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How can I find out without using AUTOCONF exactly what specifier (if any) is supported by a C compiler: inline, __inline__ or __inline?

Our project uses a lot of small one-line inline functions for simple arithmetical calculations. How can we find out exactly what inline specifier is used by user's C compiler: inline, __inline or __inline__?

We looked at how GLIB library does it. The fragment is given below:

/* inlining hassle. for compilers that don't allow the `inline' keyword,
 * mostly because of strict ANSI C compliance or dumbness, we try to fall
 * back to either `__inline__' or `__inline'.
 * we define G_CAN_INLINE, if the compiler seems to be actually
 * *capable* to do function inlining, in which case inline function bodys
 * do make sense. we also define G_INLINE_FUNC to properly export the
 * function prototypes if no inlining can be performed.
 * we special case most of the stuff, so inline functions can have a normal
 * implementation by defining G_INLINE_FUNC to extern and G_CAN_INLINE to 1.
 */
#ifndef G_INLINE_FUNC
#  define G_CAN_INLINE 1
#endif
#ifdef G_HAVE_INLINE // compiler supports the __inline__ specifier
#  if defined (__GNUC__) && defined (__STRICT_ANSI__)
#    undef inline
#    define inline __inline__
#  endif
#else /* !G_HAVE_INLINE */
#  undef inline
#  if defined (G_HAVE___INLINE__)
#    define inline __inline__
#  else /* !inline && !__inline__ */
#    if defined (G_HAVE___INLINE) // compiler supports the __inline specifier
#      define inline __inline
#    else /* !inline && !__inline__ && !__inline */
#      define inline /* don't inline, then */
#      ifndef G_INLINE_FUNC
#    undef G_CAN_INLINE
#      endif
#    endif
#  endif
#endif
#ifndef G_INLINE_FUNC
#  ifdef __GNUC__
#    ifdef __OPTIMIZE__
#      define G_INLINE_FUNC extern inline
#    else
#      undef G_CAN_INLINE
#      define G_INLINE_FUNC extern
#    endif
#  else /* !__GNUC__ */
#    ifdef G_CAN_INLINE
#      define G_INLINE_FUNC static inline
#    else
#      define G_INLINE_FUNC extern
#    endif
#  endif /* !__GNUC__ */
#endif /* !G_INLINE_FUNC */

They seem to set G_HAVE_INLINE and G_HAVE__INLINE_ in their very complicated configure file. Is there any way to do it in code without using autotools?

Solution

  • AC_C_INLINE, with this autoconf macro, you can use inline in all cases, provided you include config.h (usual name for the autoconf generated header).