conjf, conj, conjl

Defined in header <complex.h>
float complex       conjf( float complex z );
(1) (since C99)
double complex      conj( double complex z );
(2) (since C99)
long double complex conjl( long double complex z );
(3) (since C99)
Defined in header <tgmath.h>
#define conj( z )
(4) (since C99)
1-3) Computes the complex conjugate of z by reversing the sign of the imaginary part.
4) Type-generic macro: if z has type long double complex, long double imaginary, or long double, conjl is called. If z has type float complex, float imaginary, or float, conjf is called. If z has type double complex, double imaginary, double, or any integer type, conj is called.


z - complex argument

Return value

The complex conjugate of z.


On C99 implementations that do not implement I as _Imaginary_I, conj may be used to obtain complex numbers with negative zero imaginary part. In C11, the macro CMPLX is used for that purpose.


#include <stdio.h>
#include <complex.h>
int main(void)
    double complex z = 1.0 + 2.0*I;
    double complex z2 = conj(z);
    printf("The conjugate of %.1f%+.1fi is %.1f%+.1fi\n",
            creal(z), cimag(z), creal(z2), cimag(z2));
    printf("Their product is %.1f%+.1fi\n", creal(z*z2), cimag(z*z2));


The conjugate of 1.0+2.0i is 1.0-2.0i
Their product is 5.0+0.0i


  • C11 standard (ISO/IEC 9899:2011):
    • The conj functions (p: 198)
    • 7.25 Type-generic math <tgmath.h> (p: 373-375)
    • G.7 Type-generic math <tgmath.h> (p: 545)
  • C99 standard (ISO/IEC 9899:1999):
    • The conj functions (p: 179)
    • 7.22 Type-generic math <tgmath.h> (p: 335-337)
    • G.7 Type-generic math <tgmath.h> (p: 480)

See also

C++ documentation for conj

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