What's a good way to check availability of __restrict keyword?

I am looking a set of #ifdef's to check availability of __restrict keyword for GCC and Visual Studio. I assume that it needs to check compiler version, but I don't know for which versions it was introduced. Any开发者_开发技巧one that can help me out?

UPDATE: This must (and only needs to) work when compiling as C89! So I cannot rely on __STDC_VERSION__ indicating C99, or C99 support.

In a 'configure, make, make install' scenario, this should be checked in 'configure'. 'configure' should define a 'HAS_RESTRICT' in config.h. This should in turn be checked in your headers to define a suitable macro.

For visual studio, I have zero idea.. :(

Just use the C99 standard keyword restrict, and possibly #define it to something else.

You can test for C99 conformance with, for example:

#if __STDC__ != 1
#    error not conforming
#    define restrict __restrict /* use implementation __ format */
#else
#    ifndef __STDC_VERSION__
#        error not conforming
#        define restrict __restrict /* use implementation __ format */
#    else
#        if __STDC_VERSION__ < 199901L
#            error Compiler for C before C99
#            define restrict __restrict /* use implementation __ format */
#        else
#            /* all ok */
#        endif
#    endif
#endif

int fx(int *restrict a, char *restrict b) {
  *b = *a;
  return 0;
}

int main(void) {
  int a[1];
  char b[1];
  fx(a, b);
  return 0;
}

Of course the #errors should be edited out in a working version

How I fixed it:

#if defined(__GNUC__) && ((__GNUC__ > 3) || (__GNUC__ == 3 && __GNUC_MINOR__ >= 1))
#   define SKP_restrict __restrict
#elif defined(_MSC_VER) && _MSC_VER >= 1400
#   define SKP_restrict __restrict
#else
#   define SKP_restrict
#endif

IMHO, __restrict should be available in all standard compilers for both C/C++ programs. It's similar to C99 restrict in certain way.