cos man page

cos, cosf, cosl — cosine function


#include <math.h>

double cos(double x);
float cosf(float x);
long double cosl(long double x);

Link with -lm.

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

cosf(), cosl():

   || /* Since glibc 2.19: */ _DEFAULT_SOURCE
   || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE


These functions return the cosine of x, where x is given in radians.

Return Value

On success, these functions return the cosine of x.

If x is a NaN, a NaN is returned.

If x is positive infinity or negative infinity, a domain error occurs, and a NaN is returned.


See math_error(7) for information on how to determine whether an error has occurred when calling these functions.

The following errors can occur:

Domain error: x is an infinity

errno is set to EDOM (but see Bugs). An invalid floating-point exception (FE_INVALID) is raised.


For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
cos(), cosf(), cosl() Thread safety MT-Safe

Conforming to

C99, POSIX.1-2001, POSIX.1-2008.

The variant returning double also conforms to SVr4, 4.3BSD.


Before version 2.10, the glibc implementation did not set errno to EDOM when a domain error occurred.

See Also

acos(3), asin(3), atan(3), atan2(3), ccos(3), sin(3), sincos(3), tan(3)


This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at

Referenced By

acos(3), asin(3), atan(3), atan2(3), dlopen(3), sin(3), sincos(3), tan(3).

The man pages cosf(3) and cosl(3) are aliases of cos(3).

2017-09-15 Linux Programmer's Manual