Earlier GCC, this worked and produced the results you'd expect if (like previous me) you didn't properly understand the C99 tgmath, which then stopped working with more recent GCC: 
#include <tgmath.h>
void main() {
complex double z = 1.0;
z = log10(z);
printf("%f%+fi\n", creal(z), cimag(z));
}
See https://en.cppreference.com/w/c/numeric/tgmath for more. Note log10 is in the "real-only" section; GCC incorporated it into their "real or imag" tgmath for a while incorporating their own clog10 extension, but then evidently changed their minds. The presence or absence of clog10 is not relevant to log10 working or not with tgmath.

In reply to Re^6: PDL 2.058 released by etj
in thread PDL 2.058 released by etj

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