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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>acos</title></head><body bgcolor=white><center><font size=2>The Single UNIX ® Specification, Version 2<br>Copyright © 1997 The Open Group</font></center><hr size=2 noshade><h4><a name = "tag_000_001_077"> </a>NAME</h4><blockquote>acos - arc cosine function</blockquote><h4><a name = "tag_000_001_078"> </a>SYNOPSIS</h4><blockquote><pre><code>#include <<a href="math.h.html">math.h</a>>double acos(double <i>x</i>);</code></pre></blockquote><h4><a name = "tag_000_001_079"> </a>DESCRIPTION</h4><blockquote>The<i>acos()</i>function computes the principal value of the arc cosine of<i>x.</i>The value of<i>x</i>should be in the range [-1,1].<p>An application wishing to check for error situations should set<i>errno</i>to 0 before calling<i>acos()</i>.If<i>errno</i>is non-zero on return, or the value NaN is returned,an error has occurred.</blockquote><h4><a name = "tag_000_001_080"> </a>RETURN VALUE</h4><blockquote>Upon successful completion,<i>acos()</i>returns the arc cosine of<i>x,</i>in the range [0, <sub><img src="../images/pi.gif" border=0></sub>] radians.If the value of<i>x</i>is not in the range [-1,1],and is not ±Inf or NaN, either 0.0 or NaN is returnedand<i>errno</i>is set to [EDOM].<p>If<i>x</i>is NaN, NaN is returned and<i>errno</i>may be set to [EDOM].If<i>x</i>is ±Inf, either 0.0 is returned and<i>errno</i>is set to [EDOM], or NaN is returned and<i>errno</i>may be set to [EDOM].</blockquote><h4><a name = "tag_000_001_081"> </a>ERRORS</h4><blockquote>The<i>acos()</i>function will fail if:<dl compact><dt>[EDOM]<dd>The value<i>x</i>is not ±Inf or NaN andis not in the range [-1,1].</dl><p>The<i>acos()</i>function may fail if:<dl compact><dt>[EDOM]<dd>The value<i>x</i>is ±Inf or NaN.</dl><p>No other errors will occur.</blockquote><h4><a name = "tag_000_001_082"> </a>EXAMPLES</h4><blockquote>None.</blockquote><h4><a name = "tag_000_001_083"> </a>APPLICATION USAGE</h4><blockquote>None.</blockquote><h4><a name = "tag_000_001_084"> </a>FUTURE DIRECTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_000_001_085"> </a>SEE ALSO</h4><blockquote><i><a href="cos.html">cos()</a></i>,<i><a href="isnan.html">isnan()</a></i>,<i><a href="math.h.html"><math.h></a></i>.</blockquote><h4>DERIVATION</h4><blockquote>Derived from Issue 1 of the SVID.</blockquote><hr size=2 noshade><center><font size=2>UNIX ® is a registered Trademark of The Open Group.<br>Copyright © 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>⌨️ 快捷键说明
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