cargf, carg, cargl

Defined in header <complex.h> 
float       cargf( float complex z );
 (1) (since C99) 
double      carg( double complex z );
 (2) (since C99) 
long double cargl( long double complex z );
 (3) (since C99)
Defined in header <tgmath.h> 
#define carg( z )
 (4) (since C99)
1-3) Computes the argument (also called phase angle) of z, with a branch cut along the negative real axis.
4) Type-generic macro: if z has type long double complex, long double imaginary, or long double, cargl is called. If z has type float complex, float imaginary, or float, cargf is called. If z has type double complex, double imaginary, double, or any integer type, carg is called.

Parameters

z - complex argument

Return value

If no errors occur, returns the phase angle of z in the interval [−π; π].

Errors and special cases are handled as if the function is implemented as atan2(cimag(z), creal(z)).

Example

#include <stdio.h>
#include <complex.h>
 
int main(void) 
{
    double complex z1 = 1.0+0.0*I;
    printf("phase angle of %.1f%+.1fi is %f\n", creal(z1), cimag(z1), carg(z1));
 
    double complex z2 = 0.0+1.0*I;
    printf("phase angle of %.1f%+.1fi is %f\n", creal(z2), cimag(z2), carg(z2));
 
    double complex z3 = -1.0+0.0*I;
    printf("phase angle of %.1f%+.1fi is %f\n", creal(z3), cimag(z3), carg(z3));
 
    double complex z4 = conj(z3); // or CMPLX(-1, -0.0)
    printf("phase angle of %.1f%+.1fi (the other side of the cut) is %f\n",
             creal(z4), cimag(z4), carg(z4));
}

Output:

phase angle of 1.0+0.0i is 0.000000
phase angle of 0.0+1.0i is 1.570796
phase angle of -1.0+0.0i is 3.141593
phase angle of -1.0-0.0i (the other side of the cut) is -3.141593

References

  • C11 standard (ISO/IEC 9899:2011):
    • 7.3.9.1 The carg functions (p: 196)
    • 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):
    • 7.3.9.1 The carg functions (p: 178)
    • 7.22 Type-generic math <tgmath.h> (p: 335-337)
    • G.7 Type-generic math <tgmath.h> (p: 480)

See also

(C99)(C99)(C99)
 computes the magnitude of a complex number
(function)
(C99)(C99)
 computes arc tangent, using signs to determine quadrants
(function)

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