179 lines
10 KiB
HTML
179 lines
10 KiB
HTML
<!DOCTYPE html>
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<title>std::random_device</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_numeric_random_random_device skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>random_device</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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<div>定义于头文件 <code><a href="cpp-header-random.html"><random></a></code></div>
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<td></td>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">class</span> random_device<span class="sy4">;</span></span></div>
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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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<p><code>std::random_device</code> 是生成非确定随机数的均匀分布整数随机数生成器。</p>
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<p><code>std::random_device</code> 可以以实现定义的伪随机数引擎实现，若非确定源（例如硬件设备）对实现不可用。此情况下每个 <code>std::random_device</code> 对象可生成同一数值序列。</p>
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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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</tr>
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<tr class="t-dsc">
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<td><code>result_type</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">int</span></span></span></td>
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</table>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">成员函数</span></h3>
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<table class="t-dsc-begin">
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<td colspan="2">
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<h5><span class="mw-headline" id=".E6.9E.84.E9.80.A0">构造</span></h5>
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<div class="t-dsc-member-div t-dsc-member-nobold-div">
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<div><a href="cpp-numeric-random-random_device-random_device.html"><span class="t-lines"><span>(构造函数)</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>构造引擎<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><span class="t-lines"><span>operator=</span></span></div>
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<div><span class="t-lines"><span><span class="t-mark">(被删除)</span></span></span></div>
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</div>
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</td>
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<td>赋值运算符被删除<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<td colspan="2">
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<h5><span class="mw-headline" id=".E7.94.9F.E6.88.90">生成</span></h5>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-numeric-random-random_device-operator().html"><span class="t-lines"><span>operator()</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>推进引擎状态并返回生成的值<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<td colspan="2">
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<h5><span class="mw-headline" id=".E7.89.B9.E5.BE.81">特征</span></h5>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-numeric-random-random_device-entropy.html"><span class="t-lines"><span>entropy</span></span></a></div>
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</div>
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</td>
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<td>获得非确定随机数生成器的熵估计<br />
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<span class="t-mark">(公开成员函数)</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-random-random_device-min.html"><span class="t-lines"><span>min</span></span></a></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>
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<td>获取输出范围中的最小可能值<br />
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<span class="t-mark">(公开静态成员函数)</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-random-random_device-max.html"><span class="t-lines"><span>max</span></span></a></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>
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<td>获取输出范围中的最大可能值<br />
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<span class="t-mark">(公开静态成员函数)</span></td>
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</tr>
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</table>
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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>值得注意的 <code>std::random_device</code> 为确定性的实现是 MinGW 的旧版本（<a rel="nofollow" class="external text" href="https://sourceforge.net/p/mingw-w64/bugs/338/">漏洞 338</a> ， GCC 9.2 起修复）。最新的 MinGW 版本可从 <a rel="nofollow" class="external text" href="https://gcc-mcf.lhmouse.com/">GCC with the MCF thread model</a> 下载。</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 <string></span>
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<span class="co2">#include <map></span>
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<span class="co2">#include <random></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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std<span class="sy4">::</span><span class="me2">random_device</span> rd<span class="sy4">;</span>
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<a href="cpp-container-map.html"><span class="kw1281">std::<span class="me2">map</span></span></a><span class="sy1"><</span><span class="kw4">int</span>, <span class="kw4">int</span><span class="sy1">></span> hist<span class="sy4">;</span>
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<a href="cpp-numeric-random-uniform_int_distribution.html"><span class="kw1501">std::<span class="me2">uniform_int_distribution</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> dist<span class="br0">(</span><span class="nu0">0</span>, <span class="nu0">9</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">20000</span><span class="sy4">;</span> <span class="sy2">++</span>n<span class="br0">)</span> <span class="br0">{</span>
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<span class="sy2">++</span>hist<span class="br0">[</span>dist<span class="br0">(</span>rd<span class="br0">)</span><span class="br0">]</span><span class="sy4">;</span> <span class="co1">// 注意：仅用于演示：一旦熵池耗尽，</span>
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<span class="co1">// 许多 random_device 实现的性能就急剧下滑</span>
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<span class="co1">// 对于实践使用， random_device 通常仅用于</span>
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<span class="co1">// 播种类似 mt19937 的伪随机数生成器</span>
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<span class="br0">}</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">auto</span> p <span class="sy4">:</span> hist<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> p.<span class="me1">first</span> <span class="sy1"><<</span> <span class="st0">" : "</span> <span class="sy1"><<</span> <a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="br0">(</span>p.<span class="me1">second</span><span class="sy2">/</span><span class="nu0">100</span>, <span class="st0">'*'</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="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 : ********************
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1 : *******************
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2 : ********************
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3 : ********************
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4 : ********************
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5 : *******************
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6 : ********************
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7 : ********************
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8 : *******************
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9 : ********************</pre></div>
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<div class="visualClear"></div>
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