I'm trying to hunt down a problem using complex literals when compiling with GCC. Consider the following
#include <stdio.h>
#include <complex.h>
int main(void)
{
double complex z = CMPLX(0.0, -1.0);
printf("z = %.1f%+.1fi\n", creal(z), cimag(z));
return 0;
}
(slightly modified from the reference page). If I compile with Clang, it works as expected. However, if I use GCC I get an undefined reference error
gcc -std=c11 mwe.c
mwe.c: 6:24 warning: implicit declaration of function 'CMPLX' ...
mwe.c:(...) undefined reference to `CMPLX'
I have tried this with GCC 4.7 and 7.2 on Linux and GCC 9 on MacOS. The error messages change, but the net result remains the same. Reviewing the reference for CMPLX, this should be valid C11. Based on this answer and this post, it appears like GCC accepted this construct before.
My bottom line question is: Why can't I use CMPLX with GCC?
It appears like this is caused by a header/library disconnect on the systems I have. Compiling with the -save-temps flag, it appears GCC uses the system header for complex.h. This means the selected Xcode SDK's usr/include/complex.h on MacOS and /usr/include/complex.h on Linux. On MacOS, the CMPLX macro is only defined when using Clang. The Linux I have is RHEL 6 meaning the header is aimed at GCC 3 which did not have CMPLX. Based on the discussion on this bug report, it looks like making sure the macro is defined is not up to GCC.
The short answer is: The compiler/platform combination doesn't support it. Use the native compiler or update the system.