csinf, csin, csinl

Defined in header <complex.h>
float complex       csinf( float complex z );
(1) (since C99)
double complex      csin( double complex z );
(2) (since C99)
long double complex csinl( long double complex z );
(3) (since C99)
Defined in header <tgmath.h>
#define sin( z )
(4) (since C99)
1-3) Computes the complex sine of z.
4) Type-generic macro: If z has type long double complex, csinl is called. if z has type double complex, csin is called, if z has type float complex, csinf is called. If z is real or integer, then the macro invokes the corresponding real function (sinf, sin, sinl). If z is imaginary, then the macro invokes the corresponding real version of the function sinh, implementing the formula sin(iy) = i ∙ sinh(y), and the return type of the macro is imaginary.


z - complex argument

Return value

If no errors occur, the complex sine of z.

Errors and special cases are handled as if the operation is implemented by -I * csinh(I*z).


The sine is an entire function on the complex plane, and has no branch cuts. Mathematical definition of the sine is sin z =



#include <stdio.h>
#include <math.h>
#include <complex.h>
int main(void)
    double complex z = csin(1);  // behaves like real sine along the real line
    printf("sin(1+0i) = %f%+fi ( sin(1)=%f)\n", creal(z), cimag(z), sin(1));
    double complex z2 = csin(I); // behaves like sinh along the imaginary line 
    printf("sin(0+1i) = %f%+fi (sinh(1)=%f)\n", creal(z2), cimag(z2), sinh(1));


sin(1+0i) = 0.841471+0.000000i ( sin(1)=0.841471)
sin(0+1i) = 0.000000+1.175201i (sinh(1)=1.175201)


  • C17 standard (ISO/IEC 9899:2018):
    • The csin functions (p: 138-139)
    • 7.25 Type-generic math <tgmath.h> (p: 272-273)
    • G.7 Type-generic math <tgmath.h> (p: 397)
  • C11 standard (ISO/IEC 9899:2011):
    • The csin functions (p: 191-192)
    • 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 csin functions (p: 173)
    • 7.22 Type-generic math <tgmath.h> (p: 335-337)
    • G.7 Type-generic math <tgmath.h> (p: 480)

See also

computes the complex cosine
computes the complex tangent
computes the complex arc sine
computes sine (\({\small\sin{x} }\)sin(x))
C++ documentation for sin

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