Standards

Language Standards

Language standards requires the existence of pre-defined macros.

Name	Macro	Standard
C89	__STDC__	ANSI X3.159-1989
C90	__STDC_VERSION__	ISO/IEC 9899:1990
C94	__STDC_VERSION__ = 199409L	ISO/IEC 9899-1:1994
C99	__STDC_VERSION__ = 199901L	ISO/IEC 9899:1999
C11	__STDC_VERSION__ = 201112L	ISO/IEC 9899:2011
C++98	__cplusplus = 199707L	ISO/IEC 14882:1998
C++11	__cplusplus = 201103L	Draft
C++/CLI	__cplusplus_cli = 200406L	ECMA-372
DSP-C		ISO/IEC JTC1/SC22 WG14/N854
EC++	__embedded_cplusplus	Embedded C++

Example: C Standards

:::c
#if defined(__STDC__)
# define PREDEF_STANDARD_C_1989
# if defined(__STDC_VERSION__)
#  define PREDEF_STANDARD_C_1990
#  if (__STDC_VERSION__ >= 199409L)
#   define PREDEF_STANDARD_C_1994
#  endif
#  if (__STDC_VERSION__ >= 199901L)
#   define PREDEF_STANDARD_C_1999
#  endif
# endif
#endif

Please notice that not all compliant compilers provides the correct pre-defined macros. For example, Microsoft Visual C++ does not define __STDC__, or Sun Workshop 4.2 supports C94 without setting __STDC_VERSION__ to the proper value. Extra checks for such compilers must be added.

Example: Pre-C89

In continuation of the above example, pre-C89 compilers do not recognize certain keywords. Let the preprocessor remove those keywords for those compilers.

:::c
#if !defined(PREDEF_STANDARD_C_1989) && !defined(__cplusplus)
# define const
# define volatile
#endif