Here are three ways to dump the preprocessor defines in GCC. $ gcc -dM -E – < /dev/null $ gcc -E -dM -x c /dev/null $ touch foo.h; cpp -dM foo.h For gcc version 4.6.0 on 64-bit Fedora 15 these preprocessor defines are: #define __DBL_MIN_EXP__ (-1021) #define __UINT_LEAST16_MAX__ 65535 #define __FLT_MIN__ 1.17549435082228750797e-38F #define __UINT_LEAST8_TYPE__ unsigned char #define __INTMAX_C(c) c ## L #define __CHAR_BIT__ 8 #define __UINT8_MAX__ 255 #define __WINT_MAX__ 4294967295U #define __ORDER_LITTLE_ENDIAN__ 1234 #define __SIZE_MAX__ 18446744073709551615UL #define __WCHAR_MAX__ 2147483647 #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_1 1 #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_2 1 #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 1 #define __DBL_DENORM_MIN__ ((double)4.94065645841246544177e-324L) #define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_8 1 #define __FLT_EVAL_METHOD__ 0 #define __unix__ 1
