Content-type: text/html Man page of acos

# acos

Section: Mathematical Library Functions (3M)
Updated: 12 Jul 2006

## 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(5) for descriptions of the following attributes:

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

cos(3M), feclearexcept(3M), fetestexcept(3M), isnan(3M), math.h(3HEAD), matherr(3M), attributes(5), standards(5)

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUES
ERRORS
USAGE
ATTRIBUTES