105 lines
8.5 KiB
HTML
105 lines
8.5 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>std::generate_canonical</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-cpp_numeric_random_generate_canonical 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"><span style="font-size:0.7em; line-height:130%">std::</span>generate_canonical</h1>
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<div id="bodyContent">
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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-random.html">random</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><a href="cpp-header-random.html"><random></a></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-cxx11">
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<td>
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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> RealType, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> Bits, <span class="kw1">class</span> Generator <span class="sy1">></span><br />
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RealType generate_canonical<span class="br0">(</span> Generator<span class="sy3">&</span> g <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td class="t-dcl-nopad"></td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 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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<p>生成范围 <span class="mjax" style="display:none">\(\small [0,1)\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">[0, 1)</span> 中的随机浮点值。</p>
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<p>为生成足够的熵， <span class="t-c"><span class="mw-geshi cpp source-cpp">generate_canonical<span class="br0">(</span><span class="br0">)</span></span></span> 将准确调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">g<span class="br0">(</span><span class="br0">)</span></span></span> <span class="mjax" style="display:none">\(\small k\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">k</span> 次，其中 <span class="mjax" style="display:none">\(\small k = \max(1, \lceil \frac{b}{\log_2 R} \rceil)\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">k = max(1, ⌈ b / log<span class="t-su t-su-b"><br />
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2</span> R ⌉)</span> 且</p>
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<ul>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp">b <span class="sy1">=</span> <a href="cpp-algorithm-min.html"><span class="kw1641">std::<span class="me2">min</span></span></a><span class="br0">(</span>Bits, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a><span class="br0">{</span><a href="cpp-types-numeric_limits.html"><span class="kw344">std::<span class="me2">numeric_limits</span></span></a><span class="sy1"><</span>RealType<span class="sy1">></span><span class="sy4">::</span><span class="me2">digits</span><span class="br0">}</span><span class="br0">)</span></span></span> ，</li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp">R <span class="sy1">=</span> g.<span class="me1">max</span><span class="br0">(</span><span class="br0">)</span> <span class="sy2">-</span> g.<span class="me1">min</span><span class="br0">(</span><span class="br0">)</span> <span class="sy2">+</span> <span class="nu0">1</span></span></span> 。</li>
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</ul>
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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>g</td>
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<td>-</td>
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<td>用于取得熵的生成器</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>范围 <span class="mjax" style="display:none">\(\small [0,1)\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">[0, 1)</span> 中的浮点值。</p>
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<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<p>无，除了 <code>g</code> 所抛者。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>一些既存实现拥有漏洞，若 <code>RealType</code> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">float</span></span></span> ，则它们有时可以返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu16">1.0</span></span></span> <a rel="nofollow" class="external text" href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63176">GCC #63176</a> <a rel="nofollow" class="external text" href="https://bugs.llvm.org/show_bug.cgi?id=18767">LLVM #18767</a> <a rel="nofollow" class="external text" href="https://github.com/microsoft/STL/issues/1074">MSVC STL #1074</a> 。此为 <a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2524">LWG 问题 2524</a> 。</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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<p>产生有 10 位随机性的随机数：这仅可能产生 k*R 个相异值</p>
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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 <random></span>
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<span class="co2">#include <iostream></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-numeric-random-random_device.html"><span class="kw1486">std::<span class="me2">random_device</span></span></a> rd<span class="sy4">;</span>
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<a href="cpp-numeric-random-mersenne_twister_engine.html"><span class="kw1489">std::<span class="me2">mt19937</span></span></a> gen<span class="br0">(</span>rd<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">for</span><span class="br0">(</span><span class="kw4">int</span> n <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> n <span class="sy1"><</span> <span class="nu0">10</span><span class="sy4">;</span> <span class="sy2">++</span>n<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> std<span class="sy4">::</span><span class="me2">generate_canonical</span><span class="sy1"><</span><span class="kw4">double</span>, <span class="nu0">10</span><span class="sy1">></span><span class="br0">(</span>gen<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span>
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<span class="br0">}</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">0.208143 0.824147 0.0278604 0.343183 0.0173263 0.864057 0.647037 0.539467 0.0583497 0.609219</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-random-uniform_real_distribution.html"><span class="t-lines"><span>uniform_real_distribution</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></div>
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</div>
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</td>
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<td>产生在一个范围上均匀分布的实数值<br />
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<span class="t-mark">(类模板)</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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