NAME

acos, acosf, acosl - arc cosine functions

SYNOPSIS

c99 [ flag... ] file... -lm [ library... ]
#include <math.h>
double acos(double x);

float acosf(float x);

long double acosl(long double x);

DESCRIPTION

These functions compute the principal value of the arc cosine of x. The value of x should be in the range [−1,1].

RETURN VALUES

Upon successful completion, these functions return the arc cosine of x in the range [0, pi] radians.

For finite values of x not in the range [−1,1], a domain error occurs and NaN is returned.

If x is NaN, NaN is returned.

If x is +1, +0 is returned.

If x is ±Inf, a domain error occurs and NaN is returned.

For exceptional cases, matherr(3M) tabulates the values to be returned by acos() as specified by SVID3 and XPG3.

ERRORS

These functions will fail if:

Domain Error

The x argument is finite and not in the range [-1,1], or is ±Inf.

If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, the invalid floating-point exception is raised.

The acos() function sets errno to EDOM if x is not ±Inf or NaN and is not in the range [−1,1].

USAGE

An application wanting to check for exceptions should call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an exception has been raised. An application should either examine the return value or check the floating point exception flags to detect exceptions.

An application can also set errno to 0 before calling acos(). On return, if errno is non-zero, an error has occurred. The acosf() and acosl() functions do not set errno.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:

ATTRIBUTE TYPE	ATTRIBUTE VALUE
Interface Stability	Standard
MT-Level	MT-Safe