# acosl (3)

# NAME

acos, acosf, acosl - arc cosine function# SYNOPSIS

#include <math.h>

Link withdouble acos(doublex);float acosf(floatx);long double acosl(long doublex);

*-lm*.

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 versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

|| /* Since glibc 2.19: */ _DEFAULT_SOURCE

|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

# DESCRIPTION

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.

# 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 |

acos (), acosf (), acosl () | Thread safety | MT-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)