System_Identification_Macros
 The following macros have a defined value of 1 in DIGITAL C++:

 __cplusplus
 __DECCXX
 __vms
 __VMS

 For each of the following macros the defined value is a character
 string representing the operating system version:

 __vms_version
 __VMS_VERSION

Version_Number_Macros
 For each of the following macros the defined value is an
 unsigned long int that encodes the version number:

 __DECCXX_VER
 __VMS_VER

 You can use __DECCXX_VER to test that the current compiler version
 is newer than a particular version and __VMS_VER to test that the
 current OpenVMS version is newer than a particular version.
 Newer versions of the compiler and OpenVMS have larger values for
 these macros. If the compiler cannot analyze the version, the
 corresponding macro has a defined value of 0. These macros are not
 defined for releases of DIGITAL C++ prior to Version 5.0. 

Alpha_System_Macros
 DIGITAL C++ for OpenVMS Alpha Systems also supports the following
 predefined system identification macro names in all compiler modes:

 __Alpha_AXP
 __alpha
 __ALPHA
 __32BITS
 __INITIAL_POINTER_SIZE  

 DIGITAL C++ predefines __32BITS when pointers and data of type long are
 32 bits.

 For code that is intended to be portable from one system to another,
 users of both OpenVMS and Digital UNIX operating systems should use
 __alpha.

 Predefined macros (with the exception of vms_version, VMS_VERSION,
 __vms_version, __VMS_VERSION, and __INITIAL_POINTER_SIZE) are
 defined as 1 or 0, depending on the system (VAX  or Alpha processor), 
 the compiler defaults, and the qualifiers used.  For example, if you 
 compiled using G_floating format, then  __D_FLOAT and __IEEE_FLOAT 
 (Alpha processors 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

 These macros can assist in writing code that executes  conditionally.  
 They can be used in #elif, #if, #ifdef, and #ifndef
 directives to separate portable and nonportable code in a DIGITAL C++
 program.  The vms_version, VMS_VERSION, __vms_version, and
 __VMS_VERSION macros are defined with the value of the OpenVMS
 version on which you are running (for example, Version 6.0).
Floating_Point_Macros
 DIGITAL C++ automatically defines the following predefined macros
 pertaining to the format of floating-point variables.  You can use
 them to identify the format with which you are compiling your
 program:

 __D_FLOAT
 __G_FLOAT
 You can use the /FLOAT command qualifier to change the mode.
Implementation_Compatibility_Macros
 DIGITAL C++ automatically defines the following macros when the
 corresponding command-qualifier is used:

 Command-line Option           Macro Name
 -------------------           ----------
 /IMPLICIT_INCLUDE             __IMPLICIT_INCLUDE_ENABLED
 /GLOBAL_ARRAY_NEW             __GLOBAL_ARRAY_NEW
 /PCH,/CREATE_PCH,/USE_PCH     __PCH_ENABLED
 /STDNEW                       __STDNEW
 /STANDARD=ANSI                __ANSI
 /STANDARD=ARM                 __ARM
 /STANDARD=CFRONT              __CFRONT
 /STANDARD=MS                  __MS
 /STANDARD=STRICT_ANSI         __STRICT_ANSI


_BOOL_EXISTS   
   Indicates that bool is a keyword.

CC$gfloat
 When you compile using the /G_FLOAT qualifier, CC$gfloat is defined
 as 1.  When you compile without the /G_FLOAT qualifier, CC$gfloat
 is defined as 0.  The CC$gfloat macro is provided for compatiblity
 with VAX C.  The __G_FLOAT predefined macro should be used instead.

__DATE__
 The __DATE__ macro evaluates to a string specifying the date on
 which the compilation started.  The string presents the date in the
 form "Mmm dd yyyy" The names of the months are those generated by
 the asctime library function.  The first d is a space if dd is less
 than 10.

 Example:

      printf("%s",__DATE__);

__FILE__
 The __FILE__ macro evaluates to a string literal specifying the
 file specification of the current source file.

 Example:

      printf("file %s", __FILE__);


__LINE__
 The __LINE__ macro evaluates to a decimal constant specifying the
 number of the line in the source file containing the macro
 reference.

 Example:

      printf("At line %d in file %s", __LINE__, __FILE__);


__TIME__
 The __TIME__ macro evaluates to a string specifying the time that
 the compilation started.  The time has the following format:

      hh:mm:ss

 Example:

      printf("%s", __TIME__);

 The value of this macro remains constant throughout the translation
 unit.
_WCHAR_T       
  Indicates that wchar_t is a keyword.