cos, cosf, cosl

Defined in header `<math.h>`
float cosf( float arg );	(1)	(since C99)
double cos( double arg );	(2)
long double cosl( long double arg );	(3)	(since C99)
_Decimal32 cosd32( _Decimal32 arg );	(4)	(since C23)
_Decimal64 cosd64( _Decimal64 arg );	(5)	(since C23)
_Decimal128 cosd128( _Decimal128 arg );	(6)	(since C23)
Defined in header `<tgmath.h>`
#define cos( arg )	(7)	(since C99)

1-6) Computes the cosine of arg (measured in radians).

7) Type-generic macro: If the argument has type long double, (3) (cosl) is called. Otherwise, if the argument has integer type or the type double, (2) (cos) is called. Otherwise, (1) (cosf) is called. If the argument is complex, then the macro invokes the corresponding complex function (ccosf, ccos, ccosl).

The functions (4-6) are declared if and only if the implementation predefines __STDC_IEC_60559_DFP__ (i.e. the implementation supports decimal floating-point numbers).

(since C23)

Parameters

arg

floating-point value representing angle in radians

Return value

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

The result may have little or no significance if the magnitude of arg is large.

(until C99)

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 <errno.h>
#include <fenv.h>
#include <math.h>
#include <stdio.h>
 
#ifndef __GNUC__
#pragma STDC FENV_ACCESS ON
#endif
 
int main(void)
{
    const 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");
}

Possible output:

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

C23 standard (ISO/IEC 9899:2023):

7.12.4.5 The cos functions (p: TBD)
7.25 Type-generic math <tgmath.h> (p: TBD)
F.10.1.5 The cos functions (p: TBD)

C17 standard (ISO/IEC 9899:2018):

7.12.4.5 The cos functions (p: 174)
7.25 Type-generic math <tgmath.h> (p: 272-273)
F.10.1.5 The cos functions (p: 378)

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

sinsinfsinl (C99)(C99)	computes sine (\({\small\sin{x} }\)sin(x)) (function)
tantanftanl (C99)(C99)	computes tangent (\({\small\tan{x} }\)tan(x)) (function)
acosacosfacosl (C99)(C99)	computes arc cosine (\({\small\arccos{x} }\)arccos(x)) (function)
ccosccosfccosl (C99)(C99)(C99)	computes the complex cosine (function)
C++ documentation for `cos`