188 lines
16 KiB
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188 lines
16 KiB
HTML
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<title>C++ 具名要求：随机数引擎 (RandomNumberEngine)</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_named_req_RandomNumberEngine skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">C++ 具名要求：</span><span style="font-style:italic">随机数引擎</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(RandomNumberEngine)</span></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-named_req.html">named req</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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<p>随机数引擎是函数对象，返回无符号整数值，它使得可能结果范围中的每个值拥有（理想的）相等概率。</p>
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<p>任何随机数引擎亦为<a href="cpp-named_req-UniformRandomBitGenerator.html"><span style="font-style:italic">均匀随机位生成器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(UniformRandomBitGenerator)</span></a> ，从而可能插入任何<a href="cpp-numeric-random.html">随机数分布</a>，以获得随机数（正式而言是随机变量）。</p>
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<h3><span class="mw-headline" id=".E8.A6.81.E6.B1.82">要求</span></h3>
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<p>满足<a href="cpp-named_req-UniformRandomBitGenerator.html"><span style="font-style:italic">均匀随机位生成器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(UniformRandomBitGenerator)</span></a> 的类型 <code>E</code> 会另外满足随机数引擎 (<span style="font-style:italic">随机数引擎</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(RandomNumberEngine)</span> ) ，若给定</p>
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<ul>
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<li><code>T</code> ， <code>E::result_type</code> 所指名的类型</li>
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<li><code>s</code> ， <code>T</code> 类型值</li>
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<li><code>e</code> ， <code>E</code> 类型的非 const 值</li>
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<li><code>v</code> ， <code>E</code> 类型左值</li>
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<li><code>x</code> 与 <code>y</code> ， <code>E</code> 类型的可能为 const 的值</li>
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<li><code>q</code> ，某满足<a href="cpp-named_req-SeedSequence.html"><span style="font-style:italic">种子序列</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(SeedSequence)</span></a> 的类型的左值</li>
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<li><code>z</code> ， <code>unsigned long long</code> 类型值</li>
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<li><code>os</code> ，输出流</li>
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<li><code>is</code> ，输入流</li>
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</ul>
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<p>而下列表达式合法并拥有其指定的效果：</p>
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<table class="wikitable">
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<tr>
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<th>表达式</th>
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<th>返回类型</th>
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<th>要求</th>
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</tr>
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<tr>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">E<span class="br0">(</span><span class="br0">)</span></span></span></td>
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<td></td>
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<td>创建引擎，其状态与所有其他默认构造的 <code>E</code> 类型引擎相同。</td>
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</tr>
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<tr>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">E<span class="br0">(</span>x<span class="br0">)</span></span></span></td>
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<td></td>
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<td>创建引擎，其状态与 <code>x</code> 的相同。</td>
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</tr>
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<tr>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">E<span class="br0">(</span>s<span class="br0">)</span></span></span></td>
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<td></td>
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<td>创建引擎，其初始状态为 <code>s</code> 所确定。</td>
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</tr>
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<tr>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">E<span class="br0">(</span>q<span class="br0">)</span></span></span></td>
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<td></td>
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<td>创建引擎，其初始状态以单次调用 <code>q.generate</code> 确定。</td>
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</tr>
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<tr>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">e.<span class="me1">seed</span><span class="br0">(</span><span class="br0">)</span></span></span></td>
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<td><code>void</code></td>
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<td>设置 <span class="t-c"><span class="mw-geshi cpp source-cpp">e <span class="sy1">==</span> E<span class="br0">(</span><span class="br0">)</span></span></span> 。</td>
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</tr>
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<tr>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">e.<span class="me1">seed</span><span class="br0">(</span>s<span class="br0">)</span></span></span></td>
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<td><code>void</code></td>
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<td>设置 <span class="t-c"><span class="mw-geshi cpp source-cpp">e <span class="sy1">==</span> E<span class="br0">(</span>s<span class="br0">)</span></span></span> 。</td>
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</tr>
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<tr>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">e.<span class="me1">seed</span><span class="br0">(</span>q<span class="br0">)</span></span></span></td>
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<td><code>void</code></td>
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<td>设置 <span class="t-c"><span class="mw-geshi cpp source-cpp">e <span class="sy1">==</span> E<span class="br0">(</span>q<span class="br0">)</span></span></span> 。</td>
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</tr>
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<tr>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">e<span class="br0">(</span><span class="br0">)</span></span></span></td>
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<td><code>T</code></td>
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<td>返回闭区间 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">[</span>E<span class="sy4">::</span><span class="me2">min</span><span class="br0">(</span><span class="br0">)</span>, E<span class="sy4">::</span><span class="me2">max</span><span class="br0">(</span><span class="br0">)</span><span class="br0">]</span></span></span> 中的值。拥有均摊常数复杂度。</td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">e.<span class="me1">discard</span><span class="br0">(</span>z<span class="br0">)</span></span></span></td>
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<td><code>void</code></td>
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<td>令 <code>e</code> 的状态前进，如同通过 <code>z</code> 次连续调用 <code>e()</code> 。</td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">x <span class="sy1">==</span> y</span></span></td>
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<td><code>bool</code></td>
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<td>若 <code>x</code> 与 <code>y</code> 在相同状态（满足将来对 <code>x()</code> 和 <code>y()</code> 的重复调用将产生等同的数列）则为 <code>true</code> 。否则为 <code>false</code> 。</td>
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</tr>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">x <span class="sy3">!</span><span class="sy1">=</span> y</span></span></td>
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<td><code>bool</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy3">!</span><span class="br0">(</span>x <span class="sy1">==</span> y<span class="br0">)</span></span></span></td>
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</tr>
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<tr>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">os <span class="sy1"><<</span> x</span></span></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">decltype<span class="br0">(</span>os<span class="br0">)</span><span class="sy3">&</span></span></span></td>
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<td>将 <code>x</code> 当前状态的文本表示写入 <code>os</code> 。输出中，相邻的数以一或多个空格字符分隔。若 <code>os</code> 的 fmtflags 未设为 <span class="t-c"><span class="mw-geshi cpp source-cpp">ios_base<span class="sy4">::</span><span class="me2">dec</span><span class="sy3">|</span>ios_base<span class="sy4">::</span><span class="me2">left</span></span></span> ，则行为可能未定义。</td>
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</tr>
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<tr>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">is <span class="sy1">>></span> v</span></span></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">decltype<span class="br0">(</span>is<span class="br0">)</span><span class="sy3">&</span></span></span></td>
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<td>从 <code>is</code> 读取 <code>v</code> 当前状态的文本表示，满足若先前通过 <span class="t-c"><span class="mw-geshi cpp source-cpp">os <span class="sy1"><<</span> x</span></span> 写入该状态，则 <span class="t-c"><span class="mw-geshi cpp source-cpp">x <span class="sy1">==</span> v</span></span> 。若 <code>is</code> 的 fmtflags 未设为 <span class="t-c"><span class="mw-geshi cpp source-cpp">ios_base<span class="sy4">::</span><span class="me2">dec</span></span></span> ，则行为可能未定义。</td>
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</table>
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<h3><span class="mw-headline" id=".E6.A0.87.E5.87.86.E5.BA.93">标准库</span></h3>
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<p>下列标准库设施满足随机数引擎 (<span style="font-style:italic">随机数引擎</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(RandomNumberEngine)</span> ) ：</p>
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<table class="t-dsc-begin">
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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-linear_congruential_engine.html"><span class="t-lines"><span>linear_congruential_engine</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>实现<a href="https://en.wikipedia.org/wiki/Linear_congruential_generator" class="extiw" title="enwiki:Linear congruential generator">线性同余</a>算法<br />
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<span class="t-mark">(类模板)</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-mersenne_twister_engine.html"><span class="t-lines"><span>mersenne_twister_engine</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>实现<a href="https://en.wikipedia.org/wiki/Mersenne_twister" class="extiw" title="enwiki:Mersenne twister">梅森缠绕器</a>算法<br />
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<span class="t-mark">(类模板)</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-subtract_with_carry_engine.html"><span class="t-lines"><span>subtract_with_carry_engine</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>实现带进位减（一种<a href="https://en.wikipedia.org/wiki/Lagged_Fibonacci_generator" class="extiw" title="enwiki:Lagged Fibonacci generator">延迟斐波那契</a>）算法<br />
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<span class="t-mark">(类模板)</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-discard_block_engine.html"><span class="t-lines"><span>discard_block_engine</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>舍弃随机数引擎的某些输出<br />
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<span class="t-mark">(类模板)</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-independent_bits_engine.html"><span class="t-lines"><span>independent_bits_engine</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>将一个随机数引擎的输出打包为指定位数的块<br />
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<span class="t-mark">(类模板)</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-shuffle_order_engine.html"><span class="t-lines"><span>shuffle_order_engine</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>以不同顺序发送一个随机数引擎的输出<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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<p>下列标准库设施满足<a href="cpp-named_req-UniformRandomBitGenerator.html"><span style="font-style:italic">均匀随机位生成器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(UniformRandomBitGenerator)</span></a> 但不满足随机数引擎 (<span style="font-style:italic">随机数引擎</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(RandomNumberEngine)</span> ) ：</p>
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<table class="t-dsc-begin">
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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.html"><span class="t-lines"><span>random_device</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>使用硬件熵源的非确定随机数生成器<br />
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<span class="t-mark">(类)</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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