ACOS(3) Library Functions Manual ACOS(3)

acos — arc cosine function

#include <math.h>

double acos(double x);

The acos() function computes the principal value of the arc cosine of x. The value of x should be in the range [-1,1].

An application wishing to check for error situations should set errno to 0 before calling acos(). If errno is non-zero on return, or the value NaN is returned, an error has occurred.

Upon successful completion, acos() returns the arc cosine of x, in the range [0, ] radians. If the value of x is not in the range [-1,1], and is not ±Inf or NaN, either 0.0 or NaN is returned and errno is set to [EDOM].

If x is NaN, NaN is returned and errno may be set to [EDOM]. If x is ±Inf, either 0.0 is returned and errno is set to [EDOM], or NaN is returned and errno may be set to [EDOM].

The acos() function will fail if:

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

The acos() function may fail if:

The value x is ±Inf or NaN.

No other errors will occur.

None.

None.

None.

cos(3) , isnan(3) , <math.h> .

Derived from Issue 1 of the SVID.

February 1997 posix.fail