double acos(doublex);
float acosf(floatx);
long double acosl(long doublex);

DESCRIPTION

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.

RETURN VALUE

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.

ERRORS

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.

EXAMPLES

None.

APPLICATION USAGE

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.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

cos() , feclearexcept() , fetestexcept() , isnan()
, the Base Definitions volume of
IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Conditions
for
Mathematical Functions, <math.h>

COPYRIGHT

Portions 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 .