cos

float       cosf( float arg );

double      cos( double arg );

long double cosl( long double arg );

#define cos( arg )

Parameters

Return value

Return value

If no errors occur, the cosine of arg (cos(arg)) in the range [-1 ; +1], is returned.

If a domain error occurs, an implementation-defined value is returned (NaN where supported).

If a range error occurs due to underflow, the correct result (after rounding) is returned.

Error handling

Errors are reported as specified in math_errhandling.

If the implementation supports IEEE floating-point arithmetic (IEC 60559),

• if the argument is ±0, the result is 1.0
• if the argument is ±∞, NaN is returned and FE_INVALID is raised
• if the argument is NaN, NaN is returned

Notes

The case where the argument is infinite is not specified to be a domain error in C, but it is defined as a domain error in POSIX.

Example

#include <stdio.h>
#include <math.h>
#include <errno.h>
#include <fenv.h>
 
#pragma STDC FENV_ACCESS ON
int main(void)
{
    double pi = acos(-1);
    // typical usage
    printf("cos(pi/3) = %f\n", cos(pi/3));
    printf("cos(pi/2) = %f\n", cos(pi/2));
    printf("cos(-3*pi/4) = %f\n", cos(-3*pi/4));
    // special values
    printf("cos(+0) = %f\n", cos(0.0));
    printf("cos(-0) = %f\n", cos(-0.0));
    // error handling 
    feclearexcept(FE_ALL_EXCEPT);
    printf("cos(INFINITY) = %f\n", cos(INFINITY));
    if(fetestexcept(FE_INVALID)) puts("    FE_INVALID raised");
}

cos(pi/3) = 0.500000
cos(pi/2) = 0.000000
cos(-3*pi/4) = -0.707107
cos(+0) = 1.000000
cos(-0) = 1.000000
cos(INFINITY) = -nan
    FE_INVALID raised

References

• C11 standard (ISO/IEC 9899:2011):
  • 7.12.4.5 The cos functions (p: 239)
  • 7.25 Type-generic math <tgmath.h> (p: 373-375)
  • F.10.1.5 The cos functions (p: 519)
• C99 standard (ISO/IEC 9899:1999):
  • 7.12.4.5 The cos functions (p: 220)
  • 7.22 Type-generic math <tgmath.h> (p: 335-337)
  • F.9.1.5 The cos functions (p: 456)
• C89/C90 standard (ISO/IEC 9899:1990):
  • 4.5.2.5 The cos function

See also