The code below contains standard, pre-defined macros used at runtime to determine whether a C or C++ compiler was used to compile the code. For C compilers, it also determines the version of the C language standard that the compiler implements).
NOTE: Some people prefer to use STDC_HEADERS rather than __STDC__..
#ifdef __cplusplus
printf("C++ compiler\n");
#else
#ifdef __STDC__
#if (defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 199901L)) ||/*continue..
...on the next line */ (defined(__GNUC__) && !defined(__STRICT_ANSI__))
printf("ANSI X3.159-1999 / ISO 9899:1999 (C99) compiler\n");
#else
printf("ANSI X3.159-1989 (C89) / ISO/IEC 9899:1990 (C90) C compiler\n");
#endif
#else
printf("Pre-ANSI (K&R) C compiler\n");
#endif
#endif
The code below determines whether a C or C++ compiler was used to compile the code at runtime:
if (sizeof('c') != sizeof(int)) printf("C++ compiler\n");
else if ((unsigned char)1 < -1) printf("Pre-ANSI (K&R) C compiler\n");
else { int i; i = 1 //* */
+1;
if (i == 2) printf("ANSI X3.159-1999 / ISO 9899:1999 (C99) compiler\n");
else printf("ANSI X3.159-1989 (C89) / ISO/IEC 9899:1990 (C90) C compiler\n");}
