177 lines
13 KiB
HTML
177 lines
13 KiB
HTML
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<title>std::ratio</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_numeric_ratio_ratio 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>ratio</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><br /></span>
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<p> <a href="cpp-types-integer.html"><span class="kw118">std::<span class="me2">intmax_t</span></span></a> Num,<br />
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<a href="cpp-types-integer.html"><span class="kw118">std::<span class="me2">intmax_t</span></span></a> Denom <span class="sy1">=</span> <span class="nu0">1</span><br /></p>
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<span class="sy1">></span> <span class="kw1">class</span> ratio<span class="sy4">;</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>类模板 <code>std::ratio</code> 及相关的模板提供<a href="cpp-numeric-ratio.html">编译时有理数算术支持</a>。此模板的每个实例化都准确表示任一确定有理数，只要分子 <code>Num</code> 与分母 <code>Denom</code> 能表示为 <span class="t-lc"><a href="cpp-types-integer.html">std::intmax_t</a></span> 类型的编译时常量。另外， <code>Denom</code> 不可为零且不可等于最负的值。约分分子和分母到最简。</p>
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<p>静态数据成员 <code>num</code> 与 <code>den</code> 表示由将 <code>Num</code> 与 <code>Denom</code> 除以其最大公约数的分子与分母。然而，二个有相异的 <code>Num</code> 或 <code>Denom</code> 的 <code>std::ratio</code> 是不同的类型，即使它们表示同一有理数（在约分后）。能经由其 <code>type</code> 成员约分 <code>ratio</code> 类型到最简分数： <code>std::ratio<3, 6>::type</code> 为 <code>std::ratio<1, 2></code> 。</p>
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<p>标准库提供数个对应 SI 比例的便利 typedef ：</p>
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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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<td>类型</td>
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<td>定义</td>
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<td><code>yocto</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio</span><span class="sy1"><</span><span class="nu0">1</span>, <span class="nu0">1000000000000000000000000</span><span class="sy1">></span></span></span> ，若 <span class="t-lc"><a href="cpp-types-integer.html">std::intmax_t</a></span> 能表示分母</td>
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<td><code>zepto</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio</span><span class="sy1"><</span><span class="nu0">1</span>, <span class="nu0">1000000000000000000000</span><span class="sy1">></span></span></span> ，若 <span class="t-lc"><a href="cpp-types-integer.html">std::intmax_t</a></span> 能表示分母</td>
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<td><code>atto</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio</span><span class="sy1"><</span><span class="nu0">1</span>, <span class="nu0">1000000000000000000</span><span class="sy1">></span></span></span></td>
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<td><code>femto</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio</span><span class="sy1"><</span><span class="nu0">1</span>, <span class="nu0">1000000000000000</span><span class="sy1">></span></span></span></td>
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<td><code>pico</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio</span><span class="sy1"><</span><span class="nu0">1</span>, <span class="nu0">1000000000000</span><span class="sy1">></span></span></span></td>
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<td><code>nano</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio</span><span class="sy1"><</span><span class="nu0">1</span>, <span class="nu0">1000000000</span><span class="sy1">></span></span></span></td>
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<td><code>micro</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio</span><span class="sy1"><</span><span class="nu0">1</span>, <span class="nu0">1000000</span><span class="sy1">></span></span></span></td>
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<td><code>milli</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio</span><span class="sy1"><</span><span class="nu0">1</span>, <span class="nu0">1000</span><span class="sy1">></span></span></span></td>
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<td><code>centi</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio</span><span class="sy1"><</span><span class="nu0">1</span>, <span class="nu0">100</span><span class="sy1">></span></span></span></td>
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<td><code>deci</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio</span><span class="sy1"><</span><span class="nu0">1</span>, <span class="nu0">10</span><span class="sy1">></span></span></span></td>
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<td><code>deca</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio</span><span class="sy1"><</span><span class="nu0">10</span>, <span class="nu0">1</span><span class="sy1">></span></span></span></td>
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<td><code>hecto</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio</span><span class="sy1"><</span><span class="nu0">100</span>, <span class="nu0">1</span><span class="sy1">></span></span></span></td>
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<td><code>kilo</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio</span><span class="sy1"><</span><span class="nu0">1000</span>, <span class="nu0">1</span><span class="sy1">></span></span></span></td>
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<td><code>mega</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio</span><span class="sy1"><</span><span class="nu0">1000000</span>, <span class="nu0">1</span><span class="sy1">></span></span></span></td>
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<td><code>giga</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio</span><span class="sy1"><</span><span class="nu0">1000000000</span>, <span class="nu0">1</span><span class="sy1">></span></span></span></td>
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<td><code>tera</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio</span><span class="sy1"><</span><span class="nu0">1000000000000</span>, <span class="nu0">1</span><span class="sy1">></span></span></span></td>
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<td><code>peta</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio</span><span class="sy1"><</span><span class="nu0">1000000000000000</span>, <span class="nu0">1</span><span class="sy1">></span></span></span></td>
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<td><code>exa</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio</span><span class="sy1"><</span><span class="nu0">1000000000000000000</span>, <span class="nu0">1</span><span class="sy1">></span></span></span></td>
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<td><code>zetta</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio</span><span class="sy1"><</span><span class="nu0">1000000000000000000000</span>, <span class="nu0">1</span><span class="sy1">></span></span></span> ，若 <span class="t-lc"><a href="cpp-types-integer.html">std::intmax_t</a></span> 能表示分子</td>
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<td><code>yotta</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio</span><span class="sy1"><</span><span class="nu0">1000000000000000000000000</span>, <span class="nu0">1</span><span class="sy1">></span></span></span> ，若 <span class="t-lc"><a href="cpp-types-integer.html">std::intmax_t</a></span> 能表示分子</td>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E7.B1.BB.E5.9E.8B">成员类型</span></h3>
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<td>成员类型</td>
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<td>定义</td>
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<td><code>type</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">ratio</span><span class="sy1"><</span>num, den<span class="sy1">></span></span></span></td>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.AF.B9.E8.B1.A1">成员对象</span></h3>
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<div class="t-dsc-member-div">
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<div><span class="t-lines"><span><span class="t-dsc-small">constexpr intmax_t</span> num</span></span></div>
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<div><span class="t-lines"><span><span class="t-cmark">[静态]</span></span></span></div>
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<td><span class="t-lc"><a href="cpp-types-integer.html">std::intmax_t</a></span> 类型的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span></span></span> 值，等于 <code>sign(Num) * sign(Denom) * abs(Num) / gcd(Num, Denom)</code><br />
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<span class="t-mark">(公开静态成员常量)</span></td>
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<div class="t-dsc-member-div">
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<div><span class="t-lines"><span><span class="t-dsc-small">constexpr intmax_t</span> den</span></span></div>
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<div><span class="t-lines"><span><span class="t-cmark">[静态]</span></span></span></div>
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</div>
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<td><span class="t-lc"><a href="cpp-types-integer.html">std::intmax_t</a></span> 类型的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span></span></span> 值，等于 <code>abs(Denom) / gcd(Num, Denom)</code><br />
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<span class="t-mark">(公开静态成员常量)</span></td>
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