CMake/Tests/CompileFeatures/default_dialect.c

#define C_STD_99 199901L
#define C_STD_11 201112L
#define C_STD_17 201710L
#define C_STD_23 202311L

#ifdef __STDC_VERSION__
#  define C_STD __STDC_VERSION__
#endif

#if DEFAULT_C23
#  if C_STD <= C_STD_17
#    error Unexpected value for __STDC_VERSION__.
#  endif
#elif DEFAULT_C17
#  if C_STD <= C_STD_11
#    error Unexpected value for __STDC_VERSION__.
#  endif
#elif DEFAULT_C11
#  if C_STD <= C_STD_99
#    error Unexpected value for __STDC_VERSION__.
#  endif
#elif DEFAULT_C99
#  if C_STD != C_STD_99
#    error Unexpected value for __STDC_VERSION__.
#  endif
#else
#  if !DEFAULT_C90
#    error Buildsystem error
#  endif
#  if defined(__STDC_VERSION__) &&                                            \
    !(__STDC_VERSION__ == 199409L &&                                          \
      (defined(__INTEL_COMPILER) || defined(__SUNPRO_C)))
#    error Unexpected __STDC_VERSION__ definition
#  endif
#endif

int main(void)
{
  return 0;
}