17 Language support library [support]

17.14 C headers [support.c.headers]

17.14.2 Header <complex.h> synopsis [complex.h.syn]

#include <complex>
The header <complex.h> behaves as if it simply includes the header <complex>.
[Note 1: 
Names introduced by <complex> in namespace std are not placed into the global namespace scope by <complex.h>.
— end note]