HP OpenVMS Systems Documentation

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Run-Time Library Reference Manual for OpenVMS Systems

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1.4.4 Extended File Specifications

The ODS-5 volume structure provides enhanced support for mixed UNIX and OpenVMS style file names. It supports long file names, allows the use of a wider range of characters within file names, and preserves case within file names. 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, file names 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:


See Section 1.6 for more information on these and other feature logical names.

1.5 Feature-Test Macros for Header-File Control

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

The HP 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 HP 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 HP C RTL header files define symbols without restriction.

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

  • Standards
  • Multiple-version support
  • Compatibility

1.5.1 Standards Macros

The HP 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.

1.5.2 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 1-4 lists and describes the HP C RTL feature-test macros that control standards support.

Table 1-4 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 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. 1 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.

1Where 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.
2Where 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.

Features not defined by one of the previously named standards are considered HP 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 HP C extensions.

1.5.3 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 HP 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 sysconf function. 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 HP 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 are XPG4 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.

1.5.4 Multiple-Version-Support Macro

By default, the header files enable APIs in the HP 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 HP C User's Guide for OpenVMS Systems. For example, compiling on OpenVMS Version 6.2 causes only HP 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 HP 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. Define __VMS_VER appropriately, either with the /DEFINE qualifier or with a combination of the #undef and #define preprocessor directives. With /DEFINE, you may need to disable the warning regarding redefinition of a predefined macro.

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

To override the value of __VMS_VER, define __VMS_VER_OVERRIDE on the compiler command line. Defining __VMS_VER_OVERRIDE without a value sets __VMS_VER to the maximum value.

1.5.5 Compatibility Modes

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


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 typedef s 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 HP 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 HP 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 HP 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.

1.5.6 Curses and Socket Compatibility Macros

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

    This macro selects the Curses package from the 4.4BSD Berkeley Software Distribution.
    This macro selects a Curses package based on the VAX C compiler. This is the default Curses package.
    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.

1.5.7 2-Gigabyte File Size Macro

The C RTL provides support for compiling applications to use file sizes and offsets that are two gigabytes (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.

1.5.8 32-Bit UID and GID Macros (ALPHA, I64)

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.

1.5.9 Standard-Compliant stat Structure (ALPHA, I64)

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.

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.
  • 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.

1.6 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:



Some feature logical names can be set to a numeric value. For example:



  • 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 Run-Time Library 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.
      0 (zero)

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

Table 1-5 lists the C RTL feature logical names, grouped by the type of features they control.

Table 1-5 C RTL Feature Logical Names
Feature Logical Name Default
Performance Optimizations
Legacy Behaviors
File Attributes
Changes for UNIX Conformance
General UNIX Enhancements
Enhancements for UNIX Style File Names
Enhancements for UNIX Style File Attributes
UNIX Compliance Mode
New Behaviors for POSIX Conformance
File-Name Handling

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