The front end defines a number of preprocessing macros. Many of them are only defined under certain circumstances. This section describes the macros that are provided and the circumstances under which they are defined.

• __STDC__ Defined in ANSI C mode and in C++ mode. In C++ mode the value may be redefined. Not defined in Microsoft compatibility mode.
  
  
• __cplusplus Defined in C++ mode.
  
  
• c_plusplus Defined in default C++ mode, but not in strict mode.
  
  
• __STDC_VERSION__ Defined in ANSI C mode with the value 199409L. The name of this macro, and its value, are specified in Normative Addendum 1 of the ISO C Standard.
  
  
• __SIGNED_CHARS__ Defined when plain char is signed. This is used in the <limits.h> header file to get the proper definitions of CHAR_MAX and CHAR_MIN.
  
  
• _WCHAR_T Defined in C++ mode when wchar_t is a keyword. The name of this predefined macro is specified by a configuration flag. _WCHAR_T is the default.
  
  
• _BOOL Defined in C++ mode when bool is a keyword. The name of this predefined macro is specified by a configuration flag. _BOOL is the default.
  
  
• __ARRAY_OPERATORS Defined in C++ mode when array new and delete are enabled. The name of this predefined macro is specified by a configuration flag. __ARRAY_OPERATORS is the default.
  
  
• __EDG_RUNTIME_USES_NAMESPACES When the runtime uses namespaces, this macro name is also defined by default (by default, the runtime does use namespaces -- both this default and the macro name default can be changed under a custom porting arrangement).
  
  
• __EDG_IMPLICIT_USING_STD By default (this can be changed under a custom porting arrangement), the runtime does use namespaces however by default (this too can be changed under a custom porting arrangement, or by using the --using_std command line option) it does not emit an implicit using directive on the std namespace (that is, by default it does not effectively emit a using namespace std;) When it does, this macro name (which can be changed under a custom porting arrangement) is emitted.
  
  
• __EDG__ Always defined.
  
  
• __COMO__ Always defined.
  
  
• __EDG_VERSION_ Defined to an integral value that represents the version number of the front end. For example. version 2.30 is represented as 230.
  
  
• __COMO_VERSION__ Defined to an integral value that represents the version number.