Next: System-specific Predefined Macros, Previous: Standard Predefined Macros, Up: 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. Their names all start with double underscores.
__GNUC____GNUC_MINOR____GNUC_PATCHLEVEL____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__(__GNUC__ && __cplusplus).
__STRICT_ANSI____BASE_FILE____INCLUDE_LEVEL____ELF____VERSION____PIC____OPTIMIZE____OPTIMIZE_SIZE____NO_INLINE____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__inline will be
handled in GCC's traditional gnu89 mode. In this mode an extern
inline function will never be compiled as a standalone function, and
an inline function which is neither extern nor
static will always be compiled as a standalone function.
__GNUC_STDC_INLINE__inline will be
handled according to the ISO C99 standard. In this mode an
extern inline function will always be compiled as a standalone
externally visible function, and an inline function which is
neither extern nor static will never be compiled as a
standalone function.
If this macro is defined, GCC supports the gnu_inline function
attribute as a way to always get the gnu89 behaviour. 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 gnu89 mode, and the
gnu_inline function attribute will not be recognized.
__CHAR_UNSIGNED__char is
unsigned on the target machine. It exists to cause the standard header
file limits.h to work correctly. You should not use this macro
yourself; instead, refer to the standard macros defined in limits.h.
__WCHAR_UNSIGNED____CHAR_UNSIGNED__, this macro is defined if and only if the
data type wchar_t is unsigned and the front-end is in C++ mode.
__REGISTER_PREFIX__m68k-aout environment it
expands to nothing, but in the m68k-coff environment it expands
to a single `%'.
__USER_LABEL_PREFIX__m68k-aout environment it expands to an `_', but in the
m68k-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__size_t, ptrdiff_t, wchar_t, wint_t,
intmax_t, and uintmax_t
typedefs, respectively. They exist to make the standard header files
stddef.h and wchar.h work correctly. You should not use
these macros directly; instead, include the appropriate headers and use
the typedefs.
__CHAR_BIT__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____INTMAX_MAX__signed char, wchar_t,
signed short,
signed int, signed long, signed long long, and
intmax_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.
__DEPRECATED__EXCEPTIONS__USING_SJLJ_EXCEPTIONS__setjmp and longjmp for exception
handling.
__GXX_WEAK____NEXT_RUNTIME____LP64___LP64long int and pointer both use 64-bits and
int uses 32-bit.
__SSP____SSP_ALL____TIMESTAMP__"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
"??? ??? ?? ??:??:?? ????".