74 lines
7.8 KiB
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74 lines
7.8 KiB
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<title>std::ratio_divide</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>ratio_divide</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-ratio.html">ratio</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-ratio.html"><ratio></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> R1, <span class="kw1">class</span> R2 <span class="sy1">></span><br />
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<span class="kw1">using</span> ratio_divide <span class="sy1">=</span> <span class="coMULTI">/* see below */</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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<p>别名模板 <code>std::ratio_divide</code> 指代由 <span class="t-lc"><a href="cpp-numeric-ratio-ratio.html">std::ratio</a></span> 特化 <code>R1</code> 和 <code>R2</code> 表示的二个准确有理分数相除的结果。</p>
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<p>结果是 <span class="t-lc"><a href="cpp-numeric-ratio-ratio.html">std::ratio</a></span> 特化 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-numeric-ratio-ratio.html"><span class="kw1522">std::<span class="me2">ratio</span></span></a><span class="sy1"><</span>U, V<span class="sy1">></span></span></span> ,给定 <span class="t-c"><span class="mw-geshi cpp source-cpp">Num <span class="sy1">==</span> R1<span class="sy4">::</span><span class="me2">num</span> <span class="sy2">*</span> R2<span class="sy4">::</span><span class="me2">den</span></span></span> 及 <span class="t-c"><span class="mw-geshi cpp source-cpp">Denom <span class="sy1">==</span> R1<span class="sy4">::</span><span class="me2">den</span> <span class="sy2">*</span> R2<span class="sy4">::</span><span class="me2">num</span></span></span> (计算无算术溢出),则 <code>U</code> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-numeric-ratio-ratio.html"><span class="kw1522">std::<span class="me2">ratio</span></span></a><span class="sy1"><</span>Num, Denom<span class="sy1">></span><span class="sy4">::</span><span class="me2">num</span></span></span> 且 <code>V</code> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-numeric-ratio-ratio.html"><span class="kw1522">std::<span class="me2">ratio</span></span></a><span class="sy1"><</span>Num, Denom<span class="sy1">></span><span class="sy4">::</span><span class="me2">den</span></span></span> 。</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>若 <code>U</code> 或 <code>V</code> 不能以 <code>std::intmax_t</code> 表示,则程序为病式。若 <code>Num</code> 或 <code>Denom</code> 不能表示为 <code>std::intmax_t</code> ,则程序为病式,除非实现生成 <code>U</code> 与 <code>V</code> 的正确值。</p>
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<p>上述定义要求 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio_divide</span><span class="sy1"><</span>R1, R2<span class="sy1">></span></span></span> 的结果已约分到最简;例如, <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio_divide</span><span class="sy1"><</span><a href="cpp-numeric-ratio-ratio.html"><span class="kw1522">std::<span class="me2">ratio</span></span></a><span class="sy1"><</span><span class="nu0">1</span>, <span class="nu0">12</span><span class="sy1">></span>, <a href="cpp-numeric-ratio-ratio.html"><span class="kw1522">std::<span class="me2">ratio</span></span></a><span class="sy1"><</span><span class="nu0">1</span>, <span class="nu0">6</span><span class="sy1">>></span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-numeric-ratio-ratio.html"><span class="kw1522">std::<span class="me2">ratio</span></span></a><span class="sy1"><</span><span class="nu0">1</span>, <span class="nu0">2</span><span class="sy1">></span></span></span> 是同一类型。</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="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <iostream></span>
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<span class="co2">#include <ratio></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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<span class="kw1">using</span> two_third <span class="sy1">=</span> <a href="cpp-numeric-ratio-ratio.html"><span class="kw1522">std::<span class="me2">ratio</span></span></a><span class="sy1"><</span><span class="nu0">2</span>, <span class="nu0">3</span><span class="sy1">></span><span class="sy4">;</span>
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<span class="kw1">using</span> one_sixth <span class="sy1">=</span> <a href="cpp-numeric-ratio-ratio.html"><span class="kw1522">std::<span class="me2">ratio</span></span></a><span class="sy1"><</span><span class="nu0">1</span>, <span class="nu0">6</span><span class="sy1">></span><span class="sy4">;</span>
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<span class="kw1">using</span> quotient <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">ratio_divide</span><span class="sy1"><</span>two_third, one_sixth<span class="sy1">></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">"(2/3) / (1/6) = "</span> <span class="sy1"><<</span> quotient<span class="sy4">::</span><span class="me2">num</span> <span class="sy1"><<</span> <span class="st0">'/'</span> <span class="sy1"><<</span> quotient<span class="sy4">::</span><span class="me2">den</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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<p>输出:</p>
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<div class="text source-text">
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<pre class="de1">(2/3) / (1/6) = 4/1</pre></div>
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