CREAL(3) Linux Programmer's Manual CREAL(3)

creal, crealf, creall - get real part of a complex number

#include <complex.h>
double creal(double complex z);
float crealf(float complex z);
long double creall(long double complex z);
Link with -lm.

These functions return the real part of the complex number z.
One has:
    z = creal(z) + I * cimag(z)

These functions first appeared in glibc in version 2.1.

For an explanation of the terms used in this section, see attributes(7).
Interface Attribute Value
creal (), crealf (), creall () Thread safety MT-Safe

C99, POSIX.1-2001, POSIX.1-2008.

The gcc supports also __real__. That is a GNU extension.

cabs(3), cimag(3), complex(7)