#include <math.h>
double cos(double x);
float cosf(float x);
long double cosl(long double x);
These functions shall compute the cosine of their argument x, measured in radians.
An application wishing to check for error situations should set errno to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.
Upon successful completion, these functions shall return the cosine of x.
If x is NaN, a NaN shall be returned.
If x is ±0, the value 1.0 shall be returned.
If x is ±Inf, a domain error shall occur, and either a NaN (if supported), or an implementation-defined value shall be returned.
These functions shall fail if:
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [EDOM]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.
The following sections are informative.
#include <math.h> ... double radians = 45 * M_PI / 180; double result; ... result = cos(radians);
These functions may lose accuracy when their argument is near an odd multiple of pi/2 or is far from 0.
On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.
acos(), feclearexcept(), fetestexcept(), isnan(), sin(), tan(), the Base Definitions volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions for Mathematical Functions, <math.h>