Annex D (normative) Compatibility features [depr]

D.10 C headers [depr.c.headers]

D.10.2 Header <complex.h> synopsis [depr.complex.h.syn]

#include <complex>
1
#
The header <complex.h> behaves as if it simply includes the header <complex>.
2
#
[Note 1:
Names introduced by <complex> in namespace std are not placed into the global namespace scope by <complex.h>.
— end note]