191 lines
10 KiB
HTML
191 lines
10 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>浮点环境</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_fenv 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">浮点环境</h1>
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<div id="bodyContent">
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<div id="contentSub"><span class="subpages">< <a href="c.html">c</a>‎ | <a href="c-numeric.html">numeric</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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<p>浮点环境是浮点状态标志及实现所支持的控制模式的集合。它是线程局域的，每个线程从亲线程继承其浮点环境的初始状态。浮点运算会修改指示反常值或补助信息的浮点状态标志。浮点控制模式影响浮点运算的结果。</p>
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<p>仅若设置 <a href="cpp-preprocessor-impl.html"><tt>#pragma STDC FENV_ACCESS</tt></a> 为 <code>ON</code> ，浮点环境的访问及修改才有意义。否则具体实现可以自由地假设浮点控制模式始终是默认值，而且浮点状态标志始终不被检测或修改。实际上，当前只有少数编译器，如 HP aCC 、 Oracle Studio 和 IBM XL 显式支持 <code>#pragma</code> ，但总之多数编译器允许有意义地访问浮点环境。</p>
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<h3><span class="mw-headline" id=".E7.B1.BB.E5.9E.8B">类型</span></h3>
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<table class="t-dsc-begin">
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<tr class="t-dsc-header">
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<td colspan="2">
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<div>定义于头文件 <code><fenv.h></code></div>
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</td>
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</tr>
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<tr class="t-dsc">
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<td><span class="t-c"><span class="mw-geshi c source-c">fenv_t</span></span></td>
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<td>表示整体浮点环境的类型</td>
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</tr>
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<tr class="t-dsc">
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<td><span class="t-c"><span class="mw-geshi c source-c">fexcept_t</span></span></td>
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<td>集中表示所有浮点异常状态标志的类型</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E5.87.BD.E6.95.B0">函数</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="c-numeric-fenv-feclearexcept.html"><span class="t-lines"><span>feclearexcept</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>清除指定的浮点异常状态标志<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="c-numeric-fenv-fetestexcept.html"><span class="t-lines"><span>fetestexcept</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>确认设置了哪些浮点异常状态标志<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="c-numeric-fenv-feraiseexcept.html"><span class="t-lines"><span>feraiseexcept</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>引发指定的浮点异常状态标志<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="c-numeric-fenv-feexceptflag.html"><span class="t-lines"><span>fegetexceptflag</span><span>fesetexceptflag</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></div>
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</div>
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</td>
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<td>将指定的浮点异常状态标志从指定的浮点环境获取，再设置到指定浮点环境的操作。<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="c-numeric-fenv-feround.html"><span class="t-lines"><span>fegetround</span><span>fesetround</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></div>
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</div>
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</td>
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<td>获得或设置数字的舍入方向<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="c-numeric-fenv-feenv.html"><span class="t-lines"><span>fegetenv</span><span>fesetenv</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></div>
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</div>
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</td>
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<td>保存或恢复当前浮点环境，包括异常的标志和数字的舍弃模式<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="c-numeric-fenv-feholdexcept.html"><span class="t-lines"><span>feholdexcept</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>保存当前环境的异常状态标志，再清除所有异常状态标志，并忽略所有未来错误<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="c-numeric-fenv-feupdateenv.html"><span class="t-lines"><span>feupdateenv</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>恢复之前保存的浮点环境，并引发之前已经引发过的异常，使其存在于当前内存环境中<br />
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<span class="t-mark">(函数)</span></td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E5.AE.8F">宏</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="c-numeric-fenv-FE_exceptions.html"><span class="t-lines"><span>FE_ALL_EXCEPT</span><span>FE_DIVBYZERO</span><span>FE_INEXACT</span><span>FE_INVALID</span><span>FE_OVERFLOW</span><span>FE_UNDERFLOW</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>浮点异常<br />
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<span class="t-mark">(宏常量)</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="c-numeric-fenv-FE_round.html"><span class="t-lines"><span>FE_DOWNWARD</span><span>FE_TONEAREST</span><span>FE_TOWARDZERO</span><span>FE_UPWARD</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>浮点舍入方向<br />
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<span class="t-mark">(宏常量)</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="c-numeric-fenv-FE_DFL_ENV.html"><span class="t-lines"><span>FE_DFL_ENV</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>默认浮点环境<br />
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<span class="t-mark">(宏常量)</span></td>
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</tr>
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</table>
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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>7.6 Floating-point environment <fenv.h> (p: 206-215)</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>7.31.4 Floating-point environment <fenv.h> (p: 455)</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>7.6 Floating-point environment <fenv.h> (p: 187-196)</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"></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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