ACOS(3P) POSIX Programmer's Manual ACOS(3P)PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
Linux manual page for details of Linux behavior), or the interface may
not be implemented on Linux.
acos, acosf, acosl - arc cosine functions
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
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 sup‐
ported), or an implementation-defined value shall be returned.
These functions shall fail if:
The x argument is finite and is not in the range [-1,1], or is
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.
SEE ALSOcos(), feclearexcept(), fetestexcept(), isnan(), the Base Definitions
volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Condi‐
tions for Mathematical Functions, <math.h>
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 .
IEEE/The Open Group 2003 ACOS(3P)