• Ever wondered what all those pre #defined preprocessor constants expand to?
  • Execute the following:

gcc -dM -E - < /dev/null|sort

  • Sample output from Ubuntu 13.10 (gcc 4.8.1):
shahada@pc-shahada:/usr/include$ gcc -dM -E - < /dev/null
#define __DBL_MIN_EXP__ (-1021)
#define __UINT_LEAST16_MAX__ 65535
#define __ATOMIC_ACQUIRE 2
#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 __GCC_ATOMIC_CHAR_LOCK_FREE 2
#define __FLT_EVAL_METHOD__ 0
#define __unix__ 1
#define __GCC_ATOMIC_CHAR32_T_LOCK_FREE 2
#define __x86_64 1
#define __UINT_FAST64_MAX__ 18446744073709551615UL
#define __SIG_ATOMIC_TYPE__ int
#define __DBL_MIN_10_EXP__ (-307)
#define __FINITE_MATH_ONLY__ 0
#define __GNUC_PATCHLEVEL__ 1
#define __UINT_FAST8_MAX__ 255
#define __DEC64_MAX_EXP__ 385
#define __INT8_C(c) c
#define __UINT_LEAST64_MAX__ 18446744073709551615UL
#define __SHRT_MAX__ 32767
#define __LDBL_MAX__ 1.18973149535723176502e+4932L
#define __UINT_LEAST8_MAX__ 255
#define __GCC_ATOMIC_BOOL_LOCK_FREE 2
#define __UINTMAX_TYPE__ long unsigned int
#define __linux 1
#define __DEC32_EPSILON__ 1E-6DF
#define __unix 1
#define __UINT32_MAX__ 4294967295U
#define __LDBL_MAX_EXP__ 16384
#define __WINT_MIN__ 0U
#define __linux__ 1
#define __SCHAR_MAX__ 127
#define __WCHAR_MIN__ (-__WCHAR_MAX__ - 1)
#define __INT64_C(c) c ## L
#define __DBL_DIG__ 15
#define __GCC_ATOMIC_POINTER_LOCK_FREE 2
#define __SIZEOF_INT__ 4
#define __SIZEOF_POINTER__ 8
#define __USER_LABEL_PREFIX__ 
#define __STDC_HOSTED__ 1
#define __LDBL_HAS_INFINITY__ 1
#define __FLT_EPSILON__ 1.19209289550781250000e-7F
#define __LDBL_MIN__ 3.36210314311209350626e-4932L
#define __DEC32_MAX__ 9.999999E96DF
#define __INT32_MAX__ 2147483647
#define __SIZEOF_LONG__ 8
#define __STDC_IEC_559__ 1
#define __STDC_ISO_10646__ 201103L
#define __UINT16_C(c) c
#define _PREDEFS_H 
#define __DECIMAL_DIG__ 21
#define __gnu_linux__ 1
#define __LDBL_HAS_QUIET_NAN__ 1
#define __GNUC__ 4
#define __MMX__ 1
#define __FLT_HAS_DENORM__ 1
#define __SIZEOF_LONG_DOUBLE__ 16
#define __BIGGEST_ALIGNMENT__ 16
#define __DBL_MAX__ ((double)1.79769313486231570815e+308L)
#define __INT_FAST32_MAX__ 9223372036854775807L
#define __DBL_HAS_INFINITY__ 1
#define __DEC32_MIN_EXP__ (-94)
#define __INT_FAST16_TYPE__ long int
#define __LDBL_HAS_DENORM__ 1
#define __DEC128_MAX__ 9.999999999999999999999999999999999E6144DL
#define __INT_LEAST32_MAX__ 2147483647
#define __DEC32_MIN__ 1E-95DF
#define __DBL_MAX_EXP__ 1024
#define __DEC128_EPSILON__ 1E-33DL
#define __SSE2_MATH__ 1
#define __ATOMIC_HLE_RELEASE 131072
#define __PTRDIFF_MAX__ 9223372036854775807L
#define __amd64 1
#define __STDC_NO_THREADS__ 1
#define __ATOMIC_HLE_ACQUIRE 65536
#define __LONG_LONG_MAX__ 9223372036854775807LL
#define __SIZEOF_SIZE_T__ 8
#define __SIZEOF_WINT_T__ 4
#define __GCC_HAVE_DWARF2_CFI_ASM 1
#define __GXX_ABI_VERSION 1002
#define __FLT_MIN_EXP__ (-125)
#define __INT_FAST64_TYPE__ long int
#define __DBL_MIN__ ((double)2.22507385850720138309e-308L)
#define __LP64__ 1
#define __DECIMAL_BID_FORMAT__ 1
#define __DEC128_MIN__ 1E-6143DL
#define __REGISTER_PREFIX__ 
#define __UINT16_MAX__ 65535
#define __DBL_HAS_DENORM__ 1
#define __UINT8_TYPE__ unsigned char
#define __NO_INLINE__ 1
#define __FLT_MANT_DIG__ 24
#define __VERSION__ "4.8.1"
#define __UINT64_C(c) c ## UL
#define _STDC_PREDEF_H 1
#define __GCC_ATOMIC_INT_LOCK_FREE 2
#define __FLOAT_WORD_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __STDC_IEC_559_COMPLEX__ 1
#define __INT32_C(c) c
#define __DEC64_EPSILON__ 1E-15DD
#define __ORDER_PDP_ENDIAN__ 3412
#define __DEC128_MIN_EXP__ (-6142)
#define __INT_FAST32_TYPE__ long int
#define __UINT_LEAST16_TYPE__ short unsigned int
#define unix 1
#define __INT16_MAX__ 32767
#define __SIZE_TYPE__ long unsigned int
#define __UINT64_MAX__ 18446744073709551615UL
#define __INT8_TYPE__ signed char
#define __ELF__ 1
#define __FLT_RADIX__ 2
#define __INT_LEAST16_TYPE__ short int
#define __LDBL_EPSILON__ 1.08420217248550443401e-19L
#define __UINTMAX_C(c) c ## UL
#define __SSE_MATH__ 1
#define __k8 1
#define __SIG_ATOMIC_MAX__ 2147483647
#define __GCC_ATOMIC_WCHAR_T_LOCK_FREE 2
#define __SIZEOF_PTRDIFF_T__ 8
#define __x86_64__ 1
#define __DEC32_SUBNORMAL_MIN__ 0.000001E-95DF
#define __INT_FAST16_MAX__ 9223372036854775807L
#define __UINT_FAST32_MAX__ 18446744073709551615UL
#define __UINT_LEAST64_TYPE__ long unsigned int
#define __FLT_HAS_QUIET_NAN__ 1
#define __FLT_MAX_10_EXP__ 38
#define __LONG_MAX__ 9223372036854775807L
#define __DEC128_SUBNORMAL_MIN__ 0.000000000000000000000000000000001E-6143DL
#define __FLT_HAS_INFINITY__ 1
#define __UINT_FAST16_TYPE__ long unsigned int
#define __DEC64_MAX__ 9.999999999999999E384DD
#define __CHAR16_TYPE__ short unsigned int
#define __PRAGMA_REDEFINE_EXTNAME 1
#define __INT_LEAST16_MAX__ 32767
#define __DEC64_MANT_DIG__ 16
#define __INT64_MAX__ 9223372036854775807L
#define __UINT_LEAST32_MAX__ 4294967295U
#define __GCC_ATOMIC_LONG_LOCK_FREE 2
#define __INT_LEAST64_TYPE__ long int
#define __INT16_TYPE__ short int
#define __INT_LEAST8_TYPE__ signed char
#define __DEC32_MAX_EXP__ 97
#define __INT_FAST8_MAX__ 127
#define __INTPTR_MAX__ 9223372036854775807L
#define linux 1
#define __SSE2__ 1
#define __LDBL_MANT_DIG__ 64
#define __DBL_HAS_QUIET_NAN__ 1
#define __SIG_ATOMIC_MIN__ (-__SIG_ATOMIC_MAX__ - 1)
#define __code_model_small__ 1
#define __k8__ 1
#define __INTPTR_TYPE__ long int
#define __UINT16_TYPE__ short unsigned int
#define __WCHAR_TYPE__ int
#define __SIZEOF_FLOAT__ 4
#define __UINTPTR_MAX__ 18446744073709551615UL
#define __DEC64_MIN_EXP__ (-382)
#define __INT_FAST64_MAX__ 9223372036854775807L
#define __GCC_ATOMIC_TEST_AND_SET_TRUEVAL 1
#define __FLT_DIG__ 6
#define __UINT_FAST64_TYPE__ long unsigned int
#define __INT_MAX__ 2147483647
#define __amd64__ 1
#define __INT64_TYPE__ long int
#define __FLT_MAX_EXP__ 128
#define __ORDER_BIG_ENDIAN__ 4321
#define __DBL_MANT_DIG__ 53
#define __INT_LEAST64_MAX__ 9223372036854775807L
#define __GCC_ATOMIC_CHAR16_T_LOCK_FREE 2
#define __DEC64_MIN__ 1E-383DD
#define __WINT_TYPE__ unsigned int
#define __UINT_LEAST32_TYPE__ unsigned int
#define __SIZEOF_SHORT__ 2
#define __SSE__ 1
#define __LDBL_MIN_EXP__ (-16381)
#define __INT_LEAST8_MAX__ 127
#define __SSP__ 1
#define __SIZEOF_INT128__ 16
#define __LDBL_MAX_10_EXP__ 4932
#define __ATOMIC_RELAXED 0
#define __DBL_EPSILON__ ((double)2.22044604925031308085e-16L)
#define _LP64 1
#define __UINT8_C(c) c
#define __INT_LEAST32_TYPE__ int
#define __SIZEOF_WCHAR_T__ 4
#define __UINT64_TYPE__ long unsigned int
#define __INT_FAST8_TYPE__ signed char
#define __DBL_DECIMAL_DIG__ 17
#define __FXSR__ 1
#define __DEC_EVAL_METHOD__ 2
#define __UINT32_C(c) c ## U
#define __INTMAX_MAX__ 9223372036854775807L
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __FLT_DENORM_MIN__ 1.40129846432481707092e-45F
#define __INT8_MAX__ 127
#define __UINT_FAST32_TYPE__ long unsigned int
#define __CHAR32_TYPE__ unsigned int
#define __FLT_MAX__ 3.40282346638528859812e+38F
#define __INT32_TYPE__ int
#define __SIZEOF_DOUBLE__ 8
#define __FLT_MIN_10_EXP__ (-37)
#define __INTMAX_TYPE__ long int
#define __DEC128_MAX_EXP__ 6145
#define __ATOMIC_CONSUME 1
#define __GNUC_MINOR__ 8
#define __UINTMAX_MAX__ 18446744073709551615UL
#define __DEC32_MANT_DIG__ 7
#define __DBL_MAX_10_EXP__ 308
#define __LDBL_DENORM_MIN__ 3.64519953188247460253e-4951L
#define __INT16_C(c) c
#define __STDC__ 1
#define __PTRDIFF_TYPE__ long int
#define __ATOMIC_SEQ_CST 5
#define __UINT32_TYPE__ unsigned int
#define __UINTPTR_TYPE__ long unsigned int
#define __DEC64_SUBNORMAL_MIN__ 0.000000000000001E-383DD
#define __DEC128_MANT_DIG__ 34
#define __LDBL_MIN_10_EXP__ (-4931)
#define __SIZEOF_LONG_LONG__ 8
#define __GCC_ATOMIC_LLONG_LOCK_FREE 2
#define __LDBL_DIG__ 18
#define __FLT_DECIMAL_DIG__ 9
#define __UINT_FAST16_MAX__ 18446744073709551615UL
#define __GNUC_GNU_INLINE__ 1
#define __GCC_ATOMIC_SHORT_LOCK_FREE 2
#define __UINT_FAST8_TYPE__ unsigned char
#define __ATOMIC_ACQ_REL 4
#define __ATOMIC_RELEASE 3
shahada@pc-shahada:/usr/include$ gcc -dM -E - < /dev/null|sort
#define __amd64 1
#define __amd64__ 1
#define __ATOMIC_ACQ_REL 4
#define __ATOMIC_ACQUIRE 2
#define __ATOMIC_CONSUME 1
#define __ATOMIC_HLE_ACQUIRE 65536
#define __ATOMIC_HLE_RELEASE 131072
#define __ATOMIC_RELAXED 0
#define __ATOMIC_RELEASE 3
#define __ATOMIC_SEQ_CST 5
#define __BIGGEST_ALIGNMENT__ 16
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __CHAR16_TYPE__ short unsigned int
#define __CHAR32_TYPE__ unsigned int
#define __CHAR_BIT__ 8
#define __code_model_small__ 1
#define __DBL_DECIMAL_DIG__ 17
#define __DBL_DENORM_MIN__ ((double)4.94065645841246544177e-324L)
#define __DBL_DIG__ 15
#define __DBL_EPSILON__ ((double)2.22044604925031308085e-16L)
#define __DBL_HAS_DENORM__ 1
#define __DBL_HAS_INFINITY__ 1
#define __DBL_HAS_QUIET_NAN__ 1
#define __DBL_MANT_DIG__ 53
#define __DBL_MAX_10_EXP__ 308
#define __DBL_MAX__ ((double)1.79769313486231570815e+308L)
#define __DBL_MAX_EXP__ 1024
#define __DBL_MIN_10_EXP__ (-307)
#define __DBL_MIN__ ((double)2.22507385850720138309e-308L)
#define __DBL_MIN_EXP__ (-1021)
#define __DEC128_EPSILON__ 1E-33DL
#define __DEC128_MANT_DIG__ 34
#define __DEC128_MAX__ 9.999999999999999999999999999999999E6144DL
#define __DEC128_MAX_EXP__ 6145
#define __DEC128_MIN__ 1E-6143DL
#define __DEC128_MIN_EXP__ (-6142)
#define __DEC128_SUBNORMAL_MIN__ 0.000000000000000000000000000000001E-6143DL
#define __DEC32_EPSILON__ 1E-6DF
#define __DEC32_MANT_DIG__ 7
#define __DEC32_MAX__ 9.999999E96DF
#define __DEC32_MAX_EXP__ 97
#define __DEC32_MIN__ 1E-95DF
#define __DEC32_MIN_EXP__ (-94)
#define __DEC32_SUBNORMAL_MIN__ 0.000001E-95DF
#define __DEC64_EPSILON__ 1E-15DD
#define __DEC64_MANT_DIG__ 16
#define __DEC64_MAX__ 9.999999999999999E384DD
#define __DEC64_MAX_EXP__ 385
#define __DEC64_MIN__ 1E-383DD
#define __DEC64_MIN_EXP__ (-382)
#define __DEC64_SUBNORMAL_MIN__ 0.000000000000001E-383DD
#define __DEC_EVAL_METHOD__ 2
#define __DECIMAL_BID_FORMAT__ 1
#define __DECIMAL_DIG__ 21
#define __ELF__ 1
#define __FINITE_MATH_ONLY__ 0
#define __FLOAT_WORD_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __FLT_DECIMAL_DIG__ 9
#define __FLT_DENORM_MIN__ 1.40129846432481707092e-45F
#define __FLT_DIG__ 6
#define __FLT_EPSILON__ 1.19209289550781250000e-7F
#define __FLT_EVAL_METHOD__ 0
#define __FLT_HAS_DENORM__ 1
#define __FLT_HAS_INFINITY__ 1
#define __FLT_HAS_QUIET_NAN__ 1
#define __FLT_MANT_DIG__ 24
#define __FLT_MAX_10_EXP__ 38
#define __FLT_MAX__ 3.40282346638528859812e+38F
#define __FLT_MAX_EXP__ 128
#define __FLT_MIN_10_EXP__ (-37)
#define __FLT_MIN__ 1.17549435082228750797e-38F
#define __FLT_MIN_EXP__ (-125)
#define __FLT_RADIX__ 2
#define __FXSR__ 1
#define __GCC_ATOMIC_BOOL_LOCK_FREE 2
#define __GCC_ATOMIC_CHAR16_T_LOCK_FREE 2
#define __GCC_ATOMIC_CHAR32_T_LOCK_FREE 2
#define __GCC_ATOMIC_CHAR_LOCK_FREE 2
#define __GCC_ATOMIC_INT_LOCK_FREE 2
#define __GCC_ATOMIC_LLONG_LOCK_FREE 2
#define __GCC_ATOMIC_LONG_LOCK_FREE 2
#define __GCC_ATOMIC_POINTER_LOCK_FREE 2
#define __GCC_ATOMIC_SHORT_LOCK_FREE 2
#define __GCC_ATOMIC_TEST_AND_SET_TRUEVAL 1
#define __GCC_ATOMIC_WCHAR_T_LOCK_FREE 2
#define __GCC_HAVE_DWARF2_CFI_ASM 1
#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 __GCC_HAVE_SYNC_COMPARE_AND_SWAP_8 1
#define __GNUC__ 4
#define __GNUC_GNU_INLINE__ 1
#define __GNUC_MINOR__ 8
#define __GNUC_PATCHLEVEL__ 1
#define __gnu_linux__ 1
#define __GXX_ABI_VERSION 1002
#define __INT16_C(c) c
#define __INT16_MAX__ 32767
#define __INT16_TYPE__ short int
#define __INT32_C(c) c
#define __INT32_MAX__ 2147483647
#define __INT32_TYPE__ int
#define __INT64_C(c) c ## L
#define __INT64_MAX__ 9223372036854775807L
#define __INT64_TYPE__ long int
#define __INT8_C(c) c
#define __INT8_MAX__ 127
#define __INT8_TYPE__ signed char
#define __INT_FAST16_MAX__ 9223372036854775807L
#define __INT_FAST16_TYPE__ long int
#define __INT_FAST32_MAX__ 9223372036854775807L
#define __INT_FAST32_TYPE__ long int
#define __INT_FAST64_MAX__ 9223372036854775807L
#define __INT_FAST64_TYPE__ long int
#define __INT_FAST8_MAX__ 127
#define __INT_FAST8_TYPE__ signed char
#define __INT_LEAST16_MAX__ 32767
#define __INT_LEAST16_TYPE__ short int
#define __INT_LEAST32_MAX__ 2147483647
#define __INT_LEAST32_TYPE__ int
#define __INT_LEAST64_MAX__ 9223372036854775807L
#define __INT_LEAST64_TYPE__ long int
#define __INT_LEAST8_MAX__ 127
#define __INT_LEAST8_TYPE__ signed char
#define __INT_MAX__ 2147483647
#define __INTMAX_C(c) c ## L
#define __INTMAX_MAX__ 9223372036854775807L
#define __INTMAX_TYPE__ long int
#define __INTPTR_MAX__ 9223372036854775807L
#define __INTPTR_TYPE__ long int
#define __k8 1
#define __k8__ 1
#define __LDBL_DENORM_MIN__ 3.64519953188247460253e-4951L
#define __LDBL_DIG__ 18
#define __LDBL_EPSILON__ 1.08420217248550443401e-19L
#define __LDBL_HAS_DENORM__ 1
#define __LDBL_HAS_INFINITY__ 1
#define __LDBL_HAS_QUIET_NAN__ 1
#define __LDBL_MANT_DIG__ 64
#define __LDBL_MAX_10_EXP__ 4932
#define __LDBL_MAX__ 1.18973149535723176502e+4932L
#define __LDBL_MAX_EXP__ 16384
#define __LDBL_MIN_10_EXP__ (-4931)
#define __LDBL_MIN__ 3.36210314311209350626e-4932L
#define __LDBL_MIN_EXP__ (-16381)
#define __linux 1
#define __linux__ 1
#define linux 1
#define __LONG_LONG_MAX__ 9223372036854775807LL
#define __LONG_MAX__ 9223372036854775807L
#define __LP64__ 1
#define _LP64 1
#define __MMX__ 1
#define __NO_INLINE__ 1
#define __ORDER_BIG_ENDIAN__ 4321
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __ORDER_PDP_ENDIAN__ 3412
#define __PRAGMA_REDEFINE_EXTNAME 1
#define _PREDEFS_H 
#define __PTRDIFF_MAX__ 9223372036854775807L
#define __PTRDIFF_TYPE__ long int
#define __REGISTER_PREFIX__ 
#define __SCHAR_MAX__ 127
#define __SHRT_MAX__ 32767
#define __SIG_ATOMIC_MAX__ 2147483647
#define __SIG_ATOMIC_MIN__ (-__SIG_ATOMIC_MAX__ - 1)
#define __SIG_ATOMIC_TYPE__ int
#define __SIZE_MAX__ 18446744073709551615UL
#define __SIZEOF_DOUBLE__ 8
#define __SIZEOF_FLOAT__ 4
#define __SIZEOF_INT128__ 16
#define __SIZEOF_INT__ 4
#define __SIZEOF_LONG__ 8
#define __SIZEOF_LONG_DOUBLE__ 16
#define __SIZEOF_LONG_LONG__ 8
#define __SIZEOF_POINTER__ 8
#define __SIZEOF_PTRDIFF_T__ 8
#define __SIZEOF_SHORT__ 2
#define __SIZEOF_SIZE_T__ 8
#define __SIZEOF_WCHAR_T__ 4
#define __SIZEOF_WINT_T__ 4
#define __SIZE_TYPE__ long unsigned int
#define __SSE__ 1
#define __SSE2__ 1
#define __SSE2_MATH__ 1
#define __SSE_MATH__ 1
#define __SSP__ 1
#define __STDC__ 1
#define __STDC_HOSTED__ 1
#define __STDC_IEC_559__ 1
#define __STDC_IEC_559_COMPLEX__ 1
#define __STDC_ISO_10646__ 201103L
#define __STDC_NO_THREADS__ 1
#define _STDC_PREDEF_H 1
#define __UINT16_C(c) c
#define __UINT16_MAX__ 65535
#define __UINT16_TYPE__ short unsigned int
#define __UINT32_C(c) c ## U
#define __UINT32_MAX__ 4294967295U
#define __UINT32_TYPE__ unsigned int
#define __UINT64_C(c) c ## UL
#define __UINT64_MAX__ 18446744073709551615UL
#define __UINT64_TYPE__ long unsigned int
#define __UINT8_C(c) c
#define __UINT8_MAX__ 255
#define __UINT8_TYPE__ unsigned char
#define __UINT_FAST16_MAX__ 18446744073709551615UL
#define __UINT_FAST16_TYPE__ long unsigned int
#define __UINT_FAST32_MAX__ 18446744073709551615UL
#define __UINT_FAST32_TYPE__ long unsigned int
#define __UINT_FAST64_MAX__ 18446744073709551615UL
#define __UINT_FAST64_TYPE__ long unsigned int
#define __UINT_FAST8_MAX__ 255
#define __UINT_FAST8_TYPE__ unsigned char
#define __UINT_LEAST16_MAX__ 65535
#define __UINT_LEAST16_TYPE__ short unsigned int
#define __UINT_LEAST32_MAX__ 4294967295U
#define __UINT_LEAST32_TYPE__ unsigned int
#define __UINT_LEAST64_MAX__ 18446744073709551615UL
#define __UINT_LEAST64_TYPE__ long unsigned int
#define __UINT_LEAST8_MAX__ 255
#define __UINT_LEAST8_TYPE__ unsigned char
#define __UINTMAX_C(c) c ## UL
#define __UINTMAX_MAX__ 18446744073709551615UL
#define __UINTMAX_TYPE__ long unsigned int
#define __UINTPTR_MAX__ 18446744073709551615UL
#define __UINTPTR_TYPE__ long unsigned int
#define __unix 1
#define __unix__ 1
#define unix 1
#define __USER_LABEL_PREFIX__ 
#define __VERSION__ "4.8.1"
#define __WCHAR_MAX__ 2147483647
#define __WCHAR_MIN__ (-__WCHAR_MAX__ - 1)
#define __WCHAR_TYPE__ int
#define __WINT_MAX__ 4294967295U
#define __WINT_MIN__ 0U
#define __WINT_TYPE__ unsigned int
#define __x86_64 1
#define __x86_64__ 1

* Sample output from buildroot, ARM target, gcc 4.8.0:

#define __ACCUM_EPSILON__ 0x1P-15K
#define __ACCUM_FBIT__ 15
#define __ACCUM_IBIT__ 16
#define __ACCUM_MAX__ 0X7FFFFFFFP-15K
#define __ACCUM_MIN__ (-0X1P15K-0X1P15K)
#define __APCS_32__ 1
#define __arm__ 1
#define __ARM_ARCH 4
#define __ARM_ARCH_4T__ 1
#define __ARM_ARCH_ISA_ARM 1
#define __ARM_ARCH_ISA_THUMB 1
#define __ARM_EABI__ 1
#define __ARMEL__ 1
#define __ARM_FP 12
#define __ARM_NEON_FP 4
#define __ARM_PCS 1
#define __ARM_SIZEOF_MINIMAL_ENUM 4
#define __ARM_SIZEOF_WCHAR_T 32
#define __ATOMIC_ACQ_REL 4
#define __ATOMIC_ACQUIRE 2
#define __ATOMIC_CONSUME 1
#define __ATOMIC_RELAXED 0
#define __ATOMIC_RELEASE 3
#define __ATOMIC_SEQ_CST 5
#define __BIGGEST_ALIGNMENT__ 8
#define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __CHAR16_TYPE__ short unsigned int
#define __CHAR32_TYPE__ unsigned int
#define __CHAR_BIT__ 8
#define __CHAR_UNSIGNED__ 1
#define __DA_FBIT__ 31
#define __DA_IBIT__ 32
#define __DBL_DECIMAL_DIG__ 17
#define __DBL_DENORM_MIN__ ((double)4.9406564584124654e-324L)
#define __DBL_DIG__ 15
#define __DBL_EPSILON__ ((double)2.2204460492503131e-16L)
#define __DBL_HAS_DENORM__ 1
#define __DBL_HAS_INFINITY__ 1
#define __DBL_HAS_QUIET_NAN__ 1
#define __DBL_MANT_DIG__ 53
#define __DBL_MAX_10_EXP__ 308
#define __DBL_MAX__ ((double)1.7976931348623157e+308L)
#define __DBL_MAX_EXP__ 1024
#define __DBL_MIN_10_EXP__ (-307)
#define __DBL_MIN__ ((double)2.2250738585072014e-308L)
#define __DBL_MIN_EXP__ (-1021)
#define __DEC128_EPSILON__ 1E-33DL
#define __DEC128_MANT_DIG__ 34
#define __DEC128_MAX__ 9.999999999999999999999999999999999E6144DL
#define __DEC128_MAX_EXP__ 6145
#define __DEC128_MIN__ 1E-6143DL
#define __DEC128_MIN_EXP__ (-6142)
#define __DEC128_SUBNORMAL_MIN__ 0.000000000000000000000000000000001E-6143DL
#define __DEC32_EPSILON__ 1E-6DF
#define __DEC32_MANT_DIG__ 7
#define __DEC32_MAX__ 9.999999E96DF
#define __DEC32_MAX_EXP__ 97
#define __DEC32_MIN__ 1E-95DF
#define __DEC32_MIN_EXP__ (-94)
#define __DEC32_SUBNORMAL_MIN__ 0.000001E-95DF
#define __DEC64_EPSILON__ 1E-15DD
#define __DEC64_MANT_DIG__ 16
#define __DEC64_MAX__ 9.999999999999999E384DD
#define __DEC64_MAX_EXP__ 385
#define __DEC64_MIN__ 1E-383DD
#define __DEC64_MIN_EXP__ (-382)
#define __DEC64_SUBNORMAL_MIN__ 0.000000000000001E-383DD
#define __DEC_EVAL_METHOD__ 2
#define __DECIMAL_DIG__ 17
#define __DQ_FBIT__ 63
#define __DQ_IBIT__ 0
#define __ELF__ 1
#define __FINITE_MATH_ONLY__ 0
#define __FLOAT_WORD_ORDER__ __ORDER_LITTLE_ENDIAN__
#define __FLT_DECIMAL_DIG__ 9
#define __FLT_DENORM_MIN__ 1.4012984643248171e-45F
#define __FLT_DIG__ 6
#define __FLT_EPSILON__ 1.1920928955078125e-7F
#define __FLT_EVAL_METHOD__ 0
#define __FLT_HAS_DENORM__ 1
#define __FLT_HAS_INFINITY__ 1
#define __FLT_HAS_QUIET_NAN__ 1
#define __FLT_MANT_DIG__ 24
#define __FLT_MAX_10_EXP__ 38
#define __FLT_MAX__ 3.4028234663852886e+38F
#define __FLT_MAX_EXP__ 128
#define __FLT_MIN_10_EXP__ (-37)
#define __FLT_MIN__ 1.1754943508222875e-38F
#define __FLT_MIN_EXP__ (-125)
#define __FLT_RADIX__ 2
#define __FRACT_EPSILON__ 0x1P-15R
#define __FRACT_FBIT__ 15
#define __FRACT_IBIT__ 0
#define __FRACT_MAX__ 0X7FFFP-15R
#define __FRACT_MIN__ (-0.5R-0.5R)
#define __GCC_ATOMIC_BOOL_LOCK_FREE 1
#define __GCC_ATOMIC_CHAR16_T_LOCK_FREE 1
#define __GCC_ATOMIC_CHAR32_T_LOCK_FREE 1
#define __GCC_ATOMIC_CHAR_LOCK_FREE 1
#define __GCC_ATOMIC_INT_LOCK_FREE 1
#define __GCC_ATOMIC_LLONG_LOCK_FREE 1
#define __GCC_ATOMIC_LONG_LOCK_FREE 1
#define __GCC_ATOMIC_POINTER_LOCK_FREE 1
#define __GCC_ATOMIC_SHORT_LOCK_FREE 1
#define __GCC_ATOMIC_TEST_AND_SET_TRUEVAL 1
#define __GCC_ATOMIC_WCHAR_T_LOCK_FREE 1
#define __GNUC__ 4
#define __GNUC_GNU_INLINE__ 1
#define __GNUC_MINOR__ 8
#define __GNUC_PATCHLEVEL__ 0
#define __GXX_ABI_VERSION 1002
#define __GXX_TYPEINFO_EQUALITY_INLINE 0
#define __HA_FBIT__ 7
#define __HA_IBIT__ 8
#define __HQ_FBIT__ 15
#define __HQ_IBIT__ 0
#define __INT16_C(c) c
#define __INT16_MAX__ 32767
#define __INT16_TYPE__ short int
#define __INT32_C(c) c
#define __INT32_MAX__ 2147483647
#define __INT32_TYPE__ int
#define __INT64_C(c) c ## LL
#define __INT64_MAX__ 9223372036854775807LL
#define __INT64_TYPE__ long long int
#define __INT8_C(c) c
#define __INT8_MAX__ 127
#define __INT8_TYPE__ signed char
#define __INT_FAST16_MAX__ 2147483647
#define __INT_FAST16_TYPE__ int
#define __INT_FAST32_MAX__ 2147483647
#define __INT_FAST32_TYPE__ int
#define __INT_FAST64_MAX__ 9223372036854775807LL
#define __INT_FAST64_TYPE__ long long int
#define __INT_FAST8_MAX__ 127
#define __INT_FAST8_TYPE__ signed char
#define __INT_LEAST16_MAX__ 32767
#define __INT_LEAST16_TYPE__ short int
#define __INT_LEAST32_MAX__ 2147483647
#define __INT_LEAST32_TYPE__ int
#define __INT_LEAST64_MAX__ 9223372036854775807LL
#define __INT_LEAST64_TYPE__ long long int
#define __INT_LEAST8_MAX__ 127
#define __INT_LEAST8_TYPE__ signed char
#define __INT_MAX__ 2147483647
#define __INTMAX_C(c) c ## LL
#define __INTMAX_MAX__ 9223372036854775807LL
#define __INTMAX_TYPE__ long long int
#define __INTPTR_MAX__ 2147483647
#define __INTPTR_TYPE__ int
#define __LACCUM_EPSILON__ 0x1P-31LK
#define __LACCUM_FBIT__ 31
#define __LACCUM_IBIT__ 32
#define __LACCUM_MAX__ 0X7FFFFFFFFFFFFFFFP-31LK
#define __LACCUM_MIN__ (-0X1P31LK-0X1P31LK)
#define __LDBL_DENORM_MIN__ 4.9406564584124654e-324L
#define __LDBL_DIG__ 15
#define __LDBL_EPSILON__ 2.2204460492503131e-16L
#define __LDBL_HAS_DENORM__ 1
#define __LDBL_HAS_INFINITY__ 1
#define __LDBL_HAS_QUIET_NAN__ 1
#define __LDBL_MANT_DIG__ 53
#define __LDBL_MAX_10_EXP__ 308
#define __LDBL_MAX__ 1.7976931348623157e+308L
#define __LDBL_MAX_EXP__ 1024
#define __LDBL_MIN_10_EXP__ (-307)
#define __LDBL_MIN__ 2.2250738585072014e-308L
#define __LDBL_MIN_EXP__ (-1021)
#define __LFRACT_EPSILON__ 0x1P-31LR
#define __LFRACT_FBIT__ 31
#define __LFRACT_IBIT__ 0
#define __LFRACT_MAX__ 0X7FFFFFFFP-31LR
#define __LFRACT_MIN__ (-0.5LR-0.5LR)
#define __linux 1
#define __linux__ 1
#define linux 1
#define __LLACCUM_EPSILON__ 0x1P-31LLK
#define __LLACCUM_FBIT__ 31
#define __LLACCUM_IBIT__ 32
#define __LLACCUM_MAX__ 0X7FFFFFFFFFFFFFFFP-31LLK
#define __LLACCUM_MIN__ (-0X1P31LLK-0X1P31LLK)
#define __LLFRACT_EPSILON__ 0x1P-63LLR
#define __LLFRACT_FBIT__ 63
#define __LLFRACT_IBIT__ 0
#define __LLFRACT_MAX__ 0X7FFFFFFFFFFFFFFFP-63LLR
#define __LLFRACT_MIN__ (-0.5LLR-0.5LLR)
#define __LONG_LONG_MAX__ 9223372036854775807LL
#define __LONG_MAX__ 2147483647L
#define __NO_INLINE__ 1
#define __ORDER_BIG_ENDIAN__ 4321
#define __ORDER_LITTLE_ENDIAN__ 1234
#define __ORDER_PDP_ENDIAN__ 3412
#define __PRAGMA_REDEFINE_EXTNAME 1
#define __PTRDIFF_MAX__ 2147483647
#define __PTRDIFF_TYPE__ int
#define __QQ_FBIT__ 7
#define __QQ_IBIT__ 0
#define __REGISTER_PREFIX__ 
#define __SACCUM_EPSILON__ 0x1P-7HK
#define __SACCUM_FBIT__ 7
#define __SACCUM_IBIT__ 8
#define __SACCUM_MAX__ 0X7FFFP-7HK
#define __SACCUM_MIN__ (-0X1P7HK-0X1P7HK)
#define __SA_FBIT__ 15
#define __SA_IBIT__ 16
#define __SCHAR_MAX__ 127
#define __SFRACT_EPSILON__ 0x1P-7HR
#define __SFRACT_FBIT__ 7
#define __SFRACT_IBIT__ 0
#define __SFRACT_MAX__ 0X7FP-7HR
#define __SFRACT_MIN__ (-0.5HR-0.5HR)
#define __SHRT_MAX__ 32767
#define __SIG_ATOMIC_MAX__ 2147483647
#define __SIG_ATOMIC_MIN__ (-__SIG_ATOMIC_MAX__ - 1)
#define __SIG_ATOMIC_TYPE__ int
#define __SIZE_MAX__ 4294967295U
#define __SIZEOF_DOUBLE__ 8
#define __SIZEOF_FLOAT__ 4
#define __SIZEOF_INT__ 4
#define __SIZEOF_LONG__ 4
#define __SIZEOF_LONG_DOUBLE__ 8
#define __SIZEOF_LONG_LONG__ 8
#define __SIZEOF_POINTER__ 4
#define __SIZEOF_PTRDIFF_T__ 4
#define __SIZEOF_SHORT__ 2
#define __SIZEOF_SIZE_T__ 4
#define __SIZEOF_WCHAR_T__ 4
#define __SIZEOF_WINT_T__ 4
#define __SIZE_TYPE__ unsigned int
#define __SOFTFP__ 1
#define __SQ_FBIT__ 31
#define __SQ_IBIT__ 0
#define __STDC__ 1
#define __STDC_HOSTED__ 1
#define __TA_FBIT__ 63
#define __TA_IBIT__ 64
#define __THUMB_INTERWORK__ 1
#define __TQ_FBIT__ 127
#define __TQ_IBIT__ 0
#define __UACCUM_EPSILON__ 0x1P-16UK
#define __UACCUM_FBIT__ 16
#define __UACCUM_IBIT__ 16
#define __UACCUM_MAX__ 0XFFFFFFFFP-16UK
#define __UACCUM_MIN__ 0.0UK
#define __UDA_FBIT__ 32
#define __UDA_IBIT__ 32
#define __UDQ_FBIT__ 64
#define __UDQ_IBIT__ 0
#define __UFRACT_EPSILON__ 0x1P-16UR
#define __UFRACT_FBIT__ 16
#define __UFRACT_IBIT__ 0
#define __UFRACT_MAX__ 0XFFFFP-16UR
#define __UFRACT_MIN__ 0.0UR
#define __UHA_FBIT__ 8
#define __UHA_IBIT__ 8
#define __UHQ_FBIT__ 16
#define __UHQ_IBIT__ 0
#define __UINT16_C(c) c
#define __UINT16_MAX__ 65535
#define __UINT16_TYPE__ short unsigned int
#define __UINT32_C(c) c ## U
#define __UINT32_MAX__ 4294967295U
#define __UINT32_TYPE__ unsigned int
#define __UINT64_C(c) c ## ULL
#define __UINT64_MAX__ 18446744073709551615ULL
#define __UINT64_TYPE__ long long unsigned int
#define __UINT8_C(c) c
#define __UINT8_MAX__ 255
#define __UINT8_TYPE__ unsigned char
#define __UINT_FAST16_MAX__ 4294967295U
#define __UINT_FAST16_TYPE__ unsigned int
#define __UINT_FAST32_MAX__ 4294967295U
#define __UINT_FAST32_TYPE__ unsigned int
#define __UINT_FAST64_MAX__ 18446744073709551615ULL
#define __UINT_FAST64_TYPE__ long long unsigned int
#define __UINT_FAST8_MAX__ 255
#define __UINT_FAST8_TYPE__ unsigned char
#define __UINT_LEAST16_MAX__ 65535
#define __UINT_LEAST16_TYPE__ short unsigned int
#define __UINT_LEAST32_MAX__ 4294967295U
#define __UINT_LEAST32_TYPE__ unsigned int
#define __UINT_LEAST64_MAX__ 18446744073709551615ULL
#define __UINT_LEAST64_TYPE__ long long unsigned int
#define __UINT_LEAST8_MAX__ 255
#define __UINT_LEAST8_TYPE__ unsigned char
#define __UINTMAX_C(c) c ## ULL
#define __UINTMAX_MAX__ 18446744073709551615ULL
#define __UINTMAX_TYPE__ long long unsigned int
#define __UINTPTR_MAX__ 4294967295U
#define __UINTPTR_TYPE__ unsigned int
#define __ULACCUM_EPSILON__ 0x1P-32ULK
#define __ULACCUM_FBIT__ 32
#define __ULACCUM_IBIT__ 32
#define __ULACCUM_MAX__ 0XFFFFFFFFFFFFFFFFP-32ULK
#define __ULACCUM_MIN__ 0.0ULK
#define __ULFRACT_EPSILON__ 0x1P-32ULR
#define __ULFRACT_FBIT__ 32
#define __ULFRACT_IBIT__ 0
#define __ULFRACT_MAX__ 0XFFFFFFFFP-32ULR
#define __ULFRACT_MIN__ 0.0ULR
#define __ULLACCUM_EPSILON__ 0x1P-32ULLK
#define __ULLACCUM_FBIT__ 32
#define __ULLACCUM_IBIT__ 32
#define __ULLACCUM_MAX__ 0XFFFFFFFFFFFFFFFFP-32ULLK
#define __ULLACCUM_MIN__ 0.0ULLK
#define __ULLFRACT_EPSILON__ 0x1P-64ULLR
#define __ULLFRACT_FBIT__ 64
#define __ULLFRACT_IBIT__ 0
#define __ULLFRACT_MAX__ 0XFFFFFFFFFFFFFFFFP-64ULLR
#define __ULLFRACT_MIN__ 0.0ULLR
#define __unix 1
#define __unix__ 1
#define unix 1
#define __UQQ_FBIT__ 8
#define __UQQ_IBIT__ 0
#define __USACCUM_EPSILON__ 0x1P-8UHK
#define __USACCUM_FBIT__ 8
#define __USACCUM_IBIT__ 8
#define __USACCUM_MAX__ 0XFFFFP-8UHK
#define __USACCUM_MIN__ 0.0UHK
#define __USA_FBIT__ 16
#define __USA_IBIT__ 16
#define __USER_LABEL_PREFIX__ 
#define __USFRACT_EPSILON__ 0x1P-8UHR
#define __USFRACT_FBIT__ 8
#define __USFRACT_IBIT__ 0
#define __USFRACT_MAX__ 0XFFP-8UHR
#define __USFRACT_MIN__ 0.0UHR
#define __USQ_FBIT__ 32
#define __USQ_IBIT__ 0
#define __UTA_FBIT__ 64
#define __UTA_IBIT__ 64
#define __UTQ_FBIT__ 128
#define __UTQ_IBIT__ 0
#define __VERSION__ "4.8.0"
#define __VFP_FP__ 1
#define __WCHAR_MAX__ 4294967295U
#define __WCHAR_MIN__ 0U
#define __WCHAR_TYPE__ unsigned int
#define __WINT_MAX__ 4294967295U
#define __WINT_MIN__ 0U
#define __WINT_TYPE__ unsigned int