1ACOS(3P)                   POSIX Programmer's Manual                  ACOS(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
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NAME

12       acos, acosf, acosl - arc cosine functions
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SYNOPSIS

15       #include <math.h>
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17       double acos(double x);
18       float acosf(float x);
19       long double acosl(long double x);
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DESCRIPTION

23       These functions shall compute the principal value of the arc cosine  of
24       their argument x. The value of x should be in the range [-1,1].
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26       An  application  wishing to check for error situations should set errno
27       to zero and  call  feclearexcept(FE_ALL_EXCEPT)  before  calling  these
28       functions.   On return, if errno is non-zero or fetestexcept(FE_INVALID
29       | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero, an error  has
30       occurred.
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RETURN VALUE

33       Upon successful completion, these functions shall return the arc cosine
34       of x, in the range [0,pi] radians.
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36       For finite values of x not in the range [-1,1], a  domain  error  shall
37       occur,  and   either a NaN (if supported), or an implementation-defined
38       value shall be returned.
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40       If x is NaN, a NaN shall be returned.
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42       If x is +1, +0 shall be returned.
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44       If x is ±Inf, a domain error shall occur, and either  a  NaN  (if  sup‐
45       ported), or an implementation-defined value shall be returned.
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ERRORS

48       These functions shall fail if:
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50       Domain Error
51              The  x argument is finite and is not in the range [-1,1],  or is
52              ±Inf.
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54       If the integer expression (math_errhandling & MATH_ERRNO) is  non-zero,
55       then   errno  shall  be  set  to  [EDOM].  If  the  integer  expression
56       (math_errhandling &  MATH_ERREXCEPT)  is  non-zero,  then  the  invalid
57       floating-point exception shall be raised.
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60       The following sections are informative.
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EXAMPLES

63       None.
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APPLICATION USAGE

66       On   error,   the   expressions  (math_errhandling  &  MATH_ERRNO)  and
67       (math_errhandling & MATH_ERREXCEPT) are independent of each other,  but
68       at least one of them must be non-zero.
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RATIONALE

71       None.
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FUTURE DIRECTIONS

74       None.
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SEE ALSO

77       cos(),  feclearexcept(),  fetestexcept(), isnan(), the Base Definitions
78       volume of IEEE Std 1003.1-2001, Section 4.18, Treatment of Error Condi‐
79       tions for Mathematical Functions, <math.h>
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82       Portions  of  this text are reprinted and reproduced in electronic form
83       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
84       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
85       Specifications Issue 6, Copyright (C) 2001-2003  by  the  Institute  of
86       Electrical  and  Electronics  Engineers, Inc and The Open Group. In the
87       event of any discrepancy between this version and the original IEEE and
88       The  Open Group Standard, the original IEEE and The Open Group Standard
89       is the referee document. The original Standard can be  obtained  online
90       at http://www.opengroup.org/unix/online.html .
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94IEEE/The Open Group                  2003                             ACOS(3P)
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