Other Aliasacosf, acosl
double acos(double x);
float acosf(float x);
long double acosl(long double x);
These functions shall compute the principal value of the arc cosine of their argument x. The value of x should be in the range [-1,1].
An application wishing to check for error situations should set errno to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these functions. On return, if errno is non-zero or fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error has occurred.
Upon successful completion, these functions shall 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 shall occur, and either a NaN (if supported), or an implementation-defined value shall be returned.
If x is NaN, a NaN shall be returned.
If x is +1, +0 shall be returned.
If x is ±Inf, a domain error shall occur, and either a NaN (if supported), or an implementation-defined value shall be returned.
These functions shall fail if:
- Domain Error
- The x argument is finite and is not in the range [-1,1], or is ±Inf.
If the integer expression (math_errhandling & MATH_ERRNO) is non-zero, then errno shall be set to [EDOM]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non-zero, then the invalid floating-point exception shall be raised.
The following sections are informative.
On error, the expressions (math_errhandling & MATH_ERRNO) and (math_errhandling & MATH_ERREXCEPT) are independent of each other, but at least one of them must be non-zero.
COPYRIGHTPortions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .