HP C
Run-Time Library Reference Manual for OpenVMS Systems


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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.

1.3.5 Symbolic Links and POSIX Pathnames

OpenVMS provides support for Open Group compliant symbolic links and POSIX pathname processing. See Chapter 12 for more information.

1.4 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 the following broad categories for controlling the visibility of symbols in header files according to the following:

1.4.1 Standards Macros

The HP C RTL implements parts of the following standards:

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 HP 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. 1 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. 1 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. 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.
__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.


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.

1.4.3 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 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:

1.4.4 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.

1.4.5 Compatibility Modes

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

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

The following examples help clarify the use of these macros:

1.4.6 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:

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:

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 (INTEGRITY SERVERS, ALPHA)

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 HP C Version 4 or _VMS_V6_SOURCE for OpenVMS Version 6), forces use of short (16-bit) UID/GID.


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