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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2004 IEEE and The Open Group, All Rights Reserved --><title>nan</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="nan"></a> <a name="tag_03_401"></a><!-- nan --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2004 Edition<br>Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_03_401_01"></a>NAME</h4><blockquote>nan, nanf, nanl - return quiet NaN</blockquote><h4><a name="tag_03_401_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><p><code><tt>#include <<a href="../basedefs/math.h.html">math.h</a>><br><br> double nan(const char *</tt><i>tagp</i><tt>);<br> float nanf(const char *</tt><i>tagp</i><tt>);<br> long double nanl(const char *</tt><i>tagp</i><tt>);<br></tt></code></p></blockquote><h4><a name="tag_03_401_03"></a>DESCRIPTION</h4><blockquote><div class="box"><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]"border="0"> The functionality described on this reference page is aligned with the ISO C standard. Any conflict between therequirements described here and the ISO C standard is unintentional. This volume of IEEE Std 1003.1-2001 defers tothe ISO C standard. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></div><p>The function call <i>nan</i>("<i>n-char-sequence</i>") shall be equivalent to:</p><pre><tt>strtod("NAN(</tt><i>n-char-sequence</i><tt>)", (char **) NULL);</tt></pre><p>The function call <i>nan</i>("") shall be equivalent to:</p><pre><tt>strtod("NAN()", (char **) NULL)</tt></pre><p>If <i>tagp</i> does not point to an <i>n</i>- <b>char</b> sequence or an empty string, the function call shall be equivalentto:</p><pre><tt>strtod("NAN", (char **) NULL)</tt></pre><p>Function calls to <i>nanf</i>() and <i>nanl</i>() are equivalent to the corresponding function calls to <a href="../functions/strtof.html"><i>strtof</i>()</a> and <a href="../functions/strtold.html"><i>strtold</i>()</a>.</p></blockquote><h4><a name="tag_03_401_04"></a>RETURN VALUE</h4><blockquote><p>These functions shall return a quiet NaN, if available, with content indicated through <i>tagp</i>.</p><p>If the implementation does not support quiet NaNs, these functions shall return zero.</p></blockquote><h4><a name="tag_03_401_05"></a>ERRORS</h4><blockquote><p>No errors are defined.</p></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_401_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_401_07"></a>APPLICATION USAGE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_401_08"></a>RATIONALE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_401_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_401_10"></a>SEE ALSO</h4><blockquote><p><a href="strtod.html"><i>strtod</i>()</a>, <a href="strtold.html"><i>strtold</i>()</a>, the Base Definitions volume ofIEEE Std 1003.1-2001, <a href="../basedefs/math.h.html"><i><math.h></i></a></p></blockquote><h4><a name="tag_03_401_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 6. Derived from the ISO/IEC 9899:1999 standard.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr size="2" noshade><center><font size="2"><!--footer start-->UNIX ® is a registered Trademark of The Open Group.<br>POSIX ® is a registered Trademark of The IEEE.<br>[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href="../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>]</font></center><!--footer end--><hr size="2" noshade></body></html>⌨️ 快捷键说明
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