255 lines
18 KiB
HTML
255 lines
18 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>fmod, fmodf, fmodl</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_fmod 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">fmod, fmodf, fmodl</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>‎ | <a href="c-numeric-math.html">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 class="t-dcl t-since-c99">
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<div><span class="mw-geshi c source-c"><span class="kw4">float</span> fmodf<span class="br0">(</span> <span class="kw4">float</span> x, <span class="kw4">float</span> y <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</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">
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<td>
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<div><span class="mw-geshi c source-c"><span class="kw4">double</span> fmod<span class="br0">(</span> <span class="kw4">double</span> x, <span class="kw4">double</span> y <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(2)</td>
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<td class="t-dcl-nopad"></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="kw4">long</span> <span class="kw4">double</span> fmodl<span class="br0">(</span> <span class="kw4">long</span> <span class="kw4">double</span> x, <span class="kw4">long</span> <span class="kw4">double</span> y <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(3)</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-dsc-header">
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<td>
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<div>定义于头文件 <code><tgmath.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 fmod( x, y )</span></span></div>
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</td>
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<td>(4)</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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<div class="t-li1"><span class="t-li">1-3)</span> 计算除法运算 <span class="t-c"><span class="mw-geshi c source-c">x<span class="sy2">/</span>y</span></span> 的浮点余数。</div>
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<div class="t-li1"><span class="t-li">4)</span> 泛型宏：若任何参数拥有 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">long</span> <span class="kw4">double</span></span></span> 类型则调用 <code>fmodl</code> 。否则，若任何参数拥有整数类型或 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">double</span></span></span> 类型则调用 <code>fmod</code> 。否则调用 <code>fmodf</code> 。</div>
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<p>此函数计算的除法 <span class="t-c"><span class="mw-geshi c source-c">x<span class="sy2">/</span>y</span></span> 的浮点余数是 <span class="t-c"><span class="mw-geshi c source-c">x <span class="sy2">-</span> n<span class="sy2">*</span>y</span></span> 的准确值，其中 <code>n</code> 是截断小数部分的 <span class="t-c"><span class="mw-geshi c source-c">x<span class="sy2">/</span>y</span></span> 。</p>
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<p>返回值与 <code>x</code> 拥有相同符号，且绝对值小于 <code>y</code> 。</p>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<table class="t-par-begin">
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<tr class="t-par">
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<td>x, y</td>
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<td>-</td>
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<td>浮点值</td>
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</tr>
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</table>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
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<p>若成功，则返回定义于上的除法 <span class="t-c"><span class="mw-geshi c source-c">x<span class="sy2">/</span>y</span></span> 的浮点余数。</p>
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<p>若出现定义域错误，则返回实现定义值（受支持的平台上为 NaN ）。</p>
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<p>若出现下溢所指定值域错误，则返回（舍入后的）正确结果。</p>
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<h3><span class="mw-headline" id=".E9.94.99.E8.AF.AF.E5.A4.84.E7.90.86">错误处理</span></h3>
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<p>报告 <a href="c-numeric-math-math_errhandling.html"><tt>math_errhandling</tt></a> 中指定的错误。</p>
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<p>若 <code>y</code> 为零则可能发生定义域错误。</p>
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<p>若实现支持 IEEE 浮点算术（ IEC 60559 ），</p>
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<ul>
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<li>若 <code>x</code> 为 ±0 且 <code>y</code> 非零，则返回 ±0</li>
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<li>若 <code>x</code> 为 ±∞ 且 <code>y</code> 非 NaN ，则返回 NaN 并引发 <span class="t-lc"><a href="c-numeric-fenv-FE_exceptions.html">FE_INVALID</a></span></li>
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<li>若 <code>y</code> 为 ±0 且 <code>x</code> 非 NaN ，则返回 NaN 并引发 <span class="t-lc"><a href="c-numeric-fenv-FE_exceptions.html">FE_INVALID</a></span></li>
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<li>若 <code>y</code> 为 ±∞ 且 <code>x</code> 有限，则返回 <code>x</code> 。</li>
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<li>若任一参数为 NaN ，则返回 NaN 。</li>
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</ul>
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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><a rel="nofollow" class="external text" href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/fmod.html">POSIX 要求</a>若 <code>x</code> 为无穷大或 <code>y</code> 为零则出现定义域错误。</p>
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<p><code>fmod</code> ，但不是 <span class="t-lc"><a href="c-numeric-math-remainder.html">remainder</a></span> ，适于安静地包装浮点类型到无符号整数类型： <span class="t-c"><span class="mw-geshi c source-c"><span class="br0">(</span><span class="nu16">0.0</span> <span class="sy1"><=</span> <span class="br0">(</span>y <span class="sy1">=</span> fmod<span class="br0">(</span> <a href="c-numeric-math-rint.html"><span class="kw692">rint</span></a><span class="br0">(</span>x<span class="br0">)</span>, <span class="nu16">65536.0</span> <span class="br0">)</span><span class="br0">)</span> <span class="sy4">?</span> y <span class="sy4">:</span> <span class="nu16">65536.0</span> <span class="sy2">+</span> y<span class="br0">)</span></span></span> 在范围 <code>[-0.0 .. 65535.0]</code> 内，它对应 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">short</span></span></span> ，但 <span class="t-c"><span class="mw-geshi c source-c"><a href="c-numeric-math-remainder.html"><span class="kw647">remainder</span></a><span class="br0">(</span><a href="c-numeric-math-rint.html"><span class="kw692">rint</span></a><span class="br0">(</span>x<span class="br0">)</span>, <span class="nu16">65536.0</span><span class="br0">)</span></span></span> 在范围 <code>[-32767.0, +32768.0]</code> 内，它在 <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">signed</span> <span class="kw4">short</span></span></span> 的范围外。</p>
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<p><code>fmod</code> 的 <code>double</code> 版本表现为如同实现如下：</p>
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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="kw4">double</span> fmod<span class="br0">(</span><span class="kw4">double</span> x, <span class="kw4">double</span> y<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="co2">#pragma STDC FENV_ACCESS ON</span>
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<span class="kw4">double</span> result <span class="sy1">=</span> <a href="c-numeric-math-remainder.html"><span class="kw647">remainder</span></a><span class="br0">(</span><a href="c-numeric-math-fabs.html"><span class="kw644">fabs</span></a><span class="br0">(</span>x<span class="br0">)</span>, <span class="br0">(</span>y <span class="sy1">=</span> <a href="c-numeric-math-fabs.html"><span class="kw644">fabs</span></a><span class="br0">(</span>y<span class="br0">)</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span><a href="c-numeric-math-signbit.html"><span class="kw708">signbit</span></a><span class="br0">(</span>result<span class="br0">)</span><span class="br0">)</span> result <span class="sy2">+</span><span class="sy1">=</span> y<span class="sy4">;</span>
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<span class="kw1">return</span> <a href="c-numeric-math-copysign.html"><span class="kw702">copysign</span></a><span class="br0">(</span>result, x<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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<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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<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 <fenv.h></span>
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<span class="co2">#pragma STDC FENV_ACCESS ON</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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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"fmod(+5.1, +3.0) = %.1f<span class="es1">\n</span>"</span>, fmod<span class="br0">(</span><span class="nu16">5.1</span>,<span class="nu0">3</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"fmod(-5.1, +3.0) = %.1f<span class="es1">\n</span>"</span>, fmod<span class="br0">(</span><span class="sy2">-</span><span class="nu16">5.1</span>,<span class="nu0">3</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"fmod(+5.1, -3.0) = %.1f<span class="es1">\n</span>"</span>, fmod<span class="br0">(</span><span class="nu16">5.1</span>,<span class="sy2">-</span><span class="nu0">3</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"fmod(-5.1, -3.0) = %.1f<span class="es1">\n</span>"</span>, fmod<span class="br0">(</span><span class="sy2">-</span><span class="nu16">5.1</span>,<span class="sy2">-</span><span class="nu0">3</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 特殊值</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"fmod(+0.0, 1.0) = %.1f<span class="es1">\n</span>"</span>, fmod<span class="br0">(</span><span class="nu0">0</span>, <span class="nu0">1</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"fmod(-0.0, 1.0) = %.1f<span class="es1">\n</span>"</span>, fmod<span class="br0">(</span><span class="sy2">-</span><span class="nu16">0.0</span>, <span class="nu0">1</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"fmod(+5.1, Inf) = %.1f<span class="es1">\n</span>"</span>, fmod<span class="br0">(</span><span class="nu16">5.1</span>, INFINITY<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// 错误处理</span>
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<a href="c-numeric-fenv-feclearexcept.html"><span class="kw717">feclearexcept</span></a><span class="br0">(</span><a href="c-numeric-fenv-FE_exceptions.html"><span class="kw728">FE_ALL_EXCEPT</span></a><span class="br0">)</span><span class="sy4">;</span>
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<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">"fmod(+5.1, 0) = %.1f<span class="es1">\n</span>"</span>, fmod<span class="br0">(</span><span class="nu16">5.1</span>, <span class="nu0">0</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span><span class="br0">(</span><a href="c-numeric-fenv-fetestexcept.html"><span class="kw718">fetestexcept</span></a><span class="br0">(</span><a href="c-numeric-fenv-FE_exceptions.html"><span class="kw731">FE_INVALID</span></a><span class="br0">)</span><span class="br0">)</span> <a href="c-io-puts.html"><span class="kw835">puts</span></a><span class="br0">(</span><span class="st0">" FE_INVALID raised"</span><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">fmod(+5.1, +3.0) = 2.1
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fmod(-5.1, +3.0) = -2.1
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fmod(+5.1, -3.0) = 2.1
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fmod(-5.1, -3.0) = -2.1
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fmod(+0.0, 1.0) = 0.0
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fmod(-0.0, 1.0) = -0.0
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fmod(+5.1, Inf) = 5.1
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fmod(+5.1, 0) = nan
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FE_INVALID raised</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>7.12.10.1 The fmod functions (p: 254)</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>7.25 Type-generic math <tgmath.h> (p: 373-375)</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.10.7.1 The fmod functions (p: 528)</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>7.12.10.1 The fmod functions (p: 235)</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>7.22 Type-generic math <tgmath.h> (p: 335-337)</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.9.7.1 The fmod functions (p: 465)</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-c89">
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<ul>
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<li>C89/C90 标准（ISO/IEC 9899:1990）：</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>4.5.6.4 The fmod function</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="c-numeric-math-div.html"><span class="t-lines"><span>div</span><span>ldiv</span><span>lldiv</span></span></a></div>
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<div><span class="t-lines"><span></span><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>计算整数除法的商和余数<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="c-numeric-math-remainder.html"><span class="t-lines"><span>remainder</span><span>remainderf</span><span>remainderl</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>计算浮点除法运算的带符号余数<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="c-numeric-math-remquo.html"><span class="t-lines"><span>remquo</span><span>remquof</span><span>remquol</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>计算除法运算的带符号余数，以及商的后三位<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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</div>
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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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