ACOS(3M) Mathematical Library Functions ACOS(3M)

acos, acosf, acosl - arc cosine functions

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

float acosf(float x);

long double acosl(long double x);

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

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.

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].

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.

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

Interface Stability Standard
MT-Level MT-Safe

math.h(3HEAD), cos(3M), feclearexcept(3M), fetestexcept(3M), isnan(3M), matherr(3M), attributes(7), standards(7)

July 12, 2006 SunOS 5.11