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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>atan2</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_221"> </a>NAME</h4><blockquote>atan2 - arc tangent function</blockquote><h4><a name = "tag_000_001_222"> </a>SYNOPSIS</h4><blockquote><pre><code>#include <<a href="math.h.html">math.h</a>>double atan2(double <i>y</i>, double <i>x</i>);</code></pre></blockquote><h4><a name = "tag_000_001_223"> </a>DESCRIPTION</h4><blockquote>The<i>atan2()</i>function computes the principal value of the arc tangent of<i>y/x</i>,using the signs of both arguments to determine the quadrant ofthe return value.<p>An application wishing to check for error situations should set<i>errno</i>to 0 before calling<i>atan2()</i>.If<i>errno</i>is non-zero on return, or the return value is NaN,an error has occurred.</blockquote><h4><a name = "tag_000_001_224"> </a>RETURN VALUE</h4><blockquote>Upon successful completion,<i>atan2()</i>returns the arc tangent of<i>y/x</i>in the range [-, ] radians.If both arguments are 0.0, an implementation-dependent value is returned and<i>errno</i>may be set to [EDOM].<p>If<i>x</i>or<i>y</i>is NaN, NaN is returned and<i>errno</i>may be set to [EDOM].<p>If the result underflows, 0.0 is returned and<i>errno</i>may be set to [ERANGE].</blockquote><h4><a name = "tag_000_001_225"> </a>ERRORS</h4><blockquote>The<i>atan2()</i>function may fail if:<dl compact><dt>[EDOM]<dd>Both arguments are 0.0 or one or more of the arguments is NaN.<dt>[ERANGE]<dd>The result underflows.</dl><p>No other errors will occur.</blockquote><h4><a name = "tag_000_001_226"> </a>EXAMPLES</h4><blockquote>None.</blockquote><h4><a name = "tag_000_001_227"> </a>APPLICATION USAGE</h4><blockquote>None.</blockquote><h4><a name = "tag_000_001_228"> </a>FUTURE DIRECTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_000_001_229"> </a>SEE ALSO</h4><blockquote><i><a href="atan.html">atan()</a></i>,<i><a href="isnan.html">isnan()</a></i>,<i><a href="tan.html">tan()</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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