acos man page

acos, acosf, acosl — arc cosine function


#include <math.h>

double acos(double x);
float acosf(float x);
long double acosl(long double x);

Link with -lm.

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

acosf(), acosl():

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


These functions calculate the arc cosine of x; 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.


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.


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

acos(), acosf(), acosl()Thread safetyMT-Safe

Conforming to

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

The variant returning double also conforms to SVr4, 4.3BSD, C89.

See Also

asin(3), atan(3), atan2(3), cacos(3), cos(3), sin(3), tan(3)

Referenced By

asin(3), atan(3), atan2(3), cos(3), sin(3), tan(3).

Explore man page connections for acos(3).

acosf(3) and acosl(3) are aliases of acos(3).