219 lines
14 KiB
HTML
219 lines
14 KiB
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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<title>std::uniform_real_distribution</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_numeric_random_uniform_real_distribution 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>uniform_real_distribution</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-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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<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">template</span><span class="sy1"><</span> <span class="kw1">class</span> RealType <span class="sy1">=</span> <span class="kw4">double</span> <span class="sy1">></span><br />
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<span class="kw1">class</span> uniform_real_distribution<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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<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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<p>产生均匀分布在区间 <span class="mjax" style="display:none">\(\small [a, b)\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">[a, b)</span> 上的随机浮点值 <span class="mjax" style="display:none">\(\small x\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">x</span> ，分布按照概率密度函数：</p>
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<dl>
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<dd><span class="mjax" style="display:none">\({\small P(x|a,b) =} \frac{1}{b-a}\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">P(x|a,b) = <span class="t-mfrac"></span></span>
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<table>
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<td>1</td>
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<tr>
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<td>b − a</td>
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</table>
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。</dd>
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</dl>
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<p><code>std::uniform_real_distribution</code> 满足<a href="cpp-named_req-RandomNumberDistribution.html"><span style="font-style:italic">随机数分布</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(RandomNumberDistribution)</span></a> 的所有要求。</p>
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<h3><span class="mw-headline" id=".E6.A8.A1.E6.9D.BF.E5.BD.A2.E5.8F.82">模板形参</span></h3>
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<table class="t-par-begin">
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<tr class="t-par">
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<td>RealType</td>
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<td>-</td>
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<td>生成器所生成的结果类型。若它不是 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">float</span></span></span> 、 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">double</span></span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> <span class="kw4">double</span></span></span> 之一则效果未定义。</td>
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</table>
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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>result_type</code><span class="t-mark-rev t-since-cxx11">(C++11)</span></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">RealType</span></span></td>
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</tr>
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<tr class="t-dsc">
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<td><code>param_type</code><span class="t-mark-rev t-since-cxx11">(C++11)</span></td>
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<td>参数集的类型，见<a href="cpp-named_req-RandomNumberDistribution.html"><span style="font-style:italic">随机数分布</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(RandomNumberDistribution)</span></a> 。</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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<div class="t-dsc-member-div t-dsc-member-nobold-div">
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<div><a href="cpp-numeric-random-uniform_real_distribution-uniform_real_distribution.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>构造新分布<br />
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<span class="t-mark">(公开成员函数)</span></td>
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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-reset.html"><span class="t-lines"><span>reset</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>重置分布的内部状态<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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<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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</td>
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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-uniform_real_distribution-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>生成分布中的下个随机数<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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</td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-numeric-random-uniform_real_distribution-params.html"><span class="t-lines"><span>a</span><span>b</span></span></a></div>
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</div>
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</td>
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<td>返回分布参数<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-uniform_real_distribution-param.html"><span class="t-lines"><span>param</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>获取或设置随机参数对象<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-uniform_real_distribution-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-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>返回最小的潜在生成值<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-uniform_real_distribution-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-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>返回最大的潜在生成值<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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</table>
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<h3><span class="mw-headline" id=".E9.9D.9E.E6.88.90.E5.91.98.E5.87.BD.E6.95.B0">非成员函数</span></h3>
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<table class="t-dsc-begin">
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<div class="t-dsc-member-div">
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<div><a href="cpp-numeric-random-uniform_real_distribution-operator_cmp.html"><span class="t-lines"><span>operator==</span><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><span class="t-mark-rev t-since-cxx11">(C++11)</span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span></span></div>
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</div>
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</td>
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<td>比较两个分布对象<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-random-uniform_real_distribution-operator_ltltgtgt.html"><span class="t-lines"><span>operator<<</span><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>执行伪随机数分布的流输入和输出<br />
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<span class="t-mark">(函数模板)</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>为创建闭区间 <span class="mjax" style="display:none">\(\small[a, b]\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">[a, b]</span> 上的分布，可以 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-numeric-math-nextafter.html"><span class="kw1365">std::<span class="me2">nextafter</span></span></a><span class="br0">(</span>b, <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">max</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 为第二参数。</p>
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<p>某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> 则它们有时返回 <span class="mjax" style="display:none">\(\small b\)</span><span class="mjax-fallback texhtml" style="white-space: nowrap;">b</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="http://llvm.org/bugs/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> 所导致。</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>打印 10 个 1 与 2 间的随机数</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> <span class="co1">// 将用于获得随机数引擎的种子</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> <span class="co1">// 以 rd() 播种的标准 mersenne_twister_engine</span>
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std<span class="sy4">::</span><span class="me2">uniform_real_distribution</span><span class="sy1"><></span> dis<span class="br0">(</span><span class="nu0">1</span>, <span class="nu0">2</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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<span class="co1">// 用 dis 变换 gen 生成的随机 unsigned int 为 [1, 2) 中的 double</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> dis<span class="br0">(</span>gen<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">' '</span><span class="sy4">;</span> <span class="co1">// 每次调用 dis(gen) 都生成新的随机 double</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">'<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">1.80829 1.15391 1.18483 1.38969 1.36094 1.0648 1.97798 1.27984 1.68261 1.57326</pre></div>
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