This chapter describes the following topics:

• Predefined macros ( Section 6.1)
• Built-in functions ( Section 6.2)
  • For OpenVMS Alpha systems (ALPHA ONLY) ( Section 6.2.1)
  • For OpenVMS VAX systems (VAX ONLY) ( Section 6.2.2)

Predefined macros and built-in functions are extensions to the ANSI C Standard and are specific to Compaq C for OpenVMS Systems. The macros assist in transporting code and performing simple tasks that are common to many programs. The built-in functions allow you to efficiently access processor instructions.

6.1 Predefined Macros

In addition to the ANSI-compliant, implementation-independent macros described in the Compaq C Language Reference Manual, Compaq C for OpenVMS Systems provides the predefined macros described in the following sections.

6.1.1 CC$gfloat (G_Floating Identification Macro)

This macro is provided for compatibility with VAX C. The __G_FLOAT predefined macro should be used instead. See Section 6.1.4.

6.1.2 System Identification Macros

Each implementation of the Compaq C compiler automatically defines macros that can be used to identify the system on which the program is running. These macros can assist in writing code that executes conditionally, depending on the architecture or operating system on which the program is running.

Table 6-1 lists the traditional (non-ANSI) and new (ANSI) spellings of these predefined macro names for Compaq C for OpenVMS Systems. Both spellings are defined for each macro unless strict ANSI C mode (/STANDARD=ANSI89) is in effect, in which case only the new spellings are defined.

Table 6-1 Predefined System Identification Macros

	Traditional Spelling	New Spelling
Operating system name:	vms	__vms
	VMS	__VMS
	vms_version	__vms_version
	VMS_VERSION	__VMS_VERSION
		__VMS_VER
		__DECC_VER
Architecture name:	vax (VAX ONLY)	__vax (VAX ONLY)
	VAX (VAX ONLY)	__VAX (VAX ONLY)
		__alpha (ALPHA ONLY)
		__ALPHA (ALPHA ONLY)
		__Alpha_AXP (ALPHA ONLY)
		__32BITS (ALPHA ONLY)
Product name:	vaxc	__vaxc
	VAXC	__VAXC
	vax11c	__vax11c
	VAX11C	__VAX11C
		__DECC
ANSI C version of the compiler:		__STDC__ 1
Compiler is a hosted implementation		__STDC_HOSTED__ =1
ISOC94 version of the compiler		__STDC_VERSION__ =199409L 2
ISO/IEC 10646		__STDC_ISO_10646__ =yyyymmL 3
MIA version of the compiler:		__MIA 4

Most of these macros are defined as 1 or 0, as appropriate to the processor and compilation qualifiers. Refer to the end of the compiler's source listing to see the names and values of all the macros that are defined prior to processing the first line of source code. The listing shows all macros predefined by the compiler, as well as those defined on the command line by the /DEFINE qualifier, but omits any that were undefined by the /UNDEFINE qualifier.

You can use these system identification macros to separate portable and nonportable code in any of your Compaq C programs or to conditionally compile Compaq C programs used on more than one operating system to take advantage of system-specific features. For example:

#ifdef VMS #include rms /* Include RMS definitions. */ #endif

See the Compaq C Language Reference Manual for more information about using the preprocessor conditional-compilation directives.

6.1.2.1 The __DECC_VER Macro

The __DECC_VER macro provides an integer encoding of the compiler version-identifier string that is suitable for use in a preprocessor #if expression, such that a larger number corresponds to a more recent version.

The format of the compiler version-identifier string is:

TMM.mm-eee

Where:

• T is the version type (letter).
• MM is the major version number.
• mm is the update (minor version number).
• eee is the edit suffix number.

The format of the integer encoding for __DECC_VER is:

vvuuteeee

Where:

• vv is the major version number.
• uu is the update (minor version number).
• t is the numerical encoding of the alphabetic version type from the version-identifier string.
  Table 6-2 lists the possible version types and their encodings:

  Table 6-2 __DECC_VER Version-Type Encodings

  Type	Numerical Encoding	Description
  T	6	Field-test version
  S	8	Customer special
  V	9	Officially supported version

• eeee is the edit suffix number.

The following describes how the __DECC_VER integer value is calculated from the compiler version-identifier string:

1. The major version is multiplied by 10000000.
2. The minor version (the digits between the '.' and any edit suffix) is multiplied by 100000 and added to the suffix value (The suffix value has a range of 0-999).
3. If the character immediately preceding the first digit of the major version number is one of the ones listed in Table 6-2, its numerical encoding is multiplied by 10000.
4. The preceding values are added together.

The following examples show how different compiler version-identifier strings map to __DECC_VER encodings:

ident __DECC_VER string vvuuteeee T5.2-003 --> 50260003 V6.0-001 --> 60090001

6.1.2.2 The __VMS_VER Macro

The __VMS_VER macro provides an integer encoding of the OpenVMS version-identifier string that is suitable for use in a preprocessor #if expression, such that a larger number corresponds to a more recent version.

The format of the OpenVMS version-identifier string is:

TMM.mm-epp

Where:

• T is the version type (letter).
• MM is the major version number.
• mm is the update (minor version number).
• ee is the edit number.
• pp is the patch letter.

The format of the integer encoding for __VMS_VER is:

vvuuepptt

Where:

• vv is the major version.
• uu is the update (minor version)
• e is the edit number.
• pp is the patch letter (A = 01, ..., Z = 26)
• tt is the alphabetic ordinal of the version type from the version-identifier string (E = 05, ..., V = 22)
  Note that there are no version-type letters A - D and W - Z.

The following describes how the __VMS_VER integer value is calculated from the OpenVMS version-identifier string:

1. The major version is multiplied by 10000000.
2. The minor version (the digits between the '.' and any edit/patch suffix) is multiplied by 100000 and added to the suffix value.
   The suffix value is the optional edit number multiplied by 10000, added to the optional patch letter's alphabetic ordinal multiplied by 100.
3. The preceding values are added together, along with the alphabetic ordinal of the version type.

The following examples show how different OpenVMS version-identifier strings map to __VMS_VER encodings:

ident __VMS_VER string vvuuepptt V6.1 --> 60100022 V6.1-1H --> 60110822 E6.2 --> 60200005 ("IFT") F6.2 --> 60200006 ("FT1") G6.2 --> 60200007 ("FT2") V6.2 --> 60200022 T6.2-1H --> 60210820 V6.2-1I --> 60210922 V5.5-1H1 --> 50510822 (extra trailing digit ignored)

6.1.3 Standards Conformance Macros

The Compaq C RTL contains functions whose support and syntax conform to various industry standards or levels of product or operating system support.

Table 6-3 lists macros that you can explicitly define (using the /DEFINE qualifier or the #define preprocessor directive) to control which Compaq C RTL functions are declared in header files and to obtain standards conformance checking.

Table 6-3 Standards Macros---All platforms

Macro	Standard
_XOPEN_SOURCE_EXTENDED	XPG4-UNIX
_XOPEN_SOURCE	XPG4
_POSIX_C_SOURCE	POSIX
_ANSI_C_SOURCE	ISO C and ANSI C
_VMS_V6_SOURCE	OpenVMS Version 6 compatibility
_DECC_V4_SOURCE	DEC C Version 4.0 compatibility
_BSD44_CURSES	4.4BSD Curses
_VMS_CURSES	VAX C Curses
_SOCKADDR_LEN	4.4BSD sockets

These macros, with the exception of _POSIX_C_SOURCE , can be defined to 0 or 1.

The _POSIX_C_SOURCE macro can be defined to one of the following values:

0
1
2
199506

See the Compaq C Run-Time Library Reference Manual for OpenVMS Systems for more information about these feature-test macros.

6.1.4 Floating-Point Macros

Compaq C for OpenVMS Systems automatically defines the following macros that pertain to the format of floating-point variables. They can be used to identify the format with which you are compiling your program.

• __D_FLOAT
• __G_FLOAT
• __IEEE_FLOAT (ALPHA ONLY)
• __IEEE_FP (ALPHA ONLY)
• __X_FLOAT (ALPHA ONLY)

One of the first three macros listed is defined to have a value of 1 when the corresponding option of the /FLOAT qualifier is specified, or the appropriate /[NO]G_FLOAT qualifier is used. (The /G_FLOAT qualifier is kept only for compatibility with VAX C.) If the corresponding option was not specified, the associated macro is defined to have a value of 0.

The __IEEE_FP macro is defined in any IEEE floating-point mode except FAST.

On OpenVMS Alpha systems, the __X_FLOAT macro is defined to have a value of 1 when /L_DOUBLE_SIZE=128 (the default), and a value of 0 when /L_DOUBLE_SIZE=64.

These macros can assist in writing code that executes conditionally, depending on whether the program is running using D_floating, G_floating, or IEEE_floating (ALPHA ONLY) precision.

For example, if you compiled using G_floating format, then __D_FLOAT and __IEEE_FLOAT (ALPHA ONLY) are predefined to be 0, and __G_FLOAT is predefined as if the following were included before every compilation unit:

#define __G_FLOAT 1

You can conditionally assign values to variables of type double without causing an error and without being certain of how much storage was allocated for the variable. For example, you may assign values to external variables as follows:

#ifdef __G_FLOAT double x = 0.12e308; /* Range to 10 to the 308th power */ #else double x = 0.12e38; /* Range to 10 to the 38th power */ #endif

All predefined macro names, such as __G_FLOAT , are reserved by DIGITAL.

You can remove the effect of predefined macro definitions by explicitly undefining the conflicting name. For more information about undefining macros, see the #undefine directive in the Compaq C Language Reference Manual. For more information about the G_floating representation of the double data type, see Chapter 4.

6.1.5 Compiler-Mode Macros

The following predefined macros are defined if the corresponding compiler mode is selected:

• __DECC_MODE_STRICT
• __DECC_MODE_RELAXED
• __DECC_MODE_VAXC
• __DECC_MODE_COMMON
• __DECC_MODE_MS
• __MS

The following predefined macro is defined if the /POINTER_SIZE command-line qualifier is specified:

__INITIAL_POINTER_SIZE

Specifying /POINTER_SIZE, /POINTER_SIZE=32, or /POINTER_SIZE=SHORT defines __INITIAL_POINTER_SIZE to 32.

Specifying /POINTER_SIZE=64, or /POINTER_SIZE=LONG defines __INITIAL_POINTER_SIZE to 64.

If /POINTER_SIZE is not specified, __INITIAL_POINTER_SIZE is defined to 0. This lets you use #ifdef __INITIAL_POINTER_SIZE to test whether or not the compiler supports 64-bit pointers, because compilers lacking pointer-size controls will not define this macro at all.

6.1.7 The __HIDE_FORBIDDEN_NAMES Macro

The ANSI C standard specifies exactly what identifiers in the normal name space are declared by the standard header files. A compiler is not free to declare additional identifiers in a header file unless the identifiers follow defined rules (the identifier must begin with an underscore followed by an uppercase letter or another underscore).

When running the Compaq C compiler for OpenVMS systems in strict ANSI C mode (/STANDARD=ANSI89), versions of the standard header files are included that hide many identifiers that do not follow the rules. The header file <stdio.h> , for example, hides the definition of the macro TRUE. The compiler accomplishes this by predefining the macro __HIDE_FORBIDDEN_NAMES in strict ANSI mode.

You can use the /UNDEFINE="__HIDE_FORBIDDEN_NAMES" command-line qualifier to prevent the compiler from predefining this macro and, thereby, including macro definitions of the forbidden names.

The header files are modified to only define additional VAX C names if __HIDE_FORBIDDEN_NAMES is undefined. For example, <stdio.h> might contain the following:

#ifndef __HIDE_FORBIDDEN_NAMES #define TRUE 1 #endif

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