English locale, and then       */
/* inquires on the data and time format, first day of the week, */
/* and abbreviated first day of the week.                       */

#include <stdlib.h>
#include <string.h>

int main()
{
    char *return_val;
    char *nl_ptr;

    /* set the locale, with user supplied locale name  */

    return_val = setlocale(LC_ALL, "en_gb.iso8859-1");
    if (return_val == NULL) {
        printf("ERROR : The locale is unknown");
        exit(1);
    }
    printf("+----------------------------------------+\n");

    /* Get the date and time format from the locale.  */

    printf("D_T_FMT = ");

    /*  Compare the returned string from nl_langinfo with */
    /*  an empty string.                                  */

    if (!strcmp((nl_ptr = (char *) nl_langinfo(D_T_FMT)), "")) {

  /* The string returned was empty this could mean that either */
  /* 1) The locale does not contain a value for this item      */
  /* 2) The value for this item is an empty string             */

        printf("nl_langinfo returned an empty string\n");
    }
    else {
        /* Display the date and time format  */

        printf("%s\n", nl_ptr);
    }

/* Get the full name for the first day of the week from locale */
   printf("DAY_1 = ");

  /*  Compare the returned string from nl_langinfo with */
  /*  an empty string.                                  */

    if (!strcmp((nl_ptr = (char *) nl_langinfo(DAY_1)), "")) {

  /* The string returned was empty this could mean that either */
  /*    1) The locale does not contain a value for the first   */
  /*       day of the week                                     */
  /*    2) The value for the first day of the week is          */
  /*       an empty string                                     */

        printf("nl_langinfo returned an empty string\n");
    }

    else {
     /* Display the full name of the first day of the week     */

        printf("%s\n", nl_ptr);
    }
/* Get the abbreviated name for the first day of the week
                                                  from locale  */

    printf("ABDAY_1 = ");

 /* Compare the returned string from nl_langinfo with an empty */
 /* string.                                                    */

    if (!strcmp((nl_ptr = (char *) nl_langinfo(ABDAY_1)), "")) {

 /* The string returned was empty this could mean that either  */
 /*    1) The locale does not contain a value for the first    */
 /*       day of the week                                      */
 /*    2) The value for the first day of the week is an        */
 /*       empty string                                         */

        printf("nl_langinfo returned an empty string\n");
    }

    else {

 /* Display the abbreviated name of the first day of the week  */

        printf("%s\n", nl_ptr);
   }
}
Running the example program produces the following result:
+----------------------------------------+
D_T_FMT = %a %e %b %H:%M:%S %Y
DAY_1 = Sunday
ABDAY_1 = Sun

nrand48

nrand48 — Generates uniformly distributed pseudorandom-number sequences. Returns 48-bit signed long integers.

Format

#include <stdlib.h>
long int nrand48 (unsigned short int xsubi[3]);

Argument

xsubi

An array of three short ints that, when concatenated together, form a 48-bit integer.

Description

The nrand48 function generates pseudorandom numbers using the linear congruential algorithm and 48-bit integer arithmetic.

The nrand48 function returns nonnegative, long integers uniformly distributed over the range of y values, such that 0 ≤ y < 231.

The function works by generating a sequence of 48-bit integer values, Xi, according to the linear congruential formula:
       Xn+1 = (aXn+c)mod m        n >= 0
The argument m equals 2 48, so 48-bit integer arithmetic is performed. Unless you invoke the lcong48 function, the multiplier value a and the addend value c are:
      a = 5DEECE66D16 = 2736731631558
      c = B16 = 138

The nrand48 function requires that the calling program pass an array as the xsubi argument, which for the first call must be initialized to the initial value of the pseudorandom-number sequence. Unlike the drand48 function, it is not necessary to call an initialization function prior to the first call.

By using different arguments, the nrand48 function allows separate modules of a large program to generate several independent sequences of pseudorandom numbers. For example, the sequence of numbers that one module generates does not depend upon how many times the functions are called by other modules.

Return Value

n

Returns nonnegative, long integers over the range 0 ≤ y < 231.

open

open — Opens a file for reading, writing, or editing. It positions the file at its beginning (byte 0).

Format

#include <fcntl.h>
int open (const char *file_spec, int flags, mode_t mode); (ANSI C)
int open (const char *file_spec, int flags, ...); (VSI C Extension)

Arguments

file_spec

A null-terminated character string containing a valid file specification. If you specify a directory in the file_spec and it is a search list that contains an error, VSI C interprets it as a file open error.

If the file_spec parameter refers to a symbolic link, the open function opens the file pointed to by the symbolic link.

flags

The following values are defined in the <fcntl.h> header file:

O_RDONLY

Opens a file for reading only.

O_WRONLY

Opens a file for writing only.

O_RDWR

Opens a file for both reading and writing.

O_NDELAY

Opens a file for asynchronous input.

O_APPEND

Moves the file pointer to the end of the file before every write operation.

O_CREAT

Creates a file if it does not exist.

O_TRUNC

Creates a new version of this file.

O_EXCL

Returns an error if a file specified by filename exists. Applies only when used with O_CREAT.

O_CLOEXEC

Sets the FD_CLOEXEC flag on the file descriptor.

These flags are set using the bitwise OR operator (|) to separate specified flags.

Opening a file with O_APPEND causes each write on the file to be appended to the end. In contrast, with the VAX C RTL the behavior of files opened in append mode was to start at EOF and, thereafter, write at the current file position.

If O_TRUNC is specified and the file exists, open creates a new file by incrementing the version number by 1, leaving the old version in existence.

If O_CREAT is set and the named file does not exist, the C RTL creates it with any attributes specified in the fourth and subsequent arguments (. . .). If O_EXCL is set with O_CREAT and the named file exists, the attempted open returns an error.

mode

An unsigned value that specifies the file-protection mode. The compiler performs a bitwise AND operation on the mode and the complement of the current protection mode.

You can construct modes by using the bitwise OR operator (|) to separate specified modes. The modes are:

0400

OWNER:READ

0200

OWNER:WRITE

0100

OWNER:EXECUTE

0040

GROUP:READ

0020

GROUP:WRITE

0010

GROUP:EXECUTE

0004

WORLD:READ

0002

WORLD:WRITE

0001

WORLD:EXECUTE

The system is given the same access privileges as the owner. A WRITE privilege also implies a DELETE privilege.

. . .

Optional file attribute arguments. The file attribute arguments are the same as those used in the creat function. For more information, see the creat function.

Description

If a version of the file exists, a new file created with open inherits certain attributes from the existing file unless those attributes are specified in the open call. The following attributes are inherited: record format, maximum record size, carriage control, and file protection.

Notes

  • If you intend to do random writing to a file, the file must be opened for update by specifying a flags value of O_RDWR.

  • To create files with OpenVMS RMS default protections by using the UNIX system-call functions umask, mkdir, creat, and open, call mkdir, creat, and open with a file-protection mode argument of 0777 in a program that never specifically calls umask. These default protections include correctly establishing protections based on ACLs, previous versions of files, and so on.

    In programs that do vfork/ exec calls, the new process image inherits whether umask has ever been called or not from the calling process image. The umask setting and whether the umask function has ever been called are both inherited attributes.

See also creat, read, write, close, dup, dup2, and lseek.

Return Values

x

A nonnegative file descriptor number.

-1

Indicates that the file does not exist, that it is protected against reading or writing, or that it cannot be opened for another reason.

Example

#include <unixio.h>
#include <fcntl.h>
#include <stdlib.h>

main()
{
    int file,
        stat;
    int flags;

    flags = O_RDWR;  /*  Open for read and write,            */
                     /*  with user default file protection,  */
                     /*  with max fixed record size of 2048, */
                     /*  and a block size of 2048 bytes.     */

file=open("file.dat", flags, 0, "rfm=fix", "mrs=2048", "bls=2048");
    if (file == -1)
        perror("OPEN error"), exit(1);

    close(file);
}

opendir

opendir — Opens a specified directory.

Format

#include <dirent.h>
DIR *opendir (const char *dir_name);

Argument

dir_name

The name of the directory to be opened.

Description

The opendir function opens the directory specified by dir_name and associates a directory stream with it. The dir_name argument can be specified in OpenVMS style or UNIX style. The directory stream is positioned at the first entry. The type DIR, defined in the <dirent.h> header file, represents a directory stream. A directory stream is an ordered sequence of all the directory entries in a particular directory.

The opendir function also returns a pointer to identify the directory stream in subsequent operations. The NULL pointer is returned when the directory named by dir_name cannot be accessed, or when not enough memory is available to hold the entire stream.

Notes

  • An open directory must always be closed with the closedir function to ensure that the next attempt to open that directory is successful. The opendir function should be used with readdir, closedir, and rewinddir to examine the contents of the directory.

  • The opendir function supports UNIX style path name specifications. For more information about UNIX style directory specifications, see Section 1.3.3.

Example

See the program example in the description of closedir.

Return Values

x

A pointer to an object of type DIR.

NULL
Indicates an error; errno is set to one of the following values:

  • EACCES– Search permission is denied for any component of dir_name or read permission is denied for dir_name.

  • ENAMETOOLONG– The length of the dir_name string exceeds PATH_MAX, or a pathname component is longer than

    NAME_MAX.

  • ENOENT– The dir_name argument points to the name of a file that does not exist, or is an empty string.

overlay

overlay — Nondestructively superimposes win1 on win2. The function writes the contents of win1 that will fit onto win2 beginning at the starting coordinates of both windows. Blanks on win1 leave the contents of the corresponding space on win2 unaltered. The overlay function copies as much of a window's box as possible.

Format

#include <curses.h>
int overlay (WINDOW *win1, WINDOW *win2);

Arguments

win1

A pointer to the window.

win2

A pointer to the window.

Return Values

OK

Indicates success.

ERR

Indicates an error.

overwrite

overwrite — Destructively writes the contents of win1 on win2.

Format

#include <curses.h>
int overwrite (WINDOW *win1, WINDOW *win2);

Arguments

win1

A pointer to the window.

win2

A pointer to the window.

Description

The overwrite function writes the contents of win1 that will fit onto win2 beginning at the starting coordinates of both windows. Blanks on win1 are written on win2 as blanks. This function copies as much of a window's box as possible.

Return Values

OK

Indicates success.

ERR

Indicates failure.

pathconf

pathconf — Retrieves file implementation characteristics.

Format

#include <unistd.h>
long int pathconf (const char *path, int name);

Arguments

path

The pathname of a file or directory.

name

The configuration attribute to query. If this attribute is not applicable to the file specified by the path argument, the pathconf function returns an error.

Description

The pathconf function allows an application to determine the characteristics of operations supported by the file system underlying the file named by path. Read, write, or execute permission of the named file is not required, but you must be able to search all directories in the path leading to the file.

Symbolic values for the name argument are defined in the <unistd.h> header file, as follows:

_PC_LINK_MAX

The maximum number of links to the file. If the path argument refers to a directory, the value returned applies to the directory itself.

_PC_MAX_CANON

The maximum number of bytes in a canonical input line. This is applicable only to terminal devices.

_PC_MAX_INPUT

The number of types allowed in an input queue. This is applicable only to terminal devices.

_PC_NAME_MAX

Maximum number of bytes in a filename (not including a terminating null). The byte range value is between 13 and 255. This is applicable only to a directory file. The value returned applies to filenames within the directory.

_PC_PATH_MAX

Maximum number of bytes in a pathname (not including a terminating null). The value is never larger than 65,535. This is applicable only to a directory file. The value returned is the maximum length of a relative pathname when the specified directory is the working directory.

_PC_PIPE_BUF

Maximum number of bytes guaranteed to be written atomically. This is applicable only to a FIFO. The value returned applies to the referenced object. If the path argument refers to a directory, the value returned applies to any FIFO that exists or can be created within the directory.

_PC_CHOWN_RESTRICTED

This is applicable only to a directory file. The value returned applies to any files (other than directories) that exist or can be created within the directory.

_PC_NO_TRUNC

Returns 1 if supplying a component name longer than allowed by NAME_MAX causes an error. Returns 0 (zero) if long component names are truncated. This is applicable only to a directory file.

_PC_VDISABLE

This is always 0 (zero); no disabling character is defined. This is applicable only to a terminal device.

Return Values

x

Resultant value of the configuration attribute specified in name.

-1
Indicates an error; errno is set to one of the following values:

  • EACCES– Search permission is denied for a component of the path prefix.

  • EINVAL– The name argument specifies an unknown or inapplicable characteristic.

  • EFAULT– The path argument is an invalid address.

  • ENAMETOOLONG– The length of the path string exceeds PATH_MAX or a pathname component is longer than NAME_MAX.

  • ENOENT– The named file does not exist or the path argument points to an empty string.

  • ENOTDI– A component of the path prefix is not a directory.

pause

pause — Suspends the calling process until delivery of a signal whose action is either to execute a signal-catching function or to terminate the process.

Format

#include <unistd.h>
int pause (void);

Description

The pause function suspends the calling process until delivery of a signal whose action is either to execute a signal-catching function or to terminate the process.

If the action is to terminate the process, pause does not return.

If the action is to execute a signal-catching function, pause returns after the signal-catching function returns.

Return Value

Since the pause function suspends process execution indefinitely unless interrupted by a signal, there is no successful completion return value.

In cases where pause returns, the return value is -1, and errno is set to EINTR.

pclose

pclose — Closes a pipe to a process.

Format

#include <stdio.h>
int pclose (FILE *stream);

Arguments

stream

A pointer to a FILE structure for an open pipe returned by a previous call to the popen function.

Description

The pclose function closes a pipe between the calling program and a shell command to be executed. Use pclose to close any stream you have opened with popen. The pclose function waits for the associated process to end, and then returns the exit status of the command. See the description of waitpid for information on interpreting the exit status.

Beginning with OpenVMS Version 7.3-1, when compiled with the _VMS_WAIT macro defined, the pclose function returns the OpenVMS completion code of the child process.

See also popen.

Return Values

x

Exit status of child.

-1
Indicates an error. The stream argument is not associated with a popen function. errno is set to the following:

  • ECHILD – cannot obtain the status of the child process.

perror

perror — Writes a short error message to stderr describing the current value of errno.

Format

#include <stdio.h>
void perror (const char *str);

Argument

str

Usually the name of the program that caused the error.

Description

The perror function uses the error number in the external variable errno to retrieve the appropriate locale-dependent error message. The function writes out the message as follows: str (a user-supplied prefix to the error message), followed by a colon and a space, followed by the message itself, followed by a new-line character.

See the description of errno in Chapter 4 for a list of possible errors.

See also strerror.

Example

#include <stdio.h>
#include <stdlib.h>

main(argc, argv)
    int argc;
    char *argv[];
{
    FILE *fp;

    fp = fopen(argv[1], "r");   /* Open an input file. */
    if (fp == NULL) {

        /* If the fopen call failed, perror prints out a        */
        /* diagnostic:                                          */
        /*                                                      */
        /*  "open: <error message>"                             */
        /*  This error message provides a diagnostic explaining */
        /*  the cause of the failure.                           */

        perror("open");
        exit(EXIT_FAILURE);
    }
    else
        fclose(fd) ;
}

pipe

pipe — Creates a temporary mailbox that can be used to read and write data between a parent and child process. The channels through which the processes communicate are called a pipe.

Format

#include <unistd.h>
int pipe (int array_fdscptr[2]); (ISO POSIX-1)
int pipe (int array_fdscptr[2], ...); (VSI C Extension)

Arguments

array_fdscptr

An array of file descriptors. A pipe is implemented as an array of file descriptors associated with a mailbox. These mailbox descriptors are special in that these are the only file descriptors which, when passed to the isapipe function, will return 1.

The file descriptors are allocated in the following way:

  • The first available file descriptor is assigned to writing, and the next available file descriptor is assigned to reading.

  • The file descriptors are then placed in the array in reverse order; element 0 contains the file descriptor for reading, and element 1 contains the file descriptor for writing.

. . .

Represents three optional, positional arguments, flag, bufsize, and bufquota:

flag

An optional argument used as a bitmask.

If either the O_NDELAY or O_NONBLOCK bit is set, the I/O operations to the mailbox through array_fdscptr file descriptors terminate immediately, rather than waiting for another process.

If, for example, the O_NDELAY bit is set and the child issues a read request to the mailbox before the parent has put any data into it, the read terminates immediately with 0 status. If neither the O_NDELAY nor O_NONBLOCK bit is set, the child will be waiting on the read until the parent writes any data into the mailbox. This is the default behavior if no flag argument is specified.

The values of O_NDELAY and O_NONBLOCK are defined in the <fcntl.h> header file. Any other bits in the flag argument are ignored. You must specify this argument if the second optional, positional argument bufsize is specified. If the flag argument is needed only to allow specification of the bufsize argument, specify flag as 0.

bufsize

Optional argument of type int that specifies the size of the mailbox, in bytes. Specify a value from 512 to 65535.

If you specify 0 or omit this argument, the operating system creates a mailbox with a default size of 512 bytes.

If you specify a value less than 0 or larger than 65535, the results are unpredictable.

If you do specify this argument, be sure to precede it with a flag argument.

The DECC$PIPE_BUFFER_SIZE feature logical can also be used to specify the size of the mailbox. If bufsize is supplied, it takes precedence over the value of DECC$PIPE_BUFFER_SIZE. Otherwise, the value of DECC$PIPE_BUFFER_SIZE is used.

If neither bufsize nor DECC$PIPE_BUFFER_SIZE is specified, the default buffer size of 512 is used.

bufquota

Optional argument of type int that specifies the buffer quota of the pipe's mailbox. Specify a value from 512 to 2147483647.

OpenVMS Version 7.3-2 added this argument. In previous OpenVMS versions, the buffer quota was equal to the buffer size.

The DECC$PIPE_BUFFER_QUOTA feature logical can also be used to specify the buffer quota. If the optional bufquota argument of the pipe function is supplied, it takes precedence over the value of DECC$PIPE_BUFFER_QUOTA. Otherwise, the value of DECC$PIPE_BUFFER_QUOTA is used.

If neither bufquota nor DECC$PIPE_BUFFER_QUOTA is specified, then the buffer quota defaults to the buffer size.

Description

The mailbox used for the pipe is a temporary mailbox. The mailbox is not deleted until all processes that have open channels to that mailbox close those channels. The last process that closes a pipe writes a message to the mailbox, indicating the end-of-file.

The mailbox is created by using the $CREMBX system service, specifying the following characteristics:

  • A maximum message length of 512 characters

  • A buffer quota of 512 characters

  • A protection mask granting all privileges to USER and GROUP and no privileges to SYSTEM or WORLD

The buffer quota of 512 characters implies that you cannot write more than 512 characters to the mailbox before all or part of the mailbox is read. Since a mailbox record is slightly larger than the data part of the message that it contains, not all of the 512 characters can be used for message data. You can increase the size of the buffer by specifying an alternative size using the optional, third argument to the pipe function. A pipe under the OpenVMS system is a stream-oriented file with no carriage-control attributes. It is fully buffered by default in the C RTL. A mailbox used as a pipe is different than a mailbox created by the application. A mailbox created by the application defaults to a record-oriented file with carriage return, carriage control. Additionally, writing a zero-length record to a mailbox writes an EOF, as does each close of the mailbox. For a pipe, only the last close of a pipe writes an EOF.

The pipe is created by the parent process before vfork and an exec function are called. By calling pipe first, the child inherits the open file descriptors for the pipe. You can then use the getname function to return the name of the mailbox associated with the pipe, if this information is desired. The mailbox name returned by getname has the format _MBA nnnn: (Alpha only) or _MBA nnnnn: (Integrity servers only), where nnnn or nnnnn is a unique number.

Both the parent and the child need to know in advance which file descriptors will be allocated for the pipe. This information cannot be retrieved at run time. Therefore, it is important to understand how file descriptors are used in any VSI C for OpenVMS program. For more information about file descriptors, see Chapter 2.

File descriptors 0, 1, and 2 are open in a VSI C for OpenVMS program for stdin (SYS$INPUT), stdout (SYS$OUTPUT), and stderr (SYS$ERROR), respectively. Therefore, if no other files are open when pipe is called, pipe assigns file descriptor 3 for writing and file descriptor 4 for reading. In the array returned by pipe, 4 is placed in element 0 and 3 is placed in element 1.

If other files have been opened, pipe assigns the first available file descriptor for writing and the next available file descriptor for reading. In this case, the pipe does not necessarily use adjacent file descriptors. For example, assume that two files have been opened and assigned to file descriptors 3 and 4 and the first file is then closed. If pipe is called at this point, file descriptor 3 is assigned for writing and file descriptor 5 is assigned for reading. Element 0 of the array will contain 5 and element 1 will contain 3.

In large applications that do large amounts of I/O, it gets more difficult to predict which file descriptors are going to be assigned to a pipe; and, unless the child knows which file descriptors are being used, it will not be able to read and write successfully from and to the pipe.

One way to be sure that the correct file descriptors are being used is to use the following procedure:

  1. Choose two descriptor numbers that will be known to both the parent and the child. The numbers should be high enough to account for any I/O that might be done before the pipe is created.

  2. Call pipe in the parent at some point before calling an exec function.

  3. In the parent, use dup2 to assign the file descriptors returned by pipe to the file descriptors you chose. This now reserves those file descriptors for the pipe; any subsequent I/O will not interfere with the pipe.

You can read and write through the pipe using the UNIX I/O functions read and write, specifying the appropriate file descriptors. As an alternative, you can issue fdopen calls to associate file pointers with these file descriptors so that you can use the Standard I/O functions (fread and fwrite).

Two separate file descriptors are used for reading from and writing to the pipe, but only one mailbox is used so some I/O synchronization is required. For example, assume that the parent writes a message to the pipe. If the parent is the first process to read from the pipe, then it will read its own message back as shown in Figure 11.

Note

For added UNIX portability, you can use the following feature logicals to control the behavior of the C RTL pipe implementation:

  • Define the DECC$STREAM_PIPE feature logical name to ENABLE to direct the pipe function to use stream I/O instead of record I/O.

  • Define the DECC$POPEN_NO_CRLF_REC_ATTR feature logical to ENABLE to prevent CR/LF carriage control from being added to pipe records for pipes opened with the popen function. Be aware that enabling this feature might result in undesired behavior from other functions such as gets that rely on the carriage-return character.

Figure 11. Reading and Writing to a Pipe
Reading and Writing to a Pipe

Return Values

0

Indicates success.

-1

Indicates an error.

poll

poll — Provides users with a mechanism for multiplexing input/output over a set of file descriptors that reference open streams.

Format

#include <poll.h>
int poll (struct pollfd filedes [], nfds_t nfds, int timeout);

Argument

filedes

Points to an array of pollfd structures, one for each file descriptor of interest. Each pollfd structure includes the following members:
  • int fd – The file descriptor
  • int events – The requested conditions
  • int revents – The reported conditions

nfds

The number of pollfd structures in the filedes array.

timeout

The maximum length of time (in milliseconds) to wait for at least one of the specified events to occur.

Description

The poll function provides users with a mechanism for multiplexing input/output over a set of file descriptors that reference open streams. For each member of the array pointed to by filedes, poll examines the given file descriptor for the event(s) specified in events. The poll function identifies those streams on which an application can send or receive messages, or on which certain events have occurred.

The filedes parameter specifies the file descriptor to be examined and the events of interest for each file descriptor. It is a pointer to an array of pollfd structures. The fd member of each pollfd structure specifies an open file descriptor. The poll function uses the events member to determine what conditions to report for this file descriptor. If one or more of these conditions is true, the poll function sets the associated revents member. The poll function sets revents to 0 at the beginning of the call so the revents value is erased, even if no events occur.

The events and revents members of each pollfd structure are bitmasks. The calling process sets the events bitmask, and poll sets the revents bitmasks. These bitmasks contain inclusive ORed combinations of condition options. The following condition options are defined:

  • POLLERR– An error has occurred on the file descriptor. This option is only valid in the revents bitmask; it is not used in the events member. For STREAMS devices, if an error occurs on the file descriptor and the device is also disconnected, poll returns POLLERR. For pipes, POLLERR is set for a file descriptor referring to the write end of a pipe when the read end has been closed. (The POSIX standard requires that poll should set POLLHUP for an attempt to read from a pipe when all file descriptors referring to the write end of the pipe have been closed. However, the current VSI C RTL implementation does not support this behavior.)

  • POLLIN– Data other than high-priority data may be read without blocking. This option is set in revents even if the message is of zero length.

  • POLLNVAL– The value specified for fd is invalid. This option is only valid in the revents member; it is ignored in the events member.

  • POLLOUT– Normal (priority band equals 0) data may be written without blocking.

  • POLLPRI– High-priority data may be received without blocking. This option is set in revents even if the message is of zero length.

  • POLLRDBAND– Data from a nonzero priority band may be read without blocking. This option is set in revents even if the message is of zero length.

  • POLLRDNORM– Normal data (priority band equals 0) may be read without blocking. This option is set in revents even if the message is of zero length.

  • POLLWRBAND– Priority data (priority band greater than 0) may be written. This event only examines bands that have been written to at least once.

  • POLLWRNORM– Same as POLLOUT.

The conditions indicated by POLLNORM and POLLOUT are true if and only if at least one byte of data can be read or written without blocking. There are two exceptions: regular files, which always poll true for POLLNORM and POLLOUT, and pipes, when the rules for the operation specify to return zero in order to indicate end-of-file.

The condition options POLLERR and POLLNVAL are always set in revents if the conditions they indicate are true for the specified file descriptor, whether or not these options are set in events.

For each call to the poll function, the set of reportable conditions for each file descriptor consists of those conditions that are always reported, together with any further conditions for which options are set in events. If any reportable condition is true for any file descriptor, the poll function will return with options set in revents for each true condition for that file descriptor.

If no reportable condition is true for any of the file descriptors, the poll function waits up to timeout milliseconds for a reportable condition to become true. If, in that time interval, a reportable condition becomes true for any of the file descriptors, poll reports the condition in the file descriptor's associated revents member and returns. If no reportable condition becomes true, poll returns without setting any revents bitmasks.

If the timeout parameter is a negative value, the poll function does not return until at least one specified event has occurred. If the value of the timeout parameter is 0 (zero), the poll function does not wait for an event to occur but returns immediately, even if no specified event has occurred.

The behavior of the poll function is not affected by whether the O_NONBLOCK option is set on any of the specified file descriptors.

The poll function supports regular files, terminal and pseudo-terminal devices, STREAMS-based files, mailboxes, sockets, and pipes. The behavior of poll on elements of file descriptors that refer to other types of files is unspecified.

For sockets, a file descriptor for a socket that is listening for connections indicates it is ready for reading after connections are available. A file descriptor for a socket that is connecting asynchronously indicates it is ready for writing after a connection is established.

Return Values

n

Upon successful completion, a nonnegative value is returned, indicating the number of file descriptors for which poll has set the revents bitmask.

0

poll has timed out and has not set any of the revents bitmasks.

-1
An error occurred. errno is set to indicate the error:

  • EINTR – A signal was intercepted during the poll function, and the signal handler was installed with an indication that functions are not to be restarted.

  • EIO – OpenVMS system service (SYS$QIOW etc.) failed.

  • ENOMEM – Allocation of internal data structures failed. A later call to the poll function might complete successfully.

  • ENOSYS – Socket descriptors were passed to the poll function, and poll failed to load the TCP/IP library.

popen

popen — Initiates a pipe to a process.

Format

#include <stdio.h>
FILE *popen (const char *command, const char *type);

Arguments

command

A pointer to a null-terminated string containing a shell command line.

type

A pointer to a null-terminated string containing an I/O mode. Because open files are shared, you can use a type r command as an input filter and a type w command as an output filter. Specify one of the following values for the type argument:

  • r—the calling program can read from the standard output of the command by reading from the returned file stream.

  • w—the calling program can write to the standard input of the command by writing to the returned file stream.

In addition, the type argument can include a type e command, which sets the FD_CLOEXEC flag on the file descriptor.

Description

The popen function creates a pipe between the calling program and a shell command awaiting execution. It returns a pointer to a FILE structure for the stream.

The popen function uses the value of the DECC$PIPE_BUFFER_SIZE feature logical to set the buffer size of the mailbox it creates for the pipe. You can specify a DECC$PIPE_BUFFER_SIZE value of 512 to 65024 bytes. If DECC$PIPE_BUFFER_SIZE is not specified, the default buffer size of 512 is used.

Notes

  • When you use the popen function to invoke an output filter, beware of possible deadlock caused by output data remaining in the program buffer. You can avoid this by either using the setvbuf function to ensure that the output stream is unbuffered, or the fflush function to ensure that all buffered data is flushed before calling the pclose function.

  • For added UNIX portability, you can use the following feature logicals to control the behavior of the C RTL pipe implementation:

    • Define the DECC$STREAM_PIPE feature logical name to ENABLE to direct the pipe function to use stream I/O instead of record I/O.

    • Define the DECC$POPEN_NO_CRLF_REC_ATTR feature logical to ENABLE to prevent CR/LF carriage control from being added to pipe records for pipes opened with the popen function. Be aware that enabling this feature might result in undesired behavior from other functions such as gets that rely on the carriage-return character.

See also fflush, pclose, and setvbuf.

Return Values

x

A pointer to the FILE structure for the opened stream.

NULL

Indicates an error. Unable to create files or processes.

pow

pow — Returns the first argument raised to the power of the second argument.

Format

#include <math.h>
double pow (double x, double y);
float powf (float x, float y);
long double powl (long double x, long double y);

Arguments

x

A floating-point base to be raised to an exponent y.

y

The exponent to which the base x is to be raised.

Description

The pow functions raise a floating-point base x to a floating-point exponent y. The value of pow( x, y) is computed as e**(y ln(x)) for positive x.

If x is 0 and y is negative, ±HUGE_VAL is returned and errno is set to ERANGE or EDOM.

Return Values

x

The result of the first argument raised to the power of the second.

1.0

The base is 0 and the exponent is 0.

HUGE_VAL

The result overflowed; errno is set to ERANGE.

±HUGE_VAL

The base is 0 and the exponent is negative; errno is set to ERANGE or EDOM.

Example

#include <stdio.h>
#include <math.h>
#include <errno.h>

main()
{
    double x;

    errno = 0;

    x = pow(-3.0, 2.0);
    printf("%d, %f\n", errno, x);
}
This example program outputs the following:
0, 9.000000

pread

pread — Reads bytes from a given position within a file without changing the file pointer.

Format

#include <unistd.h>
ssize_t pread (int file_desc, void *buffer, size_t nbytes, off_t offset);

Arguments

file_desc

A file descriptor that refers to a file currently opened for reading.

buffer

The address of contiguous storage in which the input data is placed.

nbytes

The maximum number of bytes involved in the read operation.

offset

The offset for the desired position inside the file.

Description

The pread function performs the same action as read, except that it reads from a given position in the file without changing the file pointer. The first three arguments to pread are the same as for read, with the addition of a fourth argument offset for the desired position inside the file. An attempt to perform a pread on a file that is incapable of seeking results in an error.

Return Values

n

The number of bytes read.

-1
Upon failure, the file pointer remains unchanged and pread sets errno to one of the following values:

  • EINVAL– The offset argument is invalid. The value is negative.

  • EOVERFLOW– The file is a regular file, and an attempt was made to read or write at or beyond the offset maximum associated with the file.

  • ENXIO– A request was outside the capabilities of the device.

  • ESPIPE – fildes is associated with a pipe or FIFO.

printf

printf — Performs formatted output from the standard output (stdout). See Chapter 2 for information on format specifiers.

Format

#include <stdio.h>
int printf (const char *format_spec, ...);

Arguments

format_spec

Characters to be written literally to the output or converted as specified in the . . . arguments.

. . .

Optional expressions whose resultant types correspond to conversion specifications given in the format specification.

If no conversion specifications are given, you may omit the output sources. Otherwise, the function call must have exactly as many output sources as there are conversion specifications, and the conversion specifications must match the types of the output sources.

Conversion specifications are matched to output sources in left-to-right order. Excess output pointers, if any, are ignored.

Return Values

x

The number of bytes written.

Negative value

Indicates that an output error occurred. The function sets errno. For a list of errno values set by this function, see fprintf.

[w]printw

[w]printw — Perform a printf in the specified window, starting at the current position of the cursor. The printw function acts on the stdscr window.

Format

#include <curses.h>
printw (char *format_spec, ...);
int wprintw (WINDOW *win, char *format_spec, ...);

Arguments

win

A pointer to the window.

format_spec

A pointer to the format specification string.

. . .

Optional expressions whose resultant types correspond to conversion specifications given in the format specification.

If no conversion specifications are given, you may omit the output sources. Otherwise, the function call must have exactly as many output sources as there are conversion specifications, and the conversion specifications must match the types of the output sources.

Conversion specifications are matched to output sources in left-to-right order. Excess output pointers, if any, are ignored.

Description

The formatting specification (format_spec) and the other arguments are identical to those used with the printf function.

The printw and wprintw functions format and then print the resultant string to the window using the addstr function. For more information, see the printf and scrollok functions in this section. See Chapter 2 for information on format specifiers.

Return Values

OK

Indicates success.

ERR

Indicates that the function makes the window scroll illegally.

putc

putc — The putc macro writes a single character to a specified file.

Format

#include <stdio.h>
int putc (int character, FILE *file_ptr);

Arguments

character

The character to be written.

file_ptr

A file pointer to the output stream.

Description

The putc macro writes the byte character (converted to an unsigned char) to the output specified by the file_ptr parameter. The byte is written at the position at which the file pointer is currently pointing (if defined) and advances the indicator appropriately. If the file cannot support positioning requests, or if the output stream was opened with append mode, the byte is appended to the output stream.

Since putc is a macro, a file pointer argument with side effects (for example, putc (ch, *f++)) might be evaluated incorrectly. In such a case, use the fputc function instead.

Compiling with the _ _UNIX_PUTC macro defined enables an optimization that uses a faster, inlined version of this function.

See also putc_unlocked.

Return Values

x

The character written to the file. Indicates success.

EOF

Indicates output errors.

putc_unlocked

putc_unlocked — Same as putc, except used only within a scope protected by flockfile and funlockfile.

Format

#include <stdio.h>
int putc_unlocked (int character, FILE *file_ptr);

Argument

character

The character to be written.

file_ptr

A file pointer to the output stream.

Description

The reentrant version of the putc macro is locked against multiple threads calling it simultaneously. This incurs overhead to ensure integrity of the stream. The unlocked version of this call, putc_unlocked can be used to avoid the overhead. The putc_unlocked macro is functionally identical to the putc macro, except that it is not required to be implemented in a thread-safe manner. The putc_unlocked macro can be safely used only within a scope that is protected by the flockfile and funlockfile functions used as a pair. The caller must ensure that the stream is locked before putc_unlocked is used.

Since putc_unlocked is a macro, a file pointer argument with side effects might be evaluated incorrectly. In such a case, use the fputc_unlocked function instead.

Compiling with the _ _UNIX_PUTC macro defined enables an optimization that uses a faster, inlined version of this function.

See also flockfile, ftrylockfile, and funlockfile.

Return Values

x

The character written to the file. Indicates success.

EOF

Indicates the end-of-file or an error.

putchar

putchar — Writes a single character to the standard output (stdout) and returns the character.

Format

#include <stdio.h>
int putchar (int character);

Argument

character

An object of type int.

Description

The putchar function is identical to fputc (character, stdout).

Compiling with the _ _UNIX_PUTC macro defined enables an optimization that uses a faster, inlined version of this function.

Return Values

character

Indicates success.

EOF

Indicates output errors.

putchar_unlocked

putchar_unlocked — Same as putchar, except used only within a scope protected by flockfile and funlockfile.

Format

#include <stdio.h>
int putchar_unlocked (int character);

Argument

character

An object of type int.

Description

The reentrant version of the putchar function is locked against multiple threads calling it simultaneously. This incurs overhead to ensure integrity of the output stream. The unlocked version of this call, putchar_unlocked can be used to avoid the overhead. The putchar_unlocked function is functionally identical to the putchar function, except that it is not required to be implemented in a thread-safe manner. The putchar_unlocked function can be safely used only within a scope that is protected by the flockfile and funlockfile functions used as a pair. The caller must ensure that the stream is locked before putchar_unlocked is used.

Compiling with the _ _UNIX_PUTC macro defined enables an optimization that uses a faster, inlined version of this function.

See also flockfile, ftrylockfile, and funlockfile.

Return Values

x

The next character from stdin, converted to int.

EOF

Indicates the end-of-file or an error.

putenv

putenv — Sets an environmental variable.

Format

#include <stdlib.h>
int putenv (const char *string);

Argument

string

A pointer to a name=value string.

Description

The putenv function sets the value of an environment variable by altering an existing variable or by creating a new one. The string argument points to a string of the form name=value, where name is the environment variable and value is the new value for it.

The string pointed to by string becomes part of the environment, so altering the string changes the environment. When a new string-defining name is passed to putenv, the space used by string is no longer used.

Notes

  • The putenv function manipulates the environment pointed to by the environ external variable, and can be used with getenv. However, the third argument to the main function (the environment pointer), is not changed.

    The putenv function uses the malloc function to enlarge the environment.

    A potential error is to call putenv with an automatic variable as the argument, then exit the calling function while string is still part of the environment.

  • Do not use the setenv, getenv, and putenv functions to manipulate symbols and logicals. Instead, use the OpenVMS library calls lib$set_logical, lib$get_logical, lib$set_symbol, and lib$get_symbol. The * env functions deliberately provide UNIX behavior, and are not a substitute for these OpenVMS runtime library calls.

    OpenVMS DCL symbols, not logical names, are the closest analog to environment variables on UNIX systems. While getenv is a mechanism to retrieve either a logical name or a symbol, it maintains an internal cache of values for use with setenv and subsequent getenv calls. The setenv function does not write or create DCL symbols or OpenVMS logical names.

    This is consistent with UNIX behavior. On UNIX systems, setenv does not change or create any symbols that will be visible in the shell after the program exits.

Return Values

0

Indicates success.

-1

Indicates an error. errno is set to ENOMEM – Not enough memory available to expand the environment list.

Restriction

The putenv function cannot take a 64-bit address. See Section 1.9.

puts

puts — Writes a character string to the standard output (stdout) followed by a new-line character.

Format

#include <stdio.h>
int puts (const char *str);

Argument

str

A pointer to a character string.

Description

The puts function does not copy the terminating null character to the output stream.

Return Values

Nonnegative value

Indicates success.

EOF

Indicates output errors.

putw

putw — Writes characters to a specified file.

Format

#include <stdio.h>
int putw (int integer, FILE *file_ptr);

Arguments

integer

An object of type int or long.

file_ptr

A file pointer.

Description

The putw function writes four characters to the output file as an int. No conversion is performed.

Return Values

integer

Indicates success.

EOF

Indicates output errors.

putwc

putwc — Converts a wide character to its corresponding multibyte value, and writes the result to a specified file.

Format

#include <wchar.h>
wint_t putwc (wint_t wc, FILE *file_ptr);

Arguments

wc

An object of type wint_t.

file_ptr

A file pointer.

Description

Since putwc might be implemented as a macro, a file pointer argument with side effects (for example putwc (wc, *f++)) might be evaluated incorrectly. In such a case, use the fputwc function instead.

See also fputwc.

Return Values

x

The character written to the file. Indicates success.

WEOF

Indicates an output error. The function sets errno. For a list of the errno values set by this function, see fputwc.

putwchar

putwchar — Writes a wide character to the standard output (stdout) and returns the character.

Format

#include <wchar.h>
wint_t putwchar (wint_t wc);

Arguments

wc

An object of type wint_t.

Description

The putwchar function is identical to fputwc (wc, stdout).

Return Values

x

The character written to the file. Indicates success.

WEOF

Indicates an output error. The function sets errno. For a list of the errno values set by this function, see fputwc.

pwrite

pwrite — Writes into a given position within a file without changing the file pointer.

Format

#include <unistd.h>
ssize_t pwrite (int file_desc, const void *buffer, size_t nbytes,
off_t offset);

Arguments

file_desc

A file descriptor that refers to a file currently opened for writing or updating.

buffer

The address of contiguous storage from which the output data is taken.

nbytes

The maximum number of bytes involved in the write operation.

offset

The offset for the desired position inside the file.

Description

The pwrite function performs the same action as write, except that it writes into a given position in the file without changing the file pointer. The first three arguments to pwrite are the same as for write, with the addition of a fourth argument offset for the desired position inside the file.

Return Values

n

The number of bytes written.

-1
Upon failure, the file pointer remains unchanged and pwrite sets errno to one of the following values:

  • EINVAL– The offset argument is invalid. The value is negative.

  • ESPIPE– fildes is associated with a pipe or FIFO.

qabs, llabs

qabs, llabs — Returns the absolute value of an integer as an __int64. llabs is a synonym for qabs.

Format

#include <stdlib.h>
__int64 qabs (__int64 j);
__int64 llabs (__int64 j);

Argument

j

A value of type __int64.

qdiv, lldiv

qdiv, lldiv — Returns the quotient and the remainder after the division of its arguments. lldiv is a synonym for qdiv.

Format

#include <stdlib.h>
qdiv_t qdiv (_ _int64 numer, __int64 denom);
lldiv_t lldiv (_ _int64 numer, __int64 denom);

Arguments

numer

A numerator of type __int64.

denom

A denominator of type __int64.

Description

The types qdiv_t and lldiv_t are defined in the <stdlib.h> header file as follows:
typedef struct
         {
         __int64 quot, rem;
         }
qdiv_t, lldiv_t;

qsort

qsort — Sorts an array of objects in place. It implements the quick-sort algorithm.

Format

#include <stdlib.h>
void qsort (void *base, size_t nmemb, size_t size, int (*compar)
(const void *, const void *));

Function Variants

The qsort function has variants named _qsort32 and _qsort64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

base

A pointer to the first member of the array. The pointer should be of type pointer-to-element and cast to type pointer-to-character.

nmemb

The number of objects in the array.

size

The size of an object, in bytes.

compar

A pointer to the comparison function.

Description

Two arguments are passed to the comparison function pointed to by compar. The two arguments point to the objects being compared. Depending on whether the first argument is less than, equal to, or greater than the second argument, the comparison function returns an integer less then, equal to, or greater than 0.

The comparison function compar need not compare every byte, so arbitrary data might be contained in the objects in addition to the values being compared.

The order in the output of two objects that compare as equal is unpredictable.

Return Value

The qsort function returns no value.

qsort_r

qsort_r — Sorts an array of objects in place by implementing the quick-sort algorithm (reentrant).

Format

#include <stdlib.h>
void qsort_r (void *base, size_t nmemb, size_t size, int (*compar)
(const void *, const void *, void *), void *arg)

Function Variants

The qsort_r function has variants named _qsort_r32 and _qsort_r64 for use with 32-bit and 64-bit pointer sizes, respectively.

Arguments

base

A pointer to the first member of the array. The pointer should be of type pointer-to-element and cast to type pointer-to-character.

nmemb

The number of objects in the array.

size

The size of each object in the array, in bytes.

compar

A pointer to the comparison function.

arg

A pointer to arbitrary arguments for the comparison function.

Description

The qsort_r function is the reentrant version of qsort. qsort_r is identical to qsort except that the comparison function compar takes a third argument. A pointer is passed to the comparison function via arg.

Return Value

The qsort_r function returns no value.

raise

raise — Generates a specified software signal. Generating a signal causes the action routine established by the signal, ssignal, or sigvec function to be invoked.

Format

#include <signal.h>
int raise (int sig); (ANSI C)
int raise (int sig[, int sigcode]); (VSI C Extension)

Arguments

sig

The signal to be generated.

sigcode

An optional signal code, available only when not compiling in strict ANSI C mode. For example, signal SIGFPE—the arithmetic trap signal—has 10 different codes, each representing a different type of arithmetic trap.

The signal codes can be represented by mnemonics or numbers. The arithmetic trap codes are represented by the numbers 1 to 10; the SIGILL codes are represented by the numbers 0 to 2. The code values are defined in the <signal.h> header file. See Table 4.4 for a list of signal mnemonics, codes, and corresponding OpenVMS exceptions.

Description

Calling the raise function has one of the following results:

  • If raise specifies a sig argument that is outside the range defined in the <signal.h> header file, then the raise function returns 0, and the errno variable is set to EINVAL.

  • If signal, ssignal, or sigvec establishes SIG_DFL (default action) for the signal, then the functions do not return. The image is exited with the OpenVMS error code corresponding to the signal.

  • If signal, ssignal, or sigvec establishes SIG_IGN (ignore signal) as the action for the signal, then raise returns its argument, sig.

  • signal, ssignal, or sigvec must establish an action function for the signal. That function is called and its return value is returned by raise.

See Chapter 4 for more information on signal processing.

See also gsignal, signal, ssignal, and sigvec.

Return Values

0

If successful.

nonzero

If unsuccessful.

rand, rand_r

rand, rand_r — Returns pseudorandom numbers in the range 0 to 2 31 - 1.

Format

#include <stdlib.h>
int rand (void);
int rand_r (unsigned int seed);

Argument

seed

An initial seed value.

Description

The rand function computes a sequence of pseudorandom integers in the range 0 to {RAND_MAX} with a period of at least 2 32.

The rand_r function computes a sequence of pseudorandom integers in the range 0 to {RAND_MAX}. The value of the {RAND_MAX} macro will be at least 32767.

If rand_r is called with the same initial value for the object pointed to by seed and that object is not modified between successive returns and calls to rand_r, the same sequence is generated.

See also srand.

For other random-number algorithms, see random and all the * 48 functions.

Return Value

n

A pseudorandom number.

random

random — Generates pseudorandom numbers in a more random sequence.

Format

#include <stdlib.h>
long int random (void);

Description

The random function is a random-number generator that has virtually the same calling sequence and initialization properties as the rand function, but produces sequences that are more random. The low 12 bits generated by rand go through a cyclic pattern. All bits generated by random are usable. For example, random() &1 produces a random binary value.

The random function uses a nonlinear, additive-feedback, random-number generator employing a default state-array size of 31 integers to return successive pseudorandom numbers in the range from 0 to 231-1. The period of this random-number generator is approximately 16*(231-1). The size of the state array determines the period of the random-number generator. Increasing the state array size increases the period.

With a full 256 bytes of state information, the period of the random-number generator is greater than 269, and is sufficient for most purposes.

Like the rand function, the random function produces by default a sequence of numbers that you can duplicate by calling the srandom function with a value of 1 as the seed. The srandom function, unlike the srand function, does not return the old seed because the amount of state information used is more than a single word.

See also rand, srand, srandom, setstate, and initstate.

Return Value

n

A random number.

[no]raw

[no]raw — Raw mode only works with the Curses input routines [w]getch and [w]getstr. Raw mode is not supported with the C RTL emulation of UNIX I/O, Terminal I/O, or Standard I/O.

Format

#include <curses.h>
raw()
noraw()

Description

Raw mode reads are satisfied on one of two conditions: after a minimum number (5) of characters are input at the terminal or after waiting a fixed time (10 seconds) from receipt of any characters from the terminal.

Example

/* Example of standard and raw input in Curses package. */

#include <curses.h>

main()
{
    WINDOW *win1;
    char vert = '.',
         hor = '.',
         str[80];

    /* Initialize standard screen, turn echo off.  */

    initscr();
    noecho();

    /* Define a user window.  */

    win1 = newwin(22, 78, 1, 1);
    leaveok(win1, TRUE);
    leaveok(stdscr, TRUE);

    box(stdscr, vert, hor);

    /* Reset the video, refresh(redraw) both windows. */

    mvwaddstr(win1, 2, 2, "Test line terminated input");
    wrefresh(win1);

    /* Do some input and output it. */
    nocrmode();
    wgetstr(win1, str);

    mvwaddstr(win1, 5, 5, str);
    mvwaddstr(win1, 7, 7, "Type something to clear screen");
    wrefresh(win1);

    /* Get another character then delete the window. */

    wgetch(win1);
    wclear(win1);

    mvwaddstr(win1, 2, 2, "Test raw input");
    wrefresh(win1);

    /* Do some raw input 5 chars or timeout - and output it. */
    raw();
    getstr(str);
    noraw();
    mvwaddstr(win1, 5, 5, str);
    mvwaddstr(win1, 7, 7, "Raw input completed");
    wrefresh(win1);

    endwin();
}

read

read — Reads bytes from a file and places them in a buffer.

Format

#include <unistd.h>
ssize_t read (int file_desc, void *buffer, size_t nbytes); (ISO POSIX-1)
int read (int file_desc, void *buffer, int nbytes); (Compatibility)

Arguments

file_desc

A file descriptor. The specified file descriptor must refer to a file currently opened for reading.

buffer

The address of contiguous storage in which the input data is placed.

nbytes

The maximum number of bytes involved in the read operation.

Description

The read function returns the number of bytes read. The return value does not necessarily equal nbytes. For example, if the input is from a terminal, at most one line of characters is read.

Note

The read function does not span record boundaries in a record file and, therefore, reads at most one record. A separate read must be done for each record.

Return Values

n

The number of bytes read.

-1

Indicates a read error, including physical input errors, illegal buffer addresses, protection violations, undefined file descriptors, and so forth.

Example

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>

main()
{
    int fd,
        i;
    char buf[10];
    FILE *fp ;          /* Temporary STDIO file */

    /* Create a dummy data file  */

    if ((fp = fopen("test.txt", "w+")) == NULL) {
        perror("open");
        exit(1);
    }
    fputs("XYZ\n",fp) ;
    fclose(fp) ;

    /* And now practice "read" */

    if ((fd = open("test.txt", O_RDWR, 0, "shr=upd")) <= 0) {
        perror("open");
        exit(0);
    }

    /* Read 2 characters into buf.  */

    if ((i = read(fd, buf, 2)) < 0) {
        perror("read");
        exit(0);
    }

    /* Print out what was read.  */

    if (i > 0)
        printf("buf='%c%c'\n", buf[0], buf[1]);

    close(fd);
}

readdir, readdir_r

readdir, readdir_r — Finds entries in a directory.

Format

#include <dirent.h>
struct dirent *readdir (DIR *dir_pointer);
int readdir_r (DIR *dir_pointer, struct dirent *entry,
struct dirent **result);

Arguments

dir_pointer

A pointer to the dir structure of an open directory.

entry

A pointer to a dirent structure that will be initialized with the directory entry at the current position of the specified stream.

result

Upon successful completion, the location where a pointer to entry is stored.

Description

The readdir function returns a pointer to a structure representing the directory entry at the current position in the directory stream specified by dir_pointer, and positions the directory stream at the next entry. It returns a NULL pointer upon reaching the end of the directory stream. The dirent structure defined in the <dirent.h> header file describes a directory entry.

The type DIR defined in the <dirent.h> header file represents a directory stream. A directory stream is an ordered sequence of all the directory entries in a particular directory. Directory entries represent files. You can remove files from or add files to a directory asynchronously to the operation of the readdir function.

The pointer returned by the readdir function points to data that you can overwrite by another call to readdir on the same directory stream. This data is not overwritten by another call to readdir on a different directory stream.

If a file is removed from or added to the directory after the most recent call to the opendir or rewinddir function, a subsequent call to the readdir function might not return an entry for that file.

When it reaches the end of the directory, or when it detects an invalid seekdir operation, the readdir function returns the null value.

An attempt to seek to an invalid location causes the readdir function to return the null value the next time it is called. A previous telldir function call returns the position.

The readdir_r function is a reentrant version of readdir. In addition to dir_pointer, you must specify a pointer to a dirent structure in which the current directory entry of the specified stream is returned.

If the operation is successful, readdir_r returns 0 and stores one of the following two pointers in result:

  • Pointer to entry if the entry was found

  • NULL pointer if the end of the directory stream was reached

The storage pointed to by entry must be large enough for a dirent with an array of char d_name member containing at least NAME_MAX + 1 elements.

If an error occurred, an error value is returned that indicates the cause of the error.

Applications wishing to check for error situations should set errno to 0 before calling readdir. If errno is set to nonzero on return, then an error occurred.

Example

See the description of closedir for an example.

Return Values

x

On successful completion of readdir, a pointer to an object of type struct dirent.

0

Successful completion of readdir_r.

x

On error, an error value (readdir_r only).

NULL

An error occurred or end of the directory stream (readdir_r only). If an error occurred, errno is set to a value indicating the cause.

readv

readv — Reads from a file.

Format

#include <sys/uio.h>
ssize_t readv (int file_desc, const struct iovec *iov, int iovcnt);
ssize_t _readv64 (int file_desc, struct __iovec64 *iov, int iovcnt);

Function Variants

The readv function has variants named _readv32 and _readv64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

file_desc

A file descriptor. A file descriptor that must refer to a file currently opened for reading.

iov

Array of iovec structures into which the input data is placed.

iovcnt

The number of buffers specified by the members of the iov array.

Description

The readv function is equivalent to read, but places the input data into the iovcnt buffers specified by the members of the iov array: iov[0], iov[1], ..., iov[ iovcnt-1]. The iovcnt argument is valid if it is greater than 0 and less than or equal to IOV_MAX.

Each iovec entry specifies the base address and length of an area in memory where data should be placed. The readv function always fills an area completely before proceeding to the next.

Upon successful completion, readv marks for update the st_atime field of the file.

If the Synchronized Input and Output option is supported:

If the O_DSYNC and O_RSYNC bits have been set, read I/O operations on the file descriptor will complete as defined by synchronized I/O data integrity completion.

If the O_SYNC and O_RSYNC bits have been set, read I/O operations on the file descriptor will complete as defined by synchronized I/O file integrity completion.

If the Shared Memory Objects option is supported:

If file_desc refers to a shared memory object, the result of the read function is unspecified.

For regular files, no data transfer occurs past the offset maximum established in the open file description associated with file_desc.

Return Values

n

The number of bytes read.

- 1

Indicates a read error. The function sets errno to one of the following values:

  • EAGAIN– The O_NONBLOCK flag is set for the file descriptor, and the process would be delayed.

  • EBADF– The file_desc argument is not a valid file descriptor open for reading.

  • EBADMSG– The file is a STREAM file that is set to control-normal mode, and the message waiting to be read includes a control part.

  • EINTER– The read operation was terminated because of the receipt of a signal, and no data was transferred.

  • EINVAL– The STREAM or multiplexer referenced by file_desc is linked (directly or indirectly) downstream from a multiplexer.

    OR

    The sum of the iov_len values in the iov array overflowed an ssize_t.

  • EIO– A physical I/O error has occurred.

    OR

    The process is a member of a background process attempting to read from its controlling terminal, the process is ignoring or blocking the SIGTTIN signal, or the process group is orphaned.

  • EISDIR– The file_desc argument refers to a directory, and the implementation does not allow the directory to be read using read, pread or readv. Use the readdir function instead.

  • EOVERFLOW– The file is a regular file, nbyte is greater than 0, and the starting position is before the end-of-file and is greater than or equal to the offset maximum established in the open file description associated with file_desc.

The readv function may fail if:

  • EINVAL– The iovcnt argument was less than or equal to 0, or greater than IOV_MAX.

realloc

realloc — Changes the size of the area pointed to by the first argument to the number of bytes given by the second argument. These functions are AST-reentrant.

Format

#include <stdlib.h>
void *realloc (void *ptr, size_t size);

Function Variants

The realloc function has variants named _realloc32 and _realloc64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

ptr

Points to an allocated area, or can be NULL.

size

The new size of the allocated area.

Description

If ptr is the NULL pointer, the behavior of the realloc function is identical to the malloc function.

The contents of the area are unchanged up to the lesser of the old and new sizes. The ANSI C Standard states that, "If the new size is larger than the old size, the value of the newly allocated portion of memory is indeterminate." For compatibility with old implementations, VSI C initializes the newly allocated memory to 0.

For efficiency, the previous actual allocation could have been larger than the requested size. If it was allocated with malloc, the value of the portion of memory between the previous requested allocation and the actual allocation is indeterminate. If it was allocated with calloc, that same memory was initialized to 0. If your application relies on realloc initializing memory to 0, then use calloc instead of malloc to perform the initial allocation. The maximum amount of memory allocated at once is limited to 0xFFFFD000.

See also free, cfree, calloc, and malloc.

Return Values

x

The address of the area, quadword-aligned (Alpha only) or octaword-aligned (Integrity servers only). The address is returned because the area may have to be moved to a new address to reallocate enough space. If the area was moved, the space previously occupied is freed.

NULL

Indicates that space cannot be reallocated (for example, if there is not enough room).

realpath

realpath — Returns an absolute pathname from the POSIX root.

Format

#include <stdlib.h>
char realpath (const char *restrict file_name,
char *restrict resolved_name);

Arguments

file_name

Pointer to the text string representing the name of the file for which you want the absolute path.

resolved name

Pointer to the generated absolute path stored as a null-terminated string.

Description

The realpath function returns an absolute pathname from the POSIX root. The generated pathname is stored as a null-terminated string, up to a maximum of PATH_MAX bytes, in the buffer pointed to by resolved_name.

The realpath function is supported only in POSIX-compliant modes (that is, with DECC$POSIX_COMPLIANT_PATHNAMES defined to one of the allowed values).

See also symlink, unlink, readlink, lchown, and lstat.

Return Values

x

Upon successful completion, a pointer to the resolved_name.

NULL
Indicates an error. A null pointer is returned, the contents of the buffer pointed to by resolved_name are undefined, and errno is set to indicate the error:

  • ENAMETOOLONG– The length of the file_name argument exceeds PATH_MAX, or a pathname component is longer than NAME_MAX.

  • ENOENT– A component of file_name does not name an existing file, or file_name points to an empty string.

  • Any errno value from chdir or stat.

[w]refresh

[w]refresh — Repaint the specified window on the terminal screen. The refresh function acts on the stdscr window.

Format

#include <curses.h>
int refresh();
int wrefresh (WINDOW *win);

Argument

win

A pointer to the window.

Description

The result of this process is that the portion of the window not occluded by subwindows or other windows appears on the terminal screen. To see the entire occluded window on the terminal screen, call the touchwin function instead of the refresh or wrefresh function.

See also touchwin.

Return Values

OK

Indicates success.

ERR

Indicates an error.

remainder

remainder — Returns the floating-point remainder r = x - n*y) when y is nonzero.

Format

#include <math.h>
double remainder (double x, double y);
float remainderf (float x, float y);
ong double remainderl (long double x, long double y);

Argument

x

A real number.

y

A real number.

Description

These functions return the floating-point remainder r = x - n*y) when y is nonzero. The value n is the integral value nearest the exact value x/ y. That is, n =rint(x/y).

When |n - x/y| = 1/2, the value n is chosen to be even.

The behavior of the remainder function is independent of the rounding mode.

The remainder functions are functionally equivalent to the remquo functions.

Return Values

r

Upon successful completion, these functions return the floating-point remainder r = x - ny when y is nonzero.

Nan

If x or y is Nan.

remquo

remquo — Returns the floating-point remainder r = x - n*y) when y is nonzero.

Format

#include <math.h>
double remquo (double x, double y, int * quo);
float remquof (float x, float y, int * quo);
long double remquol (long double x, long double y, int * quo);

Argument

x

A real number.

y

A real number.

quo

Description

The remquo(), remquof(), and remquol() functions compute the same remainder as the remainder(), remainderf(), and remainderl() functions, respectively. In the object pointed to by quo, they store a value whose sign is the sign of x/ y and whose magnitude is congruent modulo 2n to the magnitude of the integral quotient of x/ y, where n is an implementation-defined integer greater than or equal to 3.

The remquo functions are functionally equivalent to the remainder functions.

Return Values

r

Upon successful completion, these functions return the floating-point remainder r = x - ny when y is nonzero.

Nan

If x or y is Nan.

remove

remove — Deletes a file.

Format

#include <stdio.h>
int remove (const char *file_spec);

Argument

file_spec

A pointer to the string that is an OpenVMS or a UNIX style file specification. The file specification can include a wildcard in its version number. So, for example, files of the form filename.txt;* can be deleted.

Description

If you specify a directory in the filename and it is a search list that contains an error, VSI C for OpenVMS systems interprets it as a file error.

Note

The DECC$ALLOW_REMOVE_OPEN_FILES feature logical controls the behavior of the remove function on open files. Ordinarily, the operation fails. However, POSIX conformance dictates that the operation succeed.

With DECC$ALLOW_REMOVE_OPEN_FILES enabled, this POSIX conformant behavior is achieved.

When remove is used to delete a symbolic link, the link itself is deleted, not the file to which it refers.

The remove and delete functions are functionally equivalent in the C RTL.

See also delete.

Return Values

0

Indicates success.

nonzero value

Indicates failure.

rename

rename — Gives a new name to an existing file.

Format

#include <stdio.h>
int rename (const char *old_file_spec, const char *new_file_spec);

Arguments

old_file_spec

A pointer to a string that is the existing name of the file to be renamed.

new_file_spec

A pointer to a string that is to be the new name of the file.

Description

If you try to rename a file that is currently open, the behavior is undefined. You cannot rename a file from one physical device to another. Both the old and new file specifications must reside on the same device.

If the new_file_spec does not contain a file extension, the file extension of old_file_spec is used. To rename a file to have no file extension, new_file_spec must contain a period (.) For example, the following renames SYS$DISK:[]FILE.DAT to SYS$DISK:[]FILE1.DAT:
rename("file.dat", "file1");
However, the following renames SYS$DISK:[]FILE.DAT to SYS$DISK:[]FILE1: 
rename("file.dat", "file1.");

Note

Because the rename function does special processing of the file extension, the caller must be careful when specifying the name of the renamed file in a call to a C Run-Time Library function that accepts a file-name argument. For example, after the following call to the rename function, the new file should be opened as fopen("bar.dat",...):
rename("foo.dat", "bar");
The rename function is affected by the setting of the DECC$RENAME_NO_INHERIT and DECC$RENAME_ALLOW_DIR feature logicals as follows:

  • DECC$RENAME_NO_INHERIT provides more UNIX compliant behavior in rename, and affects whether or not the new name for the file inherits anything (like file type) from the old name or must be specified completely.

  • DECC$RENAME_ALLOW_DIR lets you choose between the previous OpenVMS behavior of allowing the renaming of a file from one directory to another, or the more UNIX compliant behavior of not allowing the renaming of a file to a directory.

See the DECC$RENAME_NO_INHERIT and DECC$RENAME_ALLOW_DIR descriptions in Section 1.5 for more information.

Return Values

0

Indicates success.

-1
Indicates failure. The function sets errno to one of the following values:

  • EISDIR– The new argument points to a directory, and the old argument points to a file that is not a directory.

  • EEXIST– The new argument points to a directory that already exists.

  • ENOTDIR– The old argument names a directory, and new argument names a non-directory file.

  • ENOENT – The old argument points to a file, directory, or device that does not exist.

    Or the new argument points to a nonexisting directory path or device.

rewind

rewind — Sets the file to its beginning.

Format

#include <stdio.h>
void rewind (FILE *file_ptr); (ISO POSIX-1)
int rewind (FILE *file_ptr); (VSI C Extension)

Argument

file_ptr

A file pointer.

Description

The rewind function is equivalent to fseek (file_ptr, 0, SEEK_SET). You can use the rewind function with either record or stream files.

A successful call to rewind clears the error indicator for the file.

The ANSI C standard defines rewind as not returning a value; therefore, the function prototype for rewind is declared with a return type of void. However, since a rewind can fail, and since previous versions of the C RTL have declared rewind to return an int, the code for rewind does return 0 on success and -1 on failure.

See also fseek.

rewinddir

rewinddir — Resets the position of the specified directory stream to the beginning of a directory.

Format

#include <dirent.h>
void rewinddir (DIR *dir_pointer);

Argument

dir_pointer

A pointer to the dir structure of an open directory.

Description

The rewinddir function resets the position of the specified directory stream to the beginning of the directory. It also causes the directory stream to refer to the current state of the corresponding directory, the same as using the opendir function. If the dir_pointer argument does not refer to a directory stream, the effect is undefined.

The type DIR, defined in the <dirent.h> header file, represents a directory stream. A directory stream is an ordered sequence of all the directory entries in a particular directory. Directory entries represent files.

See also opendir.

rindex

rindex — Searches for a character in a string.

Format

#include <strings.h>
char *rindex (const char *s, int c);

Function Variants

The rindex function has variants named _rindex32 and _rindex64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

s

The string to search.

c

The character to search for.

Description

The rindex function is identical to the strchr function, and is provided for compatibility with some UNIX implementations.

rint

rint — Rounds its argument to an integral value according to the current IEEE rounding direction specified by the user.

Format

#include <math.h>
double rint (double x);
float rintf (float x,);
long double rintl (long double x);

Argument

x

A real number.

Description

The rint functions return the nearest integral value to x in the direction of the current IEEE rounding mode specified on the /ROUNDING_MODE command-line qualifier.

If the current rounding mode rounds toward negative Infinity, then rint is identical to floor. If the current rounding mode rounds toward positive Infinity, then rint is identical to ceil.

If |x| = Infinity, rint returns x.

Return Values

n

The nearest integral value to x in the direction of the current IEEE rounding mode.

NaN

x is NaN; errno is set to EDOM.

rmdir

rmdir — Removes a directory file.

Format

#include <unistd.h>
int rmdir (const char *path);

Argument

path

A directory pathname.

Description

The rmdir function removes a directory file whose name is specified in the path argument. The directory is removed only if it is empty.

If path names a symbolic link, then rmdir fails and sets errno to ENOTDIR.

Restriction

When using OpenVMS format names, the path argument must be in the form directory.dir.

Return Values

0

Indicates success.

-1

An error occurred; errno is set to indicate the error.

round

round — Rounds to the nearest integer value in floating-point format, rounding halfway cases away from zero.

Format

#include <math.h>
double round (double x);
float roundf (float x);
long double roundl (long double x);

Argument

x

Value to round.

Description

The round functions round x to the nearest integer value in floating-point format, rounding halfway cases away from zero, regardless of the current rounding direction.

Return Value

n

On success, the function returns the rounded integer value.

sbrk

sbrk — Determines the lowest virtual address that is not used with the program.

Format

#include <unistd.h>
void *sbrk (long int incr);

Argument

incr

The number of bytes to add to the current break address.

Description

The sbrk function adds the number of bytes specified by its argument to the current break address and returns the old break address.

When a program is executed, the break address is set to the highest location defined by the program and data storage areas. Consequently, sbrk is needed only by programs that have growing data areas.

sbrk(0) returns the current break address.

Return Values

x

The old break address.

(void *)(-1)

Indicates that the program is requesting too much memory.

Restriction

Unlike other C library implementations, the C RTL memory allocation functions (such as malloc) do not rely on brk or sbrk to manage the program heap space. Consequently, on OpenVMS systems, calling brk or sbrk can interfere with memory allocation routines. The brk and sbrk functions are provided only for compatibility purposes.

scalb

scalb — Returns the exponent of a floating-point number.

Format

#include <math.h>
double scalb (double x, double n);
float scalbf (float x, float n);
long double scalbl (long double x, long double n);

Arguments

x

A nonzero floating-point number.

n

An integer.

Description

The scalb functions return x*(2** n) for integer n.

Return Values

x

On successful completion, x*(2** n) is returned.

±HUGE_VAL

On overflow, scalb returns ±HUGE_VAL (according to the sign of x) and sets errno to ERANGE.

0

Underflow occurred; errno is set to ERANGE.

x

x is ±Infinity.

NaN

x or n is NaN; errno is set to EDOM.

scalbln

scalbln — Returns the exponent of a floating-point number using the floating-point base exponent (long int).

Format

#include <math.h>
double scalbln (double x, long int n);
float scalblnf (float x, long int n);
long double scalblnl (long double x, long int n);

Arguments

x

A nonzero floating-point number.

n

Value of the exponent (long int).

Description

These functions multiply their first argument x by FLT_RADIX (on binary systems, it has a value of 2) to the power of n, which is:
x * FLT_RADIX ** n

The definition of FLT_RADIX can be obtained by including <float.h>.

Return Values

x

On success, x * FLT_RADIX ** n is returned.

NaN

If x is NaN.

±0

If x is ±0.

If the result underflows, a range error occurs, and the functions return ±0 with a sign the same as x.

±Infinity

If x is ±Infinity.

±HUGE_VAL, HUGE_VALF, or HUGE_VALL

If the result overflows, a range error occurs, and the functions return ±HUGE_VAL, HUGE_VALF, or HUGE_VALL, respectively, with a sign the same as x.

scalbn

scalbn — Returns the exponent of a floating-point number using the floating-point base exponent.

Format

#include <math.h>
double scalbn(double x, int n);
float scalbnf(float x, int n);
long double scalbnl(long double x, int n);

Arguments

x

A nonzero floating-point number.

n

Value of the exponent (int).

Description

These functions multiply their first argument x by FLT_RADIX (on binary systems, it has a value of 2) to the power of n, which is:
x * FLT_RADIX ** n

The definition of FLT_RADIX can be obtained by including <float.h>.

Return Values

x

On success, x * FLT_RADIX ** n is returned.

NaN

If x is NaN.

±0

If x is ±0.

If the result underflows, a range error occurs, and the functions return ±0 with a sign the same as x.

±Infinity

If x is ±Infinity.

±HUGE_VAL, HUGE_VALF, or HUGE_VALL

If the result overflows, a range error occurs, and the functions return ±HUGE_VAL, HUGE_VALF, or HUGE_VALL, respectively, with a sign the same as x.

scanf

scanf — Performs formatted input from the standard input (stdin), interpreting it according to the format specification. See Chapter 2 for information on format specifiers.

Format

#include <stdio.h>
int scanf (const char *format_spec, ...);

Arguments

format_spec

Pointer to a string containing the format specification. The format specification consists of characters to be taken literally from the input or converted and placed in memory at the specified input sources. For a list of conversion characters, see Chapter 2.

. . .

Optional expressions that are pointers to objects whose resultant types correspond to conversion specifications given in the format specification.

If no conversion specifications are given, you can omit these input pointers. Otherwise, the function call must have at least as many input pointers as there are conversion specifications, and the conversion specifications must match the types of the input pointers.

Conversion specifications are matched to input sources in left-to-right order. Excess input pointers, if any, are ignored.

Return Values

x

The number of successfully matched and assigned input items.

EOF

Indicates that a read error occurred prior to any successful conversions. The function sets errno. For a list of errno values set by this function, see fscanf.

[w]scanw

[w]scanw — Perform a scanf on the window. The scanw function acts on the stdscr window.

Format

#include <curses.h>
int scanw (char *format_spec, ...);
int wscanw (WINDOW *win, char *format_spec, ...);

Arguments

win

A pointer to the window.

format_spec

A pointer to the format specification string.

. . .

Optional expressions that are pointers to objects whose resultant types correspond to conversion specifications given in the format specification. If no conversion specifications are given, you may omit these input pointers.

Otherwise, the function call must have at least as many input pointers as there are conversion specifications, and the conversion specifications must match the types of the input pointers.

Conversion specifications are matched to input sources in left-to-right order. Excess input pointers, if any, are ignored.

Description

The formatting specification (format_spec) and the other arguments are identical to those used with the scanf function.

The scanw and wscanw functions accept, format, and return a line of text from the terminal screen. For more information, see the scrollok and scanf functions.

Return Values

OK

Indicates success.

ERR

Indicates that the function makes the screen scroll illegally or that the scan was unsuccessful.

scroll

scroll — Moves all the lines on the window up one line. The top line scrolls off the window and the bottom line becomes blank.

Format

#include <curses.h>
int scroll (WINDOW *win);

Argument

win

A pointer to the window.

Return Values

OK

Indicates success.

ERR

Indicates an error.

scrollok

scrollok — Sets the scroll flag for the specified window.

Format

#include <curses.h>
scrollok (WINDOW *win, bool boolf);

Arguments

win

A pointer to the window.

boolf

A Boolean TRUE or FALSE value. If boolf is FALSE, scrolling is not allowed. This is the default setting. The bool type is defined in the <curses.h> header file as follows:
#define bool int

seed48

seed48 — Initializes a 48-bit random-number generator.

Format

#include <stdlib.h>
unsigned short *seed48 (unsigned short seed_16v[3]);

Argument

seed_16v

An array of three unsigned short ints that form a 48-bit seed value.

Description

The seed48 function initializes the random-number generator. You can use this function in your program before calling the drand48, lrand48, or mrand48 functions. (Although it is not recommended practice, constant default initializer values are supplied automatically if you call drand48, lrand48, or mrand48 without calling an initialization function).

The seed48 function works by generating a sequence of 48-bit integer values, Xi, according to the linear congruential formula:
       Xn+1 = (aXn+c)mod m        n > 0
The argument m equals 2 48, so 48-bit integer arithmetic is performed. Unless you invoke the lcong48 function, the multiplier value a and the addend value c are:
      a = 5DEECE66D16 = 2736731631558
      c = B16 = 138
The initializer function seed48:

  • Sets the value of Xi to the 48-bit value specified in the array pointed to by seed_16v.

  • Returns a pointer to a 48-bit internal buffer that contains the previous value of Xi, used only by seed48.

The returned pointer allows you to restart the pseudorandom sequence at a given point. Use the pointer to copy the previous Xi value into a temporary array. To resume where the original sequence left off, you can call seed48 with a pointer to this array.

See also drand48, lrand48, and mrand48.

Return Value

x

A pointer to a 48-bit internal buffer.

seekdir

seekdir — Sets the position of a directory stream.

Format

#include <dirent.h>
void seekdir (DIR *dir_pointer, long int location);

Arguments

dir_pointer

A pointer to the dir structure of an open directory.

location

The number of an entry relative to the start of the directory.

Description

The seekdir function sets the position of the next readdir operation on the directory stream specified by dir_pointer to the position specified by location. The value of location should be returned from an earlier call to telldir.

If the value of location was not returned by a call to the telldir function, or if there was an intervening call to the rewinddir function on this directory stream, the effect is unspecified.

The type DIR, defined in the <dirent.h> header file, represents a directory stream. A directory stream is an ordered sequence of all the directory entries in a particular directory. Directory entries represent files. You can remove files from or add files to a directory asynchronously to the operation of the readdir function.

See readdir, rewinddir, and telldir.

sem_close

sem_close — Deallocates the specified named semaphore.

Format

#include <semaphore.h>
int sem_close (sem_t *sem);

Argument

sem

The semaphore to be closed. Use the sem argument returned by the previous call to sem_open.

Description

The sem_close function makes a semaphore available for reuse by deallocating any system resources allocated for use by the current process for the named semaphore indicated by sem.

If the semaphore has not been removed with a call to sem_unlink, sem_close does not change the current state of the semaphore.

If the semaphore has been removed with a call to sem_unlink after the most recent call to sem_open with O_CREAT, the semaphore is no longer available after all processes that opened the semaphore close it.

Return Values

0

Successful completion.

-1
Indicates an error. The function sets errno to one of the following values:

  • EINVAL– The sem argument is not a valid semaphore descriptor.

  • ENOSYS– The function is not implemented.

  • EVMSERR– OpenVMS specific nontranslatable error code.

semctl

semctl — Semaphore control operations.

Format

#include <sem.h>
int semctl (int semid, int semnum, int cmd, ...);

Argument

semid

A semaphore set identifier, a positive integer. It is created by the semget function and used to identify the semaphore set on which to perform the control operation.

semnum

Semaphore number, a non-negative integer. It identifies a semaphore within the semaphore set on which to perform the control operation.

cmd

The control operation to perform on the semaphore.

. . .

Optional fourth argument of type union semun, which depends on the control operation requested in cmd.

Description

The semctl function provides a variety of semaphore control operations as specified by cmd. The fourth argument is optional and depends upon the operation requested. If required, it is of type union semun, which is explicitly declared as:
union semun {
    int val;
    struct semid_ds *buf;
    unsigned short  *array;
} arg;
The following semaphore control operations as specified by cmd are executed with respect to the semaphore specified by semid and semnum. The level of permission required for each operation is shown with each command. The symbolic names for the values of cmd are defined in the <sem.h> header:

  • GETVAL

    Returns the value of semval. Requires read permission.

  • SETVAL

    Sets the value of semval to arg.val, where arg is the value of the fourth argument to semctl. When this command is successfully executed, the semadj value corresponding to the specified semaphore in all processes is cleared. Requires alter permission.

  • GETPID

    Returns the value of sempid; requires read permission.

  • GETNCNT

    Returns the value of semncnt; requires read permission.

  • GETZCNT

    Returns the value of semzcnt; requires read permission.

The following values of cmd operate on each semval in the set of semaphores:

  • GETALL

    Returns the value of semval for each semaphore in the semaphore set and places it into the array pointed to by arg.array, where arg is the fourth argument to semctl; requires read permission.

  • SETALL

    Sets the value of semval for each semaphore in the semaphore set according to the array pointed to by arg.array, where arg is the fourth argument to semctl. When this command is successfully executed, the semadj values corresponding to each specified semaphore in all processes are cleared. Requires alter permission.

The following values of cmd are also available:

  • IPC_STAT

    Places the current value of each member of the semid_ds data structure associated with semid into the structure pointed to by arg.buf, where arg is the fourth argument to semctl. The contents of this structure are defined in <sem.h>. Requires read permission.

  • IPC_SET

    Sets the value of the following members of the semid_ds data structure associated with semid to the corresponding value found in the structure pointed to by arg.buf, where arg is the fourth argument to semctl:
    sem_perm.uid sem_perm.gid sem_perm.mode

    The mode bits specified in The Open Group Base Specifications IPC General Description section are copied into the corresponding bits of the sem_perm.mode associated with semid. The stored values of any other bits are unspecified.

    This command can only be executed by a process that has an effective user ID equal to either that of a process with appropriate privileges or to the value of sem_perm.cuid or sem_perm.uid in the semid_ds data structure associated with semid.

  • IPC_RMID

    Removes the semaphore identifier specified by semid from the system and destroys the set of semaphores and semid_ds data structure associated with it. This command can only be executed by a process that has an effective user ID equal to either that of a process with appropriate privileges or to the value of sem_perm.cuid or sem_perm.uid in the semid_ds data structure associated with semid.

Return Values

n or 0
Upon successful completion, the value returned by the function depends on cmd as follows:

  • GETVAL - The value of semval

  • GETPID - The value of sempid

  • GETNCNT - The value of semncnt

  • GETZCNT - The value of semzcnt

  • All others - 0

-1
Indicates an error. The function sets errno to one of the following values:

  • EACCES– Operation permission is denied to the calling process.

  • EFAULT– The arguments passed to the function are not accessible.

  • EINVAL– The value of semid is not a valid semaphore identifier, or the value of semnum is less than zero or greater than or equal to sem_nsems, or the value of cmd is not a valid command.

  • EPERM– The argument cmd is equal to IPC_RMID or IPC_SET and the effective user ID of the calling process is not equal to that of a process with appropriate privileges and it is not equal to the value of sem_perm.cuid or sem_perm.uid in the data structure associated with semid.

  • EVMSERR– OpenVMS specific nontranslatable error code.

sem_destroy

sem_destroy — Destroys an unnamed semaphore.

Format

#include <semaphore.h>
int sem_destroy (sem_t *sem);

Argument

sem

The unnamed semaphore to be destroyed. Use the sem argument that was supplied to, and filled in by, the previous call to sem_init.

Description

The sem_destroy function destroys an unnamed semaphore indicated by sem. Only a semaphore created using sem_init may be destroyed using sem_destroy.

The potential for deadlock exists if a process calls sem_destroy for a semaphore while there is a pending sem_wait, because a process may be waiting for a poster that has not yet opened the semaphore.

Return Values

0

Successful completion.

-1
Indicates an error. The function sets errno to one of the following values, without destroying the semaphore indicated by the sem argument:

  • EINVAL– The sem argument is not a valid semaphore.

  • ENOSYS– The function is not implemented.

  • EVMSERR– OpenVMS specific nontranslatable error code.

  • EBUSY– The processes are blocked on the semaphore.

semget

semget — Gets a set of semaphores.

Format

#include <sem.h>
int semget (key_t key, int nsems, int semflg);

Argument

key

The key for which the associated semaphore identifier is returned.

nsems

Value used to initialize the sem_nsems member of the semid_ds data structure. See the description.

semflg

Flag used to initialize the low-order 9 bits of the sem_perm.mode member of the semid_ds data structure associated with the new semaphore. See the description.

value

The initial value to be given to the semaphore. This argument is used only when the semaphore is being created.

Description

The semget function returns the semaphore identifier associated with key.

A semaphore identifier with its associated semid_ds data structure and its associated set of nsems semaphores (see the <sys/sem.h> header file) is created for key if:

  • The key argument does not already have a semaphore identifier associated with it and (semflg &IPC_CREAT) is nonzero.

When it is created, the semid_ds data structure associated with the new semaphore identifier is initialized as follows:

  • In the operation permissions structure sem_perm.cuid, sem_perm.uid, sem_perm.cgid, and sem_perm.gid are set equal to the effective user ID and effective group ID, respectively, of the calling process.

  • The low-order 9 bits of sem_perm.mode are set equal to the low-order 9 bits of the semflg argument.

  • The variable sem_nsems is set equal to the value of the nsems argument.

  • The variable sem_otime is set equal to 0 and the variable sem_ctime is set equal to the current time.

  • The data structure associated with each semaphore in the set does not need to be initialized. You can use the semctl function with the command SETVAL or SETALL to initialize each semaphore.


Note

The key argument value IPC_PRIVATE is not supported.

Return Values

n

Successful completion. The function returns a non-negative integer semaphore identifier.

-1
Indicates an error. The function sets errno to one of the following values:

  • EACCES– A semaphore identifier exists for key, but operation permission as specified by the low-order 9 bits of semflg was not granted.

  • EEXIST– A semaphore identifier exists for key but ((semflg&IPC_CREAT) && (semflg &IPC_EXCL)) is nonzero.

  • EFAULT– The arguments passed to the function are not accessible.

  • EINVAL– The value of nsems is either less than or equal to 0 or greater than the system-imposed limit, or a semaphore identifier exists for key, but the number of semaphores in the set associated with it is less than nsems and nsems is not equal to 0.

  • ENOENT– A semaphore identifier does not exist for key and (semflg &IPC_CREAT) is equal to 0.

  • ENOSPC– A semaphore identifier is to be created but the system-imposed limit on the maximum number of allowed semaphores system-wide will be exceeded.

  • EVMSERR– OpenVMS specific nontranslatable error code.

sem_getvalue

sem_getvalue — Gets the value of a specified semaphore.

Format

#include <semaphore.h>
int sem_getvalue (sem_t *sem, int *sval);

Argument

sem

The semaphore for which a value is to be returned.

sval

The location to be updated with the value of the semaphore indicated by the sem argument.

Description

The sem_getvalue function updates a location referenced by the sval argument with the value of semaphore sem. The updated value represents an actual semaphore value that occurred during the call, but may not be the actual value of the semaphore at the time that the value is returned to the calling process.

If the semaphore is locked, the value returned will either be zero or a negative number indicating the number of processes waiting for the semaphore at some time during the call.

Return Values

0

Successful completion.

-1
Indicates an error. The function sets errno to one of the following values:

  • EINVAL– The sem argument is not a valid semaphore.

  • EVMSERR– OpenVMS specific nontranslatable error code.

sem_init

sem_init — Initializes an unnamed semaphore.

Format

#include <semaphore.h>
int sem_init (sem_t *sem, int pshared, unsigned int value);

Argument

sem

The location to receive the descriptor of the initialized semaphore.

pshared

A value indicating whether the semaphore should be sharable between the creating process and its descendants (nonzero value) or not (zero).

Note

The value for pshared must be zero between threads because this release does not support unnamed semaphores to be shared across processes.

value

The initial value to be given to the semaphore.

Description

The sem_init function creates a new counting semaphore with a specific value. A semaphore is used to limit access to a critical resource. When a process requires access to the resource without interference from other processes, it attempts to establish a connection with the associated semaphore. If the semaphore value is greater than zero, the connection is established and the semaphore value is decremented by one. If the semaphore value is less than or equal to zero, the process attempting to access the resource is blocked and must wait for another process to release the semaphore and increment the semaphore value.

The sem_init function establishes a connection between an unnamed semaphore and a process; the sem_wait and sem_trywait functions lock the semaphore; and the sem_post function unlocks the semaphore. Use the sem_destroy function to deallocate system resources allocated to the process for use with the semaphore. You can use the sem_getvalue function to obtain the value of a semaphore.

A semaphore created by a call to the sem_init function remains valid until the semaphore is removed by a call to the sem_destroy function.

Return Values

0

Successful completion.

-1
Indicates an error. The function sets errno to one of the following values:

  • EINVAL– The value argument exceeds {SEM_VALUE_MAX}.

  • ENOSYS– The function is not implemented.

  • EVMSERR– OpenVMS specific nontranslatable error code.

sem_open

sem_open — Opens/creates a named semaphore for use by a process.

Format

#include <semaphore.h>
sem_t *sem_open (const char *name, int ooption...);

Argument

name

a string naming the semaphore object.

ooption

Specifies whether the semaphore is to be created (O_CREAT option bit set) or only opened (O_CREAT option bit clear). If O_CREAT is set, the O_EXCL option bit may additionally be set to specify that the call should fail if a semaphore of the same name already exists. The O_CREAT and O_EXCL options are defined in the <fcntl.h> header file.

mode

The semaphore's permission bits. This argument is used only when the semaphore is being created.

value

The initial value to be given to the semaphore. This argument is used only when the semaphore is being created.

Description

Use the sem_open function to establish the connection between a named semaphore and a process. Subsequently, the calling process can reference the semaphore by using the address returned from the call. The semaphore is available in subsequent calls to sem_wait, sem_trywait, sem_post, and sem_getvalue functions. The semaphore remains usable by the process until the semaphore is closed by a successful call to the sem_close function.

The O_CREAT option bit in the ooption parameter controls whether the semaphore is created or only opened by the call to sem_open.

A created semaphore's user ID is set to the user ID of the calling process and its group ID is set to a system default group or to the group ID of the process. The semaphore's permission bits are set to the value of the mode argument, except for those set in the file mode creation mask of the process.

After a semaphore is created, other processes can open the semaphore by calling sem_open with the same value for the name argument.

Return Values

sem

Successful completion. The function opens the semaphore and returns the semaphore's descriptor.

sem_failed
Indicates an error. The function sets errno to one of the following values:

  • EACCES – The named semaphore exists and the permissions specified by ooption are denied, or the named semaphore does not exist and the permissions specified by ooption are denied.

  • EEXIST – O_CREAT and O_EXCL are set, and the named semaphore already exists.

  • EINVAL – The sem_open operation is not supported for the given name. Or, O_CREAT was specified in ooption and value was greater than {SEM_VALUE_MAX}.

  • EMFILE – Too many semaphore descriptors or file descriptors are currently in use by this process.

  • ENAMETOOLONG – The length of the name string exceeds {PATH_MAX}, or a pathname component is longer than {NAME_MAX} while {_POSIX_NO_TRUNC} is in effect.

  • ENFILE – Too many semaphores are currently open in the system. ENOENT O_CREAT is not set, and the named semaphore does not exist.

  • ENOSPC – Insufficient space exists for the creation of a new named semaphore.

  • EVMSERR – OpenVMS specific nontranslatable error code.

semop

semop — Performs operations on semaphores in a semaphore set.

Format

#include <sem.h>
int semop (int semid, struct sembuf *sops, size_t nsops);

Argument

semid

Semaphore set identifier.

sops

Pointer to a user-defined array of semaphore operation (sembuf) structures.

nsops

Number of sembuf structures in the sops array.

Description

The semop function performs operations on semaphores in the semaphore set specified by semid. These operations are supplied in a user-defined array of semaphore operation sembuf structures specified by sops. Each sembuf structure includes the following member variables: 
struct sembuf {            /* semaphore operation structure */
  unsigned short sem_num;  /* semaphore number */
           short sem_op;   /* semaphore operation */
           short sem_flg;  /* operation flags SEM_UNDO and IPC_NOWAIT */

Each semaphore operation specified by the sem_op variable is performed on the corresponding semaphore specified by the semid function argument and the sem_num variable.

The sem_op variable specifies one of three semaphore operations:
  1. If sem_op is a negative integer and the calling process has change permission, one of the following occurs:

    • If semval (see <sem.h>) is greater than or equal to the absolute value of sem_op, the absolute value of sem_op is subtracted from semval. Also, if (sem_flg &SEM_UNDO) is non-zero, the absolute value of sem_op is added to the calling process' semadj value for the specified semaphore.

    • If semval is less than the absolute value of sem_op and (sem_flg &IPC_NOWAIT) is nonzero, semop returns immediately.

    • If semval is less than the absolute value of sem_op and ( sem_flg &IPC_NOWAIT) is 0, semop increments the semncnt associated with the specified semaphore and suspends execution of the calling thread until one of the following conditions occurs:

      • The value of semval becomes greater than or equal to the absolute value of sem_op. When this occurs, the value of semncnt associated with the specified semaphore is decremented, the absolute value of sem_op is subtracted from semval and, if (sem_flg &SEM_UNDO) is nonzero, the absolute value of sem_op is added to the calling process' semadj value for the specified semaphore.

      • The semid for which the calling thread is awaiting action is removed from the system. When this occurs, errno is set equal to EIDRM and -1 is returned.

      • The calling thread receives a signal that is to be intercepted. When this occurs, the value of semncnt associated with the specified semaphore is decremented, and the calling thread is resumes execution in the manner prescribed in sigaction.

  2. If sem_op is a positive integer and the calling process has change permission, the value of sem_op is added to semval and, if (sem_flg &SEM_UNDO) is nonzero, the value of sem_op is subtracted from the calling process' semadj value for the specified semaphore.

  3. If sem_op is 0 and the calling process has read permission, one of the following occurs:

    • If semval is 0, semop returns immediately.

    • If semval is nonzero and ( sem_flg &IPC_NOWAIT) is nonzero, semop returns immediately.

    • If semval is nonzero and (sem_flg &IPC_NOWAIT) is 0, semop increments the semzcnt associated with the specified semaphore and suspends execution of the calling thread until one of the following occurs:

      • The value of semval becomes 0, at which time the value of semzcnt associated with the specified semaphore is decremented.

      • The semid for which the calling thread is awaiting action is removed from the system. When this occurs, errno is set equal to EIDRM and -1 is returned.

      • The calling thread receives a signal that is to be intercepted. When this occurs, the value of semzcnt associated with the specified semaphore is decremented, and the calling thread resumes execution in the manner prescribed in sigaction.

On successful completion, the value of sempid for each semaphore specified in the array pointed to by sops is set equal to the process ID of the calling process.

Return Values

0

Successful completion.

-1
Indicates an error. The function sets errno to one of the following values:

  • E2BIG– The value of nsops is greater than the system-imposed maximum.

  • EACCES– Operation permission is denied to the calling process.

  • EAGAIN– The operation would result in suspension of the calling process but (sem_flg &IPC_NOWAIT) is nonzero.

  • EFAULT– The arguments passed to the function are not accessible.

  • EFBIG– The value of sem_num is less than 0 or greater than or equal to the number of semaphores in the set associated with semid.

  • EIDRM– The semaphore identifier semid is removed from the system.

  • EINVAL– The value of semid is not a valid semaphore identifier, or the number of individual semaphores for which the calling process requests a SEM_UNDO would exceed the system-imposed limit.

  • EVMSERR– OpenVMS specific nontranslatable error code.

sem_post

sem_post — Unlocks a semaphore.

Format

#include <semaphore.h>
int sem_post (sem_t *sem);

Argument

sem

The semaphore to be unlocked.

Description

The sem_post function unlocks the specified semaphore by performing the semaphore unlock operation on that semaphore. The appropriate function (sem_open for named semaphores or sem_init for unnamed semaphores) must be called for a semaphore before you can call the locking and unlocking functions, sem_wait, sem_trywait, and sem_post.

If the semaphore value after a sem_post function is positive, no processes were blocked waiting for the semaphore to be unlocked; the semaphore value is incremented. If the semaphore value after a sem_post function is zero, one of the processes blocked waiting for the semaphore is allowed to return successfully from its call to sem_wait.

If more than one process is blocked while waiting for the semaphore, only one process is unblocked and the state of the semaphore remains unchanged when the sem_post function returns. The process to be unblocked is selected according to the scheduling policies and priorities of all blocked processes. If the scheduling policy is SCHED_FIFO or SCHED_RR, the highest-priority waiting process is unblocked. If more than one process of that priority is blocked, then the process that has waited the longest is unblocked.

The sem_post function can be called from a signal-catching function.

Return Values

0

Successful completion. The sem_post function performs a semaphore unlock operation, unblocking a process.

-1
Indicates an error. The function sets errno to one of the following values:

  • EINVAL– The sem argument is not a valid semaphore.

  • EVMSERR– OpenVMS specific nontranslatable error code.

sem_timedwait

sem_timedwait — Performs a semaphore lock.

Format

#include <semaphore.h>
#include <time.h>
 int sem_timedwait (sem_t *sem, const struct timespec *abs_timeout);

Argument

sem

The semaphore to be locked.

abs_timeout

The absolute time after which the timeout expires.

Description

The sem_timedwait function locks the semaphore referenced by sem as in the sem_wait function. But if the semaphore cannot be locked without waiting for another process or thread to unlock the semaphore by performing a sem_post function, this wait terminates when the specified timeout expires.

The timeout expires when the absolute time specified by abs_timeout passes, as measured by the clock on which timeouts are based (that is, when the value of that clock equals or exceeds abs_timeout, or if the absolute time specified by abs_timeout has already been passed at the time of the call.

The function will not fail with a timeout if the semaphore can be locked immediately. The validity of abs_timeout does not need to be checked if the semaphore can be locked immediately.

Return Values

0

Successful completion. The function executes the semaphore lock operation.

-1
Indicates an error. The function sets errno to one of the following values:

  • ETIMEDOUT– The semaphore could not be locked before the specified timeout expired.

  • EINVAL– The sem argument does not refer to a valid semaphore. Or the process or thread would have blocked, and the abs_timeout parameter specified a nanoseconds field value less than zero or greater than or equal to 1000 million.

  • EVMSERR– OpenVMS specific nontranslatable error code.

sem_trywait

sem_trywait — Conditionally performs a semaphore lock.

Format

#include <semaphore.h>
int sem_trywait (sem_t *sem);

Argument

sem

The semaphore to be locked.

Description

The sem_trywait function locks a semaphore only if the semaphore is currently not locked. If the semaphore value is zero, the sem_trywait function returns without locking the semaphore.

The sem_wait and sem_trywait functions help ensure that the resource associated with the semaphore cannot be accessed by other processes. The semaphore remains locked until the process unlocks it with a call to the sem_post function.

Use the sem_wait function instead of the sem_trywait function if the process should wait for access to the semaphore.

Return Values

0

Successful completion. The function executes the semaphore lock operation.

-1
Indicates an error. The function sets errno to one of the following values:

  • EAGAIN– The semaphore was already locked and cannot be locked by the sem_trywait operation.

  • EINVAL– The sem argument does not refer to a valid semaphore.

  • EVMSERR– OpenVMS specific nontranslatable error code.

sem_wait

sem_wait — Performs a semaphore lock.

Format

#include <semaphore.h>
int sem_wait (sem_t *sem);

Argument

sem

The semaphore to be locked.

Description

The sem_wait function locks the semaphore referenced by sem by performing a semaphore lock operation on it. If the semaphore value is zero, the sem_wait function blocks until it either locks the semaphore or is interrupted by a signal.

The sem_wait and sem_trywait functions help ensure that the resource associated with the semaphore cannot be accessed by other processes. The semaphore remains locked until the process unlocks it with a call to the sem_post function.

Use the sem_wait function instead of the sem_trywait function if the process should wait for access tothe semaphore.

Return Values

0

Successful completion. The function executes the semaphore lock operation.

-1
Indicates an error. The function sets errno to one of the following values:

  • EINTR– A signal interrupted this function.

  • EVMSERR– OpenVMS specific nontranslatable error code.

[w]setattr

[w]setattr — Activate the video display attribute attr within the window. The setattr function acts on the stdscr window.

Format

#include <curses.h>
int setattr (int attr);
int wsetattr (WINDOW *win, int attr);

Arguments

win

A pointer to the window.

attr

One of a set of video display attributes, which are blinking, boldface, reverse video, and underlining, and are represented by the defined constants _BLINK, _BOLD, _REVERSE, and _UNDERLINE, respectively. You can set multiple attributes by separating them with a bitwise OR operator ( |) as follows:
setattr(_BLINK | _UNDERLINE);

Description

The setattr and wsetattr functions are specific to VSI C for OpenVMS systems and are not portable.

Return Values

OK

Indicates success.

ERR

Indicates an error.

setbuf

setbuf — Associates a new buffer with an input or output file and potentially modifies the buffering behavior.

Format

#include <stdio.h>
void setbuf (FILE *file_ptr, char *buffer);

Arguments

file_ptr

A file pointer.

buffer

A pointer to a character array or a NULL pointer.

Description

You can use the setbuf function after the specified file is opened but before any I/O operations are performed.

If buffer is a NULL pointer, then the call is equivalent to a call to setvbuf with the same file_ptr, a NULL buffer pointer, a buffering type of _IONBF (no buffering), and a buffer size of 0.

If buffer is not a NULL pointer, then the call is equivalent to a call to setvbuf with the same file_ptr, the same buffer pointer, a buffering type of _IOFBF, and a buffer size given by the value BUFSIZ (defined in <stdio.h>). Therefore, use BUFSIZ to allocate the buffer argument used in the call to setbuf. For example: 
#include <stdio.h>
   .
   .
   .
char my_buf[BUFSIZ];
   .
   .
   .
setbuf(stdout, my_buf);
   .
   .
   .

User programs must not depend on the contents of buffer once I/O has been performed on the stream. The C RTL might or might not use buffer for any given I/O operation.

The setbuf function originally allowed programmers to substitute larger buffers in place of the system default buffers in obsolete versions of UNIX. The large default buffer sizes in modern implementations of C make the use of this function unnecessary most of the time. The setbuf function is retained in the ANSI C standard for compatibility with old programs. New programs should use setvbuf instead, because it allows the programmer to bind the buffer size at run time instead of compile time, and it returns a result value that can be tested.

The setbuf function now takes 64-bit arguments. However, the buffer parameter must contain a 32-bit memory buffer, so when compiling the application with /POINTER=64 or /POINTER=LONG, malloc32 must be used to allocate the buffer.

setenv

setenv — Inserts or resets the environment variable specified by name in the current environment list.

Format

#include <stdlib.h>
int setenv (const char *name, const char *value, int overwrite);

Arguments

name

A variable name in the environment variable list.

value

The value for the environment variable.

overwrite

A value of 0 or 1 indicating whether to reset the environment variable, if it exists.

Description

The setenv function inserts or resets the environment variable name in the current environment list. If the variable name does not exist in the list, it is inserted with the value argument. If the variable does exist, the overwrite argument is tested. When the overwrite argument value is:

  • 0 then the variable is not reset.

  • 1 then the variable is reset to value.


Note

Do not use the setenv, getenv, and putenv functions to manipulate symbols and logicals. Instead, use the OpenVMS library calls lib$set_logical, lib$get_logical, lib$set_symbol, and lib$get_symbol. The * env functions deliberately provide UNIX behavior, and are not a substitute for these OpenVMS runtime library calls.

OpenVMS DCL symbols, not logical names, are the closest analog to environment variables on UNIX systems. While getenv is a mechanism to retrieve either a logical name or a symbol, it maintains an internal cache of values for use with setenv and subsequent getenv calls. The setenv function does not write or create DCL symbols or OpenVMS logical names.

This is consistent with UNIX behavior. On UNIX systems, setenv does not change or create any symbols that will be visible in the shell after the program exits.

Return Values

0

Indicates success.

-1

Indicates an error. errno is set to ENOMEM – Not enough memory available to expand the environment list.

seteuid

seteuid — Sets the process's effective user ID.

Format

#include <unistd.h>
int seteuid (uid_t euid);

Argument

euid

The value to which you want the effective user ID set.

Description

If the process has the IMPERSONATE privilege, the seteuid function sets the process's effective user ID.

An unprivileged process can set the effective user ID only if the euid argument is equal to either the real, effective, or saved user ID of the process.

This function requires that long (32-bit) UID/GID support be enabled. See Section 1.4.8 for more information.

See also getuid to know how UIC is represented.

Return Values

0

Successful completion.

-1
Indicates an error. The function sets errno to one of the following values:

  • EINVAL– The value of the euid argument is invalid and not supported.

  • EPERM– The process does not have the IMPERSONATE privilege, and euid does not match the real user ID or the saved set-user-ID.

setgid

setgid — With POSIX IDs disabled, setgid is implemented for program portability and serves no function. It returns 0 (to indicate success). With POSIX IDs enabled, setgid sets the group IDs.

Format

#include <types.h>
#include <unistd.h>
int setgid (__gid_t gid); (_DECC_V4_SOURCE)
int setgid (gid_t gid); (not _DECC_V4_SOURCE)

Argument

gid

The value to which you want the group IDs set.

Description

The setgid function can be used with POSIX style identifiers enabled or disabled.

POSIX style IDs are supported on OpenVMS Version 7.3-2 and higher.

With POSIX IDs disabled, the setgid function is implemented for program portability and serves no function. It returns 0 (to indicate success).

With POSIX style IDs enabled:

  • If the process has the IMPERSONATE privilege, the setgid function sets the real group ID, effective group ID, and the saved set-group-ID to gid.

  • If the process does not have appropriate privileges but gid is equal to the real group ID or to the saved set-group-ID, then the setgid function sets the effective group ID to gid. The real group ID and saved set-group-ID remain unchanged.

  • Any supplementary group IDs of the calling process remain unchanged.

To enable/disable POSIX style IDs, see Section 1.6.

Return Values

0

Successful completion.

-1
Indicates an error. The function sets errno to one of the following values:

  • EINVAL– The value of the gid argument is invalid and not supported by the implementation.

  • EPERM– The process does not have appropriate privileges and gid does not match the real group ID or the saved set-group-ID.

setgrent

setgrent — Rewinds the group database.

Format

#include <grp.h>
void setgrent (void);

Description

The setgrent function effectively rewinds the group database to allow repeated searches.

This function is always successful. No value is returned, and errno is not set.

setitimer

setitimer — Sets the value of interval timers.

Format

#include <time.h>
int setitimer (int which, struct itimerval *value,
struct itimerval *ovalue);

Arguments

which

The type of interval timer. The C RTL only supports ITIMER_REAL.

value

A pointer to an itimerval structure whose members specify a timer interval and the time left to the end of the interval.

ovalue

A pointer to an itimerval structure whose members specify a current timer interval and the time left to the end of the interval.

Description

The setitimer function sets the timer specified by which to the value specified by value, returning the previous value of the timer if ovalue is nonzero.

A timer value is defined by the itimerval structure:
       struct itimerval {
               struct  timeval it_interval;
               struct  timeval it_value;
       };
The value of the itimerval structure members are as follows:

itimerval Member Value

Meaning

it_interval = 0

Disables a timer after its next expiration (assumes it_value is nonzero).

it_interval = nonzero

Specifies a value used in reloading it_value when the timer expires.

it_value = 0

Disables a timer.

it_value = nonzero

Indicates the time to the next timer expiration.

Time values smaller than the resolution of the system clock are rounded up to this resolution.

The getitimer function provides one interval timer, defined in the <time.h> header file as ITIMER_REAL. This timer decrements in real time. When the timer expires, it delivers a SIGALARM signal.

Note

The interaction between setitimer and any of alarm, sleep, or usleep is unspecified.

Return Values

0

Indicates success.

-1

An error occurred; errno is set to indicate the error.

setjmp

setjmp — Provides a way to transfer control from a nested series of function invocations back to a predefined point without returning normally. It does not use a series of return statements. The setjmp function saves the context of the calling function in an environment buffer.

Format

#include <setjmp.h>
int setjmp (jmp_buf env);

Argument

env

The environment buffer, which must be an array of integers long enough to hold the register context of the calling function. The type jmp_buf is defined in the <setjmp.h> header file. The contents of the general-purpose registers, including the program counter (PC), are stored in the buffer.

Description

When setjmp is first called, it returns the value 0. If longjmp is then called, naming the same environment as the call to setjmp, control is returned to the setjmp call as if it had returned normally a second time. The return value of setjmp in this second return is the value supplied by you in the longjmp call. To preserve the true value of setjmp, the function calling setjmp must not be called again until the associated longjmp is called.

The setjmp function preserves the hardware general-purpose registers, and the longjmp function restores them. After a longjmp, all variables have their values as of the time of the longjmp except for local automatic variables not marked volatile. These variables have indeterminate values.

The setjmp and longjmp functions rely on the OpenVMS condition-handling facility to effect a nonlocal go to with a signal handler. The longjmp function is implemented by generating a C RTL specified signal that allows the OpenVMS condition-handling facility to unwind back to the desired destination.

The C RTL must be in control of signal handling for any VSI C image. For VSI C to be in control of signal handling, you must establish all exception handlers through a call to the VAXC$ESTABLISH function. See Section 4.2.5 and the VAXC$ESTABLISH function for more information.

Note

The C RTL provides nonstandard decc$setjmp and decc$fast_longjmp functions for Alpha and Integrity server systems. To use these nonstandard functions instead of the standard ones, a program must be compiled with _ _FAST_SETJMP or _ _UNIX_SETJMP macros defined.

Unlike the standard longjmp function, the decc$fast_longjmp function does not convert its second argument from 0 to 1. After a call to decc$fast_longjmp, a corresponding setjmp function returns with the exact value of the second argument specified in the decc$fast_longjmp call.

Restrictions

You cannot invoke the longjmp function from an OpenVMS condition handler. However, you may invoke longjmp from a signal handler that has been established for any signal supported by the C RTL, subject to the following nesting restrictions:

  • The longjmp function will not work if you invoke it from nested signal handlers. The result of the longjmp function, when invoked from a signal handler that has been entered as a result of an exception generated in another signal handler, is undefined.

  • Do not invoke the setjmp function from a signal handler unless the associated longjmp is to be issued before the handling of that signal is completed.

  • Do not invoke the longjmp function from within an exit handler (established with atexit or SYS$DCLEXH). Exit handlers are invoked after image tear-down, so the destination address of the longjmp no longer exists.

  • Invoking longjmp from within a signal handler to return to the main thread of execution might leave your program in an inconsistent state. Possible side effects include the inability to perform I/O or to receive any more UNIX signals. Use siglongjmp instead.

Return Values

See the Description section.

setkey

setkey — Sets an encoding key for use by the encrypt function.

Format

#include <unistd.h>
#include <stdlib.h>
void setkey (const char *key;)

Argument

key

A character array of length 64 containing 0s and 1s.

Description

The argument of setkey is a character array of length 64 containing only the characters with numerical value 0 and 1. If this string is divided into groups of 8, the low-order bit in each group is ignored, leading to a 56-bit key which is set into the machine.

No value is returned.

See also crypt and encrypt.

setlocale

setlocale — Selects the appropriate portion of the program's locale as specified by the category and locale arguments. You can use this function to change or query one category or the program's entire current locale.

Format

#include <locale.h>
char *setlocale (int category, const char *locale);

Arguments

category

The name of the category. Specify LC_ALL to change or query the entire locale. Other valid category names are:

  • LC_COLLATE

  • LC_CTYPE

  • LC_MESSAGES

  • LC_MONETARY

  • LC_NUMERIC

  • LC_TIME

locale

Pointer to a string that specifies the locale.

Description

The setlocale function sets or queries the appropriate portion of the program's locale as specified by the category and locale arguments. Specifying LC_ALL for the category argument names the entire locale; specifying the other values name only a portion of the program's locale.

The locale argument points to a character string that identifies the locale to be used. This argument can be one of the following:

  • Name of the public locale

    Specifies the public locale in the following format:
    language_country.codeset[@modifier]

    The function searches for the public locale binary file in the location defined by the logical name SYS$I18N_LOCALE. The file type defaults to .LOCALE. The period (.) and at-sign (@) characters in the name are replaced by an underscore (_).

    For example, if the specified name is "zh_CN.dechanzi@radical", the function searches for the SYS$I18N_LOCALE:ZH_CN_DECHANZI_RADICAL.LOCALE binary locale file.

  • A file specification

    Specifies the binary locale file. It can be any valid file specification. If either the device or directory is omitted, the function first applies the current caller's device and directory as defaults for any missing component. If the file is not found, the function applies the device and directory defined by the SYS$I18N_LOCALE logical name as defaults. The file type defaults to .LOCALE.

    No wildcards are allowed. The binary locale file cannot reside on a remote node.

  • "C"

    Specifies the C locale. If a program does not call setlocale, the C locale is the default.

  • "POSIX"

    This is the same as the C locale.

  • ""

    Specifies that the locale is initialized from the setting of the international environment logical names. The function checks the following logical names in the order shown until it finds a logical that is defined:

    1. LC_ALL

    2. Logical names corresponding to the category. For example, if LC_NUMERIC is specified as the category, then the first logical name that setlocale checks is LC_NUMERIC.

    3. LANG

    4. SYS$LC_ALL

    5. The system default for the category, which is defined by the SYS$LC_* logical names. For example, the default for the LC_NUMERIC category is defined by the SYS$LC_NUMERIC logical name.

    6. SYS$LANG

      If none of the logical names is defined, the C locale is used as the default. The SYS$LC_* logical names are set up at the system startup time.

    Like the locale argument, the equivalence name of the international environment logical name can be either the name of the public locale or the file specification. The setlocale function treats this equivalence name as if it were specified as the locale argument.

  • NULL

    Causes setlocale to query the current locale. The function returns a pointer to a string describing the portion of the program's locale associated with category. Specifying the LC_ALL category returns the string describing the entire locale. The locale is not changed.

  • The string returned from the previous call to setlocale

    Causes the function to restore the portion of the program's locale associated with category. If the string contains the description of the entire locale, the part of the string corresponding to category is used. If the string describes the portion of the program's locale for a single category, this locale is used. For example, this means that you can use the string returned from the call setlocale with the LC_COLLATE category to set the same locale for the LC_MESSAGES category.

    If the specified locale is available, then setlocale returns a pointer to the string that describes the portion of the program's locale associated with category. For the LC_ALL category, the returned string describes the entire program's locale. If an error occurs, a NULL pointer is returned and the program's locale is not changed.

    Subsequent calls to setlocale overwrite the returned string. If that part of the locale needs to be restored, the program should save the string. The calling program should make no assumptions about the format or length of the returned string.

Return Values

x

Pointer to a string describing the locale.

NULL

Indicates an error occurred; errno is set.

Example

#include <errno.h>
#include <stdio.h>
#include <locale.h>

/* This program calls setlocale() three times. The second call  */
/* is for a nonexistent locale. The third call is for an        */
/* existing file that is not a locale file.                     */

main()
{
    char *ret_str;

    errno = 0;
    printf("setlocale (LC_ALL, \"POSIX\")");
    ret_str = (char *) setlocale(LC_ALL, "POSIX");

    if (ret_str == NULL)
        perror("setlocale error");
    else
        printf(" call was successful\n");

    errno = 0;
    printf("\n\nsetlocale (LC_ALL, \"junk.junk_codeset\")");
    ret_str = (char *) setlocale(LC_ALL, "junk.junk_codeset");

    if (ret_str == NULL)
        perror(" returned error");
    else
        printf(" call was successful\n");

    errno = 0;
    printf("\n\nsetlocale (LC_ALL, \"sys$login:login.com\")");
    ret_str = (char *) setlocale(LC_ALL, "sys$login:login.com");

    if (ret_str == NULL)
        perror(" returned error");
    else
        printf(" call was successful\n");
}
Running the example program produces the following result:
setlocale (LC_ALL, "POSIX") call was successful

setlocale (LC_ALL, "junk.junk_codeset")
returned error: no such file or directory

setlocale (LC_ALL, "sys$login:login.com")
returned error: nontranslatable vms error code: 0x35C07C
%c-f-localebad, not a locale file

setpgid

setpgid — Sets the process group ID for job control.

Format

#include <unistd.h>
int setpgid (pid_t pid, pid_t pgid);

Arguments

pid

The process ID for which the process group ID is to be set.

pgid

The value to which the process group ID is set.

Description

The setpgid function is used either to join an existing process group or create a new process group within the session of the calling process. The process group ID of a session leader will not change.

Upon successful completion, the process group ID of the process with a process ID of pid is set to pgid. As a special case, if pid is 0, the process ID of the calling process is used. Also, if pgid is 0, the process group ID of the indicated process is used.

This function requires that long (32-bit) UID/GID support be enabled. See Section 1.4.8 for more information.

Return Values

0

Successful completion.

-1
Indicates an error. The function sets errno to one of the following values:

  • EACCES– The value of the pid argument matches the process ID of a child process of the calling process and the child process has successfully executed one of the exec functions.

  • EINVAL– The value of the pgid argument is less than 0, or is not a value supported by the implementation.

  • EPERM– The process indicated by the pid argument is a session leader. The value of the pid argument matches the process ID of a child process of the calling process, and the child process is not in the same session as the calling process. The value of the pgid argument is valid but does not match the process ID of the process indicated by the pid argument, and there is no process with a process group ID that matches the value of the pgid argument in the same session as the calling process.

  • ESRCH– The value of the pid argument does not match the process ID of the calling process or of a child process of the calling process.

setpgrp

setpgrp — Sets the process group ID.

Format

#include <unistd.h>
pid_t setpgrp (void);

Description

If the calling process is not already a session leader, setpgrp sets the process group ID of the calling process to the process ID of the calling process. If setpgrp creates a new session, then the new session has no controlling terminal.

The setpgrp function has no effect when the calling process is a session leader.

This function requires that long (32-bit) UID/GID support be enabled. See Section 1.4.8 for more information.

Return Value

x

The process group ID of the calling process.

setpwent

setpwent — Rewinds the user database.

Format

#include <pwd.h>
void setpwent (void);

Description

The setpwent function effectively rewinds the user database to allow repeated searches.

No value is returned, but errno is set to EIO if an I/O error occurred.

See also getpwent.

setregid

setregid — Sets the real and effective group IDs.

Format

#include <unistd.h>
int setregid (gid_t rgid, gid_t egid);

Arguments

rgid

The value to which you want the real group ID set.

egid

The value to which you want the effective group ID set.

Description

The setregid function is used to set the real and effective group IDs of the calling process. If rgid is -1, the real group ID is not changed; if egid is -1, the effective group ID is not changed. The real and effective group IDs can be set to different values in the same call.

Only a process with the IMPERSONATE privilege can set the real group ID and the effective group ID to any valid value.

A nonprivileged process can set either the real group ID to the saved set-group-ID from an exec function, or the effective group ID to the saved set-group-ID or the real group ID.

Any supplementary group IDs of the calling process remain unchanged.

If a set-group-ID process sets its effective group ID to its real group ID, it can still set its effective group ID back to the saved set-group-ID.

This function requires that long (32-bit) UID/GID support be enabled. See Section 1.4.8 for more information.

Return Values

0

Successful completion.

-1
Indicates an error. Neither of the group IDs is changed, and errno is set to one of the following values:

  • EINVAL– The value of the rgid or egid argument is invalid or out-of-range.

  • EPERM– The process does not have the IMPERSONATE privilege, and a change other than changing the real group ID to the saved set-group-ID, or changing the effective group ID to the real group ID or the saved group ID, was requested.

setreuid

setreuid — Sets the user IDs.

Format

#include <unistd.h>
int setreuid (uid_t ruid, uid_t euid);

Arguments

ruid

The value to which you want the real user ID set.

euid

The value to which you want the effective user ID set.

Description

The setreuid function sets the real and effective user IDs of the current process to the values specified by the ruid and euid arguments. If ruid or euid is -1, the corresponding effective or real user ID of the current process is left unchanged.

A process with the IMPERSONATE privilege can set either ID to any value. An unprivileged process can set the effective user ID only if the euid argument is equal to either the real, effective, or saved user ID of the process.

It is unspecified whether a process without the IMPERSONATE privilege is permitted to change the real user ID to match the current real, effective, or saved user ID of the process.

This function requires that long (32-bit) UID/GID support be enabled. See Section 1.4.8 for more information.

See also getuid to know how UIC is represented.

Return Values

0

Successful completion.

-1
Indicates an error. The function sets errno to one of the following values:

  • EINVAL– The value of the ruid or euid argument is invalid or out of range.

  • EPERM– The current process does not have the IMPERSONATE privilege, and either an attempt was made to change the effective user ID to a value other than the real user ID or the saved set-user-ID, or an attempt was made to change the real user ID to a value not permitted by the implementation.

setsid

setsid — Creates a session and sets the process group ID.

Format

#include <unistd.h>
pid_t setsid (void);

Description

The setsid function creates a new session if the calling process is not a process group leader. Upon return, the calling process is the session leader of this new session and the process group leader of a new process group, and it has no controlling terminal. The process group ID of the calling process is set equal to the process ID of the calling process. The calling process is the only process in the new process group and the only process in the new session.

This function requires that long (32-bit) UID/GID support be enabled. See Section 1.4.8 for more information.

Return Values

x

The process group ID of the calling process.

(pid_t ) -1
Indicates an error. The function sets errno to the following value:

  • EPERM – The calling process is already a process group leader, or the process group ID of a process other than the calling process matches the process ID of the calling process.

setstate

setstate — Restarts and changes random-number generators.

Format

char *setstate (char *state;)

Argument

state

Points to the array of state information.

Description

The setstate function handles restarting and changing random-number generators.

Once you initialize a state, the setstate function allows rapid switching between state arrays. The array defined by state is used for further random-number generation until the initstate function is called or the setstate function is called again. The setstate function returns a pointer to the previous state array.

After initialization, you can restart a state array at a different point in one of two ways:

  • Use the initstate function, with the desired seed, state array, and size of the array.

  • Use the setstate function, with the desired state, followed by the srandom function with the desired seed. The advantage of using both functions is that you do not have to save the state array size once you initialize it.

See also initstate, srandom, and random.

Return Values

x

A pointer to the previous state array information.

0
Indicates an error. The state information is damaged, and errno is set to the following value:

  • EINVAL – The state argument is invalid.

setuid

setuid — With POSIX IDs disabled, implemented for program portability and serves no function. It returns 0 (to indicate success). With POSIX IDs enabled, sets the user IDs.

Format

#include <types.h>
#include <unistd.h>
int setuid (__uid_t uid); (_DECC_V4_SOURCE)
uid_t setuid (uid_t uid); (not _DECC_V4_SOURCE)

Argument

uid

The value to which you want the user IDs set.

Description

The setuid function can be used with POSIX style identifiers enabled or disabled.

POSIX style IDs are supported on OpenVMS Version 7.3-2 and higher.

With POSIX IDs disabled (the default), the setuid function is implemented for program portability and serves no function. It returns 0 (to indicate success).

With POSIX style IDs enabled:

  • If the process has the IMPERSONATE privilege, the setuid function sets the real user ID, effective user ID, and the saved set-user-ID to uid.

  • If the process does not have appropriate privileges but uid is equal to the real user ID or to the saved set-user-ID, then the setuid function sets the effective user ID to uid. The real user ID and saved set-user-ID remain unchanged.

See also getuid to know how UIC is represented.

To enable/disable POSIX style IDs, see Section 1.6.

Return Values

0

Successful completion.

-1
Indicates an error. The function sets errno to one of the following values:

  • EINVAL– The value of the uid argument is invalid and not supported by the implementation.

  • EPERM– The process does not have appropriate privileges and uid does not match the real user ID or the saved set-user-ID.

setvbuf

setvbuf — Associates a buffer with an input or output file and potentially modifies the buffering behavior.

Format

#include <stdio.h>
int setvbuf (FILE *file_ptr, char *buffer, int type, size_t size);

Arguments

file_ptr

A pointer to a file.

buffer

A pointer to a character array, or a NULL pointer.

type

The buffering type. Use one of the following values defined in <stdio.h>: _IOFBF, _IOLBF, or _IONBF.

Use the values _IOLBF and _IOFBF (defined in <stdio.h>) for the type argument to specify line-buffered and fully buffered I/O, respectively. If type is _IONBF, file_ptr is unbuffered and size and buffer are ignored.

size

The number of bytes to be used in buffer by the C RTL for buffering this file. The buffer size must be a minimum of 8192 bytes and a maximum of 32767 bytes.

Description

You can use the setvbuf function after the file is opened but before any I/O operations are performed.

The C RTL provides the following types of ANSI-conforming file buffering:

In line-buffered I/O, characters are buffered in an area of memory until a new-line character is seen, at which point the appropriate RMS routine is called to transmit the entire buffer. Line buffering is more efficient than unbuffered I/O since it reduces the system overhead, but it delays the availability of the data to the user or disk on output.

In fully buffered I/O, characters are buffered in an area of memory until the buffer is full, regardless of the presence of break characters. Full buffering is more efficient than line buffering or unbuffered I/O, but it delays the availability of output data even longer than line buffering.

Use the values _IOLBF and _IOFBF defined in <stdio.h> for the type argument to specify line-buffered and fully buffered I/O, respectively.

If file_ptr specifies a terminal device, the C RTL uses line-buffered I/O; otherwise, it uses fully buffered I/O.

The C RTL automatically allocates a buffer to use for each I/O stream, so there are several buffer allocation possibilities:

  • If buffer is not a NULL pointer and size is not smaller than the automatically allocated buffer, then setvbuf uses buffer as the file buffer.

  • If buffer is a NULL pointer or size is smaller than the automatically allocated buffer, the automatically allocated buffer is used as the buffer area.

  • If buffer is a NULL pointer and size is larger than the automatically allocated buffer, then setvbuf allocates a new buffer equal to the specified size and uses that as the file buffer.

User programs must not depend on the contents of buffer once I/O has been performed on the stream. The C RTL might or might not use buffer for any given I/O operation.

Generally, it is unnecessary to use setvbuf or setbuf to control the buffer size used by the C RTL. The automatically allocated buffer sizes are chosen for efficiency based on the kind of I/O operations performed and the device characteristics (such as terminal, disk, or socket).

The setvbuf and setbuf functions are useful to introduce buffering for improved performance when writing a large amount of text to the stdout stream. This stream is unbuffered by default when bound to a terminal device (the normal case), and therefore incurs a large number of OpenVMS buffered I/O operations unless C RTL buffering is introduced by a call to setvbuf or setbuf.

The setvbuf function is used only to control the buffering used by the C RTL, not the buffering used by the underlying RMS I/O operations. You can modify RMS default buffering behavior by specifying various values for the ctx, fop, rat, gbc, mbc, mbf, rfm, and rop RMS keywords when the file is opened by the creat, freopen or open functions.

The setvbuf function now takes 64-bit arguments. However, the buffer parameter must contain a 32-bit memory buffer, so when compiling the application with /POINTER=64 or /POINTER=LONG, malloc32 must be used to allocate the buffer.

Return Values

0

Indicates success.

nonzero value

Indicates that an invalid input value was specified for type or file_ptr, or because file_ptr is being used by another thread (see Section 1.8.1).

shm_open

shm_open — Opens a shared memory object.

Format

#include <sys/mman.h>
int shm_open (const char *name, int oflag, mode_t mode);

Argument

name

Pointer to a string naming a shared memory object.

oflag

Specifies options that define file status and file access modes. This argument is constructed from the bitwise inclusive OR of zero or more of the options defined in the <fcntl.h> header file.

mode

The shared memory object's permission bits. This argument is used only when the shared memory object is being created.

Description

The shm_open function establishes a connection between a shared memory object and a file descriptor. It creates an open file description that refers to the shared memory object and a file descriptor that refers to that open file description. The file descriptor is used by other functions to refer to that shared memory object. The name argument points to a string naming a shared memory object. The name can be a pathname, in which case other processes referring to the same pathname refer to the same shared memory object.

When a shared memory object is created, its state and all data associated with it persist until the shared memory is unlinked.

The shm_open function returns a file descriptor for the shared memory object that is the lowest numbered file descriptor not currently open for that process.

The file status flags and file access modes of the open file description are set according to the value of oflag, and can have zero or more of the following values:
  • O_RDONLY – Open for read access only.
  • O_RDWR – Open for read or write access.
  • O_CREAT – Create the shared memory if the memory object does not exist already. The user ID and group ID of the shared memory object are identical to those of the calling process. The shared memory object's permission bits are set to the value of mode, except those set in the file mode creation mask of the process.
  • O_EXCL – Prevent the opening of a shared memory object if O_CREAT is set and the shared memory object already exists. Use this option only in combination with O_CREAT.
  • O_TRUNC – Truncate the shared memory object to zero length if it is successfully opened for read or write access (O_RDWR).

The initial contents of the shared memory object are binary zeros.

Return Values

n

Upon success, a nonnegative integer representing the lowest numbered unused file descriptor. The file descriptor points to the shared memory object.

-1
Indicates failure. errno is set to indicate the error:

  • EACCES– Permission to create the shared memory object is denied, or the shared memory object exists and the permissions specified by oflag are denied, or O_TRUNC is specified and write permission is denied.

  • EEXIST– O_CREAT and O_EXCL are set, but the named shared memory object already exists.

  • EINTR– A signal has interrupted the shm_open operation.

  • EINVAL– The shm_open operation is not supported for the given name.

  • EMFILE– Too many file descriptors are currently in use by this process.

  • ENAMETOOLONG– The length of the name argument exceeds PATH_MAX or a pathname component is longer than NAME_MAX.

  • ENFILE– Too many shared memory objects are currently open in the system.

  • ENOENT– O_CREAT is not set and the named shared memory object does not exist.

  • ENOSPC– Memory space for creation of the new shared memory object is insufficient.

shmat

shmat — Shared memory attach operation.

Format

#include <shm.h>
void *shmat(int shmid, const void *shmaddr, int shmflg);

Arguments

shmid

A shared memory identifier, a positive integer. It is created by the shmget() function and used to identify the shared memory segment on which to perform the shared memory attach operation.

shmaddr

Address within the calling process to which the shared memory segment attached. For more information, see the Description.

shmflg

Flag to indicate type of attach operation. For more information, see the Description.

Description

The shmat function attaches the shared memory segment associated with the shared memory identifier specified by shmid to the address space of the calling process.

The segment is attached at the address specified by one of the following criteria:

  • If shmaddr is a null pointer, the segment is attached at the first available address as selected by the system. This is the preferred method of using shmat.

  • If shmaddr is not a null pointer and (shmflg & SHM_RND) is non-zero, the segment is attached at the address given by (shmaddr -((__int64)shmaddr% SHMLBA)). The character '%' is the C language remainder operator.

  • If shmaddr is not a null pointer and (shmflg & SHM_RND) is zero, the segment is attached at the address given by shmaddr.

  • The segment is attached for reading if (shmflg & SHM_RDONLY) is non-zero and the calling process has read permission; otherwise, if it is zero and the calling process has both read and write permission, the segment is attached for reading and writing.

A successful shmat() function updates the members of the shmid_ds structure associated with the shared memory segment as follows:

  • shm_atime is set to the current time.

  • shm_lpid is set to the process ID of the calling process.

  • shm_nattch is incremented by one.

It is not possible to attach a shared memory segment if it has already been marked as removed.

Note

  1. For the current implementation the SHMLBA value is 8 KB.

  2. If the application passes its own valid non-zero address, the current implementation requires this address to be 32 bit; a 64 bit virtual address is not supported.

Return Values

x

Successful completion. The function returns the start address of the attached shared memory segment.

-1

Indicates an error. The function sets errno to one of the following values:

  • EACCES – Operation permission is denied to the calling process.

  • EINVAL – The value of shmid is not a valid shared memory identifier; or the shmaddr is not a null pointer, and the value of (shmaddr ((__int64)shmaddr % SHMLBA)) is an illegal address for attaching shared memory; or the shmaddr is not a null pointer, (shmflg & SHM_RND) is zero, and the value of shmaddr is an illegal address for attaching shared memory.

  • EMFILE – The number of shared memory segments attached to the calling process exceeds the system imposed limit.

  • ENOMEM – The available data space is not large enough to accommodate the shared memory segment.

  • EVMSERR – OpenVMS specific non-translatable error code.

shmctl

shmctl — Shared memory control operations.

Format

#include <shm.h>
int shmctl(int shmid, int cmd, struct shmid_ds *buf);

Arguments

shmid

A shared memory identifier, a positive integer. It is created by the shmget() function and used to identify the shared memory segment on which to perform the control operation.

cmd

The control operation (IPC_STAT, IPC_SET, or IPC_RMID) to perform on the shared memory segment. For more information, see the Description.

buf

Pointer to a shmid_ds structure, defined in <shm.h> as follows:

struct shmid_ds {
struct  ipc_perm shm_perm; /* Permissions structure defined in <ipc.h> */
size_t  shm_segsz;   /* Size of memory segment in bytes */
pid_t   shm_lpid;      /* Process ID of last memory operation */
pid_t   shm_cpid;      /* Process ID of segment creator */
shmatt_t   shm_nattch;     /* Number of current attaches */
time_t  shm_atime;     /* Time of last shmat  */
time_t  shm_dtime;     /* Time of last shmdt  */
time_t  shm_ctime;     /* Time of last change */
};

Description

The shmctl() function provides a variety of shared memory control operations as specified by the cmd argument. It can have the following values:

IPC_STAT

Place the current value of each member of the data structure associated with shmid into the structure pointed to by buf. The contents of this structure are defined in <shm.h>.

IPC_SET

Set the value of the following members of the data structure associated with shmid to the corresponding value found in the structure pointed to by buf:

shm_perm.uid
shm_perm.gid
shm_perm.mode /* only low 9 bits */

This cmd can be executed by a process that has an effective user ID equal to either that of a user having appropriate privileges or to the value of either shm_perm.uid or shm_perm.cuid in the data structure associated with shmid.

IPC_RMID

Remove the shared memory identifier specified by shmid from the system and delete the shared memory segment and data structure associated with it. If the segment is attached to one or more processes, the segment key is changed to IPC_PRIVATE and the segment is marked as removed. The segment disappears when the last attached process detaches it. This cmd can be executed by a process that has an effective user ID equal to either that of a user with appropriate privileges or to the value of either shm_perm.uid or shm_perm.cuid in the data structure associated with shmid.

Return Values

0

Successful completion.

-1

Indicates an error. The function sets errno to one of the following values:

  • EACCES – The argument cmd is equal to IPC_STAT and the calling process does not have read permission.

  • EINVAL – The value of shmid is not a valid shared memory identifier, or the value of cmd is not a valid command.

  • EFAULT – The argument cmd has value IPC_SET or IPC_STAT but the address pointed to by buf is not accessible.

  • EPERM – The argument cmd is equal to IPC_RMID or IPC_SET and the effective user ID of the calling process is not equal to that of a process with appropriate privileges and it is not equal to the value of shm_perm.cuid or shm_perm.uid in the data structure associated with shmid.

  • EVMSERR – OpenVMS specific non-translatable error code.

shmdt

shmdt — Shared memory detach operation.

Format

#include <shm.h>
int shmdt(const void *shmaddr);

Arguments

shmaddr

The address returned by a previous call to shmat.

Description

The shmdt() function detaches the shared memory segment located at the address specified by shmaddr from the address space of the calling process.

The to-be-detached segment must be currently attached with shmaddr equal to the value returned by the attaching shmat() function.

On a successful shmdt() function the system updates the members of the shmid_ds structure associated with the shared memory segment as follows:

  • shm_dtime is set to the current time.

  • shm_lpid is set to the process-ID of the calling process.

  • shm_nattch is decremented by one. If it becomes zero and the segment is marked for deletion, the segment is deleted. For more information see the shmctl function.

Upon exit, all the attached shared memory segments are detached from the process.

Return Values

0

Successful completion.

-1

Indicates an error. The function sets errno to one of the following values:

  • EINVAL – The value of shmaddr is not the data segment start address of a shared memory segment.

  • EVMSERR – OpenVMS specific non-translatable error code.

shmget

shmget — Gets a shared memory segment.

Format

#include <shm.h>
int shmget(key_t key, size_t size, int shmflg);

Arguments

key

The key for which the associated shared memory identifier is returned.

size

Shared memory segment size in bytes.

shmflg

Flag used to initialize the low order 9 bits of the shm_perm.mode member of the shmid_ds data structure associated with the new shared memory segment. For more information, see the Description.

Description

The shmget() function returns the shared memory identifier associated with the key.

A shared memory identifier with its associated shmid_ds data structure is created for a key if one of the following is TRUE:

  • The key argument is equal to IPC_PRIVATE.

  • The key argument does not already have a shared memory identifier associated with it and (shmflg and IPC_CREAT) is non-zero.

If shmflg specifies both IPC_CREAT and IPC_EXCL and a shared memory segment already exists for a key, shmget() function fails with errno set to EEXIST.

When it is created, the shmid_ds data structure associated with the new shared memory identifier is initialized as follows:

  • The values of shm_perm.cuid, shm_perm.uid, shm_perm.cgid, and shm_perm.gid are set equal to the effective user ID and effective group ID, respectively, of the calling process.

  • The low order 9 bits of shm_perm.mode are set equal to the low order 9 bits of the shmflg argument.

  • The variable shm_segsz is set equal to the value of the size argument.

  • The variables shm_lpid, shm_nattch, shm_atime, and shm_dtime are set equal to zero, the variable shm_cpid is set equal to the Process ID of the segment creator, and the variable shm_ctime is set equal to the current time.

Return Values

n

Successful completion. The function returns a non-negative integer shared memory identifier.

-1

Indicates an error. The function sets errno to one of the following values:

  • EACCES – A shared memory identifier exists for the key, but the operation permission as specified by the low order 9 bits of shmflg are not granted.

  • EEXIST – A shared memory identifier exists for a key but ((shmflg & IPC_CREAT) && (shmflg & IPC_EXCL)) is non-zero.

  • EINVAL – The value of size is either less than SHMMIN, greater than the SHMMAX, or a shared memory identifier exists for a key, but the size is greater than the size of that segment. With current implementation SHMMIN is defined to 1 byte and SHMMAX is defined to 512 MB.

  • ENOENT – A shared memory identifier does not exist for a key and (shmflg & IPC_CREAT) is equal to zero.

  • ENOSPC – A shared memory identifier is to be created but the system-imposed limit on the maximum number of allowed shared memory segments system-wide is exceeded.

  • EVMSERR – OpenVMS specific non-translatable error code.

Example

    /*
    Abstract: This test program creates a Shared Memory Segment, writes
    data to the segment then reads the data after attaching again. It also
    ensures that an EINVAL error is generated when trying to attach a
    memory that has already been deleted.
    */
    #include <errno.h>
    #include <types.h>
    #include <ipc.h>
    #include <shm.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>

    #define SHMSZ  128
    #define SHMKEY 9229

    main()
    {

        int shmid;
        char *shm_write;
        char *shm_read;

        printf("Creating Shared Memory Segment\n");
        if ((shmid = shmget(SHMKEY, SHMSZ, IPC_CREAT | 0666)) < 0)
        {
            perror("shmget");
            printf("\nshmget(): FAILED\n");
        }
        if ((shm_write = shmat(shmid, NULL, 0)) == (char *) -1)
        {
            perror("shmat");
            printf("\nshmat(): FAILED\n");
            return;
        }
        printf("Writing Data to the Created Shared Memory Segment\n\n");
        memcpy(shm_write, "Test Shared Memory Segment", SHMSZ);
        printf("Detaching Shared Memory Segment\n");
        if( shmdt(shm_write)<0)
            perror("shmdt");

        printf("Attach again to read the data from Shared Memory Segment\n\n");
        if ((shm_read = shmat(shmid, NULL, 0)) == (char *) -1)
        {
            perror("shmat");
            printf("\nshmat(): FAILED\n");
        }
        printf("Reding Data from Shared Memory Segment\n");
        printf("Data in Segment is: %s\n\n",shm_read);

        printf("Detaching Shared Memory Segment\n");
        if( shmdt(shm_read)<0)
            perror("shmdt");
        printf("Deleting Shared Memory Segment using IPC_RMID\n\n");
        if( shmctl(shmid, IPC_RMID, NULL)<0)
            perror("shmctl");

        printf("Attaching to the deleted Shared Memory Segment - error EINVAL
        should be generated\n\n");
        if ((shm_write = shmat(shmid, NULL, 0)) == (char *) -1)
        {
            perror("shmat");
        }
    }

This example produces the following output:

    Creating Shared Memory Segment
    Writing Data to the Created Shared Memory Segment

    Detaching Shared Memory Segment
    Attach again to read the data from Shared Memory Segment

    Reding Data from Shared Memory Segment
    Data in Segment is: Test Shared Memory Segment

    Detaching Shared Memory Segment
    Deleting Shared Memory Segment using IPC_RMID

    Attaching to the deleted Shared Memory Segment - error EINVAL should be
    generated

    shmat: invalid argument

sigaction

sigaction — Specifies the action to take upon delivery of a signal.

Format

#include <signal.h>
int sigaction (int sig, const struct sigaction *action,
struct sigaction *o_action);

Arguments

sig

The signal for which the action is to be taken.

action

A pointer to a sigaction structure that describes the action to take when you receive the signal specified by the sig argument.

o_action

A pointer to a sigaction structure. When the sigaction function returns from a call, the action previously attached to the specified signal is stored in this structure.

Description

When a process requests the sigaction function, the process can both examine and specify what action to perform when the specified signal is delivered. The arguments determine the behavior of the sigaction function as follows:

  • Specifying the sig argument identifies the affected signal. Use any one of the signal values defined in the <signal.h> header file, except SIGKILL.

    If sig is SIGCHLD and the SA_NOCLDSTOP flag is not set in sa_flags, then a SIGCHLD signal is generated for the calling process whenever any of its child processes stop. If sig is SIGCHLD and the SA_NOCLDSTOP flag is set in sa_flags, then SIGCHLD signal is not generated in this way.

  • Specifying the action argument, if not null, points to a sigaction structure that defines what action to perform when the signal is received. If the action argument is null, signal handling remains unchanged, so you can use the call to inquire about the current handling of the signal.

  • Specifying the o_action argument, if not null, points to a sigaction structure that contains the action previously attached to the specified signal.

The sigaction structure consists of the following members: 
  void        (*sa_handler)(int);
  sigset_t    sa_mask;
  int         sa_flags;
The sigaction structure members are defined as follows:

sa_handler
This member can contain the following values:

  • SIG_DFL – Specifies the default action taken when the signal is delivered.

  • SIG_IGN – Specifies that the signal has no effect on the receiving process.

  • Function pointer – Requests to catch the signal. The signal causes the function call.

sa_mask

This member can request that individual signals, in addition to those in the process signal mask, are blocked from delivery while the signal handler function specified by the sa_handler member is executing.

sa_flags

This member can set the flags to enable further control over the actions taken when a signal is delivered.

The sa_flags member of the sigaction structure has the following values:

SA_ONSTACK

Setting this bit causes the system to run the signal catching function on the signal stack specified by the sigstack function. If this bit is not set, the function runs on the stack of the process where the signal is delivered.

SA_RESETHAND

Setting this bit resets the signal to SIG_DFL. Be aware that you cannot automatically reset SIGILL and SIGTRAP.

SA_NODEFER

Setting this bit does not automatically block the signal as it is intercepted.

SA_NOCLDSTOP

If this bit is set and the sig argument is equal to SIGCHLD and a child process of the calling process stops, then a SIGCHLD signal is sent to the calling process only if SA_NOCLDSTOP is not set for SIGCHLD.

When a signal is intercepted by a signal-catching function installed by sigaction, a new signal mask is calculated and installed for the duration of the signal-catching function (or until a call to either sigprocmask or sigsuspend is made. This mask is formed by taking the union of the current signal mask and the value of the sa_mask for the signal being delivered unless SA_NODEFER or SA_RESETHAND is set, and then including the signal being delivered. If and when the user's signal handler returns normally, the original signal mask is restored.

Once an action is installed for a specific signal, it remains installed until another action is explicitly requested (by another call to sigaction), until the SA_RESETHAND flag causes resetting of the handler, or until one of the exec functions is called.

If the previous action for a specified signal had been established by signal, the values of the fields returned in the structure pointed to by the o_action argument of sigaction are unspecified, and in particular o_action->sa_handler is not necessarily the same value passed to signal. However, if a pointer to the same structure or a copy thereof is passed to a subsequent call to sigaction by means of the action argument of sigaction), the signal is handled as if the original call to signal were repeated.

If sigaction fails, no new signal handler is installed.

It is unspecified whether an attempt to set the action for a signal that cannot be intercepted or ignored to SIG_DFL is ignored or causes an error to be returned with errno set to EINVAL.

See Section 4.2 for more information on signal handling.

Note

The sigvec and signal functions are provided for compatibility to old UNIX systems; their function is a subset of that available with the sigaction function.

See also sigvec, signal, wait, read, and write.

Return Values

0

Indicates success.

-1
Indicates an error; A new signal handler is not installed. errno is set to one of the following values:

  • EFAULT– The action or o_action argument points to a location outside of the allocated address space of the process.

  • EINVAL– The sig argument is not a valid signal number. Or an attempt was made to ignore or supply a handler for the SIGKILL, SIGSTOP, and SIGCONT signals.

sigaddset

sigaddset — Adds the specified individual signal.

Format

#include <signal.h>
int sigaddset (sigset_t *set, int sig_number);

Arguments

set

The signal set.

sig_number

The individual signal.

Description

The sigaddset function manipulates sets of signals. This function operates on data objects that you can address by the application, not on any set of signals known to the system. For example, this function does not operate on the set blocked from delivery to a process or the set pending for a process.

The sigaddset function adds the individual signal specified by sig_number from the signal set specified by set.

Example

The following example shows how to generate and use a signal mask that blocks only the SIGINT signal from delivery: 
       #include <signal.h>
       int return_value;
       sigset_t newset;
         . . .
       sigemptyset(&newset);
       sigaddset(&newset, SIGINT);
       return_value = sigprocmask (SIG_SETMASK, &newset, NULL);

Return Values

0

Indicates success.

-1
Indicates an error; errno is set to the following value:

  • EINVAL– The value of sig_number is not a valid signal number.

sigblock

sigblock — Adds the signals in mask to the current set of signals being blocked from delivery.

Format

#include <signal.h>
int sigblock (int mask);

Argument

mask

The signals to be blocked.

Description

Signal i is blocked if the i - 1 bit in mask is a 1. For example, to add the protection-violation signal to the set of blocked signals, use the following line:
sigblock(1 << (SIGBUS - 1));

You can express signals in mnemonics (such as SIGBUS for a protection violation) or numbers as defined in the <signal.h> header file, and you can express combinations of signals by using the bitwise OR operator ( |).

Return Value

x

Indicates the previous set of masked signals.

sigdelset

sigdelset — Deletes a specified individual signal.

Format

#include <signal.h>
int sigdelset (sigset_t *set, int sig_number;)

Arguments

set

The signal set.

sig_number

The individual signal.

Description

The sigdelset function deletes the individual signal specified by sig_number from the signal set specified by set.

This function operates on data objects that you can address by the application, not on any set of signals known to the system. For example, this function does not operate on the set blocked from delivery to a process or the set pending for a process.

Return Values

0

Indicates success.

-1
Indicates an error; errno is set to the following value:

  • EINVAL– The value of sig_number is not a valid signal number.

sigemptyset

sigemptyset — Initializes the signal set to exclude all signals.

Format

#include <signal.h>
int sigemptyset (sigset_t *set);

Argument

set

The signal set.

Description

The sigemptyset function initializes the signal set pointed to by set such that you exclude all signals. A call to sigemptyset or sigfillset must be made at least once for each object of type sigset_t prior to any other use of that object.

This function operates on data objects that you can address by the application, not on any set of signals known to the system. For example, this function does not operate on the set blocked from delivery to a process or the set pending for a process.

See also sigfillset.

Example

The following example shows how to generate and use a signal mask that blocks only the SIGINT signal from delivery:
       #include <signal.h>
       int return_value;
       sigset_t newset;
         . . .
       sigemptyset(&newset);
       sigaddset(&newset, SIGINT);
       return_value = sigprocmask (SIG_SETMASK, &newset, NULL);

Return Values

0

Indicates success.

-1

Indicates an error; the global errno is set to indicate the error.

sigfillset

sigfillset — Initializes the signal set to include all signals.

Format

#include <signal.h>
int sigfillset (sigset_t *set);

Argument

set

The signal set.

Description

The sigfillset function initializes the signal set pointed to by set such that you include all signals. A call to sigemptyset or sigfillset must be made at least once for each object of type sigset_t prior to any other use of that object.

This function operates on data objects that you can address by the application, not on any set of signals known to the system. For example, this function does not operate on the set blocked from delivery to a process or the set pending for a process.

See also sigemptyset.

Return Values

0

Indicates success.

-1
Indicates an error; errno is set to the following value:

  • EINVAL– The value of the sig_number argument is not a valid signal number.

sighold

sighold — Adds the specified signal to the calling process's signal mask.

Format

#include <signal.h>
int sighold (int signal);

Argument

signal

The specified signal. The signal argument can be assigned any of the signals defined in the <signal.h> header file, except SIGKILL and SIGSTOP.

Description

The sighold, sigrelse, and sigignore functions provide simplified signal management:

  • The sighold function adds signal to the calling process's signal mask.

  • The sigrelse function removes signal from the calling process's signal mask.

  • The sigignore function sets the disposition of signal to SIG_IGN.

The sighold function, in conjunction with sigrelse and sigpause, can be used to establish critical regions of code that require the delivery of a signal to be temporarily deferred.

Upon success, the sighold function returns a value of 0. Otherwise, a value of -1 is returned, and errno is set to indicate the error.

Note

These interfaces are provided for compatibility only. New programs should use sigaction and sigprocmask to control the disposition of signals.

Return Values

0

Indicates success.

-1
Indicates an error; errno is set to the following value:

  • EINVAL– The value of the signal argument is either an invalid signal number or SIGKILL.

sigignore

sigignore — Sets the disposition of the specified signal to SIG_IGN.

Format

#include <signal.h>
int sigignore (int signal);

Argument

signal

The specified signal. The signal argument can be assigned any of the signals defined in the <signal.h> header file, except SIGKILL and SIGSTOP.

Description

The sighold, sigrelse, and sigignore functions provide simplified signal management:

  • The sighold function adds signal to the calling process's signal mask.

  • The sigrelse function removes signal from the calling process's signal mask.

  • The sigignore function sets the disposition of signal to SIG_IGN.

The sighold function, in conjunction with sigrelse and sigpause, can be used to establish critical regions of code that require the delivery of a signal to be temporarily deferred.

Upon success, the sigignore function returns a value of 0. Otherwise, a value of -1 is returned, and errno is set to indicate the error.

Note

These interfaces are provided for compatibility only. New programs should use sigaction and sigprocmask to control the disposition of signals.

Return Values

0

Indicates success.

-1
Indicates an error; errno is set to the following value:

  • EINVAL– The value of the signal argument is either an invalid signal number or SIGKILL, or an attempt is made to catch a signal that cannot be intercepted or to ignore a signal that cannot be ignored.

sigismember

sigismember — Tests whether a specified signal is a member of the signal set.

Format

#include <signal.h>
int sigismember (const sigset_t *set, int sig_number);

Arguments

set

The signal set.

sig_number

The individual signal.

Description

The sigismember function tests whether sig_number is a member of the signal set pointed to by set.

This function operates on data objects that you can address by the application, not on any set of signals known to the system. For example, this function does not operate on the set blocked from delivery to a process or the set pending for a process.

Return Values

1

Indicates success. The specified signal is a member of the specified set.

0

Indicates an error. The specified signal is not a member of the specified set.

siglongjmp

siglongjmp — Nonlocal go to with signal handling.

Format

#include <setjmp.h>
void siglongjmp (sigjmp_buf env, int value);

Arguments

env

An address for a sigjmp_buf structure.

value

A nonzero value.

Description

The siglongjmp function restores the environment saved by the most recent call to sigsetjmp in the same process with the corresponding sigjmp_buf argument.

All accessible objects have values when siglongjmp is called, with one exception: values of objects of automatic storage duration that changed between the sigsetjmp call and siglongjmp call are indeterminate.

Because it bypasses the usual function call and return mechanisms, siglongjmp executes correctly during interrupts, signals, and any of their associated functions. However, if you invoke siglongjmp from a nested signal handler (for example, from a function invoked as a result of a signal raised during the handling of another signal), the behavior is undefined.

The siglongjmp function restores the saved signal mask only if you initialize the env argument by a call to sigsetjmp with a nonzero savemask argument.

After siglongjmp is completed, program execution continues as if the corresponding call of sigsetjmp just returned the value specified by value. The siglongjmp function cannot cause sigsetjmp to return 0 (zero); if value is 0, sigsetjmp returns 1.

See also sigsetjmp.

sigmask

sigmask — Constructs the mask for a given signal number.

Format

#include <signal.h>
int sigmask (signum);

Argument

signum

The signal number for which the mask is to be constructed.

Description

The sigmask function is used to construct the mask for a given signum. This mask can be used with the sigblock function.

Return Value

x

The mask constructed for signum

signal

signal — Allows you to specify the way in which the signal sig is to be handled: use the default handling for the signal, ignore the signal, or call the signal handler at the address specified.

Format

#include <signal.h>
void (*signal (int sig, void (*func) (int))) (int);

Arguments

sig

The number or mnemonic associated with a signal. This argument is usually one of the mnemonics defined in the <signal.h> header file.

func

Either the action to take when the signal is raised, or the address of a function needed to handle the signal.

Description

If func is the constant SIG_DFL, the action for the given signal is reset to the default action, which is to terminate the receiving process. If the argument is SIG_IGN, the signal is ignored. Not all signals can be ignored.

If func is neither SIG_DFL nor SIG_IGN, it specifies the address of a signal-handling function. When the signal is raised, the addressed function is called with sig as its argument. When the addressed function returns, the interrupted process continues at the point of interruption. (This is called catching a signal. Signals are reset to SIG_DFL after they are intercepted, except as shown in Chapter 4.)

You must call the signal function each time you want to catch a signal.

See Section 4.2 for more information on signal handling.

To cause an OpenVMS exception or a signal to generate a UNIX style signal, OpenVMS condition handlers must return SS$_RESIGNAL upon receiving any exception that they do not want to handle. Returning SS$_CONTINUE prevents the correct generation of a UNIX style signal. See Chapter 4 for a list of OpenVMS exceptions that correspond to UNIX signals.

Return Values

x

The address of the function previously established to handle the signal.

SIG_ERR

Indicates that the sig argument is out of range.

sigpause

sigpause — Assigns mask to the current set of masked signals and then waits for a signal.

Format

#include <signal.h>
int sigpause (int mask);

Argument

mask

The signals to be blocked.

Description

See the sigblock function for information about the mask argument.

When control returns to sigpause, the function restores the previous set of masked signals, sets errno to EINTR, and returns -1 to indicate an interrupt. The value EINTR is defined in the <errno.h> header file.

Return Value

-1

Indicates an interrupt. errno is set to EINTR.

sigpending

sigpending — Examines pending signals.

Format

#include <signal.h>
int sigpending (sigset_t *set);

Argument

set

A pointer to a sigset_t structure.

Description

The sigpending function stores the set of signals that are blocked from delivery and pending to the calling process in the location pointed to by the set argument.

Call either the sigemptyset or the sigfillset function at least once for each object of type sigset_t prior to any other use of that object. If you do not initialize an object in this way and supply an argument to the sigpending function, the result is undefined.

See also sigemptyset and sigfillset in this section.

Return Values

0

Indicates success.

-1
Indicates an error; errno is set to the following value:

  • SIGSEGV– Bad mask argument.

sigprocmask

sigprocmask — Sets the current signal mask.

Format

#include <signal.h>
int sigprocmask (int how, const sigset_t *set, sigset_t *o_set);

Arguments

how

An integer value that indicates how to change the set of masked signals. Use one of the following values:

SIG_BLOCK

The resulting set is the union of the current set and the signal set pointed to by the set argument.

SIG_UNBLOCK

The resulting set is the intersection of the current set and the complement of the signal set pointed to by the set argument.

SIG_SETMASK

The resulting set is the signal set pointed to by the set argument.

set

The signal set. If the value of the set argument is:

  • Not NULL– It points to a set of signals used to change the currently blocked set.

  • NULL– The value of the how argument is not significant, and the process signal mask is unchanged, so you can use the call to inquire about currently blocked signals.

o_set

A non-NULL pointer to the location where the signal mask in effect at the time of the call is stored.

Description

The sigprocmask function is used to examine or change the signal mask of the calling process.

Typically, use the sigprocmask SIG_BLOCK value to block signals during a critical section of code, then use the sigprocmask SIG_SETMASK value to restore the mask to the previous value returned by the sigprocmask SIG_BLOCK value.

If there are any unblocked signals pending after the call to the sigprocmask function, at least one of those signals is delivered before the sigprocmask function returns.

You cannot block SIGKILL or SIGSTOP signals with the sigprocmask function. If a program attempts to block one of these signals, the sigprocmask function gives no indication of the error.

Example

The following example shows how to set the signal mask to block only the SIGINT signal from delivery:
  #include <signal.h>

  int return_value;
  sigset_t newset;
   . . .
  sigemptyset(&newset);
  sigaddset(&newset, SIGINT);
  return_value = sigprocmask (SIG_SETMASK, &newset, NULL);

Return Values

0

Indicates success.

-1
Indicates an error. The signal mask of the process is unchanged. errno is set to one of the following values:

  • EINVAL– The value of the how argument is not equal to one of the defined values.

  • EFAULT– The set or o_set argument points to a location outside the allocated address space of the process.

sigrelse

sigrelse — Removes the specified signal from the calling process's signal mask.

Format

#include <signal.h>
int sigrelse (int signal);

Argument

signal

The specified signal. The signal argument can be assigned any of the signals defined in the <signal.h> header file, except SIGKILL and SIGSTOP.

Description

The sighold, sigrelse, and sigignore functions provide simplified signal management:

  • The sighold function adds signal to the calling process's signal mask.

  • The sigrelse function removes signal from the calling process's signal mask.

  • The sigignore function sets the disposition of signal to SIG_IGN.

The sighold function, in conjunction with sigrelse and sigpause, can be used to establish critical regions of code that require the delivery of a signal to be temporarily deferred.

Upon success, the sigrelse function returns a value of 0. Otherwise, a value of -1 is returned, and errno is set to indicate the error.

Note

These interfaces are provided for compatibility only. New programs should use sigaction and sigprocmask to control the disposition of signals.

Return Values

0

Indicates success.

-1
Indicates an error; errno is set to the following value:

  • EINVAL– The value of the signal argument is either an invalid signal number or SIGKILL.

sigsetjmp

sigsetjmp — Sets a jump point for a nonlocal goto.

Format

#include <setjmp.h>
init sigsetjmp (sigjmp_buf env, int savemask);

Arguments

env

An address for a sigjmp_buf structure.

savemask

An integer value that specifies whether you need to save the current signal mask.

Description

The sigsetjmp function saves its calling environment in its env argument for later use by the siglongjmp function.

If the value of savemask is not 0 (zero), sigsetjmp also saves the process's current signal mask as part of the calling environment.

See also siglongjmp.

Restrictions

You cannot invoke the longjmp function from an OpenVMS condition handler. However, you may invoke longjmp from a signal handler that has been established for any signal supported by the C RTL, subject to the following nesting restrictions:

  • The longjmp function will not work if you invoke it from nested signal handlers. The result of the longjmp function, when invoked from a signal handler that has been entered as a result of an exception generated in another signal handler, is undefined.

  • Do not invoke the sigsetjmp function from a signal handler unless the associated longjmp is to be issued before the handling of that signal is completed.

  • Do not invoke the longjmp function from within an exit handler (established with atexit or SYS$DCLEXH). Exit handlers are invoked after image tear-down, so the destination address of the longjmp no longer exists.

  • Invoking longjmp from within a signal handler to return to the main thread of execution might leave your program in an inconsistent state. Possible side effects include the inability to perform I/O or to receive any more UNIX signals. Use siglongjmp instead.

Return Values

0

Indicates success.

nonzero

The return is a call to the siglongjmp function.

sigsetmask

sigsetmask — Establishes those signals that are blocked from delivery.

Format

#include <signal.h>
int sigsetmask (int mask);

Argument

mask

The signals to be blocked.

Description

See the sigblock function for information about the mask argument.

Return Value

x

The previous set of masked signals.

sigsuspend

sigsuspend — Atomically changes the set of blocked signals and waits for a signal.

Format

#include <signal.h>
int sigsuspend (const sigset_t *signal_mask);

Argument

signal_mask

A pointer to a set of signals.

Description

The sigsuspend function replaces the signal mask of the process with the set of signals pointed to by the signal_mask argument. Then it suspends execution of the process until delivery of a signal whose action is either to execute a signal catching function or to terminate the process. You cannot block the SIGKILL or SIGSTOP signals with the sigsuspend function. If a program attempts to block either of these signals, sigsuspend gives no indication of the error.

If delivery of a signal causes the process to terminate, sigsuspend does not return. If delivery of a signal causes a signal catching function to execute, sigsuspend returns after the signal catching function returns, with the signal mask restored to the set that existed prior to the call to sigsuspend.

The sigsuspend function sets the signal mask and waits for an unblocked signal as one atomic operation. This means that signals cannot occur between the operations of setting the mask and waiting for a signal. If a program invokes sigprocmask SIG_SETMASK and sigsuspend separately, a signal that occurs between these functions is often not noticed by sigsuspend.

In normal usage, a signal is blocked by using the sigprocmask function at the beginning of a critical section. The process then determines whether there is work for it to do. If there is no work, the process waits for work by calling sigsuspend with the mask previously returned by sigprocmask.

If a signal is intercepted by the calling process and control is returned from the signal handler, the calling process resumes execution after sigsuspend, which always returns a value of -1 and sets errno to EINTR.

See also sigpause and sigprocmask.

sigtimedwait

sigtimedwait — Suspends a calling thread and waits for queued signals to arrive.

Format

#include <signal.h>
int sigtimedwait (const sigset_t set, siginfo_t *info,
const struct timespec *timeout);

Arguments

set

The set of signals to wait for.

info

Pointer to a siginfo structure that is receiving data describing the signal, including any application-defined data specified when the signal was posted.

timeout

A timeout for the wait. If timeout is NULL, the argument is ignored.

Description

The sigtimedwait function behaves the same as the sigwaitinfo function except that if none of the signals specified by set are pending, sigtimedwait waits for the time interval specified in the timespec structure referenced by timeout. If the timespec structure pointed to by timeout is zero-valued and if none of the signals specified by set are pending, then sigtimedwait returns immediately with an error.

See also sigwait and sigwaitinfo.

See Section 4.2 for more information on signal handling.

Return Values

x

Upon successful completion, the signal number selected is returned.

-1
Indicates that an error occurred; errno is set to one of the following values:

  • EINVAL– The timeout argument specified a tv_nsec value less than 0 or greater than or equal to 1 billion.

  • EINTR– The wait was interrupted by an unblocked, intercepted signal.

  • EAGAIN– No signal specified by set was generated within the specified timeout period.

sigvec

sigvec — Permanently assigns a handler for a specific signal.

Format

#include <signal.h>
int sigvec (int sigint, struct sigvec *sv, struct sigvec *osv);

Arguments

sigint

The signal identifier.

sv

Pointer to a sigvec structure (see the Description section).

osv

If osv is not NULL, the previous handling information for the signal is returned.

Description

If sv is not NULL, it specifies the address of a structure containing a pointer to a handler routine and mask to be used when delivering the specified signal, and a flag indicating whether the signal is to be processed on an alternative stack. If sv–>onstack has a value of 1, the system delivers the signal to the process on a signal stack specified with sigstack.

The sigvec function establishes a handler that remains established until explicitly removed or until the image terminates.

The sigvec structure is defined in the <signal.h> header file:
struct sigvec
   {
      int   (*handler)();
      int   mask;
      int   onstack;
   };

See Section 4.2 for more information on signal handling.

Return Values

0

Indicates that the call succeeded.

-1

Indicates that an error occurred.

sigwait

sigwait — Suspends a calling thread and waits for queued signals to arrive.

Format

#include <signal.h>
int sigwait (const sigset_t set, int *sig);

Arguments

set

The set of signals to wait for.

sig

Returns the signal number of the selected signal.

Description

The sigwait function suspends the calling thread until at least one of the signals in the set argument is in the caller's set of pending signals. When this happens, one of those signals is automatically selected and removed from the set of pending signals. The signal number identifying that signal is then returned in the location referenced by sig.

The effect is unspecified if any signals in the set argument are not blocked when the sigwait function is called.

The set argument is created using the set manipulation functions sigemptyset, sigfillset, sigaddset, and sigdelset.

If, while the sigwait function is waiting, a signal occurs that is eligible for delivery (that is, not blocked by the signal mask), that signal is handled asynchronously and the wait is interrupted.

See also sigtimedwait and sigwaitinfo.

See Section 4.2 for more information on signal handling.

Return Values

0

Upon successful completion, sigwait stores the signal number of the received signal at the location referenced by sig and returns 0.

nonzero
Indicates that an error occurred; errno is set to the following value:

  • EINVAL– The set argument contains an invalid or unsupported signal number.

sigwaitinfo

sigwaitinfo — Suspends a calling thread and waits for queued signals to arrive.

Format

#include <signal.h>
int sigwaitinfo (const sigset_t set, siginfo_t *info);

Arguments

set

The set of signals to wait for.

info

Pointer to a siginfo structure that is receiving data describing the signal, including any application-defined data specified when the signal was posted.

Description

The sigwaitinfo function behaves the same as the sigwait function if the info argument is NULL.

If the info argument is non-NULL, the sigwaitinfo function behaves the same as sigwait, except that the selected signal number is stored in the si_signo member of the siginfo structure, and the cause of the signal is stored in the si_code member. If any value is queued to the selected signal, the first such queued value is dequeued and the value is stored in the si_value member of info. The system resource used to queue the signal is released and made available to queue other signals. If no value is queued, the content of the si_value member is undefined. If no further signals are queued for the selected signal, the pending indication for that signal is reset.

See also sigtimedwait and sigwait.

See Section 4.2 for more information on signal handling.

Return Values

x

Upon successful completion, the signal number selected is returned.

-1
Indicates that an error occurred; errno is set to one of the following values:

  • EINVAL– The set argument contains an invalid or unsupported signal number.

  • EINTR– The wait was interrupted by an unblocked, intercepted signal.

sin

sin — Returns the sine of its radian argument.

Format

#include <math.h>
double sin (double x);
float sinf (float x);
long double sinl (long double x);
double sind (double x);
float sindf (float x);
long double sindl (long double x);

Argument

x

A radian expressed as a floating-point number.

Description

The sin functions compute the sine of x measured in radians.

The sind functions compute the sine of x measured in degrees.

Return Values

x

The sine of the argument.

NaN

x = ±Infinity or NaN; errno is set to EDOM.

0

Underflow occurred; errno is set to ERANGE.

sinh

sinh — Returns the hyperbolic sine of its argument.

Format

#include <math.h>
double sinh (double x);
float sinhf (float x);
long double sinhl (long double x);

Argument

x

A real number.

Return Values

n

The hyperbolic sine of the argument.

HUGE_VAL

Overflow occurred; errno is set to ERANGE.

0

Underflow occurred; errno is set to ERANGE.

NaN

x is NaN; errno is set to EDOM.

sleep

sleep — Suspends the execution of the current process (or thread in a threaded program) for at least the number of seconds indicated by its argument.

Format

#include <unistd.h>
unsigned int sleep (unsigned seconds); (_DECC_V4_SOURCE)
int sleep (unsigned seconds); (not _DECC_V4_SOURCE)

Argument

seconds

The number of seconds.

Description

The sleep function sleeps for the specified number of seconds, or until a signal is received, or until the process (or thread in a threaded program) executes a call to SYS$WAKE.

If a SIGALRM signal is generated, but blocked or ignored, the sleep function returns. For all other signals, a blocked or ignored signal does not cause sleep to return.

Return Values

x

The number of seconds that the process awoke early.

0

If the process slept the full number of seconds specified by seconds.

snprintf

snprintf — Performs formatted output to a string in memory.

Format

#include <stdio.h>
int snprintf (char *str, size_t n, const char *format_spec, ...);

Arguments

str

The address of the string that will receive the formatted output.

n

The size of the buffer referred to by str.

format_spec

A pointer to a character string that contains the format specification. For more information about format specifications and conversion characters, see Chapter 2.

. . .

Optional expressions whose resultant types correspond to conversion specifications given in the format specification.

If no conversion specifications are given, you may omit the output sources. Otherwise, the function calls must have at least as many output sources as there are conversion specifications, and the conversion specifications must match the types of the output sources.

Conversion specifications are matched to output sources in left-to-right order. Excess output pointers, if any, are ignored.

Description

The snprintf function is identical to the sprintf function with the addition of the n argument, which specifies the size of the buffer referred to by str.

On successful completion, snprintf returns the number of bytes (excluding the terminating null byte) that would be written to str if n is sufficiently large.

If n is 0, nothing is written, the number of bytes (excluding the terminating null) that would be written if n were sufficiently large are returned, and str might be a NULL pointer. Otherwise, output bytes beyond the n - 1st are discarded instead of being written to the array, and a null byte is written at the end of the bytes actually written into the array.

If an output error is encountered, a negative value is returned.

For a complete description of the format specification and the output source, see Chapter 2.

Return Values

x

The number of bytes (excluding the terminating null byte) that would be written to str if n is sufficiently large.

Negative value

Indicates an output error occurred. The function sets errno. For a list of errno values set by this function, see fprintf.

sprintf

sprintf — Performs formatted output to a string in memory.

Format

#include <stdio.h>
int sprintf (char *str, const char *format_spec, ...);

Arguments

str

The address of the string that will receive the formatted output. It is assumed that this string is large enough to hold the output.

format_spec

A pointer to a character string that contains the format specification. For more information about format specifications and conversion characters, see Chapter 2.

. . .

Optional expressions whose resultant types correspond to conversion specifications given in the format specification.

If no conversion specifications are given, you may omit the output sources. Otherwise, the function calls must have at least as many output sources as there are conversion specifications, and the conversion specifications must match the types of the output sources.

Conversion specifications are matched to output sources in left-to-right order. Excess output pointers, if any, are ignored.

Description

The sprintf function places output followed by the null character ( \ 0) in consecutive bytes starting at *str. The user must ensure that enough space is available.

Consider the following example of a conversion specification: 
#include <stdio.h>
main()
{
   int  temp = 4, temp2 = 17;
   char s[80];

   sprintf(s, "The answers are %d, and %d.", temp, temp2);
}
In this example, character string s has the following contents:
The answers are 4, and 17.

For a complete description of the format specification and the output source, see Chapter 2.

Return Values

x

The number of characters placed in the output string, not including the final null character.

Negative value

Indicates an output error occurred. The function sets errno. For a list of errno values set by this function, see fprintf.

sqrt

sqrt — Returns the square root of its argument.

Format

#include <math.h>
double sqrt (double x);
float sqrtf (float x);
long double sqrtl (long double x);

Argument

x

A real number.

Return Values

val

The square root of x, if x is nonnegative.

0

x is negative; errno is set to EDOM.

NaN

x is NaN; errno is set to EDOM.

srand

srand — Initializes the pseudorandom-number generator rand.

Format

#include <stdlib.h>
void srand (unsigned int seed);

Argument

seed

An unsigned integer.

Description

The srand function uses the argument as a seed for a new sequence of pseudorandom numbers to be returned by subsequent calls to rand.

If srand is then called with the same seed value, the sequence of pseudorandom numbers is repeated.

If rand is called before any calls to srand, the same sequence of pseudorandom numbers is generated as when srand is first called with a seed value of 1.

srand48

srand48 — Initializes a 48-bit random-number generator.

Format

#include <stdlib.h>
void srand48 (long int seed_val);

Argument

seed_val

The initialization value to begin randomization. Changing this value changes the randomization pattern.

Description

The srand48 function initializes the random-number generator. You can use this function in your program before calling the drand48, lrand48, or mrand48 functions. (Although it is not recommended practice, constant default initializer values are automatically supplied if you call drand48, lrand48, or mrand48 without calling an initialization function).

The function works by generating a sequence of 48-bit integer values, Xi, according to the linear congruential formula:
       Xn+1 = (aXn+c)mod m        n >= 0
The argument m equals 2 48, so 48-bit integer arithmetic is performed. Unless you invoke the lcong48 function, the multiplier value a and the addend value c are:
      a = 5DEECE66D16 = 2736731631558
      c = B16 = 138

The initializer function srand48 sets the high-order 32 bits of Xi to the low-order 32 bits contained in its argument. The low-order 16 bits of Xi are set to the arbitrary value 330E 16.

See also drand48, lrand48, and mrand48.

srandom

srandom — Initializes the pseudorandom-number generator random.

Format

#include <stdlib.h>
void srandom (unsigned seed);

Argument

seed

An initial seed value.

Description

The srandom function uses the argument as a seed for a new sequence of pseudorandom numbers to be returned by subsequent calls to random. This function has virtually the same calling sequence and initialization properties as the srand function, but produce sequences that are more random.

The srandom function initializes the current state with the initial seed value. The srandom function, unlike the srand function, does not return the old seed because the amount of state information used is more than a single word.

See also rand, srand, random, setstate, and initstate.

sscanf

sscanf — Reads input from a character string in memory, interpreting it according to the format specification.

Format

#include <stdio.h>
int sscanf (const char *str, const char *format_spec, ...);

Arguments

str

The address of the character string that provides the input text to sscanf.

format_spec

A pointer to a character string that contains the format specification. For more information about format specifications and conversion characters, see Chapter 2.

. . .

Optional expressions whose resultant types correspond to conversion specifications given in the format specification.

If no conversion specifications are given, you can omit the input pointers. Otherwise, the function calls must have at least as many input pointers as there are conversion specifications, and the conversion specifications must match the types of the input pointers.

Conversion specifications are matched to input sources in left-to-right order. Excess input pointers, if any, are ignored.

Description

The following is an example of a conversion specification: 
main ()
{
   char str[] = "4 17";
   int   temp,
         temp2;

   sscanf(str, "%d %d", &temp, &temp2);
   printf("The answers are %d and %d.", temp, temp2);
}
This example produces the following output: 
$ RUN  EXAMPLE
The answers are 4 and 17.

For a complete description of the format specification and the input pointers, see Chapter 2.

Return Values

x

The number of successfully matched and assigned input items.

EOF

Indicates that a read error occurred before any conversion. The function sets errno. For a list of the values set by this function, see fscanf.

ssignal

ssignal — Allows you to specify the action to take when a particular signal is raised.

Format

#include <signal.h>
void (*ssignal (int sig, void (*func) (int, ...))) (int, ...);

Arguments

sig

A number or mnemonic associated with a signal. The symbolic constants for signal values are defined in the <signal.h> header file (see Chapter 4).

func

The action to take when the signal is raised, or the address of a function that is executed when the signal is raised.

Description

The ssignal function is equivalent to the signal function except for the return value on error conditions.

Since the signal function is defined by the ANSI C standard and the ssignal function is not, use signal for greater portability.

See Section 4.2 for more information on signal handling.

Return Values

x

The address of the function previously established as the action for the signal. The address may be the value SIG_DFL (0) or SIG_IGN (1).

0

Indicates errors. For this reason, there is no way to know whether a return status of 0 indicates failure, or whether it indicates that a previous action was SIG_DFL (0).

[w]standend

[w]standend — Deactivate the boldface attribute for the specified window. The standend function operates on the stdscr window.

Format

#include <curses.h>
int standend (void);
int wstandend (WINDOW *win);

Argument

win

A pointer to the window.

Description

The standend and wstandend functions are equivalent to clrattr and wclrattr called with the attribute _BOLD.

Return Values

OK

Indicates success.

ERR

Indicates an error.

[w]standout

[w]standout — Activate the boldface attribute of the specified window. The standout function acts on the stdscr window.

Format

#include <curses.h>
int standout (void);
int wstandout (WINDOW *win);

Argument

win

A pointer to the window.

Description

The standout and wstandout functions are equivalent to setattr and wsetattr called with the attribute _BOLD.

Return Values

OK

Indicates success.

ERR

Indicates an error.

stat

stat — Accesses information about the specified file.

Format

#include <stat.h>
int stat (const char *file_spec, struct stat *buffer); (ISO POSIX-1)
int stat (const char *file_spec, struct stat *buffer, ...);
(VSI C Extension)

Function Variants

Compiling with the _DECC_V4_SOURCE and _VMS_V6_SOURCE feature-test macros defined enables a local-time-based entry point to the stat function that is equivalent to the behavior before OpenVMS Version 7.0.

Compiling with the _USE_STD_STAT feature-test macro defined enables a variant of the stat function that uses an X/Open standard-compliant definition of the stat structure. The _USE_STD_STAT feature-test macro is mutually exclusive with the _DECC_V4_SOURCE and _VMS_V6_SOURCE macros.

Arguments

file_spec

A valid OpenVMS or UNIX style file specification (no wildcards). Read, write, or execute permission of the named file is not required, but you must be able to reach all directories listed in the file specification leading to the file. For more information about UNIX style file specifications, see Chapter 1.

buffer

A pointer to a structure of type stat. For convenience, a typedef stat_t is defined as struct stat in the <stat.h> header file.

This argument receives information about the particular file. The members of the structure pointed to by buffer are described in the Description section.

. . .

An optional default file-name string.

This is the only optional RMS keyword that can be specified for the stat function. See the description of the creat function for the full list of optional RMS keywords and their values.

Description

When the _USE_STD_STAT feature-test macro is not enabled, the legacy stat structure is used. When _USE_STD_STAT is enabled, the X/Open standard-compliant stat structure is used.

Legacy stat Structure

With the _USE_STD_STAT feature-test macro defined to DISABLE, the following legacy stat structure is used:

Member

Type

Definition

st_dev

dev_t

Pointer to the physical device name

st_ino[3]

ino_t

Three words to receive the file ID

st_mode

mode_t

File “mode” (prot, dir, . . .)

st_nlink

nlink_t

For UNIX system compatibility only

st_uid

uid_t

Owner user ID

st_gid

gid_t

Group member: fromst_uid

st_rdev

dev_t

UNIX system compatibility – always 0

st_size

off_t

File size, in bytes. For st_size to report a correct value, you need to flush both the C RTL and RMS buffers.

st_atime

time_t

File access time; always the same as st_mtime

st_mtime

time_t

Last modification time

st_ctime

time_t

File creation time

st_fab_rfm

char

Record format

st_fab_rat

char

Record attributes

st_fab_fsz

char

Fixed header size

st_fab_mrs

unsigned

Record size

The types dev_t, ino_t, off_t, mode_t, nlink_t, uid_t, gid_t, and time_t, are defined in the <stat.h> header file. However, when compiling for compatibility (/DEFINE=_DECC_V4_SOURCE), only dev_t, ino_t, and off_t are defined.

The off_t data type is either a 32-bit or 64-bit integer. The 64-bit interface allows for file sizes greater than 2 GB, and can be selected at compile time by defining the _LARGEFILE feature-test macro as follows: CC/DEFINE=_LARGEFILE

As of OpenVMS Version 7.0, times are given in seconds since the Epoch (00:00:00 GMT, January 1, 1970).

The st_mode structure member is the status information mode defined in the <stat.h> header file. The st_mode bits are described as follows:

Bits

Constant

Definition

0170000

S_IFMT

Type of file

0040000

S_IFDIR

Directory

0020000

S_IFCHR

Character special

0060000

S_IFBLK

Block special

0100000

S_IFREG

Regular

0030000

S_IFMPC

Multiplexed char special

0070000

S_IFMPB

Multiplexed block special

0004000

S_ISUID

Set user ID on execution

0002000

S_ISGID

Set group ID on execution

0001000

S_ISVTX

Save swapped text even after use

0000400

S_IREAD

Read permission, owner

0000200

S_IWRITE

Write permission, owner

0000100

S_IEXEC

Execute/search permission, owner

The stat function does not work on remote network files.

If the file is a record file, the st_size field includes carriage-control information. Consequently, the st_size value will not correspond to the number of characters that can be read from the file.

Also be aware that for st_size to report a correct value, you need to flush both the C RTL and RMS buffers.

Standard-Compliant stat Structure

With OpenVMS Version 8.2, the _USE_STD_STAT feature-test macro and standard-compliant stat structure are introduced in support of UNIX compatibility.

With _USE_STD_STAT defined to ENABLE, you get the following behavior:

  • Old struct stat definitions

    Old definitions of struct stat are obsolete. You must recompile your applications to access the new features. Existing applications will continue to access the old definitions and functions unless they are recompiled to use the new features.

  • Function variants

    Calls to stat, fstat, lstat, and ftw accept pointers to structures of the new type. Calls to these functions are mapped to the new library entries __std_stat, __std_fstat, __std_lstat, and __std_ftw, respectively.

  • Compatibilities with other feature macros

    _DECC_V4_SOURCE source-code compatibility is not supported. You must not enable _DECC_V4_SOURCE and _USE_STD_STAT at the same time.

    _VMS_V6_SOURCE binary compatibility is not supported. You must not enable _VMS_V6_SOURCE and _USE_STD_STAT at the same time. As a result, only UTC (rather than local-time) is supported for the time_t fields.

  • Type changes

    The following type changes are in effect:

    • 32-bit gid type gid_t is used. _DECC_SHORT_GID_T is unsupported.

    • _LARGEFILE offsets are used. off_t is forced to 64 bits.

    • Type ino_t, representing the file number, is an unsigned int quadword (64 bits). Previously, it was an unsigned short.

    • Type dev_t, representing the device id, is an unsigned int quadword (64 bits). Previously, it was a 32-bit character pointer. The new type is standard because it is arithmetic.

    • Types blksize_t and blkcnt_t are added and defined as unsigned int quadwords (64 bits).

  • Structure member Changes
    • Two members are added to struct stat: 
      blksize_t   st_blksize;
blkcnt_t    st_blocks;

      According to the X/Open standard, st_blksize is the file system-specific preferred I/O blocksize for this file. On OpenVMS systems, st_blksize is set to the device buffer size multiplied by the disk cluster size. st_blocks is set to the allocated size of the file, in blocks. The blocksize used to calculate st_blocks is not necessarily the same as st_blksize and, in most cases, will not be the same.

    • In struct stat, member st_ino is of type ino_t. In previous C RTL versions, it was of type ino_t [3] (array of 3 ino_t). Since ino_t has changed from a word to a quadword, the size of this member has increased by one word. The principal significance of this change is that it makes st_ino a scalar, which is how most open source applications define it.

    • The new definition of ino_t also affects applications that include the <dirent.h> header file. In struct dirent, member d_ino changes in the same way as the st_ino member of struct stat in <stat.h>.

    • Several macros that are not part of any standard were introduced in <stat.h> to facilitate access to the constituent parts of ino_t values:
      • S_INO_NUM(ino), S_INO_SEQ(ino), and S_INO_RVN(ino) return the FILES-11 file number, sequence number, and relative volume number of ino, respectively, as unsigned shorts.
      • S_INO_RVN_RVN(ino) returns the byte of the RVN field containing the relative volume number;
      • S_INO_RVN_NMX(ino) returns the byte of the RVN field containing the file number extension.

      Although individual components can be broken out like this, they are not part of the X/Open standard and should not be relied on in portable applications.

  • Semantic changes

    Values of type dev_t are now unique for each device across clusters. An algorithm based on device name and allocation class or SCSSYSTEMID (for single-pathed devices) calculates the device id value having these characteristics, an X/Open standard requirement. Typically, the combination of file number and device id uniquely identifies a file in a cluster.

    This change affects stat structure members st_dev and st_rdev. For compatibility with previous releases, st_rdev is set to either 0 or st_dev.


Note

(Integrity servers, Alpha) On OpenVMS Alpha and Integrity server systems, the stat, fstat, utime, and utimes functions have been enhanced to take advantage of the new file-system support for POSIX compliant file timestamps.

This support is available only on ODS-5 devices on OpenVMS Alpha systems beginning with a version of OpenVMS Alpha after Version 7.3.

Before this change, the stat and fstat functions were setting the values of the st_ctime, st_mtime, and st_atime fields based on the following file attributes:
  • st_ctime - ATR$C_CREDATE (file creation time)
  • st_mtime - ATR$C_REVDATE (file revision time)
  • st_atime - was always set to st_mtime because no support for file access time was available

Also, for the file-modification time, utime and utimes were modifying the ATR$C_REVDATE file attribute, and ignoring the file-access-time argument.

After the change, for a file on an ODS-5 device, the stat and fstat functions set the values of the st_ctime, st_mtime, and st_atime fields based on the following new file attributes:
  • st_ctime - ATR$C_ATTDATE (last attribute modification time)
  • st_mtime - ATR$C_MODDATE (last data modification time)
  • st_atime - ATR$C_ACCDATE (last access time)

If ATR$C_ACCDATE is zero, as on an ODS-2 device, the stat and fstat functions set st_atime to st_mtime.

For the file-modification time, the utime and utimes functions modify both the ATR$C_REVDATE and ATR$C_MODDATE file attributes. For the file-access time, these functions modify the ATR$C_ACCDATE file attribute. Setting the ATR$C_MODDATE and ATR$C_ACCDATE file attributes on an ODS-2 device has no effect.

For compatibility, the old behavior of stat, fstat, utime, and utimes remains the default, regardless of the kind of device.

The new behavior must be explicitly enabled by defining the DECC$EFS_FILE_TIMESTAMPS logical name to ENABLE before invoking the application. Setting this logical does not affect the behavior of stat, fstat, utime, and utimes for files on an ODS-2 device.

Return Values

0

Indicates success.

-1

Indicates an error other than a privilege violation; errno is set to indicate the error.

-2

Indicates a privilege violation.

statvfs

statvfs — Gets information about a device containing the specified file.

Format

#include <statvfs.h>
int statvfs (const char *restrict path, struct statvfs *restrict buffer);

Arguments

path

Any file on a mounted device.

buffer

Pointer to a statvfs structure to hold the returned information.

Description

The statvfs function returns descriptive information about the device containing the specified file. Read, write, or execute permission of the specified file is not required. The returned information is in the format of a statvfs structure, which is defined in the <statvfs.h> header file and contains the following members:
  • unsigned long f_bsize - Preferred block size.
  • unsigned long f_frsize - Fundamental block size.
  • fsblkcnt_t f_blocks - Total number of blocks in units of f_frsize.
  • fsblkcnt_t f_bfree - Total number of free blocks. If f_bfree would assume a meaningless value due to the misreporting of free block count by $GETDVI for a DFS disk, then f_bfree is set to the maximum block count.
  • fsblkcnt_t f_bavail - Number of free blocks available. Set to the unused portion of the caller's disk quota.
  • fsfilcnt_t f_files - Total number of file serial numbers (for example, inodes).
  • fsfilcnt_t f_ffree - Total number of free file serial numbers. For OpenVMS systems, this value is calculated as freeblocks/clustersize.
  • fsfilcnt_t f_favail - Number of file serial numbers available to a non-privileged process (0 for OpenVMS systems).
  • unsigned long f_fsid - File system identifier. This identifier is based on the allocation-class device name. This gives a unique value based on device, as long as the device is locally mounted.
  • unsigned long f_flag - Bit mask representing one or more of the following flags:

  • ST_RONLY - The volume is read-only.

  • ST_NOSUID - The volume has protected subsystems enabled.


  • unsigned long f_namemax - Maximum length of a filename.
  • char f_basetype[64] - Device-type name.
  • char f_fstr[64] - Logical volume name.
  • char __reserved[64] - Media type name.

Upon successful completion, statvfs returns 0 (zero). Otherwise, it returns -1 and sets errno to indicate the error.

See also fstatvfs.

Return Value

0

Successful completion.

-1
Indicates an error. errno is set to one of the following:

  • EACCES - Search permission is denied for a component of the path prefix.

  • EIO - An I/O error occurred while reading the device.

  • EINTR - A signal was intercepted during execution of the function.

  • EOVERFLOW - One of the values to be returned cannot be represented correctly in the structure pointed to by buffer.

  • ENAMETOOLONG - The length of a component of the path parameter exceeds NAME_MAX, or the length of the path parameter exceeds PATH_MAX.

  • ENOENT - A component of path does not name an existing file, or path is an empty string.

  • ENOTDIR - A component of the path prefix of the path parameter is not a directory.

stpcpy

stpcpy — Copies a string returning a pointer to its end.

Format

#include <string.h>
char *stpcpy(char *dest, const char *src);

Function Variants

The stpcpy function has variants named _stpcpy32 and _stpcpy64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions

Arguments

dest

A pointer to the destination character string.

src

A pointer to the character string to be copied.

Description

The function stpcpy uses strlen to determine the length of src and then copies the src to dest. The difference from the strcpy function is that stpcpy returns a pointer to the final '\0', and not to the beginning of the line.

Return Value

x

A pointer to the end of the string dest.

strcasecmp

strcasecmp — Does a case-insensitive comparison of two 7-bit ASCII strings.

Format

#include <strings.h>
int strcasecmp (const char *s1, const char *s2);

Arguments

s1

The first of two strings to compare.

s2

The second of two strings to compare.

Description

The strcasecmp function is case-insensitive. The returned lexicographic difference reflects a conversion to lowercase.

The strcasecmp function works for 7-bit ASCII compares only. Do not use this function for internationalized applications.

Return Value

n

An integer value greater than, equal to, or less than 0 (zero), depending on whether the s1 string is greater than, equal to, or less than the s2 string.

strcat

strcat — Concatenates str_2, including the terminating null character, to the end of str_1.

Format

#include <string.h>
char *strcat (char *str_1, const char *str_2);

Function Variants

The strcat function has variants named _strcat32 and _strcat64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

str_1, str_2

Pointers to null-terminated character strings.

Description

See strncat.

Return Value

x

The address of the first argument, str_1, which is assumed to be large enough to hold the concatenated result.

Example

#include <string.h>
#include <stdio.h>

/* This program concatenates two strings using the strcat       */
/* function, and then manually compares the result of strcat    */
/* to the expected result.                                      */

#define S1LENGTH 10
#define S2LENGTH 8

main()
{
    static char s1buf[S1LENGTH + S2LENGTH] = "abcmnexyz";
    static char s2buf[] = " orthis";
    static char test1[] = "abcmnexyz orthis";

    int i;
    char *status;

    /* Take static buffer s1buf, concatenate static buffer      */
    /* s2buf to it, and compare the answer in s1buf with the    */
    /* static answer in test1.                                  */

    status = strcat(s1buf, s2buf);
    for (i = 0; i <= S1LENGTH + S2LENGTH - 2; i++) {
        /* Check for correct returned string.   */

        if (test1[i] != s1buf[i])
            printf("error in strcat");
    }
}

strchr

strchr — Returns the address of the first occurrence of a given character in a null-terminated string.

Format

#include <string.h>
char *strchr (const char *str, int character);

Function Variants

The strchr function has variants named _strchr32 and _strchr64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

str

A pointer to a null-terminated character string.

character

An object of type int.

Description

This function returns the address of the first occurrence of a given character in a null-terminated string. The terminating null character is considered to be part of the string.

Compare with strrchr, which returns the address of the last occurrence of a given character in a null-terminated string.

Return Values

x

The address of the first occurrence of the specified character.

NULL

Indicates that the character does not occur in the string.

Example

#include <stdio.h>
#include <string.h>

main()
{

    static char s1buf[] = "abcdefghijkl lkjihgfedcba";

    int i;

    char *status;

/*  This program checks the strchr function by incrementally   */
/*  going through a string that ascends to the middle and then */
/*  descends towards the end.                                  */

    for (i = 0; s1buf[i] != '\0' && s1buf[i] != ' '; i++) {
        status = strchr(s1buf, s1buf[i]);

/* Check for pointer to leftmost character - test 1.           */

        if (status != &s1buf[i])
            printf("error in strchr");
    }
}

strcmp

strcmp — Compares two ASCII character strings and returns a negative, 0, or positive integer, indicating that the ASCII values of the individual characters in the first string are less than, equal to, or greater than the values in the second string.

Format

#include <string.h>
int strcmp (const char *str_1, const char*str_2);

Arguments

str_1, str_2

Pointers to character strings.

Description

The strings are compared until a null character is encountered or until the strings differ.

Return Values

< 0

Indicates that str_1 is less than str_2.

= 0

Indicates that str_1 equals str_2.

> 0

Indicates that str_1 is greater than str_2.

strcoll

strcoll — Compares two strings and returns an integer that indicates if the strings differ and how they differ. The function uses the collating information in the LC_COLLATE category of the current locale to determine how the comparison is performed.

Format

#include <string.h>
int strcoll (const char *s1, const char *s2);

Arguments

s1, s2

Pointers to character strings.

Description

The strcoll function, unlike strcmp, compares two strings in a locale-dependent manner. Because no value is reserved for error indication, the application must check for one by setting errno to 0 before the function call and testing it after the call.

See also strxfrm.

Return Values

< 0

Indicates that s1 is less than s2.

= 0

Indicates that the strings are equal.

> 0

Indicates that s1 is greater than s2.

strcpy

strcpy — Copies all of source, including the terminating null character, into dest.

Format

#include <string.h>
char *strcpy (char *dest, const char *source);

Function Variants

The strcpy function has variants named _strcpy32 and _strcpy64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

dest

Pointer to the destination character string.

source

Pointer to the source character string.

Description

The strcpy function copies source into dest, and stops after copying source's null character.

The behavior of this function is undefined if the area pointed to by dest overlaps the area pointed to by source.

Return Value

x

The address of dest.

strcspn

strcspn — Returns the length of the prefix of a string that consists entirely of characters not in a specified set of characters.

Format

#include <string.h>
size_t strcspn (const char *str, const char *charset);

Arguments

str

A pointer to a character string. If this character string is a null string, 0 is returned.

charset

A pointer to a character string containing the set of characters.

Description

The strcspn function scans the characters in the string, stops when it encounters a character found in charset, and returns the length of the string's initial segment formed by characters not found in charset.

If none of the characters match in the character strings pointed to by str and charset, strcspn returns the length of string.

Return Value

x

The length of the segment.

strdup

strdup — Duplicates the specified string.

Format

#include <string.h>
char *strdup (const char *s1);

Function Variants

The strdup function has variants named _strdup32 and _strdup64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Argument

s1

The string to be duplicated.

Description

The strdup function returns a pointer to a string that is an exact duplicate of the string pointed to by s1. The malloc function is used to allocate space for the new string. The strdup function is provided for compatibility with existing systems.

Return Values

x

A pointer to the resulting string.

NULL

Indicates an error.

strerror

strerror — Maps the error number in error_code to a locale-dependent error message string.

Format

#include <string.h>
char *strerror (int error_code); (ANSI C)
char *strerror (int error_code[, int vms_error_code]); (VSI C Extension)

Arguments

error_code

An error code.

vms_error_code

An OpenVMS error code.

Description

The strerror function uses the error number in error_code to retrieve the appropriate locale-dependent error message. The contents of the error message strings are determined by the LC_MESSAGES category of the program's current locale.

When a program is not compiled with any standards-related feature-test macros (see Section 1.4.1), strerror has a second argument (vms_error_code), which is used in the following way:

  • If error_code is EVMSERR and there is a second argument, then that second argument is used as the vaxc$errno value.

  • If error_code is EVMSERR and there is no second argument, look at vaxc$errno to get the OpenVMS error condition.

See the Example section.

Use of the second argument is not included in the ANSI C definition of strerror and is, therefore, not portable.

Because no return value is reserved to indicate an error, applications should set the value of errno to 0, call strerror, and then test the value of errno; a nonzero value indicates an error condition.

Return Value

x

A pointer to a buffer containing the appropriate error message. Do not modify this buffer in your programs. Moreover, calls to the strerror function may overwrite this buffer with a new message.

Example

#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <ssdef.h>

main()
{
    puts(strerror(EVMSERR));
    errno = EVMSERR;
    vaxc$errno = SS$_LINKEXIT;
    puts(strerror(errno));
    puts(strerror(EVMSERR, SS$_ABORT));
    exit(1);
}
Running this example produces the following output:
nontranslatable vms error code: <none>
network partner exited
abort

strerror_r

strerror_r — Maps the error number in error_code to a locale-dependent error message string (reentrant).

Format

#include <string.h>
int strerror_r(int error_code, char *buf, size_t buflen);

Arguments

error_code

An error code.

buf

A pointer to a buffer where the function can store the error message.

buflen

The length of the buffer (in characters).

Description

The strerror_r function is the reentrant version of strerror. The strerror_r function uses the error number in error_code to retrieve the appropriate locale dependent error message. The contents of the error message strings are determined by the LC_MESSAGES category of the program's current locale.

If error_code is EVMSERR, the function looks at vaxc$errno to get the OpenVMS error condition.

Return Values

0

On success, the error message is in the character array pointed to by buf. The array is buflen characters long and should have space for the error message and the terminating null character.

strfmon

strfmon — Converts a number of monetary values into a string. The conversion is controlled by a format string.

Format

#include <monetary.h>
ssize_t strfmon (char *s, size_t maxsize, const char *format, ...);

Arguments

s

A pointer to the resultant string.

maxsize

The maximum number of bytes to be stored in the resultant string.

format

A pointer to a string that controls the format of the output string.

. . .

The monetary values of type double that are to be formatted for the output string. There should be as many values as there are conversion specifications in the format string pointed to by format. The function fails if there are insufficient values. Excess arguments are ignored.

Description

The strfmon function creates a string pointed to by s, using the monetary values supplied. A maximum of maxsize bytes is copied to s.

The format string pointed to by format consists of ordinary characters and conversion specifications. All ordinary characters are copied unchanged to the output string. A conversion specification defines how one of the monetary values supplied is formatted in the output string.

A conversion specification consists of a percent character (%), followed by a number of optional characters (see Table 37), and concluding with a conversion specifier (see Table 38).

If any of the optional characters listed in Table 37 is included in a conversion specification, they must appear in the order shown.
Table 37. Optional Characters in strfmon Conversion Specifications
CharacterMeaning
= characterUse character as the numeric fill character if a left precision is specified. The default numeric fill character is the space character. The fill character must be representable as a single byte in order to work with precision and width count. This conversion specifier is ignored unless a left precision is specified, and it does not affect width filling, which always uses the space character.
^Do not use separator characters to format the number. By default, the digits are grouped according to the mon_grouping field in the LC_MONETARY category of the current locale.
+Add the string specified by the positive_sign or negative_sign fields in the current locale. If p_sign_posn or n_sign_posn is set to 0, then parentheses are used by default to indicate negative values. Otherwise, sign strings are used to indicate the sign of the value. You cannot use a + and a ( in the same conversion specification.
(Enclose negative values within parentheses. The default is taken from the p_sign_posn and n_sign_posn fields in the current locale. If p_sign_posn or n_sign_posn is set to 0, then parentheses are used by default to indicate negative values. Otherwise, sign strings are used to indicate the sign of the value. You cannot use a + and ( in the same conversion specification.
!Suppress the currency symbol. By default, the currency symbol is included.
--Left-justify the value within the field. By default, values are right-justified.
field widthA decimal integer that specifies the minimum field width in which to align the result of the conversion. The default field width is the smallest field that can contain the result.
#left_precisionA # followed by a decimal integer specifies the number of digits to the left of the radix character. Extra positions are filled by the fill character. By default the precision is the smallest required for the argument. If grouping is not suppressed with the ^ conversion specifier, and if grouping is defined for the current locale, grouping separators are inserted before any fill characters are added. Grouping separators are not applied to fill characters even if the fill character is defined as a digit.
.right_precisionA period (.) followed by a decimal integer specifies the number of digits to the right of the radix character. Extra positions are filled with zeros. The amount is rounded to this number of decimal places. If the right precision is zero, the radix character is not included in the output. By default the right precision is defined by the frac_digits or int_frac_digits field of the current locale.

Table 38. strfmon Conversion Specifiers

Specifier

Meaning

i

Use the international currency symbol defined by the int_currency_symbol field in the current locale, unless the currency symbol has been suppressed.

n

Use the local currency symbol defined by the currency_symbol field in the current locale, unless the currency symbol has been suppressed.

%

Output a % character. The conversion specification must be %%; none of the optional characters is valid with this specifier.

Return Values

x

The number of bytes written to the string pointed to by s, not including the null-terminating character.

-1
Indicates an error. The function sets errno to one of the following values:

  • EINVAL – A conversion specification is syntactically incorrect.

  • E2BIG – Processing the complete format string would produce more than maxsize bytes.

Example

#include <stdlib.h>
#include <stdio.h>
#include <locale.h>
#include <monetary.h>
#include <errno.h>

#define MAX_BUF_SIZE 124

main()
{
  size_t ret;
  char buffer[MAX_BUF_SIZE];
  double amount = 102593421;

 /* Display a monetary amount using the en_US.ISO8859-1 */
 /* locale and a range of different display formats.    */

  if (setlocale(LC_ALL, "en_US.ISO8859-1") == (char *) NULL) {
      perror("setlocale");
      exit(EXIT_FAILURE);
  }
  ret = strfmon(buffer, MAX_BUF_SIZE, "International: %i\n", amount);
  printf(buffer);

  ret = strfmon(buffer, MAX_BUF_SIZE, "National:      %n\n", amount);
  printf(buffer);

  ret = strfmon(buffer, MAX_BUF_SIZE, "National:      %=*#10n\n", amount);
  printf(buffer);

  ret = strfmon(buffer, MAX_BUF_SIZE, "National:     %(n\n", -1 * amount);
  printf(buffer);

  ret = strfmon(buffer, MAX_BUF_SIZE, "National:      %^!n\n", amount);
  printf(buffer);
}
Running the example program produces the following result:
International: USD 102,593,421.00
National:      $102,593,421.00
National:      $**102,593,421.00
National:      ($102,593,421.00)
National:      102593421.00

strftime

strftime — Uses date and time information stored in a tm structure to create an output string. The format of the output string is controlled by a format string.

Format

#include <time.h>
size_t strftime (char *s, size_t maxsize, const char *format,
const struct tm *timeptr);

Function Variants

Compiling with the _DECC_V4_SOURCE and _VMS_V6_SOURCE feature-test macros defined enables a local-time-based entry point to the strftime function that is equivalent to the behavior before OpenVMS Version 7.0.

Arguments

s

A pointer to the resultant string.

maxsize

The maximum number of bytes to be stored in the resultant string, including the null terminator.

format

A pointer to a string that controls the format of the output string.

timeptr

A pointer to the local time (tm) structure. The tm structure is defined in the <time.h> header file.

Description

The strftime function uses data in the structure pointed to by timeptr to create the string pointed to by s. A maximum of maxsize bytes is copied to s.

The format string consists of zero or more conversion specifications and ordinary characters. All ordinary characters (including the terminating null character) are copied unchanged into the output string. A conversion specification defines how data in the tm structure is formatted in the output string.

A conversion specification consists of a percent (%) character followed by one or more optional characters (see Table 39), and concluding with a conversion specifier (see Table 40). If any of the optional characters listed in Table 39 are specified, they must appear in the order shown in the table.

The strftime function behaves as if it called tzset.
Table 39. Optional Elements of strftime Conversion Specifications

Element

Meaning

–

Optional with the field width to specify that the field is left-justified and padded with spaces. This cannot be used with the 0 element.

0

Optional with the field width to specify that the field is right-justified and padded with zeros. This cannot be used with the – element.

field width

A decimal integer that specifies the maximum field width

.precision

A decimal integer that specifies the precision of data in a field.

For the d, H, I, j, m, M, o, S, U, w, W, y, and Y conversion specifiers, the precision specifier is the minimum number of digits to appear in the field. If the conversion specification has fewer digits than that specified by the precision, leading zeros are added.

For the a, A, b, B, c, D, E, h, n, N, p, r, t, T, x, X, Z, and % conversion specifiers, the precision specifier is the maximum number of characters to appear in the field. If the conversion specification has more characters than that specified by the precision, characters are truncated on the right.

The default precision for the d, H, I, m, M, o, S, U, w, W, y and Y conversion specifiers is 2; the default precision for the j conversion specifier is 3.

Note that the list of conversion specifications in Table 39 are extensions to the XPG4 specification.

Table 40 lists the conversion specifiers. The strftime function uses fields in the LC_TIME category of the program's current locale to provide a value. For example, if %B is specified, the function accesses the mon field in LC_TIME to find the full month name for the month specified in the tm structure. The result of using invalid conversion specifiers is undefined.
Table 40. strftime Conversion Specifiers

Specifier

Replaced by

%a

The locale's abbreviated weekday name.

%A

The locale's full weekday name.

%b

The locale's abbreviated month name.

%B

The locale's full month name.

%c

The locale's appropriate date and time representation.

%C

The century number (the year divided by 100 and truncated to an integer) as a decimal number (00 – 99).

%d

The day of the month as a decimal number (01 – 31).

%D

Same as %m/%d/%y.

%e

The day of the month as a decimal number (1 – 31) in a 2-digit field with the leading space character fill.

%Ec

The locale's alternative date and time representation.

%EC

The name of the base year (period) in the locale's alternative representation.

%Ex

The locale's alternative date representation.

%EX

The locale's alternative time representation.

%Ey

The offset from the base year (%EC) in the locale's alternative representation.

%EY

The locale's full alternative year representation.

%F

Same as "%Y−%m−%d" (the ISO 8601 date format). [tm_year, tm_mon, tm_mday]

%g

The last 2 digits of the week-based year as a decimal number (00−99). [tm_year, tm_wday, tm_yday]

%G

The week-based year as a decimal number (for example, 1997). [tm_year, tm_wday, tm_yday]

%h

Same as %b.

%H

The hour (24-hour clock) as a decimal number (00 – 23).

%I

The hour (12-hour clock) as a decimal number (01 – 12).

%j

The day of the year as a decimal number (001 – 366).

%k

The hour (24-hour clock) as a decimal number (range 0 to 23); single digits are preceded by a blank.

%l

The hour (12-hour clock) as a decimal number (range 1 to 12); single digits are preceded by a blank.

%m

The month as a decimal number (01 – 12).

%M

The minute as a decimal number (00 – 59).

%n

The new-line character.

%Od

The day of the month using the locale's alternative numeric symbols.

%Oe

The date of the month using the locale's alternative numeric symbols.

%OH

The hour (24-hour clock) using the locale's alternative numeric symbols.

%OI

The hour (12-hour clock) using the locale's alternative numeric symbols.

%Om

The month using the locale's alternative numeric symbols.

%OM

The minutes using the locale's alternative numeric symbols.

%OS

The seconds using the locale's alternative numeric symbols.

%Ou

The weekday as a number in the locale's alternative representation (Monday=1).

%OU

The week number of the year (Sunday as the first day of the week) using the locale's alternative numeric symbols.

%OV

The week number of the year (Monday as the first day of the week) as a decimal number (01– 53) using the locale's alternative numeric symbols. If the week containing January 1 has four or more days in the new year, it is considered as week 1. Otherwise, it is considered as week 53 of the previous year, and the next week is week 1.

%Ow

The weekday as a number (Sunday=0) using the locale's alternative numeric symbols.

%OW

The week number of the year (Monday as the first day of the week) using the locale's alternative numeric symbols.

%Oy

The year without the century using the locale's alternative numeric symbols.

%p

The locale's equivalent of the AM/PM designations associated with a 12-hour clock.

%P

Same as %p but in lowercase; "am" or "pm" or a corresponding string for the current locale.

%r

The time in AM/PM notation.

%R

The time in 24-hour notation (%H:%M).

%s

The number of seconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC).

%S

The second as a decimal number (00 – 61).

%t

The tab character.

%T

The time (%H:%M:%S).

%u

The weekday as a decimal number between 1 and 7 (Monday=1).

%U

The week number of the year (the first Sunday as the first day of week 1) as a decimal number (00 – 53).

%V

The week number of the year (Monday as the first day of the week) as a decimal number (00 – 53). If the week containing January 1 has four or more days in the new year, it is considered as week 1. Otherwise, it is considered as week 53 of the previous year, and the next week is week 1.

%w

The weekday as a decimal number (0 [Sunday] – 6).

%W

The week number of the year (the first Monday as the first day of week 1) as a decimal number (00– 53).

%x

The locale's appropriate date representation.

%X

The locale's appropriate time representation.

%y

The year without century as a decimal number (00 – 99).

%Y

The year with century as a decimal number.

%z

The +hhmm or -hhmm numeric timezone (that is, the hour and minute offset from UTC).

%Z

The time-zone name or abbreviation. If time-zone information is not available, no character is output.

%+

The date and time in date format.

%%

Literal % character.

Return Values

x

The number of characters placed into the array pointed to by s, not including the terminating null character.

0

Indicates an error occurred. The contents of the array are indeterminate.

Example

#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <locale.h>
#include <errno.h>

#define NUM_OF_DATES  7
#define BUF_SIZE 256

/* This program formats a number of different dates, once */
/* using the C locale and then using the fr_FR.ISO8859-1  */
/* locale. Date and time formatting is done using strftime(). */

main()
{
    int count,
        i;
    char buffer[BUF_SIZE];
    struct tm *tm_ptr;
    time_t time_list[NUM_OF_DATES] =
    {500, 68200000, 694223999, 694224000,
     704900000, 705000000, 705900000};

    /* Display dates using the C locale */
    printf("\nUsing the C locale:\n\n");

    setlocale(LC_ALL, "C");

    for (i = 0; i < NUM_OF_DATES; i++) {
        /* Convert to a tm structure */
        tm_ptr = localtime(&time_list[i]);

        /* Format the date and time */
        count = strftime(buffer, BUF_SIZE,
               "Date: %A %d %B %Y%nTime: %T%n%n", tm_ptr);
        if (count == 0) {
            perror("strftime");
            exit(EXIT_FAILURE);
        }

        /* Print the result */
       printf(buffer);
    }

    /* Display dates using the fr_FR.ISO8859-1 locale */
    printf("\nUsing the fr_FR.ISO8859-1 locale:\n\n");

    setlocale(LC_ALL, "fr_FR.ISO8859-1");

    for (i = 0; i < NUM_OF_DATES; i++) {
        /* Convert to a tm structure */
        tm_ptr = localtime(&time_list[i]);

        /* Format the date and time */
        count = strftime(buffer, BUF_SIZE,
               "Date: %A %d %B %Y%nTime: %T%n%n", tm_ptr);
        if (count == 0) {
            perror("strftime");
            exit(EXIT_FAILURE);
        }

        /* Print the result */
        printf(buffer);
    }
}
Running the example program produces the following result:
Using the C locale:

Date: Thursday 01 January 1970
Time: 00:08:20

Date: Tuesday 29 February 1972
Time: 08:26:40

Date: Tuesday 31 December 1991
Time: 23:59:59

Date: Wednesday 01 January 1992
Time: 00:00:00

Date: Sunday 03 May 1992
Time: 13:33:20

Date: Monday 04 May 1992
Time: 17:20:00

Date: Friday 15 May 1992
Time: 03:20:00


Using the fr_FR.ISO8859-1 locale:

Date: jeudi 01 janvier 1970
Time: 00:08:20

Date: mardi 29 février 1972
Time: 08:26:40

Date: mardi 31 décembre 1991
Time: 23:59:59

Date: mercredi 01 janvier 1992
Time: 00:00:00

Date: dimanche 03 mai 1992
Time: 13:33:20

Date: lundi 04 mai 1992
Time: 17:20:00

Date: vendredi 15 mai 1992
Time: 03:20:00

strlen

strlen — Returns the length of a string of ASCII characters. The returned length does not include the terminating null character (\0).

Format

#include <string.h>
size_t strlen (const char *str);

Argument

str

A pointer to the character string.

Return Value

x

The length of the string.

strncasecmp

strncasecmp — Does a case-insensitive comparison between two 7-bit ASCII strings.

Format

#include <strings.h>
int strncasecmp (const char *s1, const char *s2, size_t n);

Arguments

s1

The first of two strings to compare.

s2

The second of two strings to compare.

n

The maximum number of bytes in a string to compare.

Description

The strncasecmp function is case-insensitive. The returned lexicographic difference reflects a conversion to lowercase. The strncasecmp function is similar to the strcasecmp function, but also compares size. If the size specified by n is read before a NULL, the comparison stops.

The strcasecmp function works for 7-bit ASCII compares only. Do not use this function for internationalized applications.

Return Value

n

An integer value greater than, equal to, or less than 0 (zero), depending on whether s1 is greater than, equal to, or less than s2.

strncat

strncat — Appends not more than maxchar characters from str_2 to the end of str_1.

Format

#include <string.h>
char *strncat (char *str_1, const char *str_2, size_t maxchar);

Function Variants

The strncat function has variants named _strncat32 and _strncat64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

str_1, str_2

Pointers to null-terminated character strings.

maxchar

The number of characters to concatenate from str_2, unless strncat first encounters a null terminator in str_2. If maxchar is 0, no characters are copied from str_2.

Description

A null character is always appended to the result of the strncat function. If strncat reaches the specified maximum, it sets the next byte in str_1 to the null character.

Return Value

x

The address of the first argument, str_1, which is assumed to be large enough to hold the concatenated result.

strncmp

strncmp — Compares not more than maxchar characters of two ASCII character strings and returns a negative, 0, or positive integer, indicating that the ASCII values of the individual characters in the first string are less than, equal to, or greater than the values in the second string.

Format

#include <string.h>
int strncmp (const char *str_1, const char *str_2, size_t maxchar);

Arguments

str_1, str_2

Pointers to character strings.

maxchar

The maximum number of characters (beginning with the first) to search in both str_1 and str_2.If maxchar is 0, no comparison is performed and 0 is returned (the strings are considered equal).

Description

The strncmp function compares no more than maxchar characters from the string pointed to by str_1 to the string pointed to by str_2. The strings are compared until a null character is encountered, the strings differ, or maxchar is reached. Characters that follow a difference or a null character are not compared.

Return Values

< 0

Indicates that str_1 is less than str_2.

= 0

Indicates that str_1 equals str_2.

> 0

Indicates that str_1 is greater than str_2.

Examples

  1. #include <string.h>
#include <stdio.h>

main()
{
    printf( "%d\n", strncmp("abcde", "abc", 3));
}
    When linked and executed, this example returns 0, because the first 3 characters of the 2 strings are equal:
    $ run tmp
0
  2. #include <string.h>
#include <stdio.h>

    main()
    {
        printf( "%d\n", strncmp("abcde", "abc", 4));
    }
    When linked and executed, this example returns a value greater than 0 because the first 4 characters of the 2 strings are not equal (The "d" in the first string is not equal to the null character in the second):
    $ run tmp
        100

strncpy

strncpy — Copies not more than maxchar characters from source into dest.

Format

#include <string.h>
char *strncpy (char *dest, const char *source, size_t maxchar);

Function Variants

The strncpy function has variants named _strncpy32 and _strncpy64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

dest

Pointer to the destination character string.

source

Pointer to the source character string.

maxchar

The maximum number of characters to copy from source to dest up to but not including the null terminator of source.

Description

The strncpy function copies no more than maxchar characters from source to dest, up to but not including the null terminator of source. If source contains less than maxchar characters, dest is padded with null characters. If source contains greater than or equal to maxchar characters, as many characters as possible are copied to dest. Be aware that the dest argument might not be terminated by a null character after a call to strncpy.

Return Value

x

The address of dest.

strndup

strndup — Duplicates a specific number of bytes from a string.

Format

#include <string.h>
char *strndup(const char *s, size_t size);

Function Variants

The strndup function has variants named _strndup32 and _strndup64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

s

A pointer to the null-terminated byte string.

size

The number of bytes to duplicate from s.

Description

The strndup function duplicates a specific number of bytes from a string. The strndup function is equivalent to the strdup function, duplicating the provided string in a new block of memory allocated as if by using malloc, with the exception that strndup copies at most size plus one bytes into the newly allocated memory, terminating the new string with a NUL character.

If the length of s is larger than size, only size bytes will be duplicated. If size is larger than the length of s, all bytes in s will be copied into the new memory buffer, including the terminating NUL character. The newly created string will always be properly terminated.

Return Values

x

A pointer to the resulting string.

NULL

Indicates an error.

strnlen

strnlen — Returns the number of bytes in a string.

Format

#include <string.h>
size_t strnlen (const char *s, size_t n);

Arguments

s

Pointer to the string.

n

The maximum number of characters to examine.

Description

The strnlen function returns the number of bytes in the string pointed to by s. The string length value does not include the terminating null character. The strnlen function counts bytes until the first null byte or until n bytes have been examined.

Return Value

n

The length of the string.

strpbrk

strpbrk — Searches a string for the occurrence of one of a specified set of characters.

Format

#include <string.h>
char *strpbrk (const char *str, const char *charset);

Function Variants

The strpbrk function has variants named _strpbrk32 and _strpbrk64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

str

A pointer to a character string. If this character string is a null string, 0 is returned.

charset

A pointer to a character string containing the set of characters for which the function will search.

Description

The strpbrk function scans the characters in the string, stops when it encounters a character found in charset, and returns the address of the first character in the string that appears in the character set.

Return Values

x

The address of the first character in the string that is in the set.

NULL

Indicates that no character is in the set.

strptime

strptime — Converts a character string into date and time values that are stored in a tm structure. Conversion is controlled by a format string.

Format

#include <time.h>
char *strptime (const char *buf, const char *format, struct tm *timeptr);

Function Variants

The strptime function has variants named _strptime32 and _strptime64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

buf

A pointer to the character string to convert.

format

A pointer to the string that defines how the input string is converted.

timeptr

A pointer to the local time structure. The tm structure is defined in the <time.h> header file.

Description

The strptime function converts the string pointed to by buf into values that are stored in the structure pointed to by timeptr. The string pointed to by format defines how the conversion is performed.

The strptime function modifies only those fields in the tm structure that have corresponding conversion specifications in the format. In particular, strptime never sets the tm_isdst member of the tm structure.

The format string consists of zero or more directives. A directive is composed of one of the following:

  • One or more white-space characters (as defined by the isspace function). This directive causes the function to read input up to the first character that is not a white-space character.

  • Any character other than the percent character (%) or a white-space character. This directive causes the function to read the next character. The character read must be the same as the character that comprises the directive. If the character is different, the function fails.

  • A conversion specification. A conversion specification defines how characters in the input string are interpreted as values that are then stored in the tm structure. A conversion specification consists of a percent (%) character followed by a conversion specifier. Table 41 lists the valid conversion specifications.

The strptime function uses fields in the LC_TIME category of the program's current locale to provide a value.

Note

To be compliant with X/Open CAE Specification System Interfaces and Headers Issue 5 (commonly known as XPG5), the strptime function processes the "%y" directive differently than in previous versions of the C RTL.

With Version 6.4 and higher of the C compiler, for a two-digit year within the century if no century is specified, "%y" directive values range from:

  • 69 to 99 refer to years in the twentieth century (1969 to 1999 inclusive)

  • 00 to 68 refer to years in the twenty-first century (2000 to 2068 inclusive)

In previous (XPG4-compliant) versions of the C RTL, strptime interpreted a two-digit year with no century specified as a year within the twentieth century.

The XPG5-compliant strptime is now the default version in the C RTL.

To obtain the old, XPG4-compliant strptime function behavior, specify one of the following:
  • Define the DECC$XPG4_STRPTIME logical name as follows:
    $ DEFINE DECC$XPG4_STRPTIME ENABLE

    or:

  • Call the XPG4 strptime directly as the function decc$strptime_xpg4.

To return to using the XPG5 strptime version, DEASSIGN the DECC$XPG4_STRPTIME logical name: 
$ DEASSIGN DECC$XPG4_STRPTIME

Table 41. strptime Conversion Specifiers

Specification

Replaced by

%a

The weekday name. This is either the abbreviated or the full name.

%A

Same as %a.

%b

The month name. This is either the abbreviated or the full name.

%B

Same as %b.

%c

The date and time using the locale's date format.

%Ec

The locale's alternative date and time representation.

%C

The century number (the year divided by 100 and truncated to an integer) as a decimal number (00 – 99). Leading zeros are permitted.

%EC

The name of the base year (period) in the locale's alternative representation.

%d

The day of the month as a decimal number (01 – 31). Leading zeros are permitted.

%Od

The day of the month using the locale's alternative numeric symbols.

%D

Same as %m/%d/%y.

%e

Same as %d.

%Oe

The date of the month using the locale's alternative numeric symbols.

%F

Same as "%Y−%m−%d" (the ISO 8601 date format). [tm_year, tm_mon, tm_mday]

%g

The last 2 digits of the week-based year as a decimal number (00−99). [tm_year, tm_wday, tm_yday]

%G

The week-based year as a decimal number (for example, 1997). [tm_year, tm_wday, tm_yday]

%h

Same as %b.

%H

The hour (24-hour clock) as a decimal number (00 – 23). Leading zeros are permitted.

%OH

The hour (24-hour clock) using the locale's alternative numeric symbols.

%I

The hour (12-hour clock) as a decimal number (01 – 12). Leading zeros are permitted.

%OI

The hour (12-hour clock) using the locale's alternative numeric symbols.

%j

The day of the year as a decimal number (001 – 366).

%k

The hour (24-hour clock) as a decimal number (range 0 to 23); single digits are preceded by a blank.

%l

The hour (12-hour clock) as a decimal number (range 1 to 12); single digits are preceded by a blank.

%m

The month as a decimal number (01 – 12). Leading zeros are permitted.

%Om

The month using the locale's alternative numeric symbols.

%M

The minute as a decimal number (00 – 59). Leading zeros are permitted.

%OM

The minutes using the locale's alternative numeric symbols.

%n

Any white-space character.

%p

The locale's equivalent of the AM/PM designations associated with a 12-hour clock.

%P

Same as %p but in lowercase: "am" or "pm" or a corresponding string for the current locale.

%r

The time in AM/PM notation (%I:%M:%S %p).

%R

The time in 24-hour notation (%H:%M).

%s

The number of seconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC).

%S

The second as a decimal number (00 – 61). Leading zeros are permitted.

%OS

The seconds using the locale's alternative numeric symbols.

%t

Any white-space character.

%T

The time (%H:%M:%S).

%u

The weekday as a decimal number between 1 and 7 (Monday=1).

%U

The week number of the year (the first Sunday as the first day of week 1) as a decimal number (00 – 53). Leading zeros are permitted.

%OU

The week number of the year (Sunday as the first day of the week) using the locale's alternative numeric symbols.

%w

The weekday as a decimal number (0 [Sunday] – 6). Leading zeros are permitted.

%Ow

The weekday as a number (Sunday=0) using the locale's alternative numeric symbols.

%W

The week number of the year (the first Monday as the first day of week 1) as a decimal number (00 – 53). Leading zeros are permitted.

%OW

The week number of the year (Monday as the first day of the week) using the locale's alternative numeric symbols.

%x

The locale's appropriate date representation.

%Ex

The locale's alternative date representation.

%EX

The locale's alternative time representation.

%X

The locale's appropriate time representation.

%y

The year without century as a decimal number (00– 99).

%Ey

The offset from the base year (%EC) in the locale's alternative representation.

%Oy

The year without the century using the locale's alternative numeric symbols.

%Y

The year with century as a decimal number.

%EY

The locale's full alternative year representation.

%z

The +hhmm or -hhmm numeric timezone (that is, the hour and minute offset from UTC).

%Z

The time-zone name or abbreviation. If time-zone information is not available, no character is output.

%+

The date and time in date format.

%%

Literal % character.

Return Values

x

A pointer to the character following the last character parsed.

NULL

Indicates that an error occurred. The contents of the tm structure are undefined.

Example

#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <locale.h>
#include <errno.h>

#define NUM_OF_DATES  7
#define BUF_SIZE 256

/* This program takes a number of date and time strings and     */
/* converts them into tm structs using strptime().  These tm    */
/* structs are then passed to strftime() which will reverse the */
/* process.  The resulting strings are then compared with the   */
/* originals and if a difference is found then an error is      */
/* displayed.                                                   */

main()
{
int count,
    i;
char buffer[BUF_SIZE];
char *ret_val;
struct tm time_struct;
char dates[NUM_OF_DATES][BUF_SIZE] =
{
    "Thursday 01 January 1970 00:08:20",
    "Tuesday 29 February 1972 08:26:40",
    "Tuesday 31 December 1991 23:59:59",
    "Wednesday 01 January 1992 00:00:00",
    "Sunday 03 May 1992 13:33:20",
    "Monday 04 May 1992 17:20:00",
    "Friday 15 May 1992 03:20:00"};

for (i = 0; i < NUM_OF_DATES; i++) {
    /* Convert to a tm structure */
 ret_val = strptime(dates[i], "%A %d %B %Y %T", &time_struct);

    /* Check the return value */
    if (ret_val == (char *) NULL) {
        perror("strptime");
        exit(EXIT_FAILURE);
    }

    /* Convert the time structure back to a formatted string */
count = strftime(buffer, BUF_SIZE, "%A %d %B %Y %T",&time_struct);

    /* Check the return value */
    if (count == 0) {
        perror("strftime");
        exit(EXIT_FAILURE);
    }

    /* Check the result */
    if (strcmp(buffer, dates[i]) != 0) {
    printf("Error: Converted string differs from the original\n");
    }
    else {
        printf("Successfully converted <%s>\n", dates[i]);
    }
 }
}
Running the example program produces the following result:
Successfully converted <Thursday 01 January 1970 00:08:20>
Successfully converted <Tuesday 29 February 1972 08:26:40>
Successfully converted <Tuesday 31 December 1991 23:59:59>
Successfully converted <Wednesday 01 January 1992 00:00:00>
Successfully converted <Sunday 03 May 1992 13:33:20>
Successfully converted <Monday 04 May 1992 17:20:00>
Successfully converted <Friday 15 May 1992 03:20:00>

strrchr

strrchr — Returns the address of the last occurrence of a given character in a null-terminated string.

Format

#include <string.h>
char *strrchr (const char *str, int character);

Function Variants

The strrchr function has variants named _strrchr32 and _strrchr64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

str

A pointer to a null-terminated character string.

character

An object of type int.

Description

This function returns the address of the last occurrence of a given character in a null-terminated string. The terminating null character is considered to be part of the string.

Compare with strchr, which returns the address of the first occurrence of a given character in a null-terminated string.

Return Values

x

The address of the last occurrence of the specified character.

NULL

Indicates that the character does not occur in the string.

strsep

strsep — Separates strings.

Format

#include <string.h>
char *strsep (char **stringp, char *delim);

Function Variants

The strsep function has variants named _strsep32 and _strsep64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

stringp

A pointer to a pointer to a character string.

delim

A pointer to a string containing characters to be used as delimiters.

Description

The strsep function locates in stringp, the first occurrence of any character in delim (or the terminating '\0' character) and replaces it with a '\0'. The location of the next character after the delimiter character (or NULL, if the end of the string is reached) is stored in the stringp argument. The original value of the stringp argument is returned.

You can detect an "empty" field; one caused by two adjacent delimiter characters, by comparing the location referenced by the pointer returned in the stringp argument to '\0'.

The stringp argument is initially NULL, strsep returns NULL.

Return Values

x

The address of the string pointed to by stringp.

NULL

Indicates that stringp is NULL.

Example

The following example uses strsep to parse a string, containing token delimited by white space, into an argument vector:
char **ap, **argv[10], *inputstring;

for (ap = argv; (*ap = strsep(&inputstring, " \t")) != NULL;)
     if (**ap != '\0')
         ++ap;

strspn

strspn — Returns the length of the prefix of a string that consists entirely of characters from a set of characters.

Format

#include <string.h>
size_t strspn (const char *str, const char *charset);

Arguments

str

A pointer to a character string. If this string is a null string, 0 is returned.

charset

A pointer to a character string containing the characters for which the function will search.

Description

The strspn function scans the characters in the string, stops when it encounters a character not found in charset, and returns the length of the string's initial segment formed by characters found in charset.

Return Value

x

The length of the segment.

strstr

strstr — Locates the first occurrence in the string pointed to by s1 of the sequence of characters in the string pointed to by s2.

Format

#include <string.h>
char *strstr (const char *s1, const char *s2);

Function Variants

The strstr function has variants named _strstr32 and _strstr64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

s1, s2

Pointers to character strings.

Return Values

Pointer

A pointer to the located string.

NULL

Indicates that the string was not found.

Example

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

main()
{
    static char lookin[]="that this is a test was at the end";

    putchar('\n');
    printf("String: %s\n", &lookin[0] );
    putchar('\n');
    printf("Addr: %s\n", &lookin[0] );
    printf("this: %s\n", strstr( &lookin[0] ,"this") );
    printf("that: %s\n", strstr( &lookin[0] , "that" ) );
    printf("NULL: %s\n", strstr( &lookin[0], "" ) );
    printf("was: %s\n", strstr( &lookin[0], "was" ) );
    printf("at: %s\n", strstr( &lookin[0], "at" ) );
    printf("the end: %s\n", strstr( &lookin[0], "the end") );
    putchar('\n');

    exit(0);
}
This example produces the following results: 
$ RUN STRSTR_EXAMPLE
String: that this is a test was at the end
Addr: that this is a test was at the end
this: this is a test was at the end
that: that this is a test was at the end
NULL: that this is a test was at the end
was: was at the end
at: at this is a test was at the end
the end: the end
$

strtod

strtod — Converts a given string to a double-precision number.

Format

#include <stdlib.h>
double strtod (const char *nptr, char **endptr);

Function Variants

The strtod function has variants named _strtod32 and _strtod64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

nptr

A pointer to the character string to be converted to a double-precision number.

endptr

The address of an object where the function can store the address of the first unrecognized character that terminates the scan. If endptr is a NULL pointer, the address of the first unrecognized character is not retained.

Description

The strtod function recognizes an optional sequence of white-space characters (as defined by isspace), then an optional plus or minus sign, then a sequence of digits optionally containing a radix character, then an optional letter (e or E) followed by an optionally signed integer. The first unrecognized character ends the conversion.

The string is interpreted by the same rules used to interpret floating constants.

The radix character is defined the program's current locale (category LC_NUMERIC).

This function returns the converted value. For strtod, overflows are accounted for in the following manner:

  • If the correct value causes an overflow, HUGE_VAL (with a plus or minus sign according to the sign of the value) is returned and errno is set to ERANGE.

  • If the correct value causes an underflow, 0 is returned and errno is set to ERANGE.

If the string starts with an unrecognized character, then the conversion is not performed, *endptr is set to nptr, a 0 value is returned, and errno is set to EINVAL.)

Return Values

x

The converted string.

0
Indicates the conversion could not be performed. errno is set to one of the following:

  • EINVAL - No conversion could be performed.

  • ERANGE - The value would cause an underflow.

  • ENOMEM - Not enough memory available for internal conversion buffer.

±HUGE_VAL

Overflow occurred; errno is set to ERANGE.

strtof

strtof — Converts a string to a float.

Format

#include <stdlib.h>
float strtof (const char * restrict nptr,
char ** restrict endptr);

Function Variants

The strtof function has variants named _strtof32 and _strtof64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Argumants

nptr

A pointer to the character string to be converted.

endptr

If this argument is not NULL, the function stores in it a pointer to the character that follows the last character used in the conversion.

Description

The strtof function converts the initial portion of the string pointed to by nptr to float representation.

First, this function decomposes the input string into three parts: an initial, possibly empty, sequence of white-space characters (as specified by the isspace function); a subject sequence resembling a floating-point constant or representing an infinity or NaN; and a final string of one or more unrecognized characters, including the terminating null character of the input string. Then, it attempts to convert the subject sequence to a floating-point number, and returns the result as a value of type float.

The expected form of the (initial portion of the) string is optional leading white space, an optional plus ('+') or minus sign ('-') and then either (i) a decimal number, or (ii) a hexadecimal number, or (iii) an infinity, or (iv) a NaN (not-a-number).

Return Values

x

The converted value.

±HUGE_VALF

If the correct value is outside the range of representable values of the type, ±HUGE_VALF is returned according to the sign of the value; and errno is set to ERANGE.

n

If the result underflows, the function returns a value whose magnitude is no greater than the smallest normalized positive number; whether errno acquires the value ERANGE is implementation-defined.

0

If no valid conversion could be performed.

strtoimax, strtoumax

strtoimax, strtoumax — Convert a string into an integer.

Format

#include <inttypes.h>
intmax_t strtoimax(const char *nptr, char **endptr, int base);
uintmax_t strtoumax(const char *nptr, char **endptr, int base);

Function Variants

The strtoimax function has variants named _strtoimax32 and _strtoimax64 for use with 32-bit and 64-bit pointer sizes, respectively.

The strtoumax function has variants named _strtoumax32 and _strtoumax64 for use with 32-bit and 64-bit pointer sizes, respectively.

See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

nptr

A pointer to the string to be converted.

endptr

If this argument is not NULL, the function stores in it a pointer to the character that follows the last character used in the conversion.

base

The base of the conversion.

Description

The strtoimax and strtoumax functions convert a string of ASCII characters pointed to by nptr to the appropriate signed and unsigned numeric values. strtoimax is a synonym for strtoll; strtoumax is a synonym for strtoull.

The functions recognize strings in various formats, depending on the value of the base. Any leading white-space characters (as defined by isspace in <ctype.h>) in the given string are ignored. The functions recognize an optional plus or minus sign, then a sequence of digits or letters that may represent an integer constant according to the value of the base. The first unrecognized character ends the conversion and is pointed to by endptr.

If base is 16, leading zeros after the optional sign are ignored, and 0x or 0X is ignored.

If base is 0, the sequence of characters is interpreted by the same rules used to interpret an integer constant: after the optional sign, a leading 0 indicates octal conversion, a leading 0x or 0X indicates hexadecimal conversion, and any other combination of leading characters indicates decimal conversion.

Return Values

n

If successful, the function returns an integer value corresponding to the contents of nptr.

INTMAX_MAX, INTMAX_MIN, UINTMAX_MAX

If the correct value is outside the range of representable values, a range error occurs; errno is set to ERANGE.

0

If no conversion can be performed.

strtok, strtok_r

strtok, strtok_r — Split strings into tokens.

Format

#include <string.h>
char *strtok (char *s1, const char *s2);
char *strtok_r (char *s, const char *sep, char **lasts);

Function Variants

The strtok function has variants named _strtok32 and _strtok64 for use with 32-bit and 64-bit pointer sizes, respectively. Likewise, the strtok_r function has variants named _strtok_r32 and _strtok_r64. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

s1

On the first call, a pointer to a string containing zero or more text tokens. On all subsequent calls for that string, a NULL pointer.

s2

A pointer to a separator string consisting of one or more characters. The separator string may differ from call to call.

s

A null-terminated string that is a sequence of zero or more text tokens separated by spans of one or more characters from the separator string sep.

sep

A null-terminated string of separator characters. This separator string can be different from call to call.

lasts

A pointer that points to a user-provided pointer to stored information needed for strtok_r to continue scanning the same string.

Description

The strtok function locates text tokens in a given string. The text tokens are delimited by one or more characters from a separator string that you specify. The function keeps track of its position in the string between calls and, as successive calls are made, the function works through the string, identifying the text token following the one identified by the previous call.

A token in s1 starts at the first character that is not a character in the separator string s2 and ends either at the end of the string or at (but not including) a separator character.

The first call to the strtok function returns a pointer to the first character in the first token and writes a null character into s1 immediately following the returned token. Each subsequent call (with the value of the first argument remaining NULL) returns a pointer to a subsequent token in the string originally pointed to by s1. When no tokens remain in the string, the strtok function returns a NULL pointer. (This can occur on the first call to strtok if the string is empty or contains only separator characters.)

Since strtok inserts null characters into s1 to delimit tokens, s1 cannot be a const object.

The strtok_r function is the reentrant version of strtok. The function strtok_r considers the null-terminated string s as a sequence of zero or more text tokens separated by spans of one or more characters from the separator string sep. The lasts argument points to a user-provided pointer to stored information needed for strtok_r to continue scanning the same string.

In the first call to strtok_r, s points to a null-terminated string, sep points to a null-terminated string of separator characters, and the value pointed to by lasts is ignored. The strtok_r function returns a pointer to the first character of the first token, writes a null character into s immediately following the returned token, and updates the pointer to which lasts points.

In subsequent calls, s is a NULL pointer and lasts is unchanged from the previous call so that subsequent calls move through the string s, returning successive tokens until no tokens remain. The separator string sep can be different from call to call. When no token remains in s, a NULL pointer is returned.

Return Values

x

A pointer to the first character of the parsed token in the string.

NULL

Indicates that there are no tokens remaining in the string.

Examples

  1. #include <stdio.h>
#include <string.h>

main()
{
    static char str[] = "...ab..cd,,ef.hi";

    printf("|%s|\n", strtok(str, "."));
    printf("|%s|\n", strtok(NULL, ","));
    printf("|%s|\n", strtok(NULL, ",."));
    printf("|%s|\n", strtok(NULL, ",."));
}
    Running this example program produces the following results:
    $ RUN STRTOK_EXAMPLE1
|ab|
|.cd|
|ef|
|hi|
$
  2. #include <stdio.h>
#include <string.h>

main()
{
   char *ptr,
        string[30];

   /* The first character not in the string "-" is "A".  The   */
   /* token ends at "C.                                        */

    strcpy(string, "ABC");
    ptr = strtok(string, "-");
    printf("|%s|\n", ptr);

    /* Returns NULL because no characters not in separator      */
    /* string "-" were found (i.e.  only separator characters   */
    /* were found)                                              */

    strcpy(string, "-");
    ptr = strtok(string, "-");
    if (ptr == NULL)
        printf("ptr is NULL\n");

}
    Running this example program produces the following results:
    $ RUN STRTOK_EXAMPLE2
|abc|
ptr is NULL
$

strtol

strtol — Converts strings of ASCII characters to the appropriate numeric values.

Format

#include <stdlib.h>
long int strtol (const char *nptr, char **endptr, int base);

Function Variants

The strtol function has variants named _strtol32 and _strtol64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

nptr

A pointer to the character string to be converted to a long.

endptr

The address of an object where the function can store a pointer to the first unrecognized character encountered in the conversion process (that is, the character that follows the last character in the string being converted). If endptr is a NULL pointer, the address of the first unrecognized character is not retained.

base

The value, 2 through 36, to use as the base for the conversion.

Description

The strtol function recognizes strings in various formats, depending on the value of the base. This function ignores any leading white-space characters (as defined by isspace in <ctype.h>) in the given string. It recognizes an optional plus or minus sign, then a sequence of digits or letters that may represent an integer constant according to the value of the base. The first unrecognized character ends the conversion.

Leading zeros after the optional sign are ignored, and 0x or 0X is ignored if the base is 16.

If base is 0, the sequence of characters is interpreted by the same rules used to interpret an integer constant: after the optional sign, a leading 0 indicates octal conversion, a leading 0x or 0X indicates hexadecimal conversion, and any other combination of leading characters indicates decimal conversion.

Truncation from long to int can take place after assignment or by an explicit cast (arithmetic exceptions not withstanding). The function call atol (str) is equivalent to strtol (str,(char**)NULL, 10).

Return Values

x

The converted value.

LONG_MAX or LONG_MIN

Indicates that the converted value would cause an overflow.

0

Indicates that the string starts with an unrecognized character or that the value for base is invalid. If the string starts with an unrecognized character, *endptr is set to nptr.

strtold

strtold — Converts a string to a long double.

Format

#include <stdlib.h>
long double strtold (const char * restrict nptr,
char ** restrict endptr);

Function Variants

The strtold function has variants named _strtold32 and _strtold64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

nptr

A pointer to the character string to be converted.

endptr

If this argument is not NULL, the function stores in it a pointer to the character that follows the last character used in the conversion.

Description

The strtold function converts the initial portion of the string pointed to by nptr to long double representation.

First, this function decomposes the input string into three parts: an initial, possibly empty, sequence of white-space characters (as specified by the isspace function); a subject sequence resembling a floating-point constant or representing an infinity or NaN; and a final string of one or more unrecognized characters, including the terminating null character of the input string. Then, it attempts to convert the subject sequence to a floating-point number, and returns the result as a value of type long double.

The expected form of the (initial portion of the) string is optional leading white space, an optional plus ('+') or minus sign ('-') and then either (i) a decimal number, or (ii) a hexadecimal number, or (iii) an infinity, or (iv) a NaN (not-a-number).

Return Values

x

The converted value.

±HUGE_VALF

If the correct value is outside the range of representable values of the type, ±HUGE_VALL is returned according to the sign of the value; and errno is set to ERANGE.

n

If the result underflows, the function returns a value whose magnitude is no greater than the smallest normalized positive number; whether errno acquires the value ERANGE is implementation-defined.

0

If no valid conversion could be performed.

strtoq, strtoll

strtoq, strtoll — Convert strings of ASCII characters to the appropriate numeric values. strtoll is a synonym for strtoq.

Format

#include <stdlib.h>
__int64 strtoq (const char *nptr, char **endptr, int base);
__int64 strtoll (const char *nptr, char **endptr, int base);

Function Variants

These functions have variants named _strtoq32, _strtoll32 and _strtoq64, _strtoll64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

nptr

A pointer to the character string to be converted to an __int64.

endptr

The address of an object where the function can store a pointer to the first unrecognized character encountered in the conversion process (that is, the character that follows the last character in the string being converted). If endptr is a NULL pointer, the address of the first unrecognized character is not retained.

base

The value, 2 through 36, to use as the base for the conversion.

Description

The strtoq and strtoll functions recognize strings in various formats, depending on the value of the base. Any leading white-space characters (as defined by isspace in <ctype.h>) in the given string are ignored. The functions recognize an optional plus or minus sign, then a sequence of digits or letters that may represent an integer constant according to the value of the base. The first unrecognized character ends the conversion.

Leading zeros after the optional sign are ignored, and 0x or 0X is ignored if the base is 16.

If base is 0, the sequence of characters is interpreted by the same rules used to interpret an integer constant: after the optional sign, a leading 0 indicates octal conversion, a leading 0x or 0X indicates hexadecimal conversion, and any other combination of leading characters indicates decimal conversion.

The function call atoq (str) is equivalent to strtoq (str, (char**)NULL, 10).

Return Values

x

The converted value.

__INT64_MAX or __INT64_MIN

Indicates that the converted value would cause an overflow.

0

Indicates that the string starts with an unrecognized character or that the value for base is invalid. If the string starts with an unrecognized character, *endptr is set to nptr.

strtoul

strtoul — Converts the initial portion of the string pointed to by nptr to an unsigned long integer.

Format

#include <stdlib.h>
unsigned long int strtoul (const char *nptr, char **endptr, int base);

Function Variants

The strtoul function has variants named _strtoul32 and _strtoul64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

nptr

A pointer to the character string to be converted to an unsigned long.

endptr

The address of an object where the function can store a pointer to a pointer to the first unrecognized character encountered in the conversion process (that is, the character that follows the last character in the string being converted). If endptr is a NULL pointer, the address of the first unrecognized character is not retained.

base

The value, 2 through 36, to use as the base for the conversion. Leading zeros after the optional sign are ignored, and 0x or 0X is ignored if the base is 16.

If the base is 0, the sequence of characters is interpreted by the same rules used to interpret an integer constant: after the optional sign, a leading 0 indicates octal conversion, a leading 0x or 0X indicates hexadecimal conversion, and any other combination of leading characters indicates decimal conversion.

Return Values

x

The converted value.

0

Indicates that the string starts with an unrecognized character or that the value for base is invalid. If the string starts with an unrecognized character, *endptr is set to nptr.

ULONG_MAX

Indicates that the converted value would cause an overflow.

strtouq, strtoull

strtouq, strtoull — Convert the initial portion of the string pointed to by nptr to an unsigned __int64 integer. strtoull is a synonym for strtouq.

Format

#include <stdlib.h>
unsigned __int64 strtouq const char *nptr, char **endptr, int base);
unsigned __int64 strtoull (const char *nptr, char **endptr, int base);

Function Variants

These functions have variants named _strtouq32, _strtoull32 and _strtouq64, _strtoull64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

nptr

A pointer to the character string to be converted to an unsigned __int64.

endptr

The address of an object where the function can store a pointer to a pointer to the first unrecognized character encountered in the conversion process (that is, the character that follows the last character in the string being converted). If endptr is a NULL pointer, the address of the first unrecognized character is not retained.

base

The value, 2 through 36, to use as the base for the conversion. Leading zeros after the optional sign are ignored, and 0x or 0X is ignored if the base is 16.

If the base is 0, the sequence of characters is interpreted by the same rules used to interpret an integer constant: after the optional sign, a leading 0 indicates octal conversion, a leading 0x or 0X indicates hexadecimal conversion, and any other combination of leading characters indicates decimal conversion.

Return Values

x

The converted value.

0

Indicates that the string starts with an unrecognized character or that the value for base is invalid. If the string starts with an unrecognized character, *endptr is set to nptr.

__UINT64_MAX

Indicates that the converted value would cause an overflow.

strxfrm

strxfrm — Changes a string such that the changed string can be passed to the strcmp function, and produce the same result as passing the unchanged string to the strcoll function.

Format

#include <string.h>
size_t strxfrm (char *s1, const char *s2, size_t maxchar);

Arguments

s1, s2

Pointers to character strings.

maxchar

The maximum number of bytes (including the null terminator) to be stored in s1.

Description

The strxfrm function transforms the string pointed to by s2, and stores the resulting string in the array pointed to by s1. No more than maxchar bytes, including the null terminator, are placed into the array pointed to by s1.

If the value of maxchar is less than the required size to store the transformed string (including the terminating null), the contents of the array pointed to by s1 is indeterminate. In such a case, the function returns the size of the transformed string.

If maxchar is 0, then s1 is allowed to be a NULL pointer, and the function returns the required size of the s1 array before making the transformation.

The string comparison functions, strcoll and strcmp, can produce different results given the same two strings to compare. The reason for this is that strcmp does a straightforward comparison of the code point values of the characters in the strings, whereas strcoll uses the locale information to do the comparison. Depending on the locale, the strcoll comparison can be a multipass operation, which is slower than strcmp.

The purpose of the strxfrm function is to transform strings in such a way that if you pass two transformed strings to the strcmp function, the result is the same as passing the two original strings to the strcoll function. The strxfrm function is useful in applications that need to do a large number of comparisons on the same strings using strcoll. In this case, it might be more efficient (depending on the locale) to transform the strings once using strxfrm, and then do comparisons using strcmp.

Return Value

x

Length of the resulting string pointed to by s1, not including the terminating null character.

No return value is reserved for error indication. However, the function can set errno to EINVAL – The string pointed to by s2 contains characters outside the domain of the collating sequence.

Example

/* This program verifies that two transformed strings when      */
/* passed through strxfrm and then compared, provide the same   */
/* result as if passed through strcoll without any              */
/* transformation.

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <locale.h>

#define  BUFF_SIZE  256

main()
{
   char string1[BUFF_SIZE];
   char string2[BUFF_SIZE];
   int errno;
   int coll_result;
   int strcmp_result;
   size_t strxfrm_result1;
   size_t strxfrm_result2;

   /* setlocale to French locale */

   if (setlocale(LC_ALL, "fr_FR.ISO8859-1") == NULL) {
       perror("setlocale");
       exit(EXIT_FAILURE);
   }

   /* collate string 1 and string 2 and store the result */

   errno = 0;
   coll_result = strcoll("<a`>bcd", "abcz");
   if (errno) {
       perror("strcoll");
       exit(EXIT_FAILURE);
   }

   else {
       /* Transform the strings (using strxfrm) into string1   */
       /* and string2                                          */

       strxfrm_result1 = strxfrm(string1, "<a`>bcd", BUFF_SIZE);

       if (strxfrm_result1 == ((size_t) - 1)) {
           perror("strxfrm");
           exit(EXIT_FAILURE);
       }

       else if (strxfrm_result1 > BUFF_SIZE) {
           perror("\n** String is too long **\n");
           exit(EXIT_FAILURE);
       }

       else {
           strxfrm_result2 = strxfrm(string2, "abcz", BUFF_SIZE);
           if (strxfrm_result2 == ((size_t) - 1)) {
               perror("strxfrm");
               exit(EXIT_FAILURE);
           }

           else if (strxfrm_result2 > BUFF_SIZE) {
               perror("\n** String is too long **\n");
               exit(EXIT_FAILURE);
           }

           /* Compare the two transformed strings and verify   */
           /* that the result is the same as the result from   */
           /* strcoll on the original strings                  */
           else {
               strcmp_result = strcmp(string1, string2);
               if (strcmp_result == 0 && (coll_result == 0)) {
                   printf("\nReturn value from strcoll() and "
                     "return value from strcmp() are both zero.");
                  printf("\nThe program was successful\n\n");
               }

               else if ((strcmp_result < 0) && (coll_result < 0)) {
                   printf("\nReturn value from strcoll() and "
                "return value from strcmp() are less than zero.");
                   printf("\nThe program successful\n\n");
               }

               else if ((strcmp_result > 0) && (coll_result > 0)) {
                   printf("\nReturn value from strcoll() and "
             "return value from strcmp() are greater than zero.");
                   printf("\nThe program was successful\n\n");
               }

               else {
               printf("** Error **\n");
               printf("\nReturn values are not of the same type");
               }
            }
        }
   }
}
Running the example program produces the following result:
Return value from strcoll() and return value
               from strcmp() are less than zero.
The program was successful

subwin

subwin — Creates a new subwindow with numlines lines and numcols columns starting at the coordinates (begin_y, begin_x) on the terminal screen.

Format

#include <curses.h>
WINDOW *subwin (WINDOW *win, int numlines, int numcols, int begin_y,
int begin_x);

Arguments

win

A pointer to the parent window.

numlines

The number of lines in the subwindow. If numlines is 0, then the function sets that dimension to LINES - begin_y. To get a subwindow of dimensions LINES by COLS, use the following format: 
subwin (win, 0, 0, 0, 0)

numcols

The number of columns in the subwindow. If numcols is 0, then the function sets that dimension to COLS - begin_x. To get a subwindow of dimensions LINES by COLS, use the following format:
subwin (win, 0, 0, 0, 0)

begin_y

A window coordinate at which the subwindow is to be created.

begin_x

A window coordinate at which the subwindow is to be created.

Description

When creating the subwindow, begin_y and begin_x are relative to the entire terminal screen. If either numlines or numcols is 0, then the subwin function sets that dimension to (LINES - begin_y) or (COLS - begin_x), respectively.

The window pointed to by win must be large enough to contain the entire area of the subwindow. Any changes made to either window within the coordinates of the subwindow appear on both windows.

Return Values

window pointer

A pointer to an instance of the structure window corresponding to the newly created subwindow.

ERR

Indicates an error.

swab

swab — Swaps bytes.

Format

#include <unistd.h>
void swab (const void *src, void *dest, ssize_t nbytes);

Arguments

src

A pointer to the location of the string to copy.

dest

A pointer to where you want the results copied.

nbytes

The number of bytes to copy. Make this argument an even value. When it is an odd value, the swab function uses nbytes -1 instead.

Description

The swab function copies the number of bytes specified by nbytes from the location pointed to by srcto the array pointed to by dest. The function then exchanges adjacent bytes. If a copy takes place between objects that overlap, the result is undefined.

swprintf

swprintf — Writes output to an array of wide characters under control of the wide-character format string.

Format

#include <wchar.h>
int swprintf (wchar_t *s, size_t n, const wchar_t *format, ...);

Arguments

s

A pointer to the resulting wide-character sequence.

n

The maximum number of wide characters that can be written to an array pointed to by s, including a terminating null wide character.

format

A pointer to a wide-character string containing the format specifications. For more information about format and conversion specifications and their corresponding arguments, see Chapter 2.

. . .

Optional expressions whose resultant types correspond to conversion specifications given in the format specification.

If no conversion specifications are given, the output sources can be omitted. Otherwise, the function calls must have exactly as many output sources as there are conversion specifications, and the conversion specifications must match the types of the output sources.

Conversion specifications are matched to output sources in left-to-right order. Excess output pointers, if any, are ignored.

Description

The swprintf function is equivalent to the fwprintf function, except that the first argument specifies an array of wide characters instead of a stream.

No more than n wide characters are written, including a terminating null wide character, which is always added (unless n is 0).

See also fwprintf.

Return Values

x

The number of wide characters written, not counting the terminating null wide character.

Negative value

Indicates an error. Either n or more wide characters were requested to be written, or a conversion error occurred, in which case errno is set to EILSEQ.

swscanf

swscanf — Reads input from a wide-character string under control of the wide-character format string.

Format

#include <wchar.h>
int swscanf (const wchar_t *s, const wchar_t *format, ...);

Arguments

s

A pointer to a wide-character string from which the input is to be obtained.

format

A pointer to a wide-character string containing the format specifications. For more information about format and conversion specifications and their corresponding arguments, see Chapter 2.

. . .

Optional expressions whose results correspond to conversion specifications given in the format specification.

If no conversion specifications are given, you can omit the input pointers. Otherwise, the function calls must have exactly as many input pointers as there are conversion specifications, and the conversion specifications must match the types of the input pointers.

Conversion specifications are matched to input sources in left-to-right order. Excess input pointers, if any, are ignored.

Description

The swscanf function is equivalent to the fwscanf function, except that the first argument specifies a wide-character string rather than a stream. Reaching the end of the wide-character string is the same as encountering EOF for the fwscanf function.

See also fwscanf.

Return Values

x

The number of input items assigned, sometimes fewer than provided for, or even 0 in the event of an early matching failure.

EOF

Indicates an error. An input failure occurred before any conversion.

sysconf

sysconf — Gets configurable system variables.

Format

#include <unistd.h>
long int sysconf (int name);

Argument

name

Specifies the system variable to be queried.

Description

The sysconf function provides a method for determining the current value of a configurable system limit or whether optional features are supported.

You supply a symbolic constant in the name argument, and sysconf returns a value for the corresponding system variable:

  • The symbolic constants defined in the <unistd.h> header file.

  • The system variables are defined in the <limits.h> and <unistd.h> header files.

Table 42 lists the system variables returned by the sysconf function, and the symbolic constants that you can supply as the name value.
Table 42. sysconf Argument and Return Values

System Variable Returned

Symbolic Constant for name

Meaning

ISO POSIX-1

ARG_MAX

_SC_ARG_MAX

The maximum length, in bytes, of the arguments for one of the exec functions, including environment data.

CHILD_MAX

_SC_CHILD_MAX

The maximum number of simultaneous processes for each real user ID.

CLK_TCK

_SC_CLK_TCK

The number of clock ticks per second. The value of CLK_TCK can be variable. Do not assume that CLK_TCK is a compile-time constant.

NGROUPS_MAX

_SC_NGROUPS_MAX

The maximum number of simultaneous supplementary group IDs for each process.

OPEN_MAX

_SC_OPEN_MAX

The maximum number of files that one process can have open at one time.

STREAM_MAX

_SC_STREAM_MAX

The number of streams that one process can have open at one time.

TZNAME_MAX

_SC_TZNAME_MAX

The maximum number of bytes supported for the name of a time zone (not the length of the TZ environmental variable).

_POSIX_JOB_CONTROL

_SC_JOB_CONTROL

This variable has a value of 1 if the system supports job control; otherwise, -1 is returned.

_POSIX_SAVED_IDS

_SC_SAVED_IDS

This variable has a value of 1 if each process has a saved set user ID and a saved set group ID; otherwise, -1 is returned.

_POSIX_VERSION

_SC_VERSION

The date of approval of the most current version of the POSIX-1 standard that the system supports. The date is a 6-digit number, with the first 4 digits signifying the year and the last 2 digits the month.

If _POSIX_VERSION is not defined, -1 is returned.

Different versions of the POSIX-1 standard are periodically approved by the IEEE Standards Board, and the date of approval is used to distinguish between different versions.

ISO POSIX-2

BC_BASE_MAX

_SC_BC_BASE_MAX

The maximum value allowed for the obase variable with the bc command.

BC_DIM_MAX

_SC_BC_DIM_MAX

The maximum number of elements permitted in an array by the bc command.

BC_SCALE_MAX

_SC_BC_SCALE_MAX

The maximum value allowed for the scale variable with the bc command.

BC_STRING_MAX

_SC_BC_STRING_MAX

The maximum length of string constants accepted by the bc command.

COLL_WEIGHTS_MAX

_SC_COLL_WEIGHTS_
MAX

The maximum number of weights that can be assigned to an entry in the LC_COLLATE locale-dependent information in a locale definition file.

EXPR_NEST_MAX

_SC_EXPR_NEST_MAX

The maximum number of expressions that you can nest within parentheses by the expr command.

LINE_MAX

_SC_LINE_MAX

The maximum length, in bytes, of a command input line (either standard input or another file) when the utility is described as processing text files. The length includes room for the trailing new-line character.

RE_DUP_MAX

_SC_RE_DUP_MAX

The maximum number of repeated occurrences of a regular expression permitted when using the interval notation arguments, such as the m and n arguments with the ed command.

_POSIX2_CHAR_TERM

_SC_2_CHAR_TERM

This variable has a value of 1 if the system supports at least one terminal type; otherwise, -1 is returned.

_POSIX2_C_BIND

_SC_2_C_BIND

This variable has a value of 1 if the system supports the C language binding option; otherwise, -1 is returned.

_POSIX2_C_DEV

_SC_2_C_DEV

This variable has a value of 1 if the system supports the optional C Language Development Utilities from the ISO POSIX-2 standard; otherwise, -_POSIX_THREAD_ATTR_STAC_ KSSCI_ZT1 is returned.

_POSIX2_C_VERSION

_SC_2_C_VERSION

Integer value indicating the version of the ISO POSIX-2 standard (C language binding). It changes with each new version of the ISO POSIX-2 standard.

_POSIX2_VERSION

_SC_2_VERSION

Integer value indicating the version of the ISO POSIX-2 standard (Commands). It changes with each new version of the ISO POSIX-2 standard.

_POSIX2_FORT_DEV

_SC_2_FORT_DEV

The variable has a value of 1 if the system supports the Fortran Development Utilities Option from the ISO POSIX-2 standard; otherwise, -1 is returned.

_POSIX2_FORT_RUN

_SC_2_FORT_RUN

The variable has a value of 1 if the system supports the Fortran Runtime Utilities Option from the ISO POSIX-2 standard; otherwise, -1 is returned.

_POSIX2_LOCALEDEF

_SC_2_LOCALEDEF

The variable has a value of 1 if the system supports the creation of new locales with the localedef command; otherwise, -1 is returned.

_POSIX2_SW_DEV

_SC_2_SW_DEV

The variable has a value of 1 if the system supports the Software Development Utilities Option from the ISO POSIX-2 standard; otherwise, -1 is returned.

_POSIX2_UPE

_SC_2_UPE

The variable has a value of 1 if the system supports the User Portability Utilities Option; otherwise, -1 is returned.

POSIX 1003.1c-1995

_POSIX_THREADS

_SC_THREADS

This variable has a value of 1 if the system supports POSIX threads; otherwise, -1 is returned.

_POSIX_THREAD_ATTR

_STACKSIZE

_SC_THREAD_ATTR

_STACKSIZE

This variable has a value of 1 if the system supports the POSIX threads stack size attribute; otherwise, -1 is returned.

_POSIX_THREAD_
PRIORITY

_SCHEDULING

_SC_THREAD_
PRIORITY

_SCHEDULING

The 1003.1c implementation supports the real time scheduling functions.

_POSIX_THREAD_SAFE_
FUNCTIONS

_SC_THREAD_SAFE

_FUNCTIONS

TRUE if the implementation supports the thread-safe ANSI C functions in POSIX 1003.1c.

PTHREAD_DESTRUCTOR

_ITERATIONS

_SC_THREAD_

DESTRUCTOR_
ITERATIONS

When a thread terminates, DECthreads iterates through all non-NULL thread-specific data values in the thread, and calls a registered destructor routine (if any) for each. It is possible for a destructor routine to create new values for one or more thread-specific data keys. In that case, DECthreads goes through the entire process again.

_SC_THREAD_DESTRUCTOR_ ITERATIONS is the maximum number of times the implementation loops before it terminates the thread even if there are still non-NULL values.

PTHREAD_KEYS_MAX

_SC_THREAD_KEYS_
MAX

The maximum number of thread-specific data keys that an application can create.

PTHREAD_STACK_MIN

_SC_THREAD_STACK_
MIN

The minimum allowed size of a stack for a new thread. Any lower value specified for the "stacksize" thread attribute is rounded up.

UINT_MAX

_SC_THREAD_THREADS

_MAX

The maximum number of threads an application is allowed to create. Since DECthreads does not enforce any fixed limit, this value is -1.

X/Open

_XOPEN_VERSION

_SC_XOPEN_VERSION

An integer indicating the most current version of the X/Open standard that the system supports.

PASS_MAX

_SC_PASS_MAX

Maximum number of significant bytes in a password (not including terminating null).

XOPEN_CRYPT

_SC_XOPEN_CRYPT

This variable has a value of 1 if the system supports the X/Open Encryption Feature Group; otherwise, -1 is returned.

XOPEN_ENH_I18N

_SC_XOPEN_ENH_I18N

This variable has a value of 1 if the system supports the X/Open enhanced Internationalization Feature Group; otherwise, -1 is returned.

XOPEN_SHM

_SC_XOPEN_SHM

This variable has a value of 1 if the system supports the X/Open Shared Memory Feature Group; otherwise, -1 is returned.

X/Open Extended

ATEXIT_MAX

_SC_ATEXIT_MAX

The maximum number of functions that you can register with atexit per process.

PAGESIZE

_SC_PAGESIZE

Size, in bytes, of a page.

PAGE_SIZE

_SC_PAGE_SIZE

Same as PAGESIZE. If either PAGESIZE or PAGE_SIZE is defined, the other is defined with the same value.

IOV_MAX

_SC_IOV_MAX

Maximum number of iovec structures that one process has available for use with readv or writev.

XOPEN_UNIX

_SC_XOPEN_UNIX

This variable has a value of 1 if the system supports the X/Open CAE Specification, August 1994, System Interfaces and Headers, Issue 4, Version 2,(ISBN: 1-85912-037-7, C435); otherwise, -1 is returned.

Other

N/A

_SC_CPU_CHIP_TYPE

Returns information for the processor type. See the description after this table.

For the _SC_CPU_CHIP_TYPE symbolic constant:

  • On Alpha servers, sysconf returns the architecture type (2), as given by the $GETSYI system service.

  • Integrity processor information is stored in CPUID register 3. This register contains a 64-bit integer divided into 1-byte fields indicating version information related to the processor implementation. The sysconf function returns the low-order longword with the following information:
    31     24 23    16 15    8 7     0
----------------------------------
| family | model  | rev   |number|
----------------------------------
These fields are described in the following table:

Field

Bits

Description

number

7:0

Index of the largest implemented CPUID register (one less than the number of implemented CPUID registers). This value will be at least 4.

rev

15:8

Processor revision number. An 8-bit value that represents the revision or stepping of this processor implementation within the processor model.

model

23:16

Processor model number. A unique 8-bit value representing the processor model within the processor family.

family

31:24

Processor family number. A unique 8-bit value representing the processor family.

Return Values

x

The current variable value on the system. The value does not change during the lifetime of the calling process.

-1

Indicates an error.

If the value of the name argument is invalid, errno is set to indicate the error.

If the value of the name argument is undefined, errno is unchanged.

system

system — Passes a given string to the host environment to be executed by a command processor. This function is non-reentrant.

Format

#include <stdlib.h>
int system (const char *string);

Argument

string

A pointer to the string to be executed. If string is NULL, a nonzero value is returned. The string is a DCL command, not the name of an image. To execute an image, use one of the exec routines.

Description

The system function spawns a subprocess and executes the command specified by string in that subprocess. The system function waits for the subprocess to complete before returning the subprocess status as the return value of the function.

The subprocess is spawned within the system call by a call to vfork. Because of this, a call to system should not be made after a call to vfork and before the corresponding call to an exec function.

For OpenVMS Version 7.0 and higher systems, if you include <stdlib.h> and compile with the _POSIX_EXIT feature-test macro set, then the system function returns the status as if it called waitpid to wait for the child. Therefore, use the WIFEXITED and WEXITSTATUS macros (described in the wait* routines) to retrieve the exit status in the range of 0 to 255.

You set the _POSIX_EXIT feature-test macro by using /DEFINE=_POSIX_EXIT or #define _POSIX_EXIT at the top of your file, before any file inclusions.

Return Value

nonzero value

If string is NULL, a value of 1 is returned, indicating that the system function is supported. If string is not NULL, the value is the subprocess OpenVMS return status.

Example

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>     /* write, close */
#include <fcntl.h>      /* Creat */

main()
{
    int status,
        fd;

    /* Creat a file we are sure is there        */

    fd = creat("system.test", 0);
    write(fd, "this is an example of using system", 34);
    close(fd);

    if (system(NULL)) {
        status = system("DIR/NOHEAD/NOTRAIL/SIZE SYSTEM.TEST");
        printf("system status = %d\n", status);
    }
    else
        printf("system() not supported.\n");
}
Running this example program produces the following result:
DISK3$:[JONES.CRTL.2059.SRC]SYSTEM.TEST;1
                           1
system status = 1

tan

tan — Returns a double value that is the tangent of its radian argument.

Format

#include <math.h>
double tan (double x);
float tanf (float x);
long double tanl (long double x);
double tand (double x);
float tandf (float x);
long double tandl (long double x);

Argument

x

A radian expressed as a real number.

Description

The tan functions compute the tangent of x, measured in radians.

The tand functions compute the tangent of x, measured in degrees.

Return Values

x

The tangent of the argument.

HUGE_VAL

x is a singular point (. . . -3 π/2, - π/2, π/2 . . .).

NaN

x is NaN; errno is set to EDOM.

0

x is ±Infinity; errno is set to EDOM.

±HUGE_VAL

Overflow occurred; errno is set to ERANGE.

0

Underflow occurred; errno is set to ERANGE.

tanh

tanh — Returns the hyperbolic tangent of its argument.

Format

#include <math.h>
double tanh (double x);
float tanhf (float x);
long double tanhl (long double x);

Argument

x

A real number.

Description

The tanh functions return the hyperbolic tangent their argument, calculated as (e** x - e**( - x))/(e**x + e**( - x)).

Return Values

n

The hyperbolic tangent of the argument.

HUGE_VAL

The argument is too large; errno is set to ERANGE.

NaN

x is NaN; errno is set to EDOM.

0

Underflow occurred; errno is set to ERANGE.

telldir

telldir — Returns the current location associated with a specified directory stream. Performs operations on directories.

Format

#include <dirent.h>
long int telldir (DIR *dir_pointer);

Argument

dir_pointer

A pointer to the DIR structure of an open directory.

Description

The telldir function returns the current location associated with the specified directory stream.

Return Values

x

The current location.

-1

Indicates an error and is further specified in the global errno.

tempnam

tempnam — Constructs the name for a temporary file.

Format

#include <stdio.h>
char *tempnam (const char *directory, const char *prefix, ...;)

Arguments

directory

A pointer to the pathname of the directory where you want to create a file.

prefix

A pointer to an initial character sequence of the filename. The prefix argument can be null, or it can point to a string of up to five characters used as the first characters of the temporary filename.

. . .

An optional argument that can be either 1 or 0. If you specify 1, tempnam returns the file specification in OpenVMS format. If you specify 0, tempnam returns the file specification in UNIX style format. For more information about UNIX style directory specifications, see Section 1.3.3.

Description

The tempnam function generates filenames for temporary files. It allows you to control the choice of a directory.

If the directory argument is null or points to a string that is not a pathname for an appropriate directory, the pathname defined as P_tmpdir in the <stdio.h> header file is used. For programs running under a detached process, the directory argument cannot be null.

You can bypass the selection of a pathname by providing the TMPDIR environment variable in the user environment. The value of the TMPDIR variable is a pathname for the desired temporary file directory.

Use the prefix argument to specify a prefix of up to five characters for the temporary filename.

The tempnam function returns a pointer to the generated pathname, suitable for use in a subsequent call to the free function.

See also free.

Note

In contrast to tmpnam, tempnam does not have to generate a different filename on each call. tempnam generates a new filename only if the file with the specified name exists. If you need a unique filename on each call, use tmpnam instead of tempnam.

Return Values

x

A pointer to the generated pathname, suitable for use in a subsequent call to the free function.

NULL

An error occurred; errno is set to indicate the error.

tgamma

tgamma — Returns the gamma function of its argument.

Format

#include <math.h>
double tgamma (double x);
float tgammaf (float x);
long double tgammal (long double x);

Argument

x

A real value.

Description

The tgamma functions compute the gamma function of x.

Return Values

n

Upon success, the gamma function of x.

-1

If x is negative. errno is set to EDOM.

±HUGE_VAL

Overflow occurred or x is ±0. errno is set to ERANGE.

NaN

If x is NaN or -Inf. errno is set to EDOM.

x

If x is +Inf.

time

time — Returns the time (expressed as Universal Coordinated Time) elapsed since 00:00:00, January 1, 1970, in seconds.

Format

#include <time.h>
time_t time (time_t *time_location);

Function Variants

Compiling with the _DECC_V4_SOURCE and _VMS_V6_SOURCE feature-test macros defined enables a local-time-based entry point to the time function that is equivalent to the behavior before OpenVMS Version 7.0.

Argument

time_location

Either NULL or a pointer to the place where the returned time is also stored. The time_t type is defined in the <time.h> header file as follows:
typedef unsigned long int time_t;

Return Values

x

The time elapsed past the Epoch.

(time_t)(-1)

Indicates an error. If the value of SYS$TIMEZONE_DIFFERENTIAL logical is wrong, the function will fail with errno set to EINVAL.

times

times — Passes back the accumulated times of the current process and its terminated child processes.

Format

#include <times.h>
clock_t times (struct tms *buffer); (OpenVMS V7.0 and higher)
void times (tbuffer_t *buffer); (pre OpenVMS V7.0)

Argument

buffer

A pointer to the terminal buffer.

Description

For both process and children times, the structure breaks down the time by user and system time. Since the OpenVMS system does not differentiate between system and user time, all system times are returned as 0. Accumulated CPU times are returned in 10-millisecond units.

Only the accumulated times for child processes running a C main program or a program that calls VAXC$CRTL_INIT or DECC$CRTL_INIT are included.

On OpenVMS Version 7.0 and higher systems, the times function returns the elapsed real time in clock ticks since an arbitrary reference time in the past (for example, system startup time). This reference time does not change from one times function call to another. The return value can overflow the possible range of type clock_t values. When times fails, it returns a value of -1. The C RTL uses system-boot time as its reference time.

Return Values

x

The elapsed real time in clock ticks since system-boot time.

(clock_t)(-1)

Indicates an error.

tmpfile

tmpfile — Creates a temporary file that is opened for update.

Format

#include <stdio.h>
FILE *tmpfile (void);

Description

The file exists only for the duration of the process, or until the file is closed and is preserved across calls to vfork.

Return Values

x

The address of a file pointer (defined in the <stdio.h> header file).

NULL

Indicates an error.

tmpnam

tmpnam — Generates filenames that can be safely used for a temporary file.

Format

#include <stdio.h>
char *tmpnam (char *name);

Function Variants

The tmpnam function has variants named _tmpnam32 and _tmpnam64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Argument

name

A character string containing a name to use in place of file-name arguments in functions or macros. Successive calls to tmpnam with a null argument cause the function to overwrite the current name.

Return Value

x

If the name argument is the NULL pointer value NULL, tmpnam returns the address of an internal storage area. If name is not NULL, then it is considered the address of an area of length L_tmpnam (defined in the <stdio.h> header file). In this case, tmpnam returns the name argument as the result.

toascii

toascii — Converts its argument, an 8-bit ASCII character, to a 7-bit ASCII character.

Format

#include <ctype.h>
int toascii (char character);

Argument

character

An object of type char.

Return Value

x

A 7-bit ASCII character.

tolower

tolower — Converts a character to lowercase.

Format

#include <ctype.h>
int tolower (int character);

Argument

character

An object of type int representable as an unsigned char or the value of EOF. For any other value, the behavior is undefined.

Description

If the argument represents an uppercase letter, and there is a corresponding lowercase letter, as defined by character type information in the program locale category LC_CTYPE, the corresponding lowercase letter is returned.

If the argument is not an uppercase character, it is returned unchanged.

Return Value

x

The lowercase letter corresponding to the argument. Or, the unchanged argument, if it is not an uppercase character.

_tolower

_tolower — Converts an uppercase character to lowercase.

Format

#include <ctype.h>
int _tolower (int character);

Argument

character

This argument must be an uppercase letter.

Description

The _tolower macro is equivalent to the tolower function except that its argument must be an uppercase letter (not lowercase, not EOF).

As of OpenVMS Version 8.3 and to comply with the C99 ANSI standard and X/Open Specification, the _tolower macro by default does not evaluate its parameter more than once. It simply calls the tolower function. This avoids side effects (such as i++ or function calls) where the user can tell how many times an expression is evaluated.

To keep the older, optimized _tolower macro behavior, compile with /DEFINE=_FAST_TOUPPER. Then, as in previous releases, _tolower optimizes the call to avoid the overhead of a runtime call. The parameters are checked to determine how to calculate the result, thereby creating unwanted side effects. Therefore, when compiling with /DEFINE=_FAST_TOUPPER, do not use the _tolower macro with arguments that contain side-effect operations. For instance, the following example will not return the expected result:
d = _tolower (C++);

Return Value

x

The lowercase letter corresponding to the argument.

touchwin

touchwin — Places the most recently edited version of the specified window on the terminal screen.

Format

#include <curses.h>
int touchwin (WINDOW *win);

Argument

win

A pointer to the window.

Description

The touchwin function is normally used only to refresh overlapping windows.

Return Values

OK

Indicates success.

ERR

Indicates an error.

toupper

toupper — Converts a character to uppercase.

Format

#include <ctype.h>
int toupper (int character);

Argument

character

An object of type int representable as an unsigned char or the value of EOF. For any other value, the behavior is undefined.

Description

If the argument represents a lowercase letter, and there is a corresponding uppercase letter, as defined by character type information in the program locale category LC_CTYPE, the corresponding uppercase letter is returned.

If the argument is not a lowercase character, it is returned unchanged.

Return Value

x

The uppercase letter corresponding to the argument. Or, the unchanged argument, if the argument is not a lowercase character.

_toupper

_toupper — Converts a lowercase character to uppercase.

Format

#include <ctype.h>
int _toupper (int character);

Argument

character

This argument must be a lowercase letter.

Description

The _toupper macro is equivalent to the toupper function except that its argument must be a lowercase letter (not uppercase, not EOF).

As of OpenVMS Version 8.3 and to comply with the C99 ANSI standard and X/Open Specification, the _toupper macro by default does not evaluate parameters more than once. It simply calls the toupper function. This avoids side effects (such as i++ or function calls) where the user can tell how many times an expression is evaluated.

To keep the older, optimized _toupper macro behavior, compile with /DEFINE=_FAST_TOUPPER. Then, as in previous releases, _toupper optimizes the call to avoid the overhead of a runtime call. The parameters are checked to determine how to calculate the result, thereby creating unwanted side effects. So when compiling with /DEFINE=_FAST_TOUPPER, do not use the _toupper macro with arguments that contain side-effect operations. For instance, the following example will not return the expected result:
d = _toupper (c++);

Return Value

x

The uppercase letter corresponding to the argument.

towctrans

towctrans — Maps one wide character to another according to a specified mapping descriptor.

Format

#include <wctype.h>
wint_t towctrans (wint_t wc, wctrans_t desc);

Arguments

wc

The wide character that you want to map.

desc

Description of the mapping obtained through a call to the wctrans function.

Description

The towctrans function maps the wide character specified in wc, using the mapping described by desc.

The current setting of the LC_CTYPE category must be the same as during the call to the wctrans function that returned the value of desc.

Return Value

x

The mapped value of the wc wide character, if this character exists in the mapping described by desc. Otherwise, the value of wc is returned.

towlower

towlower — Converts the argument, a wide-character code, to lowercase. If the argument is not an uppercase character, it is returned unchanged.

Format

#include <wctype.h> (ISO C)
#include <wchar.h> (XPG4)
int towlower (wint_t wc);

Argument

wc

An object of type wint_t representable as a valid wide character in the current locale, or the value of WEOF. For any other value, the behavior is undefined.

Description

If the argument is an uppercase wide character, the corresponding lowercase wide character (as defined in the LC_CTYPE category of the locale) is returned, if it exists. If it does not exist, the function returns the input argument unchanged.

towupper

towupper — Converts the argument, a wide character, to uppercase. If the argument is not a lowercase character, it is returned unchanged.

Format

#include <wctype.h> (ISO C)
#include <wchar.h> (XPG4)
int towupper (wint_t wc);

Argument

wc

An object of type wint_t representable as a valid wide character in the current locale, or the value of WEOF. For any other value, the behavior is undefined.

Description

If the argument is a lowercase wide character, the corresponding uppercase wide character (as defined in the LC_CTYPE category of the locale) is returned, if it exists. If it does not exist, the function returns the input argument unchanged.

trunc

trunc — Truncates the argument to an integral value.

Format

#include <math.h>
double trunc (double x);
float truncf (float x,);
long double truncl (long double x);

Argument

x

A floating-point number.

Return Value

n

The truncated, integral value of the argument.

truncate

truncate — Changes file length to a specified length, in bytes.

Format

#include <unistd.h>
int truncate (const char *path, off_t length);

Arguments

path

The name of a file that is to be truncated. This argument must point to a pathname that names a regular file for which the calling process has write permission.

length

The new length of the file, in bytes. The off_t type of length is either a 64-bit or 32-bit integer. The 64-bit interface allows for file sizes greater than 2 GB, and can be selected at compile time by defining the _LARGEFILE feature-test macro as follows:
CC/DEFINE=_LARGEFILE

Description

The truncate function changes the length of a file to the size, in bytes, specified by the length argument.

If the new length is less than the previous length, the function removes all data beyond length bytes from the specified file. All file data between the new End-of-File and the previous End-of-File is discarded.

For stream files, if the new length is greater than the previous length, new file data between the previous End-of-File and the new End-of-File is added, consisting of all zeros. For record files, it is not possible to extend the file in this manner.

Return Values

0

Indicates success.

-1

An error occurred; errno is set to indicate the error.

ttyname, ttyname_r

ttyname, ttyname_r — Find the pathname of a terminal.

Format

#include <unixio.h> (Compatibility)
char *ttyname (void); (Compatibility)
#include <unistd.h> (OpenVMS V7.3-2 and higher)
char *ttyname (int filedes); (OpenVMS V7.3-2 and higher)
int ttyname_r (int filedes, char name, size_t namesize);
(OpenVMS V7.3-2 and higher)

Arguments

filedes

An open file descriptor.

name

Pointer to a buffer in which the terminal name is stored.

namesize

The length of the buffer pointed to by the name argument.

Description

The implementation of the ttyname function that takes no argument is provided only for backward compatibility. This legacy implementation returns a pointer to the null-terminated name of the terminal device associated with file descriptor 0, the default input device (stdin). A value of 0 is returned if SYS$INPUT is not a TTY device.

The ttyname_r function and the implementation of ttyname that takes a filedes argument are UNIX standard compliant and are available with only OpenVMS Version 7.3-2 and higher.

The standard compliant ttyname function returns a pointer to a string containing a null-terminated pathname of the terminal associated with file descriptor filedes. The return value might point to static data whose content is overwritten by each call. The ttyname interface need not be reentrant.

The ttyname_r function returns a pointer to store the null-terminated pathname of the terminal associated with the file descriptor filedes in the character array referenced by name. The array is namesize characters long and should have space for the name and the terminating null character. The maximum length of the terminal name is TTY_NAME_MAX.

If successful, ttyname returns a pointer to a string. Otherwise, a NULL pointer is returned and errno is set to indicate the error.

If successful, ttyname_r stores the terminal name as a null-terminated string in the buffer pointed to by name and returns 0. Otherwise, an error number is returned to indicate the error.

Return Values

x

Upon successful completion, ttyname returns a pointer to a null-terminated string.

NULL
Upon failure, ttyname returns a NULL pointer and sets errno to indicate the failure:

  • EBADF – The fildes argument is not a valid file descriptor.

  • ENOTTY– The fildes argument does not refer to a terminal device.

0

Upon successful completion, ttyname_r returns 0.

n
Upon failure, ttyname_r sets errno to indicate the failure, and returns the same errno code:

  • EBADF – The fildes argument is not a valid file descriptor.

  • ENOTTY– The fildes argument does not refer to a TTY device.

  • ERANGE– The value of namesize is smaller than the length of the string to be returned including the terminating null character.

0

For the legacy ttyname, indicates that SYS$INPUT is not a TTY device.

tzset

tzset — Sets and accesses time-zone conversion.

Format

#include <time.h>
void tzset (void);
extern char *tzname[];
extern long int timezone;
extern int daylight;

Description

The tzset function initializes time-conversion information used by the ctime, localtime, mktime, strftime, and wcsftime functions.

The tzset function sets the following external variables:
  • tzname is set as follows, where "std" is a 3-byte name for the standard time zone, and "dst" is a 3-byte name for the Daylight Savings Time zone:
    tzname[0] = "std" tzname[1] = "dst"

  • daylight is set to 0 if Daylight Savings Time should never be applied to the time zone. Otherwise, daylight is set to 1.

  • timezone is set to the difference between UTC and local standard time.

The environment variable TZ specifies how tzset initializes time conversion information:
  • If TZ is absent from the environment, the implementation-dependent time-zone information is used, as follows:
    • The best available approximation to local wall-clock time is used, as defined by the SYS$LOCALTIME system logical, which points to a tzfile format file that describes default time-zone rules.
    • This system logical is set during the installation of OpenVMS Version 7.0 or higher to define a time-zone file based off the root directory SYS$COMMON:[SYS$ZONEINFO.SYSTEM].?

  • If TZ appears in the environment but its value is a null string, Coordinated Universal Time (UTC) is used (without leap-second correction).

  • If TZ appears in the environment and its value is not a null string, the value has one of three formats, as described in Table 43.


Table 43. Time-Zone Initialization Rules

TZ Format

Meaning

:

UTC is used.

: pathname

The characters following the colon specify the pathname of a tzfile format file from which to read the time-conversion information. A pathname beginning with a slash (/) represents an absolute pathname; otherwise, the pathname is relative to the system time-conversion information directory specified by SYS$TZDIR, which by default is SYS$COMMON:[SYS$ZONEINFO.SYSTEM].

stdoffset[ dst[ offset] [,rule]]

The value is first used as the pathname of a file (as described for the :pathname format) from which to read the time-conversion information.

If that file cannot be read, the value is then interpreted as a direct specification of the time-conversion information, as follows:
std and dst – Three or more characters that are the designation for the time zone:

  • std – Standard time zone. Required.

  • dst – Daylight Savings Time zone. Optional. If dst is omitted, Daylight Savings Time does not apply.

Uppercase and lowercase letters are explicitly allowed. Any characters are allowed, except the following:

  • digits

  • leading colon (:)

  • comma (,)

  • minus ( -)

  • plus (+)

  • ASCII null character
offset – The value added to the local time to arrive at UTC. The offset has the following format: 
hh[:mm[:ss]]
In this format:

  • hh (hours) is a one-or two-digit value of 0–24.

  • mm (minutes) is a value of 0–59. (optional)

  • ss (seconds) is a value of 0–59. (optional)

The offset following std is required. If no offset follows dst, summer time is assumed, one hour ahead of standard time. You can use one or more digits; the value is always interpreted as a decimal number.

If the time zone is preceded by a minus sign ( -), the time zone is East of Greenwich; otherwise, it is West, which can also be indicated by a preceding plus sign (+).
rule – Indicates when to change to and return from summer time. The rule has the form:
start[/time], end[/time]
where:

  • start is the date when the change from standard time to summer time occurs.

  • end is the date for returning from summer time to standard time.
If start and end are omitted, the default is the US Daylight Savings Time start and end dates. The format for start and end must be one of the following:

  • Jn – The Julian day n (1 < n < 365). Leap days are not counted. That is, in all years, including leap years, February 28 is day 59 and March 1 is day 60. You cannot explicitly refer to February 29.

  • n – The zero based Julian day (0 < n < 365). Leap days are counted, making it possible to refer to February 29.

  • Mm.n.d – The nth d day of month m, where:
    • 0 < n < 5
    • 0 < d < 6
    • 1 < m < 12

    When n is 5, it refers to the last d day of month m. Sunday is day 0.

time – The time when, in current time, the change to or return from summer time occurs. The time argument has the same format as offset, except that you cannot use a leading minus ( -) or plus (+) sign. If time is not specified, the default is 02:00:00.

If no rule is present in the TZ specification, the rules used are those specified by the tzfile format file defined by the SYS$POSIXRULES system logical in the system time-conversion information directory, with the standard and summer time offsets from UTC replaced by those specified by the offset values in TZ.

If TZ does not specify a tzfile format file and cannot be interpreted as a direct specification, UTC is used.


Note

The UTC-based time functions, introduced in OpenVMS Version 7.0, had degraded performance compared with the non-UTC-based time functions.

OpenVMS Version 7.1 added a cache for time-zone files to improve performance. The size of the cache is determined by the logical name DECC$TZ_CACHE_SIZE. To accommodate most countries changing the time twice per year, the default cache size is large enough to hold two time-zone files.

See also ctime, localtime, mktime, strftime, and wcsftime.

Sample TZ Specification

EST5EDT4,M4.1.0,M10.5.0
This sample TZ specification describes the rule defined in 1987 for the Eastern time zone in the US:

  • EST (Eastern Standard Time) is the designation for standard time, which is 5 hours behind UTC.

  • EDT (Eastern Daylight Time) is the designation for summer time, which is 4 hours behind UTC. EDT starts on the first Sunday in April and ends on the last Sunday in October.

Because time was not specified in either case, the changes occur at the default time, which is 2:00 A.M. The start and end dates did not need to be specified, because they are the defaults.

ualarm

ualarm — Sets or changes the timeout of interval timers.

Format

#include <unistd.h>
useconds_t ualarm (useconds_t mseconds, useconds_t interval);

Arguments

mseconds

Specifies a number of real-time microseconds.

interval

Specifies the interval for repeating the timer.

Description

The ualarm function causes the SIGALRM signal to be generated for the calling process after the number of real-time microseconds specified by useconds has elapsed. When the interval argument is nonzero, repeated timeout notification occurs with a period in microseconds specified by interval. If the notification signal SIGALRM is not intercepted or is ignored, the calling process is terminated.

If you call a combination of ualarm and setitimer functions, and the AST status is disabled, the return value is invalid.

If you call a combination of ualarm and setitimer functions, and the AST status is enabled, the return value is valid.

This is because you cannot invoke an AST handler to clear the previous value of the timer when ASTs are disabled or invoked from a handler that was invoked at AST level.

Note

Interactions between ualarm and either alarm, or sleep are unspecified.

See also setitimer.

Return Values

n

The number of microseconds remaining from the previous ualarm or setitimer call.

0

No timeouts are pending or ualarm not previously called.

-1

Indicates an error.

umask

umask — Creates a file protection mask that is used when a new file is created, and returns the previous mask value.

Format

#include <stat.h>
mode_t umask (mode_t mode_complement);

Argument

mode_complement

Shows which bits to turn off when a new file is created. See the description of chmod to determine what the bits represent.

Description

Initially, the file protection mask is set from the current process's default file protection. This is done when the C main program starts up or when DECC$CRTL_INIT (or VAXC$CRTL_INIT) is called. You can change this for all files created by your program by calling umask or you can use chmod to change the file protection on individual files. The file protection of a file created by open or creat is the bitwise AND of the open and creat mode argument with the complement of the value passed to umask on the previous call.

Note

The way to create files with OpenVMS RMS default protections using the UNIX system-call functions umask, mkdir, creat, and open is to call mkdir, creat, and open with a file-protection mode argument of 0777 in a program that never specifically calls umask. These default protections include correctly establishing protections based on ACLs, previous versions of files, and so on.

In programs that do vfork/exec calls, the new process image inherits whether umask has ever been called or not from the calling process image. The umask setting and whether the umask function has ever been called are both inherited attributes.

Return Value

x

The old mask value.

uname

uname — Gets system identification information.

Format

#include <utsname.h>
int uname (struct utsname *name);

Argument

name

The current system identifier.

Description

The uname function stores null-terminated strings of information identifying the current system into the structure referenced by the name argument.

The utsname structure is defined in the <utsname.h> header file and contains the following members:

sysname

Name of the operating system implementation

nodename

Network name of this machine

release

Release level of the operating system

version

Version level of the operating system

machine

Machine hardware platform

Return Values

0

Indicates success.

-1

Indicates an error; errno or vaxc$errno is set as appropriate.

ungetc

ungetc — Pushes a character back into the input stream and leaves the stream positioned before the character.

Format

#include <stdio.h>
int ungetc (int character, FILE *file_ptr);

Arguments

character

A value of type int.

file_ptr

A file pointer.

Description

When using the ungetc function, the character is pushed back onto the file indicated by file_ptr.

One push-back is guaranteed, even if there has been no previous activity on the file. The fseek function erases all memory of pushed-back characters. The pushed-back character is not written to the underlying file. If the character to be pushed back is EOF, the operation fails, the input stream is left unchanged, and EOF is returned.

See also fseek and getc.

Return Values

x

The push-back character.

EOF

Indicates it cannot push the character back.

ungetwc

ungetwc — Pushes a wide character back into the input stream.

Format

#include <wchar.h>
wint_t ungetwc (wint_t wc, FILE *file_ptr);

Arguments

wc

A value of type wint_t.

file_ptr

A file pointer.

Description

When using the ungetwc function, the wide character is pushed back onto the file indicated by file_ptr.

One push-back is guaranteed, even if there has been no previous activity on the file. If a file positioning function (such as fseek) is called before the pushed back character is read, the bytes representing the pushed back character are lost.

If the character to be pushed back is WEOF, the operation fails, the input stream is left unchanged, and WEOF is returned.

See also getwc.

Return Values

x

The push-back character.

WEOF
Indicates that the function cannot push the character back. errno is set to one of the following:

  • EBADF – The file descriptor is not valid.

  • EALREADY – Operation is already in progress on the same file.

  • EILSEQ – Invalid wide-character code detected.

unordered

unordered — Returns the value 1 (TRUE) if either or both of the arguments is a NaN. Otherwise, it returns the value 0 (FALSE).

Format

#include <math.h>
double unordered (double x, double y);
float unorderedf (float x, float y);
long double unorderedl (long double x, long double y);

Arguments

x

A real number.

y

A real number.

Return Values

1

Either or both of the arguments is a NaN.

0

Neither argument is a NaN.

unsetenv

unsetenv — Deletes all instances of the environment variable name from the environment list.

Format

#include <stdlib.h>
void unsetenv (const char *name);

Argument

name

The environment variable to delete from the environment list.

Description

The unsetenv function deletes all instances of the variable name pointed to by the name argument from the environment list.

usleep

usleep — Suspends execution for an interval.

Format

#include <unistd.h>
int usleep (unsigned int mseconds);

Argument

mseconds

The number of microseconds to suspend execution for.

Description

The usleep function suspends the current process from execution for the number of microseconds specified by the mseconds argument. This argument must be less than 1,000,000. However, if its value is 0, then the call has no effect.

Be aware that usleep time specifications are rounded up approximately to the next millisecond because that is the finest time interval granularity possible on OpenVMS systems.

There is one real-time interval timer for each process. The usleep function does not interfere with a previous setting of this timer. If the process set this timer before calling usleep and if the time specified by mseconds equals or exceeds the interval timer's prior setting, then the process is awakened shortly before the timer was set to expire.

Return Values

0

Indicates success.

-1

Indicates an error occurred; errno is set to EINVAL.

utime

utime — Sets file access and modification times.

Format

#include <utime.h>
int utime (const char *path, const struct utimbuf *times);

Arguments

path

A pointer to a file.

times

A NULL pointer or a pointer to a utimbuf structure.

Description

The utime function sets the access and modification times of the file named by the path argument. The file must be openable for write-access to use this function.

If times is a NULL pointer, the access and modification times of the file are set to the current time. To use utime in this way, the effective user ID of the process must match the owner of the file, or the process must have write permission to the file or have appropriate privileges.

If times is not a NULL pointer, it is interpreted as a pointer to a utimbuf structure, and the access and modification times are set to the values in the specified structure. Only a process with an effective user ID equal to the user ID of the file or a process with appropriate privileges can use utime this way.

The utimbuf structure is defined by the <utime.h> header. The times in the utimbuf structure are measured in seconds since the Epoch.

Upon successful completion, utime marks the time of the last file status change, st_ctime, to be updated. See the <stat.h> header file.

Note

(Integrity servers, Alpha) On OpenVMS Alpha and Integrity server systems, the stat, fstat, utime, and utimes functions have been enhanced to take advantage of the new file-system support for POSIX compliant file timestamps.

This support is available only on ODS-5 devices on OpenVMS Alpha systems beginning with a version of OpenVMS Alpha after Version 7.3.

Before this change, stat and fstat set the values of the st_ctime, st_mtime, and st_atime fields based on the following file attributes:
  • st_ctime – ATR$C_CREDATE (file creation time)
  • st_mtime – ATR$C_REVDATE (file revision time)
  • st_atime – was always set to st_mtime because no support for file access time was available

Also, for the file-modification time, utime and utimes were modifying the ATR$C_REVDATE file attribute, and ignoring the file-access-time argument.

After the change, for a file on an ODS-5 device, the stat and fstat functions set the values of the st_ctime, st_mtime, and st_atime fields based on the following new file attributes:
  • st_ctime – ATR$C_ATTDATE (last attribute modification time)
  • st_mtime – ATR$C_MODDATE (last data modification time)
  • st_atime – ATR$C_ACCDATE (last access time)

If ATR$C_ACCDATE is 0, as on an ODS-2 device, the stat and fstat functions set st_atime to st_mtime.

For the file-modification time, the utime and utimes functions modify both the ATR$C_REVDATE and ATR$C_MODDATE file attributes. For the file-access time, these functions modify the ATR$C_ACCDATE file attribute. Setting the ATR$C_MODDATE and ATR$C_ACCDATE file attributes on an ODS-2 device has no effect.

For compatibility, the old behavior of stat, fstat, utime, and utimes remains the default, regardless of the kind of device.

The new behavior must be explicitly enabled by defining the DECC$EFS_FILE_TIMESTAMPS logical name to "ENABLE" before invoking the application. Setting this logical does not affect the behavior of stat, fstat, utime, and utimes for files on an ODS-2 device.

Return Values

0

Successful execution.

-1

Indicates an error. The function sets errno to one of the following values:

The utime function will fail if:

  • EACCES– Search permission is denied by a component of the path prefix; or the times argument is a NULL pointer and the effective user ID of the process does not match the owner of the file and write access is denied.

  • ELOOP– Too many symbolic links were encountered in resolving path.

  • ENAMETOOLONG– The length of the path argument exceeds PATH_MAX, a pathname component is longer than NAME_MAX, or a pathname resolution of a symbolic link produced an intermediate result whose length exceeds PATH_MAX.

  • ENOENT– path does not name an existing file, or path is an empty string.

  • ENOTDIR– A component of the path prefix is not a directory.

  • EPERM– times is not a NULL pointer and the calling process's effective user ID has write-access to the file but does not match the owner of the file, and the calling process does not have the appropriate privileges.

  • EROFS– The file system containing the file is read-only.

utimes

utimes — Sets file access and modification times.

Format

#include <time.h>
int utimes (const char *path, const struct timeval times[2]);

Arguments

path

A pointer to a file.

times

an array of timeval structures. The first array member represents the date and time of last access, and the second member represents the date and time of last modification. The times in the timeval structure are measured in seconds and microseconds since the Epoch, although rounding toward the nearest second may occur.

Description

The utimes function sets the access and modification times of the file pointed to by the path argument to the value of the times argument. The utimes function allows time specifications accurate to the microsecond.

If the times argument is a NULL pointer, the access and modification times of the file are set to the current time. The effective user ID of the process must be the same as the owner of the file, or must have write access to the file or appropriate privileges to use this call in this manner.

Upon completion, utimes marks the time of the last file status change, st_ctime, for update.

Note

(Integrity servers, Alpha) On OpenVMS Alpha and Integrity server systems, the stat, fstat, utime, and utimes functions have been enhanced to take advantage of the new file-system support for POSIX compliant file timestamps.

This support is available only on ODS-5 devices on OpenVMS Alpha systems beginning with a version of OpenVMS Alpha after Version 7.3.

Before this change, the stat and fstat functions were setting the values of the st_ctime, st_mtime, and st_atime fields based on the following file attributes:
  • st_ctime – ATR$C_CREDATE (file creation time)
  • st_mtime – ATR$C_REVDATE (file revision time)
  • st_atime – was always set to st_mtime because no support for file access time was available

Also, for the file-modification time, utime and utimes were modifying the ATR$C_REVDATE file attribute, and ignoring the file-access-time argument.

After the change, for a file on an ODS-5 device, the stat and fstat functions set the values of the st_ctime, st_mtime, and st_atime fields based on the following new file attributes:
  • st_ctime – ATR$C_ATTDATE (last attribute modification time)
  • st_mtime – ATR$C_MODDATE (last data modification time)
  • st_atime – ATR$C_ACCDATE (last access time)

If ATR$C_ACCDATE is 0, as on an ODS-2 device, the stat and fstat functions set st_atime to st_mtime.

For the file-modification time, the utime and utimes functions modify both the ATR$C_REVDATE and ATR$C_MODDATE file attributes. For the file-access time, these functions modify the ATR$C_ACCDATE file attribute. Setting the ATR$C_MODDATE and ATR$C_ACCDATE file attributes on an ODS-2 device has no effect.

For compatibility, the old behavior of stat, fstat, utime, and utimes remains the default, regardless of the kind of device.

The new behavior must be explicitly enabled by defining the DECC$EFS_FILE_TIMESTAMPS logical name to "ENABLE" before invoking the application. Setting this logical does not affect the behavior of stat, fstat, utime, and utimes for files on an ODS-2 device.

Return Values

0

Successful execution.

-1

Indicates an error. The file times do not change and the function sets errno to one of the following values:

The utimes function will fail if:

  • EACCES– Search permission is denied by a component of the path prefix; or the times argument is a NULL pointer and the effective user ID of the process does not match the owner of the file and write access is denied.

  • ELOOP– Too many symbolic links were encountered in resolving path.

  • ENAMETOOLONG– The length of the path argument exceeds PATH_MAX, a pathname component is longer than NAME_MAX, or a pathname resolution of a symbolic link produced an intermediate result whose length exceeds PATH_MAX.

  • ENOENT– A component of path does not name an existing file, or path is an empty string.

  • ENOTDIR– A component of the path prefix is not a directory.

  • EPERM–The times argument is not a NULL pointer and the calling process's effective user ID has write-access to the file but does not match the owner of the file and the calling process does not have the appropriate privileges.

  • EROFS– The file system containing the file is read-only.

VAXC$CRTL_INIT

VAXC$CRTL_INIT — Allows you to call the C RTL from other languages or to use the C RTL when your main function is not in C. It initializes the run-time environment and establishes both an exit and condition handler. VAXC$CRTL_INIT is a synonym for DECC$CRTL_INIT. Either name invokes the same routine.

Format

#include <signal.h>
void VAXC$CRTL_INIT();

Description

The following example shows a Pascal program that calls the C RTL using the VAXC$CRTL_INIT function:

On OpenVMS Alpha systems:
$ PASCAL EXAMPLE
$ LINK EXAMPLE,SYS$LIBRARY:VAXCRTL/LIB
$ TY EXAMPLE.PAS
PROGRAM TESTC(input, output);
PROCEDURE VAXC$CRTL_INIT; extern;
BEGIN
   VAXC$CRTL_INIT;
END
$

A shareable image need only call this function if it contains an VSI C function for signal handling, environment variables, I/O, exit handling, a default file protection mask, or if it is a child process that should inherit context.

Although many of the initialization activities are performed only once, DECC$CRTL_INIT can safely be called multiple times. On OpenVMS VAX systems, DECC$CRTL_INIT establishes the C RTL internal OpenVMS exception handler in the frame of the routine that calls DECC$CRTL_INIT each time DECC$CRTL_INIT is called.

At least one frame in the current call stack must have that handler established for OpenVMS exceptions to get mapped to UNIX signals.

VAXC$ESTABLISH

VAXC$ESTABLISH — Used for establishing an OpenVMS exception handler for a particular routine. This function establishes a special C RTL exception handler in the routine that called it. This special handler catches all RTL-related exceptions that occur in later routines, and passes on all other exceptions to your handler.

Format

#include <signal.h>
void VAXC$ESTABLISH (unsigned int (*exception_handler)(void *sigarr,
void *mecharr));

Arguments

exception_handler

The name of the function that you want to establish as an OpenVMS exception handler. You pass a pointer to this function as the parameter to VAXC$ESTABLISH.

sigarr

A pointer to the signal array.

mecharr

A pointer to the mechanism array.

Description

VAXC$ESTABLISH must be used in place of LIB$ESTABLISH when programs use the C RTL routines setjmp or longjmp. See setjmp and longjmp, or sigsetjmp and siglongjmp.

You can only invoke the VAXC$ESTABLISH function from a VSI C for OpenVMS function, because it relies on the allocation of data space on the run-time stack by the VSI C compiler. Calling the OpenVMS system library routine LIB$ESTABLISH directly from an VSI C function results in undefined behavior from the setjmp and longjmp functions.

To cause an OpenVMS exception to generate a UNIX style signal, user exception handlers must return SS$_RESIGNAL upon receiving any exception that they do not want to handle. Returning SS$_NORMAL prevents the generation of a UNIX style signal. UNIX signals are generated as if by an exception handler in the stack frame of the main C program. Not all OpenVMS exceptions correspond to UNIX signals. See Chapter 4 for more information on the interaction of OpenVMS exceptions and UNIX style signals.

Calling VAXC$ESTABLISH with an argument of NULL cancels an existing handler in that routine.

Note

On OpenVMS Alpha systems, VAXC$ESTABLISH is implemented as a compiler built-in function, not as a C RTL function. (Alpha only)

va_arg

va_arg — Returns the next item in the argument list.

Format

#include <stdarg.h> (ANSI C)
#include <varargs.h> (VSI C Extension)
type va_arg (va_list ap, type);

Arguments

ap

A variable list containing the next argument to be obtained.

type

A data type that is used to determine the size of the next item in the list. An argument list can contain items of varying sizes, but the calling routine must determine what type of argument is expected since it cannot be determined at run time.

Description

The va_arg macro interprets the object at the address specified by the list increment or according to type. If there is no corresponding argument, the behavior is undefined.

When using va_arg to write portable applications, include the <stdarg.h> header file (defined by the ANSI C standard), not the <varargs.h> header file, and use va_arg only in conjunction with other functions and macros defined in <stdarg.h>.

For an example of argument-list processing using the <stdarg.h> functions and definitions, see Example 3.6.

va_copy

va_copy — Copies one argument list to another.

Format

#include <stdarg.h>
void va_copy (va_list dest, va_list src);

Arguments

dest

Argument list that is a copy of src.

src

Source argument list to be copied to dest.

Description

The va_copy macro initializes dest as a copy of src, as if the va_start macro had been applied to dest followed by the same sequence of uses of the va_arg macro as had previously been used to reach the present state of src. Neither the va_copy nor va_start macro should be invoked to reinitialize dest without an intervening invocation of the va_end macro for the same dest.

Note

The va_copy macro requires VSI C Compiler Version 7.5 or later.

va_count

va_count — Returns the number of quadwords (Alpha only) in the argument list.

Format

#include <stdarg.h> (ANSI C)
OR
#include <varargs.h> (VSI C Extension)
void va_count (int count);

Argument

count

An integer variable name in which the number of quadwords (Alpha only) is returned.

Description

The va_count macro places the number of quadwords (Alpha only) in the argument list into count. The value returned in count is the number of quadwords (Alpha only) in the function argument block not counting the count field itself.

If the argument list contains items whose storage requirements are a quadword (Alpha only) of memory or less, the number in the count argument is also the number of arguments. However, if the argument list contains items that are longer than a quadword (Alpha only), count must be interpreted to obtain the number of arguments. Because a double is 8 bytes, it occupies one argument-list position on OpenVMS Alpha and Integrity server systems.

The va_count macro is specific to VSI C for OpenVMS systems and is not portable.

va_end

va_end — Finishes the <varargs.h> or <stdarg.h> session.

Format

#include <stdarg.h> (ANSI C)
#include <varargs.h> (VSI C Extension)
void va_end (va_list ap);

Argument

ap

The object used to traverse the argument list length. You must declare and use the argument ap as shown in this format section.

Description

You can execute multiple traversals of the argument list, each delimited by va_start . . . va_end. The va_end function sets ap equal to NULL.

When using this function to write portable applications, include the <stdarg.h> header file (defined by the ANSI C standard), not the <varargs.h> header file, and use va_end only in conjunction with other routines defined in <stdarg.h>.

For an example of argument-list processing using the <stdarg.h> functions and definitions, see Example 3.6.

va_start, va_start_1

va_start, va_start_1 — Used for initializing a variable to the beginning of the argument list.

Format

#include <varargs.h> (VSI C Extension)
void va_start (va_list ap);
void va_start_1 (va_list ap, int offset);

Arguments

ap

An object pointer. You must declare and use the argument ap as shown in the format section.

offset

The number of bytes by which ap is to be incremented so that it points to a subsequent argument within the list (that is, not to the start of the argument list). Using a nonzero offset can initialize ap to the address of the first of the optional arguments that follow a number of fixed arguments.

Description

The va_start macro initializes the variable ap to the beginning of the argument list.

The va_start_1 macro initializes ap to the address of an argument that is preceded by a known number of defined arguments. The printf function is an example of a C RTL function that contains a variable-length argument list offset from the beginning of the entire argument list. The variable-length argument list is offset by the address of the formatting string.

When determining the value of the offset argument used in va_start_1, the implications of the OpenVMS calling standard must be considered.

On OpenVMS Alpha and Integrity server systems, each argument item is a quadword.

Note

When accessing argument lists, especially those passed to a subroutine (written in C) by a program written in another programming language, consider the implications of the OpenVMS calling standard. For more information about the OpenVMS calling standard, see the VSI C User Manual or the VSI OpenVMS Calling Standard.

The preceding version of va_start and va_start_1 is specific to the C RTL, and is not portable.

The following syntax describes the va_start macro in the <stdarg.h> header file, as defined in the ANSI C standard.

Format

#include <stdarg.h> (ANSI C)
void va_start (va_list ap, parmN);

Arguments

ap

An object pointer. You must declare and use the argument ap as shown in the format section.

parmN

The name of the last of the known fixed arguments.

Description

The pointer ap is initialized to point to the first of the optional arguments that follow parmN in the argument list.

Always use this version of va_start in conjunction with functions that are declared and defined with function prototypes. Also use this version of va_start to write portable programs.

For an example of argument-list processing using the <stdarg.h> functions and definitions, see Example 3.6.

vfork

vfork — Creates an independent child process. This function is nonreentrant.

Format

#include <unistd.h>
int vfork (void); (_DECC_V4_SOURCE)
pid_t vfork (void); (not _DECC_V4_SOURCE)

Description

The vfork function provided by VSI C for OpenVMS systems differs from the fork function provided by other C implementations. Table 44 shows the two major differences.
Table 44. The vfork and fork Functions

The vfork Function

The fork Function

Used with the exec functions.

Can be used without an exec function for asynchronous processing.

Creates an independent child process that shares some of the parent's characteristics.

Creates an exact duplicate of the parent process that branches at the point where vfork is called, as if the parent and the child are the same process at different stages of execution.

The vfork function provides the setup necessary for a subsequent call to an exec function. Although no process is created by vfork, it performs the following steps:

  • It saves the return address (the address of the vfork call) to be used later as the return address for the call to an exec function.

  • It saves the current context.

  • It returns the integer 0 the first time it is called (before the call to an exec function is made). After the corresponding exec function call is made, the exec function returns control to the parent process, at the point of the vfork call, and it returns the process ID of the child as the return value. Unless the exec function fails, control appears to return twice from vfork even though one call was made to vfork and one call was made to the exec function.

The behavior of the vfork function is similar to the behavior of the setjmp function. Both vfork and setjmp establish a return address for later use, both return the integer 0 when they are first called to set up this address, and both pass back the second return value as though it were returned by them rather than by their corresponding exec or longjmp function calls.

However, unlike setjmp, with vfork, all local automatic variables, even those with volatile-qualified type, can have indeterminate values if they are modified between the call to vfork and the corresponding call to an exec routine.

Return Values

0

Indicates successful creation of the context.

nonzero

Indicates the process ID (PID) of the child process.

-1

Indicates an error – failure to create the child process.

vfprintf

vfprintf — Prints formatted output based on an argument list.

Format

#include <stdio.h>
int vfprintf (FILE *file_ptr, constchar *format, va_list ap);

Arguments

file_ptr

A pointer to the file to which the output is directed.

format

A pointer to a string containing the format specification. For more information about format and conversion specifications and their corresponding arguments, see Chapter 2.

ap

A list of expressions whose resultant types correspond to the conversion specifications given in the format specifications.

Description

See also vprintf and vsprintf.

Return Values

x

The number of bytes written.

Negative value

Indicates an output error. The function sets errno. For a list of possible errno values set, see fprintf.

vfscanf

vfscanf — Reads formatted input based on an argument list.

Format

#include <stdio.h>
int vfscanf (FILE *file_ptr, constchar *format, va_list ap);

Arguments

file_ptr

A pointer to the file that provides input text.

format

A pointer to a string containing the format specification.

ap

A list of expressions whose resultant types correspond to the conversion specifications given in the format specifications.

Description

The vfscanf function is the same as the fscanf function except that instead of being called with a variable number of arguments, it is called with an argument list that has been initialized by va_start (and possibly subsequent va_arg calls).

If no conversion specifications are given, you can omit the input pointers. Otherwise, the function calls must have exactly as many input pointers as there are conversion specifications, and the conversion specifications must match the types of the input pointers.

Conversion specifications are matched to input sources in left-to-right order. Excess input pointers, if any, are ignored.

For more information about format and conversion specifications and their corresponding arguments, see Chapter 2.

This function returns the number of successfully matched and assigned input items.

See also vscanf and vsscanf.

Return Values

n

The number of successfully matched and assigned input items.

EOF

Indicates that the end-of-file was encountered or a read error occurred. If a read error occurs, the function sets errno to one of the following:

  • EILSEQ– Invalid character detected.

  • EINVAL– Insufficient arguments.

  • ENOMEM– Not enough memory available for conversion.

  • ERANGE– Floating-point calculations overflow.

  • EVMSERR– Nontranslatable OpenVMS error. vaxc$errno contains the OpenVMS error code. This can indicate that conversion to a numeric value failed due to overflow.

  • The function can also set errno to the following as a result of errors returned from the I/O subsystem:

    • EBADF– The file descriptor is not valid.

    • EIO– I/O error.

    • ENXIO– Device does not exist.

    • EPIPE– Broken pipe.

    • EVMSERR– Nontranslatable OpenVMS error. vaxc$errno contains the OpenVMS error code. This indicates that an I/O error occurred for which there is no equivalent C error code.

vfwprintf

vfwprintf — Writes output to the stream under control of the wide-character format string.

Format

#include <wchar.h>
int vfwprintf (FILE *stream, const wchar_t *format, va_list ap);

Arguments

stream

A file pointer.

format

A pointer to a wide-character string containing the format specifications. For more information about format and conversion specifications and their corresponding arguments, see Chapter 2.

ap

A variable list of the items needed for output.

Description

The vfwprintf function is equivalent to the fwprintf function, with the variable argument list replaced by the ap argument. Initialize ap with the va_start macro (and possibly with subsequent va_arg calls) from <stdarg.h>.

If the stream pointed to by stream has no orientation, vfwprintf makes the stream wide-oriented.

See also fwprintf.

Return Values

n

The number of wide characters written.

Negative value

Indicates an error. The function sets errno to one of the following:

  • EILSEQ – Invalid character detected.

  • EINVAL – Insufficient arguments.

  • ENOMEM – Not enough memory available for conversion.

  • ERANGE – Floating-point calculations overflow.

  • EVMSERR – Nontranslatable OpenVMS error. vaxc$errno contains the OpenVMS error code. This might indicate that conversion to a numeric value failed because of overflow.

The function can also set errno to the following as a result of errors returned from the I/O subsystem:

  • EBADF – The file descriptor is not valid.

  • EIO – I/O error.

  • ENOSPC – No free space on the device containing the file.

  • ENXIO – Device does not exist.

  • EPIPE – Broken pipe.

  • ESPIPE – Illegal seek in a file opened for append.

  • EVMSERR – Nontranslatable OpenVMS error. vaxc$errno contains the OpenVMS error code. This indicates that an I/O error occurred for which there is no equivalent C error code.

Examples

The following example shows the use of the vfwprintf function in a general error reporting routine:

 #include <stdarg.h>
 #include <stdio.h>
 #include <wchar.h>

 void error(char *function_name, wchar_t *format, ...);
 {
    va_list args;

    va_start(args, format);
    /* print out name of function causing error */
    fwprintf(stderr, L"ERROR in %s: ", function_name);
    /* print out remainder of message */
    vfwprintf(stderr, format, args);
    va_end(args);
 }

vfwscanf

vfwscanf — Reads input from the stream under control of a wide-character format string.

Format

#include <wchar.h>
int vfwscanf (FILE *stream, const wchar_t *format, va_list ap);

Arguments

stream

A file pointer.

format

A pointer to a wide-character string containing the format specifications.

ap

A list of expressions whose resultant types correspond to the conversion specifications given in the format specifications.

Description

The vfwscanf function is equivalent to the fwscanf function, except that instead of being called with a variable number of arguments, it is called with an argument list (ap) that has been initialized by va_start (and possibly with subsequent va_arg calls).

If the stream pointed to by stream has no orientation, vfwscanf makes the stream wide-oriented.

For more information about format and conversion specifications and their corresponding arguments, see Chapter 2.

Return Values

n

The number of successfully matched and assigned wide-character input items.

EOF

Indicates that a read error occurred before any conversion. The function sets errno. For a list of the values set by this function, see vfscanf.

vprintf

vprintf — Prints formatted output based on an argument list. This function is the same as the printf function except that instead of being called with a variable number of arguments, it is called with an argument list that has been initialized by the va_start macro (and possibly with subsequent va_arg calls) from <stdarg.h>.

Format

#include <stdio.h>
int vprintf (const char *format, va_list ap);

Arguments

format

A pointer to the string containing the format specification. For more information about format and conversion specifications and their corresponding arguments, see Chapter 2.

ap

A variable list of the items needed for output.

Description

See the vfprintf and vsprintf functions.

Return Values

x

The number of bytes written.

Negative value

Indicates an output error. The function sets errno. For a list of possible errno values set, see fprintf.

vscanf

vscanf — Reads formatted input based on an argument list.

Format

#include <stdio.h>
int vscanf (const char *format, va_list ap);

Arguments

format

A pointer to the string containing the format specification.

ap

A list of expressions whose resultant types correspond to the conversion specifications given in the format specifications.

Description

The vscanf function is the same as the scanf function except that instead of being called with a variable number of arguments, it is called with an argument list (ap) that has been initialized by the va_start macro (and possibly with subsequent va_arg calls).

For more information about format and conversion specifications and their corresponding arguments, see Chapter 2.

See also scanf, vfscanf, and vsscanf.

Return Values

n

The number of successfully matched and assigned input items.

EOF

Indicates that a read error occurred before any conversion. The function sets errno. For a list of the values set by this function, see vfscanf.

vsnprintf

vsnprintf — Prints formatted output based on an argument list.

Format

#include <stdio.h>
int vsnprintf (char *str, size_t n, const char *format, va_list ap);

Arguments

str

A pointer to a string that will receive the formatted output.

format

A pointer to a character string that contains the format specification. For more information about format and conversion specifications and their corresponding arguments, see Chapter 2.

ap

A list of expressions whose resultant types correspond to the conversion specifications given in the format specifications.

Description

The vsnprintf function is the same as the snprintf function, but instead of being called with a variable number of arguments, it is called with an argument list that has been initialized by va_start (and possibly with subsequent va_arg calls).

This function does not invoke the va_end macro. Because the function invokes the va_arg macro, the value of ap after the return is unspecified.

Applications using vsnprintf should call va_end (ap) afterwards to clean up.

Return Values

x

The number of bytes (excluding the terminating null byte) that would be written to str if n is sufficiently large.

Negative value

Indicates an output error occurred. The function sets errno. For a list of possible errno values set, see fprintf.

vsprintf

vsprintf — Prints formatted output based on an argument list. This function is the same as the sprintf function except that instead of being called with a variable number of arguments, it is called with an argument list that has been initialized by va_start (and possibly with subsequent va_arg calls).

Format

#include <stdio.h>
int vsprintf (char *str, const char *format, va_list ap);

Arguments

str

A pointer to a string that will receive the formatted output. This string is assumed to be large enough to hold the output.

format

A pointer to a character string that contains the format specification. For more information about format and conversion specifications and their corresponding arguments, see Chapter 2.

ap

A list of expressions whose resultant types correspond to the conversion specifications given in the format specifications.

Return Value

x

The number of bytes written.

Negative value

Indicates an output error occurred. The function sets errno. For a list of possible errno values set, see fprintf.

vsscanf

vsscanf — Reads formatted input based on an argument list.

Format

#include <stdio.h>
int vsscanf (char *str, const char *format, va_list ap);

Arguments

str

The address of the character string that provides the input text to sscanf.

format

A pointer to a character string that contains the format specification.

ap

A list of expressions whose resultant types correspond to the conversion specifications given in the format specifications.

Description

The vsscanf function is the same as the sscanf function except that instead of being called with a variable number of arguments, it is called with an argument list that has been initialized by va_start (and possibly with subsequent va_arg calls).

The vsscanf function is also equivalent to the vfscanf function, except that the first argument specifies a wide-character string rather than a stream. Reaching the end of the wide-character string is the same as encountering EOF for the vfscanf function.

For more information about format and conversion specifications and their corresponding arguments, see Chapter 2.

See also vsscanf and sscanf.

Return Values

n

The number of successfully matched and assigned input items.

EOF

Indicates that a read error occurred before any conversion. The function sets errno. For a list of the values set by this function, see vfscanf.

vswprintf

vswprintf — Writes output to the stream under control of the wide-character format string.

Format

#include <wchar.h>
int vswprintf (wchar_t *s, size_t n, const wchar_t *format, va_list ap);

Arguments

s

A pointer to a multibyte character sequence.

n

The maximum number of bytes that comprise the multibyte character.

format

A pointer to a wide-character string containing the format specifications. For more information about format and conversion specifications and their corresponding arguments, see Chapter 2.

ap

A variable list of the items needed for output.

Description

The vswprintf function is equivalent to the swprintf function, with the variable argument list replaced by the ap argument. Initialize ap with the va_start macro, and possibly with subsequent va_arg calls.

See also swprintf.

Return Values

n

The number of wide characters written.

Negative value

Indicates an error. The function sets errno to one of the following:

  • EILSEQ – Invalid character detected.

  • EINVAL – Insufficient arguments.

  • ENOMEM – Not enough memory available for conversion.

  • ERANGE – Floating-point calculations overflow.

  • EVMSERR – Nontranslatable OpenVMS error. vaxc$errno contains the OpenVMS error code. This might indicate that conversion to a numeric value failed because of overflow.

The function can also set errno to the following as a result of errors returned from the I/O subsystem:

  • EBADF – The file descriptor is not valid.

  • EIO – I/O error.

  • ENOSPC – No free space on the device containing the file.

  • ENXIO – Device does not exist.

  • EPIPE – Broken pipe.

  • ESPIPE – Illegal seek in a file opened for append.

  • EVMSERR – Nontranslatable OpenVMS error. vaxc$errno contains the OpenVMS error code. This indicates that an I/O error occurred for which there is no equivalent C error code.

vswscanf

vswscanf — Reads input from the stream under control of the wide-character format string.

Format

#include <wchar.h>
int vswscanf (wchar_t *s, const wchar_t *format, va_list ap);

Arguments

s

A pointer to a wide-character string from which the input is to be obtained.

format

A pointer to a wide-character string containing the format specifications.

ap

A list of expressions whose results correspond to conversion specifications given in the format specification.

Description

The vswscanf function is equivalent to the swscanf function, except that instead of being called with a variable number of arguments, it is called with an argument list (ap) that has been initialized by va_start (and possibly with subsequent va_arg calls).

The vswscanf function is also equivalent to the vfwscanf function, except that the first argument specifies a wide-character string rather than a stream. Reaching the end of the wide-character string is the same as encountering EOF for the vfwscanf function.

For more information about format and conversion specifications and their corresponding arguments, see Chapter 2.

See also vfwscanf and swscanf.

Return Values

n

The number of wide characters read.

EOF

Indicates that a read error occurred before any conversion. The function sets errno. For a list of the values set by this function, see vfscanf.

vwprintf

vwprintf — Writes output to an array of wide characters under control of the wide-character format string.

Format

#include <wchar.h>
int vwprintf (const wchar_t *format, va_list ap);

Arguments

format

A pointer to a wide-character string containing the format specifications. For more information about format and conversion specifications and their corresponding arguments, see Chapter 2.

ap

The variable list of items needed for output.

Description

The vwprintf function is equivalent to the wprintf function, with the variable argument list replaced by the ap argument. Initialize ap with the va_start macro, and possibly with subsequent va_arg calls. The vwprintf function does not invoke the va_end macro.

See also wprintf.

Return Values

x

The number of wide characters written, not counting the terminating null wide character.

Negative value

Indicates an error. Either n or more wide characters were requested to be written, or a conversion error occurred, in which case errno is set to EILSEQ.

vwscanf

vwscanf — Reads input from an array of wide characters under control of a wide-character format string.

Format

#include <wchar.h>
int vwscanf (const wchar_t *format, va_list ap);

Arguments

format

A pointer to a wide-character string containing the format specifications.

ap

A list of expressions whose resultant types correspond to the conversion specifications given in the format specifications.

Description

The vwscanf function is equivalent to the wscanf function, except that instead of being called with a variable number of arguments, it is called with an argument list (ap) that has been initialized by va_start (and possibly with subsequent va_arg calls).

For more information about format and conversion specifications and their corresponding arguments, see Chapter 2.

See also wscanf.

Return Values

n

The number of wide characters read.

EOF

Indicates that a read error occurred before any conversion. The function sets errno. For a list of the values set by this function, see vfscanf.

wait

wait — Checks the status of the child process before exiting. A child process is terminated when the parent process terminates.

Format

#include <wait.h>
pid_t wait (int *status);

Argument

status

The address of a location to receive the final status of the terminated child. The child can set the status with the exit function and the parent can retrieve this value by specifying status.

Description

The wait function suspends the parent process until the final status of a terminated child is returned from the child.

On OpenVMS Version 7.0 and higher systems, the wait function is equivalent to waitpid( 0, status, 0) if you include <wait.h> and compile with the _POSIX_EXIT feature-test macro set (either with /DEFINE=_POSIX_EXIT or with #define _POSIX_EXIT at the top of your file, before any file inclusions).

Return Values

x

The process ID (PID) of the terminated child. If more than one child process was created, wait will return the PID of the terminated child that was most recently created. Subsequent calls will return the PID of the next most recently created, but terminated, child.

-1

No child process was spawned.

wait3

wait3 — Waits for a child process to stop or terminate.

Format

#include <wait.h>
pid_t wait3 (int *status_location, int options,
struct rusage *resource_usage);

Arguments

status_location

A pointer to a location that contains the termination status of the child process as defined in the <wait.h> header file.

Beginning with OpenVMS Version 7.2, when compiled with the _VMS_WAIT macro defined, the wait3 function puts the OpenVMS completion code of the child process at the address specified in the status_location argument.

options

Flags that modify the behavior of the function. These flags are defined in the Description section.

resource_usage

The location of a structure that contains the resource utilization information for terminated child processes.

Description

The wait3 function suspends the calling process until the request is completed, and redefines it so that only the calling thread is suspended.

The options argument modifies the behavior of the function. You can combine the flags for the options argument by specifying their bitwise inclusive OR. The flags are:

WNOWAIT

Specifies that the process whose status is returned in status_location is kept in a waitable state. You can wait for the process again with the same results.

WNOHANG

Prevents the suspension of the calling process. If there are child processes that stopped or terminated, one is chosen and the waitpid function returns its process ID, as when you do not specify the WNOHANG flag. If there are no terminated processes (that is, if waitpid suspends the calling process without the WNOHANG flag), 0 (zero) is returned. Because you can never wait for process 0, there is no confusion arising from this return.

WUNTRACED

Specifies that the call return additional information when the child processes of the current process stop because the child process received a SIGTTIN, SIGTTOU, SIGSTOP, or SIGTSTOP signal.

If the wait3 function returns because the status of a child process is available, the process ID of the child process is returned. Information is stored in the location pointed to by status_location, if this pointer is not null.

The value stored in the location pointed to by status_location is 0 (zero) only if the status is returned from a terminated child process that did one of the following:

  • Returned 0 from the main function.

  • Passed 0 as the status argument to the _exit or exit function.

Regardless of the status_location value, you can define this information using the macros defined in the <wait.h> header file, which evaluate to integral expressions. In the following macro descriptions, the status_value argument is equal to the integer value pointed to by the status_location argument:

WIFEXITED(status_value)

Evaluates to a nonzero value if status was returned for a child process that terminated normally.

WEXITSTATUS(status_value)

If the value of WIFEXITED (status_value) is nonzero, this macro evaluates to the low-order 8 bits of the status argument that the child process passed to the _exit or exit function, or to the value the child process returned from the main function.

WIFSIGNALED(status_value)

Evaluates to a nonzero value if status was returned for a child process that terminated due to the receipt of a signal that was not intercepted.

WTERMSIG(status_value)

If the value of WIFSIGNALED (status_value) is nonzero, this macro evaluates to the number of the signal that caused the termination of the child process.

WIFSTOPPED(status_value)

Evaluates to a nonzero value if status was returned for a child process that is currently stopped.

WSTOPSIG(status_value)

If the value of WIFSTOPPED (status_value) is nonzero, this macro evaluates to the number of the signal that caused the child process to stop.

WIFCONTINUED(status_value)

Evaluates to a nonzero value if status was returned for a child process that has continued.

If the information stored at the location pointed to by status_location was stored there by a call to wait3 that specified the WUNTRACED flag, one of the following macros evaluates to a nonzero value:

  • WIFEXITED(*status_value)

  • WIFSIGNALED(*status_value)

  • WIFSTOPPED(*status_value)

  • WIFCONTINUED(*status_value)

If the information stored in the location pointed to by status_location resulted from a call to wait3 without the WUNTRACED flag specified, one of the following macros evaluates to a nonzero value:

  • WIFEXITED(*status_value)

  • WIFSIGNALED(*status_value)

The wait3 function provides compatibility with BSD systems. The resource_usage argument points to a location that contains resource usage information for the child processes as defined in the <resource.h> header file.

If a parent process terminates without waiting for all of its child processes to terminate, the remaining child processes is assigned a parent process ID equal to the process ID of the init process.

See also exit, -exit, and init.

Return Values

0

Indicates success. There are no stopped or exited child processes, the WNOHANG option is specified.

x

The process_id of the child process. The status of a child process is available.

-1
Indicates an error; errno is set to one of the following values:

  • ECHILD – There are no child processes to wait for.

  • EINTR – Terminated by receipt of a signal intercepted by the calling process.

  • EFAULT– The status_location or resource_usage argument points to a location outside of the address space of the process.

  • EINVAL – The value of the options argument is not valid.

wait4

wait4 — Waits for a child process to stop or terminate.

Format

#include <wait.h>
pid_t wait4 (pid_t process_id union wait *status_location, int options,
struct rusage *resource_usage);

Arguments

status_location

A pointer to a location that contains the termination status of the child process as defined in the <wait.h> header file.

Beginning with OpenVMS Version 7.2, when compiled with the _VMS_WAIT macro defined, the wait4 function puts the OpenVMS completion code of the child process at the address specified in the status_location argument.

process_id

The child process or set of child processes.

options

Flags that modify the behavior of the function. These flags are defined in the Description section.

resource_usage

The location of a structure that contains the resource utilization information for terminated child processes.

Description

The wait4 function suspends the calling process until the request is completed.

The process_id argument allows the calling process to gather status from a specific set of child processes, according to the following rules:

If the process_id is

Then status is requested

Equal to -1

For any child process. In this respect, the waitpid function is equivalent to the wait function.

Greater than 0

For a single child process and specifies the process ID.

The wait4 function only returns the status of a child process from this set.

The options argument to the wait4 function modifies the behavior of the function. You can combine the flags for the options argument by specifying their bitwise-inclusive OR. The flags are:

WNOWAIT

Specifies that the process whose status is returned in status_location is kept in a waitable state. You can wait for the process again with the same results.

WNOHANG

Prevents the suspension of the calling process. If there are child processes that stopped or terminated, one is chosen and the waitpid function returns its process ID, as when you do not specify the WNOHANG flag. If there are no terminated processes (that is, if waitpid suspends the calling process without the WNOHANG flag), 0 is returned. Because you can never wait for process 0, there is no confusion arising from this return.

WUNTRACED

Specifies that the call return additional information when the child processes of the current process stop because the child process received a SIGTTIN, SIGTTOU, SIGSTOP, or SIGTSTOP signal.

If the wait4 function returns because the status of a child process is available, the process ID of the child process is returned. Information is stored in the location pointed to by status_location, if this pointer is not null.

The value stored in the location pointed to by status_location is 0 only if the status is returned from a terminated child process that did one of the following:

  • Returned 0 from the main function.

  • Passed 0 as the status argument to the _exit or exit function.

Regardless of the status_location value, you can define this information using the macros defined in the <wait.h> header file, which evaluate to integral expressions. In the following macro descriptions, status_value is equal to the integer value pointed to by status_location:

WIFEXITED(status_value)

Evaluates to a nonzero value if status was returned for a child process that terminated normally.

WEXITSTATUS(status_value)

If the value of WIFEXITED (status_value) is nonzero, this macro evaluates to the low-order 8 bits of the status argument that the child process passed to the _exit or exit function, or to the value the child process returned from the main function.

WIFSIGNALED(status_value)

Evaluates to a nonzero value if status was returned for a child process that terminated due to the receipt of a signal that was not intercepted.

WTERMSIG(status_value)

If the value of WIFSIGNALED (status_value) is nonzero, this macro evaluates to the number of the signal that caused the termination of the child process.

WIFSTOPPED(status_value)

Evaluates to a nonzero value if status was returned for a child process that is currently stopped.

WSTOPSIG(status_value)

If the value of WIFSTOPPED (status_value) is nonzero, this macro evaluates to the number of the signal that caused the child process to stop.

WIFCONTINUED(status_value)

Evaluates to a nonzero value if status was returned for a child process that has continued.

If the information stored at the location pointed to by status_location was stored there by a call to wait4 that specified the WUNTRACED flag, one of the following macros evaluates to a nonzero value:

  • WIFEXITED(*status_value)

  • WIFSIGNALED(*status_value)

  • WIFSTOPPED(*status_value)

  • WIFCONTINUED(*status_value)

If the information stored in the location pointed to by status_location resulted from a call to wait4 without the WUNTRACED flag specified, one of the following macros evaluates to a nonzero value:

  • WIFEXITED(*status_value)

  • WIFSIGNALED(*status_value)

The wait4 function is similar to the wait3 function. However, the wait4 function waits for a specific child as indicated by the process_id argument. The resource_usage argument points to a location that contains resource usage information for the child processes as defined in the <resource.h> header file.

See also exit and _exit.

Return Values

0

Indicates success. There are no stopped or exited child processes, the WNOHANG option is specified.

x

The process_id of the child process. The status of a child process is available.

-1
Indicates an error; errno is set to one of the following values:

  • ECHILD – There are no child processes to wait for.

  • EINTR – Terminated by receipt of a signal intercepted by the calling process.

  • EFAULT– The status_location or resource_usage argument points to a location outside of the address space of the process.

  • EINVAL – The value of the options argument is not valid.

waitpid

waitpid — Waits for a child process to stop or terminate.

Format

#include <wait.h>
pid_t waitpid (pid_t process_id, int *status_location, int options);

Arguments

process_id

The child process or set of child processes.

status_location

A pointer to a location that contains the termination status of the child process as defined in the <wait.h> header file.

Beginning with OpenVMS Version 7.2, when compiled with the _VMS_WAIT macro defined, the waitpid function puts the OpenVMS completion code of the child process at the address specified in the status_location argument.

options

Flags that modify the behavior of the function. These flags are defined in the Description section.

Description

The waitpid function suspends the calling process until the request is completed. It is redefined so that only the calling thread is suspended.

If the process_id argument is -1 and the options argument is 0, the waitpid function behaves the same as the wait function. If these arguments have other values, the waitpid function is changed as specified by those values.

The process_id argument allows the calling process to gather status from a specific set of child processes, according to the following rules:

If the process_id is

Then status is requested

Equal to -1

For any child process. In this respect, the waitpid function is equivalent to the wait function.

Greater than 0

For a single child process and specifies the process ID.

The waitpid function only returns the status of a child process from this set.

The options argument to the waitpid function modifies the behavior of the function. You can combine the flags for the options argument by specifying their bitwise-inclusive OR. The flags are:

WCONTINUED

Specifies that the following is reported to the calling process: the status of any continued child process specified by the process_id argument whose status is unreported since it continued.

WNOWAIT

Specifies that the process whose status is returned in status_location is kept in a waitable state. You can wait for the process again with the same results.

WNOHANG

Prevents the calling process from being suspended. If there are child processes that stopped or terminated, one is chosen and waitpid returns its PID, as when you do not specify the WNOHANG flag. If there are no terminated processes (that is, if waitpid suspends the calling process without the WNOHANG flag), 0 (zero) is returned. Because you can never wait for process 0, there is no confusion arising from this return.

WUNTRACED

Specifies that the call return additional information when the child processes of the current process stop because the child process received a SIGTTIN, SIGTTOU, SIGSTOP, or SIGTSTOP signal.

If the waitpid function returns because the status of a child process is available, the process ID of the child process is returned. Information is stored in the location pointed to by status_location, if this pointer is not null. The value stored in the location pointed to by status_location is 0 only if the status is returned from a terminated child process that did one of the following:

  • Returned 0 from the main function.

  • Passed 0 as the status argument to the _exit or exit function.

Regardless of the value of status_location, you can define this information using the macros defined in the <wait.h> header file, which evaluate to integral expressions. In the following function descriptions, status_value is equal to the integer value pointed to by status_location:

WIFEXITED(status_value)

Evaluates to a nonzero value if status was returned for a child process that terminated normally.

WEXITSTATUS(status_value)

If the value of WIFEXITED (status_value) is nonzero, this macro evaluates to the low-order 8 bits of the status argument that the child process passed to the _exit or exit function, or to the value the child process returned from the main function.

WIFSIGNALED(status_value)

Evaluates to a nonzero value if status returned for a child process that terminated due to the receipt of a signal not intercepted.

WTERMSIG(status_value)

If the value of WIFSIGNALED (status_value) is nonzero, this macro evaluates to the number of the signal that caused the termination of the child process.

WIFSTOPPED(status_value)

Evaluates to a nonzero value if status was returned for a child process that is currently stopped.

WSTOPSIG(status_value)

If the value of WIFSTOPPED (status_value) is nonzero, this macro evaluates to the number of the signal that caused the child process to stop.

WIFCONTINUED(status_value)

Evaluates to a nonzero value if status returned for a child process that continued.

If the information stored at the location pointed to by status_location is stored there by a call to waitpid that specified the WUNTRACED flag, one of the following macros evaluates to a nonzero value:

  • WIFEXITED(*status_value)

  • WIFSIGNALED(*status_value)

  • WIFSTOPPED(*status_value)

  • WIFCONTINUED(*status_value)

If the information stored in the buffer pointed to by status_location resulted from a call to waitpid without the WUNTRACED flag specified, one of the following macros evaluates to a nonzero value:

  • WIFEXITED(*status_value)

  • WIFSIGNALED(*status_value)

If a parent process terminates without waiting for all of its child processes to terminate, the remaining child processes is assigned a parent process ID equal to the process ID of the in it process.

See also exit, _exit, and wait.

Return Values

0

Indicates success. If the WNOHANG option was specified, and there are no stopped or exited child processes, the waitpid function also returns a value of 0.

-1
Indicates an error; errno is set to one of the following values:

  • ECHILD – The calling process has no existing unwaited-for child processes. The process or process group ID specified by the process_id argument does not exist or is not a child process of the calling process.

  • EINTR – The function was terminated by receipt of a signal.

    If the waitpid function returns because the status of a child process is available, the process ID of the child is returned to the calling process. If they return because a signal was intercepted by the calling process, -1 is returned.

  • EFAULT – The status_location argument points to a location outside of the address space of the process.

  • EINVAL – The value of the options argument is not valid.

wcrtomb

wcrtomb — Converts the wide character to its multibyte character representation.

Format

#include <wchar.h>
size_t wcrtomb (char *s, wchar_t wc, mbstate_t *ps);

Arguments

s

A pointer to the resulting multibyte character.

wc

A wide character.

ps

A pointer to the mbstate_t object. If a NULL pointer is specified, the function uses its internal mbstate_t object. mbstate_t is an opaque datatype intended to keep the conversion state for the state-dependent codesets.

Description

If s is a NULL pointer, the wcrtomb function is equivalent to the call:
   wcrtomb (buf, L'\0', ps)

where buf is an internal buffer.

If s is not a NULL pointer, the wcrtomb function determines the number of bytes needed to represent the multibyte character that corresponds to the wide character specified by wc (including any shift sequences), and stores the resulting bytes in the array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored.

If wc is a null wide character, a null byte is stored preceded by any shift sequence needed to restore the initial shift state. The resulting state described is the initial conversion state.

Return Values

n

The number of bytes stored in the resulting array, including any shift sequences to represent the multibyte character.

-1

Indicates an encoding error. The wc argument is not a valid wide character. The global errno is set to EILSEQ; the conversion state is undefined.

wcscat

wcscat — Concatenates two wide-character strings.

Format

#include <wchar.h>
wchar_t *wcscat (wchar_t *wstr_1, const wchar_t *wstr_2);

Function Variants

The wcscat function has variants named _wcscat32 and _wcscat64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

wstr_1, wstr_2

Pointers to null-terminated wide-character strings.

Description

The wcscat function appends the wide-character string wstr_2, including the terminating null character, to the end of wstr_1.

See also wcsncat.

Return Value

x

The first argument, wstr_1, which is assumed to be large enough to hold the concatenated result.

Example

#include <stdlib.h>
#include <stdio.h>
#include <wchar.h>
#include <string.h>

/* This program concatenates two wide-character strings using */
/* the wcscat function, and then manually compares the result */
/* to the expected result                                     */

#define S1LENGTH 10
#define S2LENGTH 8

main()
{
    int i;
    wchar_t s1buf[S1LENGTH + S2LENGTH];
    wchar_t s2buf[S2LENGTH];
    wchar_t test1[S1LENGTH + S2LENGTH];

    /* Initialize the three wide-character strings */


    if (mbstowcs(s1buf, "abcmnexyz", S1LENGTH) == (size_t)-1) {

        perror("mbstowcs");
        exit(EXIT_FAILURE);
    }


    if (mbstowcs(s2buf, " orthis", S2LENGTH) == (size_t)-1) {

        perror("mbstowcs");
        exit(EXIT_FAILURE);
    }

    if (mbstowcs(test1, "abcmnexyz orthis", S1LENGTH + S2LENGTH)

        == (size_t)-1) {

        perror("mbstowcs");
        exit(EXIT_FAILURE);
    }

/* Concatenate s1buf with s2buf, placing the result    */
/* into * s1buf.  Then compare s1buf with the expected */
/* result in test1.                                    */

    wcscat(s1buf, s2buf);

    for (i = 0; i < S1LENGTH + S2LENGTH - 2; i++) {
        /* Check that each character is correct */
        if (test1[i] != s1buf[i]) {
            printf("Error in wcscat\n");
            exit(EXIT_FAILURE);
        }
    }

    printf("Concatenated string: <%S>\n", s1buf);
}
Running the example produces the following result:
Concatenated string: <abcmnexyz orthis>

wcschr

wcschr — Scans for a wide character in a specified wide-character string.

Format

#include <wchar.h>
wchar_t *wcschr (const wchar_t *wstr, wchar_t wc);

Function Variants

The wcschr function has variants named _wcschr32 and _wcschr64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

wstr

A pointer to a null-terminated wide-character string.

wc

A character of type wchar_t.

Description

The wcschr function returns the address of the first occurrence of a specified wide character in a null-terminated wide-character string. The terminating null character is considered to be part of the string.

See also wcsrchr.

Return Values

x

The address of the first occurrence of the specified wide character.

NULL

Indicates that the wide character does not occur in the string.

Example

#include <stdlib.h>
#include <stdio.h>
#include <wchar.h>
#include <string.h>

#define BUFF_SIZE 50

main()
{
    int i;
    wchar_t s1buf[BUFF_SIZE];
    wchar_t *status;

    /* Initialize the buffer */

    if (mbstowcs(s1buf, "abcdefghijkl lkjihgfedcba", BUFF_SIZE)

        == (size_t)-1) {

        perror("mbstowcs");
        exit(EXIT_FAILURE);
    }

 /* This program checks the wcschr function by incrementally */
 /* going through a string that ascends to the middle and    */
 /* then descends towards the end.                           */

    for (i = 0; (s1buf[i] != '\0') && (s1buf[i] != ' '); i++) {
        status = wcschr(s1buf, s1buf[i]);
        /* Check for pointer to leftmost character - test 1. */
        if (status != &s1buf[i]) {
            printf("Error in wcschr\n");
            exit(EXIT_FAILURE);
        }
    }

    printf("Program completed successfully\n");
}
When this example program is run, it produces the following result:
Program completed successfully

wcscmp

wcscmp — Compares two wide-character strings. It returns an integer that indicates if the strings are different, and how they differ.

Format

#include <wchar.h>
int wcscmp (const wchar_t *wstr_1, const wchar_t *wstr_2);

Arguments

wstr_1, wstr_2

Pointers to null-terminated wide-character strings.

Description

The wcscmp function compares the wide characters in wstr_1 with those in wstr_2. If the characters differ, the function returns:

  • An integer less than 0, if the codepoint of the first differing character in wstr_1 is less than the codepoint of the corresponding character in wstr_2

  • An integer greater than 0, if the codepoint of the first differing character in wstr_1 is greater than the codepoint of the corresponding character in wstr_2

If the wide-characters strings are identical, the function returns 0.

Unlike the wcscoll function, the wcscmp function compares the string based on the binary value of each wide character.

See also wcsncmp.

Return Values

< 0

Indicates that wstr_1 is less than wstr_2.

= 0

Indicates that wstr_1 equals wstr_2.

> 0

Indicates that wstr_1 is greater than wstr_2.

wcscoll

wcscoll — Compares two wide-character strings and returns an integer that indicates if the strings differ, and how they differ. The function uses the collating information in the LC_COLLATE category of the current locale to determine how the comparison is performed.

Format

#include <wchar.h>
int wcscoll (const wchar_t *ws1, const wchar_t *ws2);

Arguments

ws1, ws2

Pointers to wide-character strings.

Description

The wcscoll function, unlike wcscmp, compares two strings in a locale-dependent manner. Because no value is reserved for error indication, the application must check for one by setting errno to 0 before the function call and testing it after the call.

See also wcsxfrm.

Return Values

< 0

Indicates that ws1 is less than ws2.

0

Indicates that the strings are equal.

> 0

Indicates that ws1 is greater than ws2.

wcscpy

wcscpy — Copies the wide-character string source, including the terminating null character, into dest.

Format

#include <wchar.h>
wchar_t *wcscpy (wchar_t *dest, const wchar_t *source);

Function Variants

The wcscpy function has variants named _wcscpy32 and _wcscpy64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

dest

Pointer to the null-terminated wide-character destination string.

source

Pointer to the null-terminated wide-character source string.

Description

The wcscpy function copies source into dest, and stops after copying source's null character. If copying takes place between two overlapping strings, the behavior is undefined.

See also wcsncpy.

Return Value

x

The address of source.

wcscspn

wcscspn — Compares the characters in a wide-character string against a set of wide characters. The function returns the length of the initial substring that is comprised entirely of characters that are not in the set of wide characters.

Format

#include <wchar.h>
size_t wcscspn (const wchar_t *wstr1, const wchar_t *wstr2);

Arguments

wstr1

A pointer to a null-terminated wide-character string. If this is a null string, 0 is returned.

wstr2

A pointer to a null-terminated wide-character string that contains the set of wide characters for which the function will search.

Description

The wcscspn function scans the wide characters in the string pointed to by wstr1 until it encounters a character found in wstr2. The function returns the length of the initial segment of wstr1 that is formed by characters not found in wstr2.

Return Value

x

The length of the segment.

Example

#include <stdlib.h>
#include <stdio.h>
#include <wchar.h>
#include <string.h>

/* This test sets up 2 strings, buffer and w_string, and */
/* then uses wcscspn() to calculate the maximum segment  */
/* of w_string, which consists entirely of characters    */
/* NOT from buffer.                                      */

#define BUFF_SIZE 20
#define STRING_SIZE 50

main()
{
    wchar_t buffer[BUFF_SIZE];
    wchar_t w_string[STRING_SIZE];
    size_t result;

    /* Initialize the buffer */


    if (mbstowcs(buffer, "abcdefg", BUFF_SIZE) == (size_t)-1) {

        perror("mbstowcs");
        exit(EXIT_FAILURE);
    }

    /* Initialize the string */

    if (mbstowcs(w_string, "jklmabcjklabcdehjklmno", STRING_SIZE)

        == (size_t)-1) {

        perror("mbstowcs");
        exit(EXIT_FAILURE);
    }

/* Using wcscspn - work out the largest string in w_string */
/* which consists entirely of characters NOT from buffer   */

    result = wcscspn(w_string, buffer);
    printf("Longest segment NOT found in w_string is: %d", result);

}
Running the example program produces the following result:
Longest segment NOT found in w_string is: 4

wcsftime

wcsftime — Uses date and time information stored in a tm structure to create a wide-character output string. The format of the output string is controlled by a format string.

Format

#include <wchar.h>
size_t wcsftime (wchar_t *wcs, size_t maxsize, const char *format,
const struct tm *timeptr); (XPG4)
size_t wcsftime (wchar_t *wcs, size_t maxsize, const wchar_t *format,
const struct tm *timeptr); (ISO C)

Function Variants

Compiling with the _DECC_V4_SOURCE and _VMS_V6_SOURCE feature-test macros defined enables a local-time-based entry point to the wcsftime function that is equivalent to the behavior before OpenVMS Version 7.0.

Arguments

wcs

A pointer to the resultant wide-character string.

maxsize

The maximum number of wide characters to be stored in the resultant string.

format

A pointer to the string that controls the format of the output string. For the XPG4 interface, this argument is a pointer to a constant character string. For the ISO C interface, it is a pointer to a constant wide-character string.

timeptr

A pointer to the local time structure. The tm structure is defined in the <time.h> header file.

Description

The wcsftime function uses data in the structure pointed to by timeptr to create the wide-character string pointed to by wcs. A maximum of maxsize wide characters is copied to wcs.

The format string consists of zero or more conversion specifications and ordinary characters. All ordinary characters (including the terminating null character) are copied unchanged into the output string. A conversion specification defines how data in the tm structure is formatted in the output string.

A conversion specification consists of a percent (%) character followed by one or more optional characters (see Table 45), and ending with a conversion specifier (see Table 46). If any of the optional characters listed in Table 45 are specified, they must appear in the order shown in the table.
Table 45. Optional Elements of wcsftime Conversion Specifications

Element

Meaning

–

Optional with the field width to specify that the field is left-justified and padded with spaces. This cannot be used with the 0 element.

0

Optional with the field width to specify that the field is right-justified and padded with zeros. This cannot be used with the – element.

field width

A decimal integer that specifies the maximum field width.

.precision

A decimal integer that specifies the precision of data in a field.

For the d, H, I, j, m, M, o, S, U, w, W, y, and Y conversion specifiers, the precision specifier is the minimum number of digits to appear in the field. If the conversion specification has fewer digits than that specified by the precision, leading zeros are added.

For the a, A, b, B, c, D, E, h, n, N, p, r, t, T, x, X, Z, and % conversion specifiers, the precision specifier is the maximum number of wide characters to appear in the field. If the conversion specification has more characters than that specified by the precision, characters are truncated on the right.

The default precision for the d, H, I, m, M, o, S, U, w, W, y, and Y conversion specifiers is 2, and the default precision for the j conversion specifier is 3.

Note that the list of optional elements of conversion specifications from Table 45 are VSI extensions to the XPG4 specification.

Table 46 lists the conversion specifiers. The wcsftime function uses fields in the LC_TIME category of the program's current locale to provide a value. For example, if %B is specified, the function accesses the mon field in LC_TIME to find the full month name for the month specified in the tm structure. The result of using invalid conversion specifiers is undefined.
Table 46. wcsftime Conversion Specifiers

Specifier

Replaced by

%a

The locale's abbreviated weekday name.

%A

The locale's full weekday name.

%b

The locale's abbreviated month name.

%B

The locale's full month name.

%c

The locale's appropriate date and time representation.

%C

The century number (the year divided by 100 and truncated to an integer) as a decimal number (00 – 99).

%d

The day of the month as a decimal number (01 – 31).

%D

Same as %m/%d/%y.

%e

The day of the month as a decimal number (1 – 31) in a 2-digit field with the leading space character fill.

%Ec

The locale's alternative date and time representation.

%EC

The name of the base year (period) in the locale's alternative representation.

%Ex

The locale's alternative date representation.

%Ey

The offset from the base year (%EC) in the locale's alternative representation.

%EY

The locale's full alternative year representation.

%F

Same as "%Y−%m−%d" (the ISO 8601 date format). [tm_year, tm_mon, tm_mday]

%g

The last 2 digits of the week-based year as a decimal number (00−99). [tm_year, tm_wday, tm_yday]

%G

The week-based year as a decimal number (for example, 1997). [tm_year, tm_wday, tm_yday]

%h

Same as %b.

%H

The hour (24-hour clock) as a decimal number (00 – 23).

%I

The hour (12-hour clock) as a decimal number (01 – 12).

%j

The day of the year as a decimal number (001 – 366).

%k

The hour (24-hour clock) as a decimal number (range 0 to 23); single digits are preceded by a blank.

%l

The hour (12-hour clock) as a decimal number (range 1 to 12); single digits are preceded by a blank.

%m

The month as a decimal number (01 – 12).

%M

The minute as a decimal number (00 – 59).

%n

The new-line character.

%Od

The day of the month using the locale's alternative numeric symbols.

%Oe

The date of the month using the locale's alternative numeric symbols.

%OH

The hour (24-hour clock) using the locale's alternative numeric symbols.

%OI

The hour (12-hour clock) using the locale's alternative numeric symbols.

%Om

The month using the locale's alternative numeric symbols.

%OM

The minutes using the locale's alternative numeric symbols.

%OS

The seconds using the locale's alternative numeric symbols.

%Ou

The weekday as a number in the locale's alternative representation (Monday=1).

%OU

The week number of the year (Sunday as the first day of the week) using the locale's alternative numeric symbols.

%OV

The week number of the year (Monday as the first day of the week) as a decimal number (01–53) using the locale's alternative numeric symbols. If the week containing January 1 has four or more days in the new year, it is considered as week 1. Otherwise, it is considered as week 53 of the previous year, and the next week is week 1.

%Ow

The weekday as a number (Sunday=0) using the locale's alternative numeric symbols.

%OW

The week number of the year (Monday as the first day of the week) using the locale's alternative numeric symbols.

%Oy

The year without the century using the locale's alternative numeric symbols.

%p

The locale's equivalent of the AM/PM designations associated with a 12-hour clock.

%P

Same as %p but in lowercase: "am" or "pm" or a corresponding string for the current locale.

%r

The time in AM/PM notation.

%R

The time in 24-hour notation (%H:%M).

%s

The number of seconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC).

%S

The second as a decimal number (00 – 61).

%t

The tab character.

%T

The time (%H:%M:%S).

%u

The weekday as a decimal number between 1 and 7 (Monday=1).

%U

The week number of the year (the first Sunday as the first day of week 1) as a decimal number (00 – 53).

%V

The week number of the year (Monday as the first day of the week) as a decimal number (00 – 53). If the week containing January 1 has four or more days in the new year, it is considered as week 1. Otherwise, it is considered as week 53 of the previous year, and the next week is week 1.

%w

The weekday as a decimal number (0 [Sunday] – 6).

%W

The week number of the year (the first Monday as the first day of week 1) as a decimal number (00 – 53).

%x

The locale's appropriate date representation

%X

The locale's appropriate time representation

%y

The year without century as a decimal number (00– 99).

%Y

The year with century as a decimal number.

%z

The +hhmm or -hhmm numeric timezone (that is, the hour and minute offset from UTC).

%Z

The time-zone name or abbreviation. If time-zone information is not available, no character is output.

%+

The date and time in date format.

%%

Literal % character.

Return Values

x

The number of wide characters placed into the array pointed to by wcs, not including the terminating null character.

0

Indicates an error occurred. The contents of the array are indeterminate.

Example

 /* Exercise the wcsftime formatting routine.             */
 /* NOTE: the format string is an "L" (or wide character) */
 /*       string indicating that this call is NOT in      */
 /*       the XPG4 format, but rather in ISO C format.    */

#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <wchar.h>
#include <locale.h>
#include <errno.h>

#define NUM_OF_DATES  7
#define BUF_SIZE 256

 /* This program formats a number of different dates, once using the   */
 /* C locale and then using the fr_FR.ISO8859-1 locale.  Date and time */
 /* formatting is done using wcsftime().                               */

main()

{
  int count,
      i;
  wchar_t buffer[BUF_SIZE];
  struct tm *tm_ptr;
  time_t time_list[NUM_OF_DATES] =
  {500, 68200000, 694223999,
   694224000, 704900000, 705000000,
   705900000};

  /* Display dates using the C locale */
  printf("\nUsing the C locale:\n\n");

  setlocale(LC_ALL, "C");

  for (i = 0; i < NUM_OF_DATES; i++) {
      /* Convert to a tm structure */
      tm_ptr = localtime(&time_list[i]);

      /* Format the date and time */
      count = wcsftime(buffer, BUF_SIZE, L"Date: %A %d %B %Y%nTime: %T%n%n",
                      tm_ptr);
      if (count == 0) {
          perror("wcsftime");
          exit(EXIT_FAILURE);
      }

      /* Print the result */
      printf("%S", buffer);
  }

  /* Display dates using the fr_FR.ISO8859-1 locale */
  printf("\nUsing the fr_FR.ISO8859-1 locale:\n\n");

  setlocale(LC_ALL, "fr_FR.ISO8859-1");

  for (i = 0; i < NUM_OF_DATES; i++) {
      /* Convert to a tm structure */
      tm_ptr = localtime(&time_list[i]);

      /* Format the date and time */
      count = wcsftime(buffer, BUF_SIZE, L"Date: %A %d %B %Y%nTime: %T%n%n",
                       tm_ptr);
      if (count == 0) {
          perror("wcsftime");
          exit(EXIT_FAILURE);
      }

      /* Print the result */
      printf("%S", buffer);
  }
}
Running the example program produces the following result:
Using the C locale:

Date: Thursday 01 January 1970
Time: 00:08:20

Date: Tuesday 29 February 1972
Time: 08:26:40

Date: Tuesday 31 December 1991
Time: 23:59:59

Date: Wednesday 01 January 1992
Time: 00:00:00

Date: Sunday 03 May 1992
Time: 13:33:20

Date: Monday 04 May 1992
Time: 17:20:00

Date: Friday 15 May 1992
Time: 03:20:00


Using the fr_FR.ISO8859-1 locale:

Date: jeudi 01 janvier 1970
Time: 00:08:20

Date: mardi 29 février 1972
Time: 08:26:40

Date: mardi 31 décembre 1991
Time: 23:59:59

Date: mercredi 01 janvier 1992
Time: 00:00:00

Date: dimanche 03 mai 1992
Time: 13:33:20

Date: lundi 04 mai 1992
Time: 17:20:00

Date: vendredi 15 mai 1992
Time: 03:20:00

wcslen

wcslen — Returns the number of wide characters in a wide-character string. The returned length does not include the terminating null character.

Format

#include <wchar.h>
size_t wcslen (const wchar_t *wstr);

Argument

wstr

A pointer to a null-terminated wide-character string.

Return Value

x

The length of the wide-character string, excluding the terminating null wide character.

wcsncat

wcsncat — Concatenates a counted number of wide-characters from one string to another.

Format

#include <wchar.h>
wchar_t *wcsncat (wchar_t *wstr_1, const wchar_t *wstr_2, size_t maxchar);

Function Variants

The wcsncat function has variants named _wcsncat32 and _wcsncat64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

wstr_1, wstr_2

Pointers to null-terminated wide-character strings.

maxchar

The maximum number of wide characters from wstr_2 that are copied to wstr_1. If maxchar is 0, no characters are copied from wstr_2.

Description

The wcsncat function appends wide characters from the wide-character string wstr_2 to the end of wstr_1, up to a maximum of maxchar characters. A terminating null wide character is always appended to the result of the wcsncat function. Therefore, the maximum number of wide characters that can end up in wstr_1 is wcslen(wstr_1) + maxchar + 1).

See also wcscat.

Return Value

x

The first argument, wstr_1, which is assumed to be large enough to hold the concatenated result.

Example

#include <stdlib.h>
#include <stdio.h>
#include <wchar.h>
#include <string.h>

/* This program concatenates two wide-character strings using   */
/* the wcsncat function, and then manually compares the result  */
/* to the expected result                                       */

#define S1LENGTH 10
#define S2LENGTH 8
#define SIZE     3

main()
{
    int i;
    wchar_t s1buf[S1LENGTH + S2LENGTH];
    wchar_t s2buf[S2LENGTH];
    wchar_t test1[S1LENGTH + S2LENGTH];

    /* Initialize the three wide-character strings */


    if (mbstowcs(s1buf, "abcmnexyz", S1LENGTH) == (size_t)-1) {

        perror("mbstowcs");
        exit(EXIT_FAILURE);
    }


    if (mbstowcs(s2buf, " orthis", S2LENGTH) == (size_t)-1) {

        perror("mbstowcs");
        exit(EXIT_FAILURE);
    }

    if (mbstowcs(test1, "abcmnexyz orthis", S1LENGTH + SIZE)

        == (size_t)-1) {

        perror("mbstowcs");
        exit(EXIT_FAILURE);
    }

/* Concatenate s1buf with SIZE characters from s2buf, */
/* placing the result into s1buf. Then compare s1buf  */
/* with the expected result in test1.                 */

    wcsncat(s1buf, s2buf, SIZE);

    for (i = 0; i <= S1LENGTH + SIZE - 2; i++) {
        /* Check that each character is correct */
        if (test1[i] != s1buf[i]) {
            printf("Error in wcsncat\n");
            exit(EXIT_FAILURE);
        }

    }

    printf("Concatenated string: <%S>\n", s1buf);
}
Running the example produces the following result:
Concatenated string: <abcmnexyz or>

wcsncmp

wcsncmp — Compares not more than maxchar characters of two wide-character strings. It returns an integer that indicates if the strings are different, and how they differ.

Format

#include <wchar.h>
int wcsncmp (const wchar_t *wstr_1, const wchar_t *wstr_2, size_t maxchar);

Arguments

wstr_1, wstr_2

Pointers to null-terminated wide-character strings.

maxchar

The maximum number of characters to search in both wstr_1 and wstr_2.If maxchar is 0, no comparison is performed and 0 is returned (the strings are considered equal).

Description

The strings are compared until a null character is encountered, the strings differ, or maxchar is reached. If characters differ, wcsncmp returns:

  • An integer less than 0 if the codepoint of the first differing character in wstr_1 is less than the codepoint of the corresponding character in wstr_2

  • An integer greater than 0 if the codepoint of the first differing character in wstr_1 is greater than the codepoint of the corresponding character in wstr_2

If no differences are found after comparing maxchar characters, the function returns 0.

See also wcscmp.

Return Values

< 0

Indicates that wstr_1 is less than wstr_2.

0

Indicates that wstr_1 equals wstr_2.

> 0

Indicates that wstr_1 is greater than wstr_2.

wcsncpy

wcsncpy — Copies wide characters from source into dest. The function copies up to a maximum of maxchar characters.

Format

#include <wchar.h>
wchar_t *wcsncpy (wchar_t *dest, const wchar_t *source, size_t maxchar);

Function Variants

The wcsncpy function has variants named _wcsncpy32 and _wcsncpy64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

dest

Pointer to the null-terminated wide-character destination string.

source

Pointer to the null-terminated wide-character source string.

maxchar

The maximum number of wide characters to copy from source to dest.

Description

The wcsncpy function copies no more than maxchar characters from source to dest. If source contains less than maxchar characters, null characters are added to dest until maxchar characters have been written to dest.

If source contains maxchar or more characters, as many characters as possible are copied to dest. The null terminator of source is not copied to dest.

See also wcscpy.

Return Value

x

The address of dest.

wcspbrk

wcspbrk — Searches a wide-character string for the first occurrence of one of a specified set of wide characters.

Format

#include <wchar.h>
wchar_t *wcspbrk (const wchar_t *wstr, const wchar_t *charset);

Function Variants

The wcspbrk function has variants named _wcspbrk32 and _wcspbrk64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

wstr

A pointer to a wide-character string. If this is a null string, NULL is returned.

charset

A pointer to a wide-character string containing the set of wide characters for which the function will search.

Description

The wcspbrk function scans the wide characters in the string, stops when it encounters a wide character found in charset, and returns the address of the first character in the string that appears in the character set.

Return Values

x

The address of the first wide character in the string that is in the set.

NULL

Indicates that none of the characters are in charset.

wcsrchr

wcsrchr — Scans for the last occurrence of a wide character in a given string.

Format

#include <wchar.h>
wchar_t *wcsrchr (const wchar_t *wstr, wchar_t wc);

Function Variants

The wcsrchr function has variants named _wcsrchr32 and _wcsrchr64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

wstr

A pointer to a null-terminated wide-character string.

wc

A character of type wchar_t.

Description

The wcsrchr function returns the address of the last occurrence of a given wide character in a null-terminated wide-character string. The terminating null character is considered to be part of the string.

See also wcschr.

Return Values

x

The address of the last occurrence of the specified wide character.

NULL

Indicates that the wide character does not occur in the string.

Example

#include <stdlib.h>
#include <stdio.h>
#include <wchar.h>
#include <string.h>

#define BUFF_SIZE 50
#define STRING_SIZE 6

main()
{
    int i;
    wchar_t s1buf[BUFF_SIZE],
            w_string[STRING_SIZE];
    wchar_t *status;
    wchar_t *pbuf = s1buf;

    /* Initialize the buffer */

    if (mbstowcs(s1buf, "hijklabcdefg ytuhijklfedcba", BUFF_SIZE)

        == (size_t)-1) {

        perror("mbstowcs");
        exit(EXIT_FAILURE);
    }

    /* Initialize the string to be searched for */


    if (mbstowcs(w_string, "hijkl", STRING_SIZE) == (size_t)-1) {

        perror("mbstowcs");
        exit(EXIT_FAILURE);
   }

/* This program checks the wcsrchr function by searching for */
/* the last occurrence of a string in the buffer s1buf and   */
/* prints out the contents of s1buff from the location of
/* the string found.                                         */

    status = wcsrchr(s1buf, w_string[0]);
/* Check for pointer to start of rightmost character string. */
    if (status == pbuf) {
        printf("Error in wcsrchr\n");
        exit(EXIT_FAILURE);
    }

    printf("Program completed successfully\n");
    printf("String found : [%S]\n", status);

}
Running the example produces the following result:
Program completed successfully
String found : [hijklfedcba]

wcsrtombs

wcsrtombs — Converts a sequence of wide characters into a sequence of corresponding multibyte characters.

Format

#include <wchar.h>
size_t wcsrtombs (char *dst, const wchar_t **src, size_t len,
mbstate_t *ps);

Function Variants

The wcsrtombs function has variants named _wcsrtombs32 and _wcsrtombs64 for use with32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

dst

A pointer to the destination array for converted multibyte character sequence.

src

An address of the pointer to an array containing the sequence of wide characters to be converted.

len

The maximum number of bytes that can be stored in the array pointed to by dst.

ps

A pointer to the mbstate_t object. If a NULL pointer is specified, the function uses its internal mbstate_t object. mbstate_t is an opaque datatype intended to keep the conversion state for the state-dependent codesets.

Description

The wcsrtombs function converts a sequence of wide characters from the array indirectly pointed to by src into a sequence of corresponding multibyte characters, beginning in the conversion state described by the object pointed to by ps.

If dst is a not a NULL pointer, the converted characters are then stored into the array pointed to by dst. Conversion continues up to and including a terminating null wide character, which is also stored.

Conversion stops earlier in two cases:

  • When a code is reached that does not correspond to a valid multibyte character

  • If dst is not a NULL pointer, when the next multibyte character would exceed the limit of len total bytes to be stored into the array pointed to by dst

Each conversion takes place as if by a call to the wcrtomb function.

If dst is not a NULL pointer, the pointer object pointed to by src is assigned either a NULL pointer (if the conversion stopped because it reached a terminating null wide character) or the address just beyond the last wide character converted (if any). If conversion stopped because it reached a terminating null wide character, the resulting state described is the initial conversion state.

If the wcsrtombs function is called as a counting function, which means that dst is a NULL pointer, the value of the internal mbstate_t object will remain unchanged.

See also wcrtomb.

Return Values

x

The number of bytes stored in the resulting array, not including the terminating null (if any).

-1

Indicates an encoding error – a character that does not correspond to a valid multibyte character was encountered; errno is set to EILSEQ; the conversion state is undefined.

wcsspn

wcsspn — Compares the characters in a wide-character string against a set of wide characters. The function returns the length of the first substring comprised entirely of characters in the set of wide characters.

Format

#include <wchar.h>
size_t wcsspn (const wchar_t *wstr1, const wchar_t *wstr2);

Arguments

wstr1

A pointer to a null-terminated wide-character string. If this string is a null string, 0 is returned.

wstr2

A pointer to a null-terminated wide-character string that contains the set of wide characters for which the function will search.

Description

The wcsspn function scans the wide characters in the wide-character string pointed to by wstr1 until it encounters a character not found in wstr2. The function returns the length of the first segment of wstr1 formed by characters found in wstr2.

Return Value

x

The length of the segment.

Example

#include <stdlib.h>
#include <stdio.h>
#include <wchar.h>
#include <string.h>

/* This test sets up 2 strings, buffer and w_string. It */
/* then uses wcsspn() to calculate the maximum segment  */
/* of w_string that consists entirely of characters     */
/* from buffer.                                         */

#define BUFF_SIZE 20
#define STRING_SIZE 50

main()
{
    wchar_t buffer[BUFF_SIZE];
    wchar_t w_string[STRING_SIZE];
    size_t result;

    /* Initialize the buffer */


    if (mbstowcs(buffer, "abcdefg", BUFF_SIZE) == (size_t)-1) {

        perror("mbstowcs");
        exit(EXIT_FAILURE);
    }

    /* Initialize the string */

    if (mbstowcs(w_string, "abcedjklmabcjklabcdehjkl", STRING_SIZE)

        == (size_t)-1) {

        perror("mbstowcs");
        exit(EXIT_FAILURE);
    }

/* Using wcsspn - work out the largest string in w_string */
/* that consists entirely of characters from buffer       */

    result = wcsspn(w_string, buffer);
    printf("Longest segment found in w_string is: %d", result);

}
Running the example program produces the following result:
Longest segment found in w_string is: 5

wcsstr

wcsstr — Locates the first occurrence in the string pointed to by s1 of the sequence of wide characters in the string pointed to by s2.

Format

#include <wchar.h>
wchar_t *wcsstr (const wchar_t *s1, const wchar_t *s2);

Function Variants

The wcsstr function has variants named _wcsstr32 and _wcsstr64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

s1, s2

Pointers to null-terminated, wide-character strings.

Description

If s2 points to a wide-character string of 0 length, the wcsstr function returns s1.

Return Values

x

A pointer to the located string.

NULL

Indicates an error; the string was not found.

wcstod

wcstod — Converts a given wide-character string to a double-precision number.

Format

#include <wchar.h>
double wcstod (const wchar_t *nptr, wchar_t **endptr);

Arguments

nptr

A pointer to the wide-character string to be converted to a double-precision number.

endptr

The address of an object where the function can store the address of the first unrecognized wide character that terminates the scan. If endptr is a NULL pointer, the address of the first unrecognized wide character is not retained.

Description

The wcstod function recognizes an optional sequence of white-space characters (as defined by iswspace), then an optional plus or minus sign, then a sequence of digits optionally containing a radix character, then an optional letter (e or E) followed by an optionally signed integer. The first unrecognized character ends the conversion.

The string is interpreted by the same rules used to interpret floating constants.

The radix character is defined in the program's current locale (category LC_NUMERIC).

This function returns the converted value. For wcstod, overflows are accounted for in the following manner:

  • If the correct value causes an overflow, HUGE_VAL (with a plus or minus sign according to the sign of the value) is returned and errno is set to ERANGE.

  • If the correct value causes an underflow, 0 is returned and errno is set to ERANGE.

If the string starts with an unrecognized wide character, *endptr is set to nptr and a 0 value is returned.

Return Values

x

The converted string.

0
Indicates the conversion could not be performed. The function sets errno to one of:

  • EINVAL – No conversion could be performed.

  • ERANGE – The value would cause an underflow.

  • ENOMEM – Not enough memory available for internal conversion buffer.

±HUGE_VAL

Overflow occurred; errno is set to ERANGE.

wcstof

wcstof — Converts a wide-character string to a float.

Format

#include <wchar.h>
float wcstof (const wchar_t * restrict nptr,
wchar_t ** restrict endptr);

Function Variants

The wcstof function has variants named _wcstof32 and _wcstof64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

nptr

A pointer to the wide-character string to be converted.

endptr

If this argument is not NULL, the function stores in it a pointer to the character that follows the last character used in the conversion.

Description

The wcstof function converts the initial portion of the wide-character string pointed to by nptr to float representation.

First, this function decomposes the input string into three parts: an initial, possibly empty, sequence of white-space characters (as specified by the isspace function); a subject sequence resembling a floating-point constant or representing an infinity or NaN; and a final string of one or more unrecognized characters, including the terminating null character of the input string. Then, it attempts to convert the subject sequence to a floating-point number, and returns the result as a value of type float.

The expected form of the (initial portion of the) wide string is optional leading white space, an optional plus ('+') or minus sign ('-') and then either (i) a decimal number, or (ii) a hexadecimal number, or (iii) an infinity, or (iv) a NaN (not-a-number).

Return Values

x

The converted value.

±HUGE_VALF

If the correct value is outside the range of representable values of the type, ±HUGE_VALF is returned according to the sign of the value; and errno is set to ERANGE.

n

If the result underflows, the function returns a value whose magnitude is no greater than the smallest normalized positive number; whether errno acquires the value ERANGE is implementation-defined.

0

If no valid conversion could be performed.

wcstok

wcstok — Locates text tokens in a given wide-character string.

Format

#include <wchar.h>
wchar_t *wcstok (wchar_t *ws1, const wchar_t *ws2); (XPG4)
wchar_t *wcstok (wchar_t *ws1, const wchar_t *ws2, wchar_t **ptr); (ISO C)

Function Variants

The wcstok function has variants named _wcstok32 and _wcstok64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

ws1

A pointer to a wide-character string containing zero or more text tokens.

ws2

A pointer to a separator string consisting of one or more wide characters. The separator string can differ from call to call.

ptr

ISO C Standard only. Used only when ws1 is NULL, ptr is a caller-provided wchar_t pointer into which wcstok stores information necessary for it to continue scanning the same wide-character string.

Description

A sequence of calls to wcstok breaks the wide-character string pointed to by ws1 into a sequence of tokens, each of which is delimited by a wide character from the wide-character string pointed to by ws2.

The wcstok function keeps track of its position in the wide-character string between calls and, as successive calls are made, the function works through the wide-character string, identifying the text token following the one identified by the previous call.

Tokens in ws1 are delimited by null characters that wcstok inserts into ws1. Therefore, ws1 cannot be a const object.

The following sections describe differences between the XPG4 Standard and ISO C Standard interface to wcstok.

XPG4 Standard Behavior

The first call to the wcstok function searches the wide-character string for the first character that is not found in the separator string pointed to by ws2. The first call returns a pointer to the first wide character in the first token and writes a null wide character into ws1 immediately following the returned token.

Subsequent calls to wcstok search for a wide character that is in the separator string pointed to by ws2. Each subsequent call (with the value of the first argument remaining NULL) returns a pointer to the next token in the string originally pointed to by ws1. When no tokens remain in the string, wcstok returns a NULL pointer.

ISO C Standard Behavior

For the first call in the sequence, ws1 points to a wide-character string. In subsequent calls for the same string, ws1 is NULL. When ws1 is NULL, the value pointed to by ptr matches that stored by the previous call for the same wide-character string. Otherwise, the value pointed to by ptr is ignored.

The first call in the sequence searches the wide-character string pointed to by ws1 for the first wide character that is not contained in the current separator wide-character string pointed to by ws2. If no such wide character is found, then there are no tokens in the wide-character string pointed to by ws1, and wcstok returns a NULL pointer.

The wcstok function then searches from there for a wide character that is contained in the current separator wide-character string. If no such wide character is found, the current token extends to the end of the wide-character string pointed to by ws1, and subsequent searches in the same wide-character string for a token return a NULL pointer. If such a wide character is found, it is overwritten by a null wide character, which terminates the current token.

In all cases, wcstok stores sufficient information in the pointer pointed to by ptr so that subsequent calls with a NULL pointer for ws1 and the unmodified pointer value for ptr start searching just past the element overwritten by a null wide character (if any).

Return Values

x

A pointer to the first character of a token.

NULL

Indicates that no token was found.

Examples

  1. /* XPG4 version of wcstok call */

#include <wchar.h>
#include <string.h>
#include <stdio.h>

main()
{
    wchar_t str[] = L"...ab..cd,,ef.hi";

    printf("|%S|\n", wcstok(str, L"."));
    printf("|%S|\n", wcstok(NULL, L","));
    printf("|%S|\n", wcstok(NULL, L",."));
    printf("|%S|\n", wcstok(NULL, L",."));
}
  2. /* ISO C version of wcstok call */

#include <wchar.h>
#include <string.h>
#include <stdio.h>

main()
{
    wchar_t str[] = L"...ab..cd,,ef.hi";
    wchar_t *savptr = NULL;

    printf("|%S|\n", wcstok(str, L".", &savptr));
    printf("|%S|\n", wcstok(NULL, L",", &savptr));
    printf("|%S|\n", wcstok(NULL, L",.", &savptr));
    printf("|%S|\n", wcstok(NULL, L",.", &savptr));
}
Running this example produces the following results:
$ $ RUN WCSTOK_EXAMPLE
|ab|
|.cd|
|ef|
|hi|
$

wcstol

wcstol — Converts a wide-character string in a specified base to a long integer value.

Format

#include <wchar.h>
long long int wcstol (const wchar_t *nptr, wchar_t **endptr, int base);

Function Variants

The wcstol function has variants named _wcstol32 and _wcstol64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

nptr

A pointer to the wide-character string to be converted to a long integer.

endptr

The address of an object where the function can store a pointer to the first unrecognized character encountered in the conversion process (the character that follows the last character processed in the string being converted). If endptr is a NULL pointer, the address of the first unrecognized character is not retained.

base

The value, 2 through 36, to use as the base for the conversion.

If base is 16, leading zeros after the optional sign are ignored, and 0x or 0X is ignored.

If base is 0, the sequence of characters is interpreted by the same rules used to interpret an integer constant. After the optional sign:

  • A leading 0 indicates octal conversion.

  • A leading 0x or 0X indicates hexadecimal conversion.

  • Any other combination of leading characters indicates decimal conversion.

Description

The wcstol function recognizes strings in various formats, depending on the value of the base. This function ignores any leading white-space characters (as defined by the iswspace function) in the given string. It recognizes an optional plus or minus sign, then a sequence of digits or letters that can represent an integer constant according to the value of the base. The first unrecognized character ends the conversion.

Return Values

x

The converted value.

0

Indicates that the string starts with an unrecognized wide character or that the value for base is invalid. If the string starts with an unrecognized wide character, *endptr is set to nptr. The function sets errno to EINVAL.

LONG_MAX or LONG_MIN

Indicates that the converted value would cause a positive or negative overflow, respectively. The function sets errno to ERANGE.

wcstold

wcstold — Converts a wide-character string to a long double.

Format

#include <wchar.h>
long double wcstold (const wchar_t * restrict nptr,
wchar_t ** restrict endptr);

Function Variants

The wcstold function has variants named _wcstold32 and _wcstold64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Argumants

nptr

A pointer to the wide-character string to be converted.

endptr

If this argument is not NULL, the function stores in it a pointer to the character that follows the last character used in the conversion.

Description

The wcstold function converts the initial portion of the wide-character string pointed to by nptr to long double representation.

First, this function decomposes the input string into three parts: an initial, possibly empty, sequence of white-space characters (as specified by the isspace function); a subject sequence resembling a floating-point constant or representing an infinity or NaN; and a final string of one or more unrecognized characters, including the terminating null character of the input string. Then, it attempts to convert the subject sequence to a floating-point number, and returns the result as a value of type long double.

The expected form of the (initial portion of the) wide string is optional leading white space, an optional plus ('+') or minus sign ('-') and then either (i) a decimal number, or (ii) a hexadecimal number, or (iii) an infinity, or (iv) a NaN (not-a-number).

Return Values

x

The converted value.

±HUGE_VALL

If the correct value is outside the range of representable values for the type, ±HUGE_VALL is returned according to the sign of the value; and errno is set to ERANGE.

n

If the result underflows, the function returns a value whose magnitude is no greater than the smallest normalized positive number; whether errno acquires the value ERANGE is implementation-defined.

0

If no valid conversion could be performed.

wcstoll

wcstoll — Converts a wide-character string in a specified base to a long long integer value.

Format

#include <wchar.h>
long int wcstoll (const wchar_t *nptr, wchar_t **endptr, int base);

Function Variants

The wcstoll function has variants named _wcstoll32 and _wcstoll64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

nptr

A pointer to the wide-character string to be converted to a long long integer.

endptr

The address of an object where the function can store a pointer to the first unrecognized character encountered in the conversion process (the character that follows the last character processed in the string being converted). If endptr is a NULL pointer, the address of the first unrecognized character is not retained.

base

The value, 2 through 36, to use as the base for the conversion.

If base is 16, leading zeros after the optional sign are ignored, and 0x or 0X is ignored.

If base is 0, the sequence of characters is interpreted by the same rules used to interpret an integer constant. After the optional sign:

  • A leading 0 indicates octal conversion.

  • A leading 0x or 0X indicates hexadecimal conversion.

  • Any other combination of leading characters indicates decimal conversion.

Description

The wcstoll function recognizes strings in various formats, depending on the value of the base. This function ignores any leading white-space characters (as defined by the iswspace function) in the given string. It recognizes an optional plus or minus sign, then a sequence of digits or letters that can represent an integer constant according to the value of the base. The first unrecognized character ends the conversion.

Return Values

x

The converted value.

0

Indicates that the string starts with an unrecognized wide character or that the value for base is invalid. If the string starts with an unrecognized wide character, *endptr is set to nptr. The function sets errno to EINVAL.

LLONG_MAX or LLONG_MIN

Indicates that the converted value would cause a positive or negative overflow, respectively. The function sets errno to ERANGE.

wcstombs

wcstombs — Converts a sequence of wide-character codes to a sequence of multibyte characters.

Format

#include <stdlib.h>
size_t wcstombs (char *s, const wchar_t *pwcs, size_t n);

Arguments

s

A pointer to the array containing the resulting multibyte characters.

pwcs

A pointer to the array containing the sequence of wide-character codes.

n

The maximum number of bytes to be stored in the array pointed to by s.

Description

The wcstombs function converts a sequence of codes corresponding to multibyte characters from the array pointed to by pwcs to a sequence of multibyte characters that are stored into the array pointed to by s, up to a maximum of n bytes. The value returned is equal to the number of characters converted or a -1 if an error occurred.

This function is affected by the LC_CTYPE category of the program's current locale.

If s is NULL, this function call is a counting operation and n is ignored.

See also wctomb.

Return Values

x

The number of bytes stored in s, not including the null terminating byte. If s is NULL, wcstombs returns the number of bytes required for the multibyte character array.

(size_t) -1

Indicates an error occurred. The function sets errno to EILSEQ – invalid character sequence, or a wide-character code does not correspond to a valid character.

wcstoul

wcstoul — Converts the initial portion of the wide-character string pointed to by nptr to an unsigned long integer.

Format

#include <wchar.h>
unsigned long int wcstoul (const wchar_t *nptr, wchar_t **endptr,
int base);

Function Variants

The wcstoul function has variants named _wcstoul32 and _wcstoul64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

nptr

A pointer to the wide-character string to be converted to an unsigned long.

endptr

The address of an object where the function can store the address of the first unrecognized character encountered in the conversion process (the character that follows the last character in the string being converted). If endptr is a NULL pointer, the address of the first unrecognized character is not retained.

base

The value, 2 through 36, to use as the base for the conversion.

If base is 16, leading zeros after the optional sign are ignored, and 0x or 0X is ignored.

If base is 0, the sequence of characters is interpreted by the same rules used to interpret an integer constant: after the optional sign, a leading 0 indicates octal conversion, a leading 0x or 0X indicates hexadecimal conversion, and any other combination of leading characters indicates decimal conversion.

Description

The wcstoul function recognizes strings in various formats, depending on the value of the base. It ignores any leading white-space characters (as defined by the iswspace function) in the string. It recognizes an optional plus or minus sign, then a sequence of digits or letters that may represent an integer constant according to the value of the base. The first unrecognized wide character ends the conversion.

Return Values

x

The converted value.

0

Indicates that the string starts with an unrecognized wide character or that the value for base is invalid. If the string starts with an unrecognized wide character, *endptr is set to nptr. The function sets errno to EINVAL.

ULONG_MAX

Indicates that the converted value would cause an overflow. The function sets errno to ERANGE.

Example

#include <stdlib.h>
#include <stdio.h>
#include <wchar.h>
#include <errno.h>
#include <limits.h>

/* This test calls wcstoul() to convert a string to an     */
/* unsigned long integer. wcstoul outputs the resulting    */
/* integer and any characters that could not be converted. */

#define MAX_STRING 128

main()
{

    int base = 10,
        errno;
    char *input_string = "1234.56";
    wchar_t string_array[MAX_STRING],
           *ptr;
    size_t size;
    unsigned long int val;
    printf("base = [%d]\n", base);
    printf("String to convert = %s\n", input_string);
    if ((size = mbstowcs(string_array, input_string, MAX_STRING)) ==

        (size_t)-1) {

        perror("mbstowcs");
        exit(EXIT_FAILURE);
    }
    printf("wchar_t string is = [%S]\n", string_array);

    errno = 0;
    val = wcstoul(string_array, &ptr, base);
    if (errno == 0) {
printf("returned unsigned long int from wcstoul = [%u]\n", val);
      printf("wide char terminating scan(ptr) = [%S]\n\n", ptr);
    }
    if (errno == ERANGE) {
        perror("error value is :");
        printf("ULONG_MAX = [%u]\n", ULONG_MAX);
        printf("wcstoul failed, val = [%d]\n\n", val);
    }

}
Running the example program produces the following result:
base = [10]
String to convert = 1234.56
wchar_t string is = [1234.56]
returned unsigned long int from wcstoul = [1234]
wide char terminating scan(ptr) = [.56]

wcstoull

wcstoull — Converts the initial portion of the wide-character string pointed to by nptr to an unsigned long long integer.

Format

#include <wchar.h>
unsigned long long int wcstoull (const wchar_t *nptr, wchar_t **endptr,
int base);

Function Variants

The wcstoull function has variants named _wcstoull32 and _wcstoull64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

nptr

A pointer to the wide-character string to be converted to an unsigned long long.

endptr

The address of an object where the function can store the address of the first unrecognized character encountered in the conversion process (the character that follows the last character in the string being converted). If endptr is a NULL pointer, the address of the first unrecognized character is not retained.

base

The value, 2 through 36, to use as the base for the conversion.

If base is 16, leading zeros after the optional sign are ignored, and 0x or 0X is ignored.

If base is 0, the sequence of characters is interpreted by the same rules used to interpret an integer constant: after the optional sign, a leading 0 indicates octal conversion, a leading 0x or 0X indicates hexadecimal conversion, and any other combination of leading characters indicates decimal conversion.

Description

The wcstoull function recognizes strings in various formats, depending on the value of the base. It ignores any leading white-space characters (as defined by the iswspace function) in the string. It recognizes an optional plus or minus sign, then a sequence of digits or letters that may represent an integer constant according to the value of the base. The first unrecognized wide character ends the conversion.

Return Values

x

The converted value.

0

Indicates that the string starts with an unrecognized wide character or that the value for base is invalid. If the string starts with an unrecognized wide character, *endptr is set to nptr. The function sets errno to EINVAL.

ULLONG_MAX

Indicates that the converted value would cause an overflow. The function sets errno to ERANGE.

wcswcs

wcswcs — Locates the first occurrence in the string pointed to by wstr1 of the sequence of wide characters in the string pointed to by wstr2.

Format

#include <wchar.h>
wchar_t *wcswcs (const wchar_t *wstr1, const wchar_t *wstr2);

Function Variants

The wcswcs function has variants named _wcswcs32 and _wcswcs64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

wstr1, wstr2

Pointers to null-terminated wide-character strings.

Return Values

Pointer

A pointer to the located wide-character string.

NULL

Indicates that the wide-character string was not found.

Example

#include <stdlib.h>
#include <stdio.h>
#include <wchar.h>

/* This test uses wcswcs() to find the occurrence of each */
/* subwide-character string, string1 and string2, within  */
/* the main wide-character string, lookin.                */

#define BUF_SIZE 50

main()
{
  static char lookin[] = "that this is a test was at the end";

  char string1[] = "this",
       string2[] = "the end";

  wchar_t buffer[BUF_SIZE],
          input_buffer[BUF_SIZE];

  /* Convert lookin to wide-character format.         */
  /* Buffer and print it out.                         */


  if (mbstowcs(buffer, lookin, BUF_SIZE) == (size_t)-1) {

      perror("mbstowcs");
      exit(EXIT_FAILURE);
  }

  printf("Buffer to look in: %S\n", buffer);

  /* Convert string1 to wide-character format and use */
  /* wcswcs() to locate it within buffer              */


  if (mbstowcs(input_buffer, string1, BUF_SIZE) == (size_t)-1) {

      perror("mbstowcs");
      exit(EXIT_FAILURE);
  }

  printf("this: %S\n", wcswcs(buffer, input_buffer));

  /* Convert string2 to wide-character format and use */
  /* wcswcs() to locate it within buffer              */


  if (mbstowcs(input_buffer, string2, BUF_SIZE) == (size_t)-1) {

      perror("mbstowcs");
      exit(EXIT_FAILURE);
  }
  printf("the end: %S\n", wcswcs(buffer, input_buffer));

  exit(1);
}
Running this example produces the following results:
Buffer to look in: that this is a test was at the end
this: this is a test was at the end
the end: the end

wcswidth

wcswidth — Determines the number of printing positions on a display device that are required for a wide-character string.

Format

#include <wchar.h>
int wcswidth (const wchar_t *pwcs, size_t n);

Arguments

pwcs

A pointer to a wide-character string.

n

The maximum number of characters in the string.

Description

The wcswidth function returns the number of printing positions required to display the first n characters of the string pointed to by pwcs. If there are less than n wide characters in the string, the function returns the number of positions required for the whole string.

Return Values

x

The number of printing positions required.

0

If pwcs is a null character.

-1

Indicates that one (or more) of the wide characters in the string pointed to by pwcs is not a printable character.

wcsxfrm

wcsxfrm — Changes a wide-character string such that the changed string can be passed to the wcscmp function and produce the same result as passing the unchanged string to the wcscoll function.

Format

#include <wchar.h>
size_t wcsxfrm (wchar_t *ws1, const wchar_t *ws2, size_t maxchar);

Arguments

ws1, ws2

Pointers to wide-character strings.

maxchar

The maximum number of wide characters, including the null wide-character terminator, allowed to be stored in s1.

Description

The wcsxfrm function transforms the string pointed to by ws2 and stores the resulting string in the array pointed to by ws1. No more than maxchar wide characters, including the null wide terminator, are placed into the array pointed to by ws1.

If the value of maxchar is less than the required size to store the transformed string (including the terminating null), the contents of the array pointed to by ws1 is indeterminate. In such a case, the function returns the size of the transformed string.

If maxchar is 0, then, ws1 is allowed to be a NULL pointer, and the function returns the required size of the ws1 array before making the transformation.

The wide-character string comparison functions, wcscoll and wcscmp, can produce different results given the same two wide-character strings to compare. This is because wcscmp does a straightforward comparison of the code point values of the characters in the strings, whereas wcscoll uses the locale information to do the comparison. Depending on the locale, the wcscoll comparison can be a multipass operation, which is slower than wcscmp.

The wcsxfrm function transforms wide-character strings in such a way that if you pass two transformed strings to the wcscmp function, the result is the same as passing the two original strings to the wcscoll function. The wcsxfrm function is useful in applications that need to do a large number of comparisons on the same wide-character strings using wcscoll. In this case, it may be more efficient (depending on the locale) to transform the strings once using wcsxfrm and then use the wcscmp function to do comparisons.

Return Values

x

Length of the resulting string pointed to by ws1, not including the terminating null character.

(size_t) -1

Indicates that an error occurred. The function sets errno to EINVAL – The string pointed to by ws2 contains characters outside the domain of the collating sequence.

Example

#include <wchar.h>
#include <stdio.h>
#include <stdlib.h>
#include <locale.h>

 /* This program verifies that two transformed strings,    */
 /* when passed through wcsxfrm and then compared, provide */
 /* the same result as if passed through wcscoll without   */
 /* any transformation.                                    */

#define  BUFF_SIZE  20

main()
{
    wchar_t w_string1[BUFF_SIZE];
    wchar_t w_string2[BUFF_SIZE];
    wchar_t w_string3[BUFF_SIZE];
    wchar_t w_string4[BUFF_SIZE];
    int errno;
    int coll_result;
    int wcscmp_result;
    size_t wcsxfrm_result1;
    size_t wcsxfrm_result2;

    /* setlocale to French locale */

    if (setlocale(LC_ALL, "fr_FR.ISO8859-1") == NULL) {
        perror("setlocale");
        exit(EXIT_FAILURE);
    }

    /* Convert each of the strings into wide-character format. */


    if (mbstowcs(w_string1, "<a`>bcd", BUFF_SIZE) == (size_t)-1) {

        perror("mbstowcs");
        exit(EXIT_FAILURE);
    }


    if (mbstowcs(w_string2, "abcz", BUFF_SIZE) == (size_t)-1) {

        perror("mbstowcs");
        exit(EXIT_FAILURE);
    }

    /* Collate string 1 and string 2 and store the result. */

    errno = 0;
    coll_result = wcscoll(w_string1, w_string2);
    if (errno) {
        perror("wcscoll");
        exit(EXIT_FAILURE);
    }
    else {

       /*  Transform the strings (using wcsxfrm) into  */
       /*  w_string3 and w_string4.                    */

       wcsxfrm_result1 = wcsxfrm(w_string3, w_string1, BUFF_SIZE);

       if (wcsxfrm_result1 == ((size_t) - 1))
           perror("wcsxfrm");
       else if (wcsxfrm_result1 > BUFF_SIZE) {
           perror("\n** String is too long **\n");
           exit(EXIT_FAILURE);
       }
       else {
          wcsxfrm_result2 = wcsxfrm(w_string4, w_string2, BUFF_SIZE);
          if (wcsxfrm_result2 == ((size_t) - 1)) {
              perror("wcsxfrm");
              exit(EXIT_FAILURE);
           }
          else if (wcsxfrm_result2 > BUFF_SIZE) {
              perror("\n** String is too long **\n");
              exit(EXIT_FAILURE);
           }

        /* Compare the two transformed strings and verify that  */
        /* the result is the same as the result from wcscoll on */
        /* the original strings.                                */

          else {
              wcscmp_result = wcscmp(w_string3, w_string4);
              if (wcscmp_result == 0 && (coll_result == 0)) {
                  printf("\nReturn value from wcscoll() and return value"
                                       " from wcscmp() are both zero.");
                  printf("\nThe program was successful\n\n");
              }
              else if ((wcscmp_result < 0) && (coll_result < 0)) {
                  printf("\nReturn value from wcscoll() and return value"
                                  " from wcscmp() are less than zero.");
                  printf("\nThe program was successful\n\n");
              }
              else if ((wcscmp_result > 0) && (coll_result > 0)) {
                  printf("\nReturn value from wcscoll() and return value"
                                " from wcscmp() are greater than zero.");
                  printf("\nThe program was successful\n\n");
              }
              else {
                  printf("** Error **\n");
                  printf("\nReturn values are not of the same type");
              }
           }
       }
    }
}
Running the example program produces the following result:
Return value from wcscoll() and return value
       from wcscmp() are less than zero.
The program was successful

wctob

wctob — Determines if a wide character corresponds to a single-byte multibyte character and returns its multibyte character representation.

Format

#include <stdio.h>
#include <wchar.h>
int wctob (wint_t c);

Argument

c

The wide character to be converted to a single-byte multibyte character.

Description

The wctob function determines whether the specified wide character corresponds to a single-byte multibyte character when in the initial shift state and, if so, returns its multibyte character representation.

Return Values

x

The single-byte representation of the wide character specified.

EOF

Indicates an error. The wide character specified does not correspond to a single-byte multibyte character.

wctomb

wctomb — Converts a wide character to its multibyte character representation.

Format

#include <stdlib.h>
int wctomb (char *s, wchar_t wchar);

Arguments

s

A pointer to the resulting multibyte character.

wchar

The code for the wide character.

Description

The wctomb function converts the wide character specified by wchar to its multibyte character representation. If s is NULL, then 0 is returned. Otherwise, the number of bytes comprising the multibyte character is returned. At most, MB_CUR_MAX bytes are stored in the array object pointed to by s.

This function is affected by the LC_CTYPE category of the program's current locale.

Return Values

x

The number of bytes comprising the multibyte character corresponding to wchar.

0

If s is NULL.

-1

If wchar is not a valid character.

wctrans

wctrans — Returns the description of a mapping, corresponding to specified property, that can later be used in a call to towctrans.

Format

#include <wctype.h>
wctrans_t wctrans (const char *property);

Argument

property

The name of the mapping. The following property names are defined for all locales:

  • "toupper"

  • "tolower"

Additional property names may also be defined in the LC_CTYPE category of the current locale.

Description

The wctrans function constructs a value with type wctrans_t that describes a mapping between wide characters identified by the property argument.

See also towctrans.

Return Values

nonzero

According to the LC_CTYPE category of the current program locale, the string specified as a property argument is the name of an existing character mapping. The value returned can be used in a call to the towctrans function.

0

Indicates an error. The property argument does not identify a character mapping in the current program's locale.

wctype

wctype — Used for defining a character class. The value returned by this function is used in calls to the iswctype function.

Format

#include <wctype.h> (ISO C)
#include <wchar.h> (XPG4)
wctype_t wctype (const char *char_class);

Argument

char_class

A pointer to a valid character class name.

Description

The wctype function converts a valid character class defined for the current locale to an object of type wctype_t. The following character class names are defined for all locales:
alnum        cntrl        lower        space
alpha        digit        print        upper
blank        graph        punct        xdigit

Additional character class names may also be defined in the LC_CTYPE category of the current locale.

See also iswctype.

Return Values

x

An object of type wctype_t that can be used in calls to the iswctype function.

0

If the character class name is not valid for the current locale.

Example

#include <locale.h>
#include <wchar.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>


 /* This test will set up a number of character class using wctype() */
 /* and then verify whether calls to iswctype() using these classes  */
 /* produce the same results as calls to the is**** routines.        */

main()
{

    wchar_t w_char;
    wctype_t ret_val;

    char *character = "A";

    /* Convert character to wide character format - w_char */

    if (mbtowc(&w_char, character, 1) == -1) {
        perror("mbtowc");
        exit(EXIT_FAILURE);
    }

    /* Check if results from iswalnum() matches check on */
    /* alnum character class                             */

    if ((iswalnum((wint_t) w_char)) &&
        (iswctype((wint_t) w_char, wctype("alnum"))))
        printf("[%C] is a member of the character class alnum\n", w_char);
 else
    printf("[%C] is not a member of the character class alnum\n", w_char);

    /* Check if results from iswalpha() matches check on */
    /* alpha character class                             */

    if ((iswalpha((wint_t) w_char)) &&
        (iswctype((wint_t) w_char, wctype("alpha"))))
      printf("[%C] is a member of the character class alpha\n", w_char);
    else
     printf("[%C] is not a member of the character class alpha\n", w_char);

    /* Check if results from iswcntrl() matches check on */
    /* cntrl character class                             */

    if ((iswcntrl((wint_t) w_char)) &&
        (iswctype((wint_t) w_char, wctype("cntrl"))))
        printf("[%C] is a member of the character class cntrl\n", w_char);
    else
     printf("[%C] is not a member of the character class cntrl\n", w_char);

    /* Check if results from iswdigit() matches check on */
    /* digit character class                             */

    if ((iswdigit((wint_t) w_char)) &&
        (iswctype((wint_t) w_char, wctype("digit"))))
        printf("[%C] is a member of the character class digit\n", w_char);
    else
     printf("[%C] is not a member of the character class digit\n", w_char);

    /* Check if results from iswgraph() matches check on */
    /* graph character class                             */

    if ((iswgraph((wint_t) w_char)) &&
        (iswctype((wint_t) w_char, wctype("graph"))))
        printf("[%C] is a member of the character class graph\n", w_char);
    else
     printf("[%C] is not a member of the character class graph\n", w_char);

    /* Check if results from iswlower() matches check on */
    /* lower character class                             */

    if ((iswlower((wint_t) w_char)) &&
        (iswctype((wint_t) w_char, wctype("lower"))))
        printf("[%C] is a member of the character class lower\n", w_char);
    else
     printf("[%C] is not a member of the character class lower\n", w_char);

    /* Check if results from iswprint() matches check on */
    /* print character class                             */

    if ((iswprint((wint_t) w_char)) &&
        (iswctype((wint_t) w_char, wctype("print"))))
        printf("[%C] is a member of the character class print\n", w_char);
    else
     printf("[%C] is not a member of the character class print\n", w_char);

    /* Check if results from iswpunct() matches check on */
    /* punct character class                             */

    if ((iswpunct((wint_t) w_char)) &&
        (iswctype((wint_t) w_char, wctype("punct"))))
        printf("[%C] is a member of the character class punct\n", w_char);
    else
     printf("[%C] is not a member of the character class punct\n", w_char);

    /* Check if results from iswspace() matches check on */
    /* space character class                             */

    if ((iswspace((wint_t) w_char)) &&
        (iswctype((wint_t) w_char, wctype("space"))))
        printf("[%C] is a member of the character class space\n", w_char);
    else
    printf("[%C] is not a member of the character class space\n", w_char);

    /* Check if results from iswupper() matches check on */
    /* upper character class                             */

    if ((iswupper((wint_t) w_char)) &&
        (iswctype((wint_t) w_char, wctype("upper"))))
        printf("[%C] is a member of the character class upper\n", w_char);
    else
    printf("[%C] is not a member of the character class upper\n", w_char);

    /* Check if results from iswxdigit() matches check on */
    /* xdigit character class                             */

    if ((iswxdigit((wint_t) w_char)) &&
        (iswctype((wint_t) w_char, wctype("xdigit"))))
        printf("[%C] is a member of the character class xdigit\n", w_char);
    else
     printf("[%C] is not a member of the character class xdigit\n", w_char);

}
Running this example produces the following result:
[A] is a member of the character class alnum
[A] is a member of the character class alpha
[A] is not a member of the character class cntrl
[A] is not a member of the character class digit
[A] is a member of the character class graph
[A] is not a member of the character class lower
[A] is a member of the character class print
[A] is not a member of the character class punct
[A] is not a member of the character class space
[A] is a member of the character class upper
[A] is a member of the character class xdigit

wcwidth

wcwidth — Determines the number of printing positions on a display device required for the specified wide character.

Format

#include <wchar.h>
int wcwidth (wchar_t wc);

Argument

wc

A wide character.

Description

The wcwidth function determines the number of column positions needed for the specified wide character wc. The value of wc must be a valid wide character in the current locale.

Return Values

x

The number of printing positions required for wc.

0

If wc is a null character.

-1

Indicates that wc does not represent a valid printing wide character.

wmemchr

wmemchr — Locates the first occurrence of a specified wide character in an array of wide characters.

Format

#include <wchar.h>
wchar_t wmemchr (const wchar_t *s, wchar_t c, size_t n);

Function Variants

The wmemchr function has variants named _wmemchr32 and _wmemchr64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

s

A pointer to an array of wide characters to be searched.

c

The wide character value to search for.

n

The maximum number of wide characters in the array to be searched.

Description

The wmemchr function locates the first occurrence of the specified wide character in the initial n wide characters of the array pointed to by s.

Return Values

x

A pointer to the first occurrence of the wide character in the array.

NULL

The specified wide character does not occur in the array.

wmemcmp

wmemcmp — Compares two arrays of wide characters.

Format

#include <wchar.h>
int wmemcmp (const wchar_t *s1, const wchar_t *s2, size_t n);

Arguments

s1, s2

Pointers to wide-character arrays.

n

The maximum number of wide characters to be compared.

Description

The wmemcmp function compares the first n wide characters of the array pointed to by s1 with the first n wide characters of the array pointed to by s2. The wide characters are compared not according to locale-dependent collation rules, but as integral objects of type wchar_t.

Return Values

0

Arrays are equal.

Positive value

The first array is greater than the second.

Negative value

The first array is less than the second.

wmemcpy

wmemcpy — Copies a specified number of wide characters from one wide-character array to another.

Format

#include <wchar.h>
wchar_t wmemcpy (wchar_t *dest, const wchar_t *source, size_t n);

Function Variants

The wmemcpy function has variants named _wmemcpy32 and _wmemcpy64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

dest

A pointer to the destination array.

source

A pointer to the source array.

n

The number of wide characters to be copied.

Description

The wmemcpy function copies n wide characters from the array pointed to by source to the array pointed to by dest.

Return Value

x

The value of dest.

wmemmove

wmemmove — Copies a specified number of wide characters from one wide-character array to another.

Format

#include <wchar.h>
wchar_t wmemmove (wchar_t *dest, const wchar_t *source, size_t n);

Function Variants

The wmemmove function has variants named _wmemmove32 and _wmemmove64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

dest

A pointer to the destination array.

source

A pointer to the source array.

n

The number of wide characters to be moved.

Description

The wmemmove function copies n wide characters from the location pointed to by source to the location pointed to by dest.

The wmemmove and wmemcpy routines perform the same function, except that wmemmove ensures that the original contents of the source array are copied to the destination array even if the two arrays overlap. Where such overlap is possible, programs that require portability should use wmemmove, not wmemcopy.

Return Value

x

The value of dest.

wmemset

wmemset — Sets a specified value to a specified number of wide characters in an array of wide characters.

Format

#include <wchar.h>
wchar_t wmemset (wchar_t *s, wchar_t c, size_t n);

Function Variants

The wmemset function has variants named _wmemset32 and _wmemset64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

s

A pointer to the array of wide characters.

c

The value to be placed in the first n wide characters of the array.

n

The number of wide characters to be set to the specified value c.

Description

The wmemset function copies the value of c into each of the first n wide characters of the array pointed to by s.

Return Value

x

The value of s.

wprintf

wprintf — Performs formatted output from the standard output (stdout). See Chapter 2 for information on format specifiers.

Format

#include <wchar.h>
int wprintf (const wchar_t *format, ...);

Arguments

format

A pointer to a wide-character string containing the format specifications. For more information about format and conversion specifications and their corresponding arguments, see Chapter 2.

. . .

Optional expressions whose resultant types correspond to conversion specifications given in the format specification.

If no conversion specifications are given, the output sources can be omitted. Otherwise, the function calls must have exactly as many output sources as there are conversion specifications, and the conversion specifications must match the types of the output sources.

Conversion specifications are matched to output sources in left-to-right order. Excess output pointers, if any, are ignored.

Description

The wprintf function is equivalent to the fwprintf function with the stdout argument interposed before the wprintf arguments.

Return Values

n

The number of wide characters written.

Negative value

Indicates an error. The function sets errno to one of the following:

  • EILSEQ – Invalid character detected.

  • EINVAL – Insufficient arguments.

  • ENOMEM – Not enough memory available for conversion.

  • ERANGE – Floating-point calculations overflow.

  • EVMSERR – Nontranslatable OpenVMS error. vaxc$errno contains the OpenVMS error code. This might indicate that conversion to a numeric value failed because of overflow.

The function can also set errno to the following as a result of errors returned from the I/O subsystem:

  • EBADF – The file descriptor is not valid.

  • EIO – I/O error.

  • ENOSPC – No free space on the device containing the file.

  • ENXIO – Device does not exist.

  • EPIPE – Broken pipe.

  • ESPIPE – Illegal seek in a file opened for append.

  • EVMSERR – Nontranslatable OpenVMS error. vaxc$errno contains the OpenVMS error code. This indicates that an I/O error occurred for which there is no equivalent C error code.

wrapok

wrapok — In the UNIX system environment, allows the wrapping of a word from the right border of the window to the beginning of the next line. This routine is provided only for UNIX software compatibility and serves no function in the OpenVMS environment.

Format

#include <curses.h>
wrapok (WINDOW *win, bool boolf);

Arguments

win

A pointer to the window.

boolf

A Boolean TRUE or FALSE value. If boolf is FALSE, scrolling is not allowed. This is the default setting. The bool type is defined in the <curses.h> header file as follows: 
#define bool int

write

write — Writes a specified number of bytes from a buffer to a file.

Format

#include <unistd.h>
ssize_t write (int file_desc, void *buffer, size_t nbytes); (ISO POSIX-1)
int write (int file_desc, void *buffer, int nbytes); (Compatibility)

Arguments

file_desc

A file descriptor that refers to a file currently opened for writing or updating.

buffer

The address of contiguous storage from which the output data is taken.

nbytes

The maximum number of bytes involved in the write operation.

Description

If the write is to an RMS record file and the buffer contains embedded new-line characters, more than one record may be written to the file. Even if there are no embedded new-line characters, if nbytes is greater than the maximum record size for the file, more than one record will be written to the file. The write function always generates at least one record.

If the write is to a mailbox and the third argument, nbytes, specifies a length of 0, an end-of-file message is written to the mailbox. This occurs for mailboxes created by the application using SYS$CREMBX, but not for mailboxes created to implement POSIX pipes. For more information, see Chapter 5.

Return Values

x

The number of bytes written.

-1

Indicates errors, including undefined file descriptors, illegal buffer addresses, and physical I/O errors.

writev

writev — Writes to a file.

Format

#include <uio.h>
ssize_t writev (int file_desc, const struct iovec *iov,
int iovcnt);
ssize_t __writev64 (int file_desc, const struct __iovec64 *iov,
int iovcnt);

Function Variants

The writev function has variants named _writev32 and __writev64 for use with 32-bit and 64-bit pointer sizes, respectively. See Section 1.9 for more information on using pointer-size-specific functions.

Arguments

file_desc

A file descriptor that refers to a file currently opened for writing or updating.

iov

Array of iovec structures from which the output data is gathered.

iovcnt

The number of buffers specified by the members of the iov array.

Description

The writev function is equivalent to write but gathers the output data from the iovcnt buffers specified by the members of the iov array: iov[0], iov[1], ..., iov[iovcnt -1]. The iovcnt argument is valid if greater than 0 and less than or equal to {IOV_MAX}, defined in <limits.h>.

Each iovec entry specifies the base address and length of an area in memory from which data should be written. The writev function writes a complete area before proceeding to the next.

If filedes refers to a regular file and all of the iov_len members in the array pointed to by iov are 0, writev returns 0 and has no other effect.

For other file types, the behavior is unspecified.

If the sum of the iov_len values is greater than SSIZE_MAX, the operation fails and no data is transferred.

Upon successful completion, writev returns the number of bytes actually written. Otherwise, it returns a value of -1, the file pointer remains unchanged, and errno is set to indicate an error.

Return Values

x

The number of bytes written.

-1
Indicates an error. The file times do not change, and the function sets errno to one of the following values:

  • EBADF– The file_desc argument is not a valid file descriptor open for writing.

  • EINTR– The write operation was terminated due to the receipt of a signal, and no data was transferred.

  • EINVAL– The sum of the iov_len values in the iov array would overflow an ssize_t, or the iovcnt argument was less than or equal to 0, or greater than {IOV_MAX}.

  • EIO – A physical I/O error has occurred.

  • ENOSPC– There was no free space remaining on the device containing the file.

  • EPIPE– An attempt is made to write to a pipe or FIFO that is not open for reading by any process, or that only has one end open. A SIGPIPE signal will also be sent to the thread.

wscanf

wscanf — Reads input from the standard input (stdin) under control of the wide-character format string.

Format

#include <wchar.h>
int wscanf (const wchar_t *format, ...);

Arguments

format

A pointer to a wide-character string containing the format specifications. For more information about format and conversion specifications and their corresponding arguments, see Chapter 2.

. . .

Optional expressions whose results correspond to conversion specifications given in the format specification.

If no conversion specifications are given, you can omit the input pointers. Otherwise, the function calls must have exactly as many input pointers as there are conversion specifications, and the conversion specifications must match the types of the input pointers.

Conversion specifications are matched to input sources in left-to-right order. Excess input pointers, if any, are ignored.

Description

The wscanf function is equivalent to the fwscanf function with the stdin arguments interposed before the wscanf arguments.

Return Values

n

The number of input items assigned. The number can be less than provided for, even zero, in the event of an early matching failure.

EOF

Indicates an error. An input failure occurred before any conversion.

y0, y1, yn

y0, y1, yn — Compute Bessel functions of the second kind.

Format

#include <math.h>
double y0 (double x);
float y0f (float x);
long double y0l (long double x);
double y1 (double x);
float y1f (float x);
long double y1l (long double x);
double yn (int n, double x);
float ynf (int n, float x);
long double ynl (int n, long double x);

Arguments

x

A positive, real value.

n

An integer.

Description

The y0 functions return the value of the Bessel function of the second kind of order 0.

The y1 functions return the value of the Bessel function of the second kind of order 1.

The yn functions return the value of the Bessel function of the second kind of order n.

Return Values

x

The relevant Bessel value of x of the second kind.

-HUGE_VAL

The x argument is 0.0; errno is set to ERANGE.

NaN

The x argument is negative or NaN; errno is set to EDOM.

0

Underflow occurred; errno is set to ERANGE.

HUGE_VAL

Overflow occurred; errno is set to ERANGE.

Appendix A. Version-Dependency Tables

New functions are added to the VSI C Run-Time Library with each version of VSI C. These functions are implemented and shipped with the OpenVMS operating system, while the documentation and header files containing their prototypes are shipped with versions of the VSI C compiler.

You might have a newer version of VSI C that has header files and documentation for functions that are not supported on your older OpenVMS system. For example, if your target operating system platform is OpenVMS Version 7.2, you cannot use C RTL functions introduced on OpenVMS Version 7.3, even though they are documented in this manual.

This appendix contains several tables that list what C RTL functions are supported on recent OpenVMS versions. This is helpful for determining the functions to avoid using on your target OpenVMS platforms.

A.1. Functions Available on all OpenVMS VAX, Alpha, and Integrity servers Versions

Table A.1 lists functions available on all OpenVMS VAX and OpenVMS Alpha versions.
Table A.1. Functions Available on All OpenVMS Systems

abort

abs

access

acos

alarm

asctime

asin

assert

atan2

atan

atexit

atof

atoi

atoll (Alpha)

atol

atoq (Alpha)

box

brk

bsearch

cabs

calloc

ceil

cfree

chdir

chmod

chown

clearerr

clock

close

cosh

cos

creat

ctermid

ctime

cuserid

decc$crtl_init

decc$fix_time

decc$from_vms

decc$match_wild

decc$record_read

decc$record_write

decc$set_reentrancy

decc$to_vms

decc$translate_vms

delete

delwin

difftime

div

dup2

dup

ecvt

endwin

execle

execlp

execl

execve

execvp

execv

exit

_exit

exp

fabs

fclose

fcvt

fdopen

feof

ferror

fflush

fgetc

fgetname

fgetpos

fgets

fileno

floor

fmod

fopen

fprintf

fputc

fputs

fread

free

freopen

frexp

fscanf

fseek

fsetpos

fstat

fsync

ftell

ftime

fwait

fwrite

gcvt

getchar

getcwd

getc

getegid

getenv

geteuid

getgid

getname

getpid

getppid

gets

getuid

getw

gmtime

gsignal

hypot

initscr

isalnum

isalpha

isapipe

isascii

isatty

iscntrl

isdigit

isgraph

islower

isprint

ispunct

isspace

isupper

isxdigit

kill

labs

ldexp

ldiv

llabs (Alpha)

lldiv (Alpha)

localeconv

localtime

log10

log

longjmp

longname

lseek

lwait

malloc

mblen

mbstowcs

mbtowc

memchr

memcmp

memcpy

memmove

memset

mkdir

mktemp

mktime

modf

mvwin

mv[w]addstr

newwin

nice

open

overlay

overwrite

pause

perror

pipe

pow

printf

putchar

putc

puts

putw

qabs (Alpha)

qdiv (Alpha)

qsort

raise

rand

read

realloc

remove

rename

rewind

sbrk

scanf

scroll

setbuf

setgid

setjmp

setlocale

setuid

setvbuf

sigblock

signal

sigpause

sigstack (VAX)

sigvec

sinh

sin

sleep

sprintf

sqrt

srand

sscanf

ssignal

stat

strcat

strchr

strcmp

strcoll

strcpy

strcspn

strerror

strftime

strlen

strncat

strncmp

strncpy

strpbrk

strrchr

strspn

strstr

strtod

strtok

strtoll (Alpha)

strtol

strtoq (Alpha)

strtoull (Alpha)

strtoul

strtouq (Alpha)

strxfrm

subwin

system

tanh

tan

times

time

tmpfile

tmpnam

toascii

tolower

_tolower

touchwin

toupper

_toupper

ttyname

umask

ungetc

vaxc$calloc_opt

vaxc$cfree_opt

vaxc$crtl_init

vaxc$establish

vaxc$free_opt

vaxc$malloc_opt

vaxc$realloc_opt

va_arg

va_count

va_end

va_start

va_start_1

vfork

vfprintf

vprintf

vsprintf

wait

wcstombs

wctomb

write

[w]addch

[w]addstr

[w]clear

[w]clrattr

[w]clrtobot

[w]clrtoeol

[w]delch

[w]deleteln

[w]erase

[w]getch

[w]getstr

[w]inch

[w]insch

[w]insertln

[w]insstr

[w]move

[w]printw

[w]refresh

[w]scanw

[w]setattr

[w]standend

[w]standout

A.2. Functions Available on OpenVMS Version 6.2 and Higher

Table A.2 lists additional functions available on OpenVMS VAX and OpenVMS Alpha Version 6.2 and higher.
Table A.2. Functions Added in OpenVMS Version 6.2

catclose

catgets

catopen

fgetwc

fgetws

fputwc

fputws

getopt

getwc

getwchar

iconv

iconv_close

iconv_open

iswalnum

iswalpha

iswcntrl

iswctype

iswdigit

iswgraph

iswlower

iswprint

iswpunct

iswspace

iswupper

iswxdigit

nl_langinfo

putwc

putwchar

strnlen

strptime

towlower

towupper

ungetwc

wcscat

wcschr

wcscmp

wcscoll

wcscpy

wcscspn

wcsftime

wcslen

wcsncat

wcsncmp

wcsncpy

wcspbrk

wcsrchr

wcsspn

wcstol

wcstoul

wcswcs

wcswidth

wcsxfrm

wcstod

wctype

wcwidth

wcstok

A.3. Functions Available on OpenVMS Version 7.0 and Higher

Table A.3 lists additional functions available on OpenVMS VAX and OpenVMS Alpha Version 7.0 and higher.
Table A.3. Functions Added in OpenVMS Version 7.0

basename

bcmp

bcopy

btowc

bzero

closedir

confstr

dirname

drand48

erand48

ffs

fpathconf

ftruncate

ftw

fwide

fwprintf

fwscanf

getclock

getdtablesize

getitimer

getlogin

getpagesize

getpwnam

getpwuid

gettimeofday

index

initstate

jrand48

lcong48

lrand48

mbrlen

mbrtowc

mbsinit

mbsrtowcs

memccpy

mkstemp

mmap

mprotect

mrand48

msync

munmap

nrand48

opendir

pathconf

pclose

popen

putenv

random

readdir

rewinddir

rindex

rmdir

seed48

seekdir

setenv

setitimer

setstate

sigaction

sigaddset

sigdelset

sigemptyset

sigfillset

sigismember

siglongjmp

sigpending

sigprocmask

sigsetjmp

sigsuspend

srand48

srandom

strcasecmp

strdup

strfmon

strncasecmp

strsep

swab

swprintf

swscanf

sysconf

telldir

tempnam

towctrans

truncate

tzset

ualarm

uname

unlink

unsetenv

usleep

vfwprintf

vswprintf

vwprintf

wait3

wait4

waitpid

wcrtomb

wcsrtombs

wcsstr

wctob

wctrans

wmemchr

wmemcmp

wmemcpy

wmemmove

wmemset

wprintf

wscanf

A.4. Functions Available on OpenVMS Alpha Version 7.0 and Higher

Table A.4 lists additional functions available on OpenVMS Alpha Version 7.0 and higher.
Table A.4. Functions Added in OpenVMS Alpha Version 7.0

_basename32

_basename64

_bsearch32

_bsearch64

_calloc32

_calloc64

_catgets32

_catgets64

_ctermid32

_ctermid64

_cuserid32

_cuserid64

_dirname32

_dirname64

_fgetname32

_fgetname64

_fgets32

_fgets64

_fgetws32

_fgetws64

_gcvt32

_gcvt64

_getcwd32

_getcwd64

_getname32

_getname64

_gets32

_gets64

_index32

_index64

_longname32

_longname64

_malloc32

_malloc64

_mbsrtowcs32

_mbsrtowcs64

_memccpy32

_memccpy64

_memchr32

_memchr64

_memcpy32

_memcpy64

_memmove32

_memmove64

_memset32

_memset64

_mktemp32

_mktemp64

_mmap32

_mmap64

_qsort32

_qsort64

_realloc32

_realloc64

_rindex32

_rindex64

_strcat32

_strcat64

_strchr32

_strchr64

_strcpy32

_strcpy64

_strdup32

_strdup64

_strncat32

_strncat64

_strncpy32

_strncpy64

_strpbrk32

_strpbrk64

_strptime32

_strptime64

_strrchr32

_strrchr64

_strsep32

_strsep64

_strstr32

_strstr64

_strtod32

_strtod64

_strtok32

_strtok64

_strtol32

_strtol64

_strtoll32

_strtoll64

_strtoq32

_strtoq64

_strtoul32

_strtoul64

_strtoull32

_strtoull64

_strtouq32

_strtouq64

_tmpnam32

_tmpnam64

_wcscat32

_wcscat64

_wcschr32

_wcschr64

_wcscpy32

_wcscpy64

_wcsncat32

_wcsncat64

_wcsncpy32

_wcsncpy64

_wcspbrk32

_wcspbrk64

_wcsrchr32

_wcsrchr64

_wcsrtombs32

_wcsrtombs64

_wcsstr32

_wcsstr64

_wcstok32

_wcstok64

_wcstol32

_wcstol64

_wcstoul32

_wcstoul64

_wcswcs32

_wcswcs64

_wmemchr32

_wmemchr64

_wmemcpy32

_wmemcpy64

_wmemmove32

_wmemmove64

_wmemset32

_wmemset64

A.5. Functions Available on OpenVMS Version 7.2 and Higher

Table A.5 lists additional functions available on OpenVMS VAX and OpenVMS Alpha Version 7.2 and higher.
Table A.5. Functions Added in OpenVMS Version 7.2

asctime_r

dlerror

ctime_r

dlopen

decc$set_child_standard_streams

dlsym

decc$validate_wchar

fcntl

decc$write_eof_to_mbx

gmtime_r

dlclose

localtime_r

A.6. Functions Available on OpenVMS Version 7.3 and Higher

Table A.6 lists additional functions available on OpenVMS VAX and OpenVMS Alpha Version 7.3 and higher.
Table A.6. Functions Added in OpenVMS Version 7.3

fchown

link

utime

utimes

writev

A.7. Functions Available on OpenVMS Version 7.3-1 and Higher

Table A.7 lists additional functions available on OpenVMS Alpha Version 7.3-1 and higher.
Table A.7. Functions Added in OpenVMS Version 7.3-1

access

ftello

chmod

ftw

chown

readdir_r

decc$feature_get_index

stat

decc$feature_get_name

vfscanf

decc$feature_get_value

vfwscanf

decc$feature_set_value

vscanf

fseeko

vwscanf

fstat

vsscanf

vswscanf

A.8. Functions Available on OpenVMS Version 7.3-2 and Higher

Table A.8 lists additional functions available on OpenVMS Alpha Version 7.3-2 and higher.
Table A.8. Functions Added in OpenVMS Version 7.3-2

a64l

clock_getres

clock_gettime

clock_settime

endgrent

getgrent

getgrgid

getgrgid_r

getgrnam

getgrnam_r

getpgid

getpgrp

_getpwnam64

getpwnam_r

_getpwnam_r64

_getpwent64

getpwuid

_getpwuid64

getpwuid_r

_getpwuid_r64

getsid

l64a

nanosleep

poll

pread

pwrite

rand_r

readv

_readv64

seteuid

setgrent

setpgid

setpgrp

setregid

setreuid

setsid

sighold

sigignore

sigrelse

sigtimedwait

sigwait

sigwaitinfo

snprintf

ttyname_r

vsnprintf

__writev64

decc$set_child_default_dir

A.9. Functions Available on OpenVMS Version 8.2 and Higher

Table A.9 lists additional functions available on OpenVMS Alpha and Integrity servers Version 8.2 and higher.
Table A.9. Functions Added in OpenVMS Version 8.2

clearerr_unlocked

feof_unlocked

ferror_unlocked

fgetc_unlocked

fputc_unlocked

flockfile

ftrylockfile

funlockfile

getc_unlocked

getchar_unlocked

putc_unlocked

putchar_unlocked

statvfs

fstatvfs

_glob32

_glob64

_globfree32

_globfree64

socketpair

A.10. Functions Available on OpenVMS Version 8.3 and Higher

Table A.10 lists additional functions available on OpenVMS Alpha and Integrity servers Version 8.3 and higher.
Table A.10. Functions Added in OpenVMS Version 8.3

crypt

readlink

encrypt

realpath

setkey

symlink

lchown

unlink

lstat

fchmod

A.11. Functions Available on OpenVMS Version 8.4 and Higher

Table A.11 lists additional functions available on OpenVMS Alpha and Integrity servers Version 8.4 and higher.
Table A.11. Functions Added in OpenVMS Version 8.4

ftok

sem_init

semctl

sem_open

semget

sem_post

semop

sem_timedwait

sem_close

sem_trywait

sem_destroy

sem_unlink

sem_getvalue

sem_wait

Appendix B. Prototypes Duplicated to Nonstandard Headers

The various standards dictate which header file must define each of the standard functions. This is the included header file documented with each function prototype in the Reference Section of this manual.

However, many of the functions defined by the standards already existed on several operating systems and were defined in different header files. This is especially true on OpenVMS systems with the header files <processes.h>, <unixio.h>, and <unixlib.h>.

So, to provide upward compatibility for these functions, their prototypes are duplicated in both the expected header file as well as the header file defined by the standards.

Table B.1 lists these functions.
Table B.1. Duplicated Prototypes

Function

Duplicated in

Standard says

access

<unixio.h>

<unistd.h>

alarm

<signal.h>

<unistd.h>

bcmp

<string.h>

<strings.h>

bcopy

<string.h>

<strings.h>

bzero

<string.h>

<strings.h>

chdir

<unixio.h>

<unistd.h>

chmod

<unixio.h>

<stat.h>

chown

<unixio.h>

<unistd.h>

close

<unixio.h>

<unistd.h>

creat

<unixio.h>

<fcntl.h>

ctermid

<stdio.h>

<unistd.h>

cuserid

<stdio.h>

<unistd.h>

dirname

<string.h>

<libgen.h>

dup

<unixio.h>

<unistd.h>

dup2

<unixio.h>

<unistd.h>

ecvt

<unixlib.h>

<stdlib.h>

execl

<processes.h>

<unistd.h>

execle

<processes.h>

<unistd.h>

execlp

<processes.h>

<unistd.h>

execv

<processes.h>

<unistd.h>

execve

<processes.h>

<unistd.h>

execvp

<processes.h>

<unistd.h>

_exit

<stdlib.h>

<unistd.h>

fcvt

<unixlib.h>

<stdlib.h>

ffs

<string.h>

<strings.h>

fsync

<stdio.h>

<unistd.h>

ftime

<time.h>

<timeb.h>

gcvt

<unixlib.h>

<stdlib.h>

getcwd

<unixlib.h>

<unistd.h>

getegid

<unixlib.h>

<unistd.h>

getenv

<unixlib.h>

<stdlib.h>

geteuid

<unixlib.h>

<unistd.h>

getgid

<unixlib.h>

<unistd.h>

getopt

<stdio.h>

<unistd.h>

getpid

<unixlib.h>

<unistd.h>

getppid

<unixlib.h>

<unistd.h>

getuid

<unixlib.h>

<unistd.h>

index

<string.h>

<strings.h>

isatty

<unixio.h>

<unistd.h>

lseek

<unixio.h>

<unistd.h>

mkdir

<unixlib.h>

<stat.h>

mktemp

<unixio.h>

<stdlib.h>

nice

<stdlib.h>

<unistd.h>

open

<unixio.h>

<fcntl.h>

pause

<signal.h>

<unistd.h>

pipe

<processes.h>

<unistd.h>

read

<unixio.h>

<unistd.h>

rindex

<string.h>

<strings.h>

sbrk

<stdlib.h>

<unistd.h>

setgid

<unixlib.h>

<unistd.h>

setuid

<unixlib.h>

<unistd.h>

sleep

<signal.h>

<unistd.h>

strcasecmp

<string.h>

<strings.h>

strncasecmp

<string.h>

<strings.h>

system

<processes.h>

<stdlib.h>

times

<time.h>

<times.h>

umask

<stdlib.h>

<stat.h>

vfork

<processes.h>

<unistd.h>

wait

<processes.h>

<wait.h>

write

<unixio.h>

<unistd.h>

1

Where the ISO C Amendment 1 includes symbols not specified by XPG4, defining __STDC_VERSION__ == 199409 and _XOPEN_SOURCE (or _XOPEN_SOURCE_EXTENDED) selects both ISO C and XPG4 APIs. Conflicts that arise when compiling with both XPG4 and ISO C Amendment 1 resolve in favor of ISO C Amendment 1.

2

Where XPG4 extends the ISO C Amendment 1, defining _XOPEN_SOURCE or _XOPEN_SOURCE_EXTENDED selects ISO C APIs as well as the XPG4 extensions available in the header file. This mode of compilation makes XPG4 extensions visible.

1

Either byte or wide-character. Where neither is shown for a given specifier, the specifier description applies to both.

1

Either byte or wide-character. Where neither is shown for a given specifier, the specifier description applies to both.

1

Cannot be reset when intercepted.

4

Setting SIGINT can affect processing of Ctrl/Y interrupts. For example, in response to a caller's request to block or ignore SIGINT, the C RTL disables the Ctrl/Y interrupt.

2

Cannot be intercepted or ignored.

3

Cannot be blocked.

5

"Not implemented" for SIGQUIT means that there is no external event, including a Ctrl/Y interrupt, that would trigger a SIGQUIT signal, thereby causing a signal handler established for SIGQUIT to be invoked. This signal can be generated only through an appropriate C RTL function, such as raise.

6

Supported on OpenVMS Version 7.3 and higher.

1

Supported on OpenVMS Version 7.3 and higher.

2

SS$_BADWINCNT when C$_SIGWINCH not defined (OpenVMS versions before 7.3).

1

Copyright (c) 1981 Regents of the University of California.

All rights reserved.

1

This substitution assumes that the locale name is of the form language_territory.codeset@mode

1

This field is an extension to the ANSI C structure. It is present unless you compile your program with /STANDARD=ANSI89 or with _DECC_V4_SOURCE defined.

2

The C RTL uses a public-domain, time-zone handling package that puts time-zone conversion rules in easily accessible and modifiable files. These files reside in the SYS$COMMON:[SYS$ZONEINFO.SYSTEM.SOURCES] directory.

The time-zone compiler zic converts these files to a special format described by the <tzfile.h> header file. The converted files are created with a root directory of SYS$COMMON:[SYS$ZONEINFO.SYSTEM], which is pointed to by the SYS$TZDIR system logical. This format is readable by the C library functions that handle time-zone information. For example, in the eastern United Stated, SYS$LOCALTIME is defined to be SYS$COMMON:[SYS$ZONEINFO.SYSTEM.US]EASTERN. )