acos(P)                                                 acos(P)





NAME
       acos, acosf, acosl - arc cosine functions

SYNOPSIS
       #include <math.h>

       double acos(double x);
       float acosf(float x);
       long double acosl(long double x);


DESCRIPTION
       The  functionality  described  on this reference page is
       aligned with the ISO C standard.  Any  conflict  between
       the  requirements  described here and the ISO C standard
       is unintentional.  This volume  of  IEEE Std 1003.1-2001
       defers to the ISO C standard.

       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   feclearex-
       cept(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,] 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],     <img    src="../images/opt-start.gif"
              alt="[Option Start]" border="0">  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  Operat-
       ing System Interface (POSIX), The Open Group Base Speci-
       fications Issue 6, Copyright (C) 2001-2003 by the Insti-
       tute  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.open-
       group.org/unix/online.html .



POSIX                         2003                      acos(P)
