3.7.2 Common Predefined Macros
The common predefined macros are GNU C extensions. They are available with the same meanings regardless of the machine or operating system on which you are using GNU C or GNU Fortran. Their names all start with double underscores.
__COUNTER__
- This macro expands to sequential integral values starting from 0. In conjunction with the
##
operator, this provides a convenient means to generate unique identifiers. Care must be taken to ensure that__COUNTER__
is not expanded prior to inclusion of precompiled headers which use it. Otherwise, the precompiled headers will not be used. __GFORTRAN__
- The GNU Fortran compiler defines this.
-
__GNUC__
__GNUC_MINOR__
__GNUC_PATCHLEVEL__
- These macros are defined by all GNU compilers that use the C preprocessor: C, C++, Objective-C and Fortran. Their values are the major version, minor version, and patch level of the compiler, as integer constants. For example, GCC 3.2.1 will define
__GNUC__
to 3,__GNUC_MINOR__
to 2, and__GNUC_PATCHLEVEL__
to 1. These macros are also defined if you invoke the preprocessor directly.__GNUC_PATCHLEVEL__
is new to GCC 3.0; it is also present in the widely-used development snapshots leading up to 3.0 (which identify themselves as GCC 2.96 or 2.97, depending on which snapshot you have).If all you need to know is whether or not your program is being compiled by GCC, or a non-GCC compiler that claims to accept the GNU C dialects, you can simply test
__GNUC__
. If you need to write code which depends on a specific version, you must be more careful. Each time the minor version is increased, the patch level is reset to zero; each time the major version is increased (which happens rarely), the minor version and patch level are reset. If you wish to use the predefined macros directly in the conditional, you will need to write it like this:/* Test for GCC > 3.2.0 */ #if __GNUC__ > 3 || \ (__GNUC__ == 3 && (__GNUC_MINOR__ > 2 || \ (__GNUC_MINOR__ == 2 && \ __GNUC_PATCHLEVEL__ > 0))
Another approach is to use the predefined macros to calculate a single number, then compare that against a threshold:
#define GCC_VERSION (__GNUC__ * 10000 \ + __GNUC_MINOR__ * 100 \ + __GNUC_PATCHLEVEL__) ... /* Test for GCC > 3.2.0 */ #if GCC_VERSION > 30200
Many people find this form easier to understand.
__GNUG__
- The GNU C++ compiler defines this. Testing it is equivalent to testing
(__GNUC__ && __cplusplus)
. __STRICT_ANSI__
- GCC defines this macro if and only if the
-ansi
switch, or a-std
switch specifying strict conformance to some version of ISO C or ISO C++, was specified when GCC was invoked. It is defined to ‘1
’. This macro exists primarily to direct GNU libc's header files to restrict their definitions to the minimal set found in the 1989 C standard. __BASE_FILE__
- This macro expands to the name of the main input file, in the form of a C string constant. This is the source file that was specified on the command line of the preprocessor or C compiler.
__INCLUDE_LEVEL__
- This macro expands to a decimal integer constant that represents the depth of nesting in include files. The value of this macro is incremented on every ‘
#include
’ directive and decremented at the end of every included file. It starts out at 0, its value within the base file specified on the command line. __ELF__
- This macro is defined if the target uses the ELF object format.
__VERSION__
- This macro expands to a string constant which describes the version of the compiler in use. You should not rely on its contents having any particular form, but it can be counted on to contain at least the release number.
-
__OPTIMIZE__
__OPTIMIZE_SIZE__
__NO_INLINE__
- These macros describe the compilation mode.
__OPTIMIZE__
is defined in all optimizing compilations.__OPTIMIZE_SIZE__
is defined if the compiler is optimizing for size, not speed.__NO_INLINE__
is defined if no functions will be inlined into their callers (when not optimizing, or when inlining has been specifically disabled by-fno-inline
).These macros cause certain GNU header files to provide optimized definitions, using macros or inline functions, of system library functions. You should not use these macros in any way unless you make sure that programs will execute with the same effect whether or not they are defined. If they are defined, their value is 1.
__GNUC_GNU_INLINE__
- GCC defines this macro if functions declared
inline
will be handled in GCC's traditional gnu90 mode. Object files will contain externally visible definitions of all functions declaredinline
withoutextern
orstatic
. They will not contain any definitions of any functions declaredextern inline
. __GNUC_STDC_INLINE__
- GCC defines this macro if functions declared
inline
will be handled according to the ISO C99 standard. Object files will contain externally visible definitions of all functions declaredextern inline
. They will not contain definitions of any functions declaredinline
withoutextern
.If this macro is defined, GCC supports the
gnu_inline
function attribute as a way to always get the gnu90 behavior. Support for this and__GNUC_GNU_INLINE__
was added in GCC 4.1.3. If neither macro is defined, an older version of GCC is being used:inline
functions will be compiled in gnu90 mode, and thegnu_inline
function attribute will not be recognized. __CHAR_UNSIGNED__
- GCC defines this macro if and only if the data type
char
is unsigned on the target machine. It exists to cause the standard header filelimits.h
to work correctly. You should not use this macro yourself; instead, refer to the standard macros defined inlimits.h
. __WCHAR_UNSIGNED__
- Like
__CHAR_UNSIGNED__
, this macro is defined if and only if the data typewchar_t
is unsigned and the front-end is in C++ mode. __REGISTER_PREFIX__
- This macro expands to a single token (not a string constant) which is the prefix applied to CPU register names in assembly language for this target. You can use it to write assembly that is usable in multiple environments. For example, in the
m68k-aout
environment it expands to nothing, but in them68k-coff
environment it expands to a single ‘%
’. __USER_LABEL_PREFIX__
- This macro expands to a single token which is the prefix applied to user labels (symbols visible to C code) in assembly. For example, in the
m68k-aout
environment it expands to an ‘_
’, but in them68k-coff
environment it expands to nothing.This macro will have the correct definition even if
-f(no-)underscores
is in use, but it will not be correct if target-specific options that adjust this prefix are used (e.g. the OSF/rose-mno-underscores
option). -
__SIZE_TYPE__
__PTRDIFF_TYPE__
__WCHAR_TYPE__
__WINT_TYPE__
__INTMAX_TYPE__
__UINTMAX_TYPE__
__SIG_ATOMIC_TYPE__
__INT8_TYPE__
__INT16_TYPE__
__INT32_TYPE__
__INT64_TYPE__
__UINT8_TYPE__
__UINT16_TYPE__
__UINT32_TYPE__
__UINT64_TYPE__
__INT_LEAST8_TYPE__
__INT_LEAST16_TYPE__
__INT_LEAST32_TYPE__
__INT_LEAST64_TYPE__
__UINT_LEAST8_TYPE__
__UINT_LEAST16_TYPE__
__UINT_LEAST32_TYPE__
__UINT_LEAST64_TYPE__
__INT_FAST8_TYPE__
__INT_FAST16_TYPE__
__INT_FAST32_TYPE__
__INT_FAST64_TYPE__
__UINT_FAST8_TYPE__
__UINT_FAST16_TYPE__
__UINT_FAST32_TYPE__
__UINT_FAST64_TYPE__
__INTPTR_TYPE__
__UINTPTR_TYPE__
- These macros are defined to the correct underlying types for the
size_t
,ptrdiff_t
,wchar_t
,wint_t
,intmax_t
,uintmax_t
,sig_atomic_t
,int8_t
,int16_t
,int32_t
,int64_t
,uint8_t
,uint16_t
,uint32_t
,uint64_t
,int_least8_t
,int_least16_t
,int_least32_t
,int_least64_t
,uint_least8_t
,uint_least16_t
,uint_least32_t
,uint_least64_t
,int_fast8_t
,int_fast16_t
,int_fast32_t
,int_fast64_t
,uint_fast8_t
,uint_fast16_t
,uint_fast32_t
,uint_fast64_t
,intptr_t
, anduintptr_t
typedefs, respectively. They exist to make the standard header filesstddef.h
,stdint.h
, andwchar.h
work correctly. You should not use these macros directly; instead, include the appropriate headers and use the typedefs. Some of these macros may not be defined on particular systems if GCC does not provide astdint.h
header on those systems. __CHAR_BIT__
- Defined to the number of bits used in the representation of the
char
data type. It exists to make the standard header given numerical limits work correctly. You should not use this macro directly; instead, include the appropriate headers. -
__SCHAR_MAX__
__WCHAR_MAX__
__SHRT_MAX__
__INT_MAX__
__LONG_MAX__
__LONG_LONG_MAX__
__WINT_MAX__
__SIZE_MAX__
__PTRDIFF_MAX__
__INTMAX_MAX__
__UINTMAX_MAX__
__SIG_ATOMIC_MAX__
__INT8_MAX__
__INT16_MAX__
__INT32_MAX__
__INT64_MAX__
__UINT8_MAX__
__UINT16_MAX__
__UINT32_MAX__
__UINT64_MAX__
__INT_LEAST8_MAX__
__INT_LEAST16_MAX__
__INT_LEAST32_MAX__
__INT_LEAST64_MAX__
__UINT_LEAST8_MAX__
__UINT_LEAST16_MAX__
__UINT_LEAST32_MAX__
__UINT_LEAST64_MAX__
__INT_FAST8_MAX__
__INT_FAST16_MAX__
__INT_FAST32_MAX__
__INT_FAST64_MAX__
__UINT_FAST8_MAX__
__UINT_FAST16_MAX__
__UINT_FAST32_MAX__
__UINT_FAST64_MAX__
__INTPTR_MAX__
__UINTPTR_MAX__
__WCHAR_MIN__
__WINT_MIN__
__SIG_ATOMIC_MIN__
- Defined to the maximum value of the
signed char
,wchar_t
,signed short
,signed int
,signed long
,signed long long
,wint_t
,size_t
,ptrdiff_t
,intmax_t
,uintmax_t
,sig_atomic_t
,int8_t
,int16_t
,int32_t
,int64_t
,uint8_t
,uint16_t
,uint32_t
,uint64_t
,int_least8_t
,int_least16_t
,int_least32_t
,int_least64_t
,uint_least8_t
,uint_least16_t
,uint_least32_t
,uint_least64_t
,int_fast8_t
,int_fast16_t
,int_fast32_t
,int_fast64_t
,uint_fast8_t
,uint_fast16_t
,uint_fast32_t
,uint_fast64_t
,intptr_t
, anduintptr_t
types and to the minimum value of thewchar_t
,wint_t
, andsig_atomic_t
types respectively. They exist to make the standard header given numerical limits work correctly. You should not use these macros directly; instead, include the appropriate headers. Some of these macros may not be defined on particular systems if GCC does not provide astdint.h
header on those systems. -
__INT8_C
__INT16_C
__INT32_C
__INT64_C
__UINT8_C
__UINT16_C
__UINT32_C
__UINT64_C
__INTMAX_C
__UINTMAX_C
- Defined to implementations of the standard
stdint.h
macros with the same names without the leading__
. They exist the make the implementation of that header work correctly. You should not use these macros directly; instead, include the appropriate headers. Some of these macros may not be defined on particular systems if GCC does not provide astdint.h
header on those systems. -
__SIZEOF_INT__
__SIZEOF_LONG__
__SIZEOF_LONG_LONG__
__SIZEOF_SHORT__
__SIZEOF_POINTER__
__SIZEOF_FLOAT__
__SIZEOF_DOUBLE__
__SIZEOF_LONG_DOUBLE__
__SIZEOF_SIZE_T__
__SIZEOF_WCHAR_T__
__SIZEOF_WINT_T__
__SIZEOF_PTRDIFF_T__
- Defined to the number of bytes of the C standard data types:
int
,long
,long long
,short
,void *
,float
,double
,long double
,size_t
,wchar_t
,wint_t
andptrdiff_t
. -
__BYTE_ORDER__
__ORDER_LITTLE_ENDIAN__
__ORDER_BIG_ENDIAN__
__ORDER_PDP_ENDIAN__
-
__BYTE_ORDER__
is defined to one of the values__ORDER_LITTLE_ENDIAN__
,__ORDER_BIG_ENDIAN__
, or__ORDER_PDP_ENDIAN__
to reflect the layout of multi-byte and multi-word quantities in memory. If__BYTE_ORDER__
is equal to__ORDER_LITTLE_ENDIAN__
or__ORDER_BIG_ENDIAN__
, then multi-byte and multi-word quantities are laid out identically: the byte (word) at the lowest address is the least significant or most significant byte (word) of the quantity, respectively. If__BYTE_ORDER__
is equal to__ORDER_PDP_ENDIAN__
, then bytes in 16-bit words are laid out in a little-endian fashion, whereas the 16-bit subwords of a 32-bit quantity are laid out in big-endian fashion.You should use these macros for testing like this:
/* Test for a little-endian machine */ #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
__FLOAT_WORD_ORDER__
-
__FLOAT_WORD_ORDER__
is defined to one of the values__ORDER_LITTLE_ENDIAN__
or__ORDER_BIG_ENDIAN__
to reflect the layout of the words of multi-word floating-point quantities. __DEPRECATED
- This macro is defined, with value 1, when compiling a C++ source file with warnings about deprecated constructs enabled. These warnings are enabled by default, but can be disabled with
-Wno-deprecated
. __EXCEPTIONS
- This macro is defined, with value 1, when compiling a C++ source file with exceptions enabled. If
-fno-exceptions
is used when compiling the file, then this macro is not defined. __GXX_RTTI
- This macro is defined, with value 1, when compiling a C++ source file with runtime type identification enabled. If
-fno-rtti
is used when compiling the file, then this macro is not defined. __USING_SJLJ_EXCEPTIONS__
- This macro is defined, with value 1, if the compiler uses the old mechanism based on
setjmp
andlongjmp
for exception handling. __GXX_EXPERIMENTAL_CXX0X__
- This macro is defined when compiling a C++ source file with the option
-std=c++0x
or-std=gnu++0x
. It indicates that some features likely to be included in C++0x are available. Note that these features are experimental, and may change or be removed in future versions of GCC. __GXX_WEAK__
- This macro is defined when compiling a C++ source file. It has the value 1 if the compiler will use weak symbols, COMDAT sections, or other similar techniques to collapse symbols with “vague linkage” that are defined in multiple translation units. If the compiler will not collapse such symbols, this macro is defined with value 0. In general, user code should not need to make use of this macro; the purpose of this macro is to ease implementation of the C++ runtime library provided with G++.
__NEXT_RUNTIME__
- This macro is defined, with value 1, if (and only if) the NeXT runtime (as in
-fnext-runtime
) is in use for Objective-C. If the GNU runtime is used, this macro is not defined, so that you can use this macro to determine which runtime (NeXT or GNU) is being used. -
__LP64__
_LP64
- These macros are defined, with value 1, if (and only if) the compilation is for a target where
long int
and pointer both use 64-bits andint
uses 32-bit. __SSP__
- This macro is defined, with value 1, when
-fstack-protector
is in use. __SSP_ALL__
- This macro is defined, with value 2, when
-fstack-protector-all
is in use. __SSP_STRONG__
- This macro is defined, with value 3, when
-fstack-protector-strong
is in use. __SANITIZE_ADDRESS__
- This macro is defined, with value 1, when
-fsanitize=address
or-fsanitize=kernel-address
are in use. __TIMESTAMP__
- This macro expands to a string constant that describes the date and time of the last modification of the current source file. The string constant contains abbreviated day of the week, month, day of the month, time in hh:mm:ss form, year and looks like
"Sun Sep 16 01:03:52 1973"
. If the day of the month is less than 10, it is padded with a space on the left.If GCC cannot determine the current date, it will emit a warning message (once per compilation) and
__TIMESTAMP__
will expand to"??? ??? ?? ??:??:?? ????"
. -
__GCC_HAVE_SYNC_COMPARE_AND_SWAP_1
__GCC_HAVE_SYNC_COMPARE_AND_SWAP_2
__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4
__GCC_HAVE_SYNC_COMPARE_AND_SWAP_8
__GCC_HAVE_SYNC_COMPARE_AND_SWAP_16
- These macros are defined when the target processor supports atomic compare and swap operations on operands 1, 2, 4, 8 or 16 bytes in length, respectively.
__GCC_HAVE_DWARF2_CFI_ASM
- This macro is defined when the compiler is emitting Dwarf2 CFI directives to the assembler. When this is defined, it is possible to emit those same directives in inline assembly.
-
__FP_FAST_FMA
__FP_FAST_FMAF
__FP_FAST_FMAL
- These macros are defined with value 1 if the backend supports the
fma
,fmaf
, andfmal
builtin functions, so that the include filemath.h
can define the macrosFP_FAST_FMA
,FP_FAST_FMAF
, andFP_FAST_FMAL
for compatibility with the 1999 C standard. __GCC_IEC_559
- This macro is defined to indicate the intended level of support for IEEE 754 (IEC 60559) floating-point arithmetic. It expands to a nonnegative integer value. If 0, it indicates that the combination of the compiler configuration and the command-line options is not intended to support IEEE 754 arithmetic for
float
anddouble
as defined in C99 and C11 Annex F (for example, that the standard rounding modes and exceptions are not supported, or that optimizations are enabled that conflict with IEEE 754 semantics). If 1, it indicates that IEEE 754 arithmetic is intended to be supported; this does not mean that all relevant language features are supported by GCC. If 2 or more, it additionally indicates support for IEEE 754-2008 (in particular, that the binary encodings for quiet and signaling NaNs are as specified in IEEE 754-2008).This macro does not indicate the default state of command-line options that control optimizations that C99 and C11 permit to be controlled by standard pragmas, where those standards do not require a particular default state. It does not indicate whether optimizations respect signaling NaN semantics (the macro for that is
__SUPPORT_SNAN__
). It does not indicate support for decimal floating point or the IEEE 754 binary16 and binary128 types. __GCC_IEC_559_COMPLEX
- This macro is defined to indicate the intended level of support for IEEE 754 (IEC 60559) floating-point arithmetic for complex numbers, as defined in C99 and C11 Annex G. It expands to a nonnegative integer value. If 0, it indicates that the combination of the compiler configuration and the command-line options is not intended to support Annex G requirements (for example, because
-fcx-limited-range
was used). If 1 or more, it indicates that it is intended to support those requirements; this does not mean that all relevant language features are supported by GCC.
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Licensed under the GNU Free Documentation License, Version 1.3.
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