Name
acos, acosf, acosl - arc cosine functionLibrary
Math library ( libm ", " -lm )Synopsis
#include <math.h> double acos(double x );
float acosf(float x );
long double acosl(long double x );
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
acosf() acosl()
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
Description
These functions calculate the arc cosine ofx ; that is the value whose cosine is x. Return Value
On success, these functions return the arc cosine of x in radians; the return value is in the range [0,\ pi].If x is a NaN, a NaN is returned.
If x is +1, +0 is returned.
If x is positive infinity or negative infinity, a domain error occurs, and a NaN is returned.
If x is outside the range [-1,\ 1], a domain error occurs, and a NaN is returned.
Errors
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 outside the range [-1,\ 1] errno is set to EDOM .An invalid floating-point exception ( FE_INVALID ) is raised.
Attributes
For an explanation of the terms used in this section, see attributes(7).| Interface | Attribute | Value |
| T} | Thread safety | MT-Safe |
Standards
C11, POSIX.1-2008.History
C99, POSIX.1-2001.The variant returning double also conforms to C89, SVr4, 4.3BSD.