137 lines
6.2 KiB
HTML
137 lines
6.2 KiB
HTML
<!DOCTYPE html>
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<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
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<head><meta http-equiv="x-ua-compatible" content="ie=edge">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>NAN</title>
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<link rel="stylesheet" href="ext.css" />
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<link rel="stylesheet" href="site_modules.css" />
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</head>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_numeric_math_NAN skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<div id="content"><a id="top"></a>
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<h1 id="firstHeading" class="firstHeading">NAN</h1>
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<div id="bodyContent">
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<div id="contentSub"><span class="subpages">< <a href="https://zh.cppreference.com/w/c.html" title="c">c</a>‎ | <a href="https://zh.cppreference.com/w/c/numeric.html" title="c/numeric">numeric</a>‎ | <a href="https://zh.cppreference.com/w/c/numeric/math.html" title="c/numeric/math">math</a></span></div>
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<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<table class="t-dcl-begin">
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<tbody>
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<tr class="t-dsc-header">
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<td>
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<div>定义于头文件 <code><math.h></code></div>
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</td>
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<td></td>
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<td></td>
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</tr>
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<tr class="t-dcl t-since-c99">
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<td>
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<div><span class="mw-geshi c source-c"><span class="co2">#define NAN /*implementation defined*/</span></span></div>
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</td>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-c99">(C99 起)</span></td>
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</tr>
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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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</tr>
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</tbody>
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</table>
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<p>宏 <code>NAN</code> 展开成求值为安静非数（ QNaN ）的 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">float</span></span></span> 类型常量表达式。若实现不支持 QNaN ，则不定义此宏。</p>
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<p>用于打印 NaN 的风格是实现定义的。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h3>
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<p>有许多不同的 NaN 值，区别于其载荷与其符号位。宏 <code>NAN</code> 所生成的 NaN 的载荷与符号位的内容是实现定义的。</p>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<p>显示用于打印 NaN 的风格和 IEEE 格式。</p>
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<div class="t-example-live-link"></div>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="c source-c">
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<pre class="de1"><span class="co2">#include <stdio.h></span>
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<span class="co2">#include <math.h></span>
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<span class="co2">#include <stdint.h></span>
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<span class="co2">#include <inttypes.h></span>
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<span class="co2">#include <string.h></span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">double</span> f <span class="sy1">=</span> NAN<span class="sy4">;</span>
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<a href="https://zh.cppreference.com/w/c/types/integer.html"><span class="kw123">uint64_t</span></a> fn<span class="sy4">;</span> <a href="https://zh.cppreference.com/w/c/string/byte/memcpy.html"><span class="kw572">memcpy</span></a><span class="br0">(</span><span class="sy3">&</span>fn, <span class="sy3">&</span>f, <span class="kw4">sizeof</span> f<span class="br0">)</span><span class="sy4">;</span>
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<a href="https://zh.cppreference.com/w/c/io/fprintf.html"><span class="kw851">printf</span></a><span class="br0">(</span><span class="st0">"NAN: %f %"</span> <a href="https://zh.cppreference.com/w/c/types/integer.html"><span class="kw235">PRIx64</span></a> <span class="st0">"<span class="es1">\n</span>"</span>, f, fn<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>可能的输出：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="text source-text">
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<pre class="de1">NAN: nan 7ff8000000000000</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E5.BC.95.E7.94.A8">引用</span></h3>
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<div class="t-ref-std-11">
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<ul>
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<li>C11 标准（ISO/IEC 9899:2011）：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>7.12/5 NAN (p: 232)</li>
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</ul>
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</dd>
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</dl>
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<dl>
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<dd>
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<ul>
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<li>F.10/11/13 NAN (p: 518)</li>
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</ul>
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</dd>
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</dl>
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<div class="t-ref-std-c99">
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<ul>
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<li>C99 标准（ISO/IEC 9899:1999）：</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li>7.12/5 NAN (p: 213)</li>
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</ul>
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</dd>
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</dl>
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<dl>
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<dd>
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<ul>
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<li>F.9/11/13 NAN (p: 455)</li>
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</ul>
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</dd>
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</dl>
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</div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<table class="t-dsc-begin">
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="https://zh.cppreference.com/w/c/numeric/math/nan.html" title="c/numeric/math/nan"><span class="t-lines"><span>nan</span><span>nanf</span><span>nanl</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span><span><span class="t-mark-rev t-since-c99">(C99)</span></span><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div>
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</div>
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</td>
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<td>返回 NaN （非数）<br />
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<span class="t-mark">(函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="https://zh.cppreference.com/w/c/numeric/math/isnan.html" title="c/numeric/math/isnan"><span class="t-lines"><span>isnan</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div>
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</div>
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</td>
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<td>检查给定数是否为 NaN<br />
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<span class="t-mark">(宏函数)</span></td>
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</tr>
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</table>
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</div>
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</div>
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<div class="visualClear"></div>
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</div>
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</div>
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</div>
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</body>
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</html>
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