带有__has_include的_Static_assert

Question

I wanna make macro, that checks that file is "includable". Something like this:

#define CHECK(__file)    \
    _Static_assert( __has_include(__file), "Error")
CHECK("header.h");

But it produces errors like

f.c:28:3: __has_include must be used within a preprocessing directive
f.c:28:3: Implicit declaration of function '__has_include' is invalid in C99
f.c:28:3: Static_assert expression is not an integral constant expression

Is this even possible? Or maybe there is different solution that will give similar result?

Thanks for any help!

Answer 1

If all fails (and you can hardly argue with: "__has_include must be used within a preprocessing directive"), throw another layer of indirection at it:

h_assert(){
    for h; do
printf '
#if !__has_include("%s")
_Static_assert(0,"__has_include(\"%s\")");
#endif
' "$h" "$h"
    done
}
h_assert foo.h bar.h baz.h #Generate the header assertions with a POSIX shell