217 lines
21 KiB
HTML
217 lines
21 KiB
HTML
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<title>std::fmod, std::fmodf, std::fmodl</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_numeric_math_fmod skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>fmod, <span style="font-size:0.7em; line-height:130%">std::</span>fmodf, <span style="font-size:0.7em; line-height:130%">std::</span>fmodl</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-numeric.html">numeric</a>‎ | <a href="cpp-numeric-math.html">math</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-cmath.html"><cmath></a></code></div>
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<td></td>
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<td rowspan="142">(1)</td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">float</span> fmod <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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<div><span class="mw-geshi cpp source-cpp"><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><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><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>(2)</td>
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<td rowspan="142">(3)</td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span> fmod <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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<div><span class="mw-geshi cpp source-cpp"><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><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp">Promoted fmod <span class="br0">(</span> Arithmetic1 x, Arithmetic2 y <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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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 cpp source-cpp">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> 所有 1-3 不覆盖的<a href="cpp-types-is_arithmetic.html">算术类型</a>参数组合的重载集或函数模板。若任何参数拥有<a href="cpp-types-is_integral.html">整数类型</a>，则将它转型到 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span> 。若任何其他参数为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> ，则返回类型是 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> ，否则是 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span> 。</div>
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<p>此函数计算的除法 <span class="t-c"><span class="mw-geshi cpp source-cpp">x<span class="sy2">/</span>y</span></span> 的浮点余数是 <span class="t-c"><span class="mw-geshi cpp source-cpp">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 cpp source-cpp">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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<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 cpp source-cpp">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 <span class="t-lc"><a href="cpp-numeric-math-math_errhandling.html">math_errhandling</a></span> 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="cpp-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="cpp-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>std::fmod</code> ，但不是 <span class="t-lc"><a href="cpp-numeric-math-remainder.html">std::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 cpp source-cpp"><span class="br0">(</span><span class="nu16">0.0</span> <span class="sy1"><=</span> <span class="br0">(</span>y <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">fmod</span><span class="br0">(</span> <a href="cpp-numeric-math-rint.html"><span class="kw1356">std::<span class="me2">rint</span></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 cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">short</span></span></span> ，但 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-numeric-math-remainder.html"><span class="kw1311">std::<span class="me2">remainder</span></span></a><span class="br0">(</span><a href="cpp-numeric-math-rint.html"><span class="kw1356">std::<span class="me2">rint</span></span></a><span class="br0">(</span>x<span class="br0">)</span>, <span class="nu16">65536.0</span></span></span> 在范围 <code>[-32767.0, +32768.0]</code> 内，它在 <span class="t-c"><span class="mw-geshi cpp source-cpp"><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="cpp source-cpp">
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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="cpp-numeric-math-remainder.html"><span class="kw1311">std::<span class="me2">remainder</span></span></a><span class="br0">(</span><a href="cpp-numeric-math-fabs.html"><span class="kw1302">std::<span class="me2">fabs</span></span></a><span class="br0">(</span>x<span class="br0">)</span>, <span class="br0">(</span>y <span class="sy1">=</span> <a href="cpp-numeric-math-fabs.html"><span class="kw1302">std::<span class="me2">fabs</span></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="cpp-numeric-math-signbit.html"><span class="kw1372">std::<span class="me2">signbit</span></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="cpp-numeric-math-copysign.html"><span class="kw1366">std::<span class="me2">copysign</span></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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<p>舍入 x/y 到 trunc 的参数损失过多精度时，表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">x <span class="sy2">-</span> trunc<span class="br0">(</span>x<span class="sy2">/</span>y<span class="br0">)</span><span class="sy2">*</span>y</span></span> 可以不等于 <span class="t-c"><span class="mw-geshi cpp source-cpp">fmod<span class="br0">(</span>x,y<span class="br0">)</span></span></span> （例如： x = 30.508474576271183309, y = 6.1016949152542370172 ）。</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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<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="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <iostream></span>
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<span class="co2">#include <cmath></span>
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<span class="co2">#include <cfenv></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="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"fmod(+5.1, +3.0) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">fmod</span><span class="br0">(</span><span class="nu16">5.1</span>,<span class="nu0">3</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
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<span class="sy1"><<</span> <span class="st0">"fmod(-5.1, +3.0) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">fmod</span><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="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
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<span class="sy1"><<</span> <span class="st0">"fmod(+5.1, -3.0) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">fmod</span><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="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
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<span class="sy1"><<</span> <span class="st0">"fmod(-5.1, -3.0) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">fmod</span><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="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="co1">// 特殊值</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"fmod(+0.0, 1.0) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">fmod</span><span class="br0">(</span><span class="nu0">0</span>, <span class="nu0">1</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
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<span class="sy1"><<</span> <span class="st0">"fmod(-0.0, 1.0) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">fmod</span><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="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
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<span class="sy1"><<</span> <span class="st0">"fmod(5.1, Inf) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">fmod</span><span class="br0">(</span><span class="nu16">5.1</span>, <a href="cpp-numeric-math-INFINITY.html"><span class="kw1376">INFINITY</span></a><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="co1">// 错误处理</span>
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<a href="cpp-numeric-fenv-feclearexcept.html"><span class="kw1449">std::<span class="me2">feclearexcept</span></span></a><span class="br0">(</span><a href="cpp-numeric-fenv-FE_exceptions.html"><span class="kw1460">FE_ALL_EXCEPT</span></a><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"fmod(+5.1, 0) = "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">fmod</span><span class="br0">(</span><span class="nu16">5.1</span>, <span class="nu0">0</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="kw1">if</span><span class="br0">(</span><a href="cpp-numeric-fenv-fetestexcept.html"><span class="kw1450">std::<span class="me2">fetestexcept</span></span></a><span class="br0">(</span><a href="cpp-numeric-fenv-FE_exceptions.html"><span class="kw1463">FE_INVALID</span></a><span class="br0">)</span><span class="br0">)</span>
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<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">" FE_INVALID raised<span class="es1">\n</span>"</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
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fmod(-0.0, 1.0) = -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=".E5.8F.82.E9.98.85">参阅</span></h3>
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<table class="t-dsc-begin">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-numeric-math-div.html"><span class="t-lines"><span>div<span class="t-dsc-small">(int)</span></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-cxx11">(C++11)</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="cpp-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-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>除法运算的有符号余数<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="cpp-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-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>除法运算的有符号余数和最后三个二进制位<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 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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