#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)):
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99
The cos() function returns the cosine of x, where x is given in radians.
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.
The cos(), cosf(), and cosl() functions are thread-safe.
C99, POSIX.1-2001. 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.
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