Is it possible to tell the C preprocessor to check whether a function (not a macro) is declared? I tried the following, but it doesn't appear to work:
#include <stdio.h>
int main(void)
{
#if defined(printf)
printf("You support printf!\n");
#else
puts("Either you don't support printf, or this test doesn't work.");
#endif
return 0;
}
Strictly speaking no, the preprocessor can't do it on its own. However, you can give it a little help by creating appropriate #defines automatically.
Normally as was mentioned above, you'd use autotools if on a unix type system. However, you can also create the same effect using a makefile. I recently had cause to detect the "posix_fallocate" function being defined in headers, because I was using uClibc which seemed to omit it in earlier versions. This works in gnu make, but you can probably get a similar thing to work in other versions:
NOFALLOC := $(shell echo "\#include <fcntl.h>\nint main() { posix_fallocate(0,0,0);}" | $(CC) -o /dev/null -Werror -xc - >/dev/null 2>/dev/null && echo 0 || echo 1)
ifeq "$(NOFALLOC)" "1"
DFLAGS += -DNO_POSIX_FALLOCATE
endif