128 lines
11 KiB
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128 lines
11 KiB
HTML
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<title>std::seed_seq::seed_seq</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_numeric_random_seed_seq_seed_seq 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::seed_seq::</span>seed_seq</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>‎ | <a href="cpp-numeric-random-seed_seq.html">seed seq</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">seed_seq<span class="br0">(</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp">seed_seq<span class="br0">(</span> <span class="kw4">const</span> seed_seq<span class="sy3">&</span> <span class="br0">)</span> <span class="sy1">=</span> delete<span class="sy4">;</span></span></div>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></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> InputIt <span class="sy1">></span><br />
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seed_seq<span class="br0">(</span> InputIt begin, InputIt end <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(3)</td>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></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> T <span class="sy1">></span><br />
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seed_seq<span class="br0">(</span> <a href="cpp-utility-initializer_list.html"><span class="kw960">std::<span class="me2">initializer_list</span></span></a><span class="sy1"><</span>T<span class="sy1">></span> il <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(4)</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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<div class="t-li1"><span class="t-li">1)</span> 默认构造函数创建拥有零长度初始种子序列的 <code>std::seed_seq</code> 对象。</div>
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<div class="t-li1"><span class="t-li">2)</span> 复制构造函数被删除： <code>std::seed_seq</code> 不可复制。</div>
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<div class="t-li1"><span class="t-li">3)</span> 构造 <code>std::seed_seq</code> ，以拥有从范围 <code>[begin, end)</code> 上迭代并以解引用迭代器复制值获得的值 <span class="texhtml" style="white-space: nowrap;">modulo 2<span class="t-su">32<br /></span></span> （即复制低 32 位）为初始种子序列。</div>
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<div class="t-li1"><span class="t-li">4)</span> 等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">seed_seq<span class="br0">(</span>il.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, il.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 。此构造函数启用源自种子值列表的<a href="cpp-language-list_initialization.html">列表初始化</a>。此重载仅若 <code>T</code> 为整数类型才参与重载决议。</div>
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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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<td>begin, end</td>
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<td>-</td>
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<td>初始种子序列，表示为一对 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><></span><span class="sy4">::</span><span class="me2">value_type</span></span></span> 为整数类型的输入迭代器</td>
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<tr class="t-par">
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<td>il</td>
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<td>-</td>
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<td>整数类型对象的 <span class="t-lc"><a href="cpp-utility-initializer_list.html">std::initializer_list</a></span> ，提供初始种子序列</td>
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<tr class="t-par-hitem">
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<td colspan="3">类型要求</td>
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<tr class="t-par-req">
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<td colspan="3">-
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<div class="spacer"></div>
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<code>InputIt</code> 必须满足<a href="cpp-named_req-InputIterator.html"><span style="font-style:italic">老式输入迭代器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LegacyInputIterator)</span></a> 的要求。</td>
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<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<div class="t-li1"><span class="t-li">3-4)</span> 在分配失败时抛出 <span class="t-lc"><a href="cpp-memory-new-bad_alloc.html">std::bad_alloc</a></span> 。</div>
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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 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 <sstream></span>
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<span class="co2">#include <iterator></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-seed_seq.html"><span class="kw1501">std::<span class="me2">seed_seq</span></span></a> s1<span class="sy4">;</span> <span class="co1">// 可默认构造</span>
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<a href="cpp-numeric-random-seed_seq.html"><span class="kw1501">std::<span class="me2">seed_seq</span></span></a> s2<span class="br0">{</span><span class="nu0">1</span>, <span class="nu0">2</span>, <span class="nu0">3</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 能用列表初始化</span>
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<a href="cpp-numeric-random-seed_seq.html"><span class="kw1501">std::<span class="me2">seed_seq</span></span></a> s3 <span class="sy1">=</span> <span class="br0">{</span><span class="sy2">-</span><span class="nu0">1</span>, <span class="nu0">0</span>, <span class="nu0">1</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 列表初始化的另一种形式</span>
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<span class="kw4">int</span> a<span class="br0">[</span><span class="nu0">10</span><span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">1</span>, <span class="nu0">2</span>, <span class="nu0">3</span>, <span class="nu0">4</span>, <span class="nu0">5</span>, <span class="nu0">6</span>, <span class="nu0">7</span>, <span class="nu0">8</span>, <span class="nu0">9</span>, <span class="nu0">10</span><span class="br0">}</span><span class="sy4">;</span>
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<a href="cpp-numeric-random-seed_seq.html"><span class="kw1501">std::<span class="me2">seed_seq</span></span></a> s4<span class="br0">(</span>a, a <span class="sy2">+</span> <span class="nu0">10</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 能用迭代器</span>
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<a href="cpp-io-basic_istringstream.html"><span class="kw1735">std::<span class="me2">istringstream</span></span></a> buf<span class="br0">(</span><span class="st0">"1 2 3 4 5"</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-iterator-istream_iterator.html"><span class="kw668">std::<span class="me2">istream_iterator</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> beg<span class="br0">(</span>buf<span class="br0">)</span>, end<span class="sy4">;</span>
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<a href="cpp-numeric-random-seed_seq.html"><span class="kw1501">std::<span class="me2">seed_seq</span></span></a> s5<span class="br0">(</span>beg, end<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 即使是流输入迭代器</span>
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<span class="br0">}</span></pre></div>
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</div>
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<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
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<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。</p>
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<table class="dsctable" style="font-size:0.8em">
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<tr>
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<th>DR</th>
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<th>应用于</th>
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<th>出版时的行为</th>
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<th>正确行为</th>
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<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue3422">LWG 3422</a></td>
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<td>C++11</td>
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<td>默认构造函数决不失败但可以不是 noexcept ；<br />
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初始化器列表构造函数禁用源自迭代器对的列表初始化</td>
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<td>使之为 noexcept ；<br />
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已约束</td>
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</table>
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</div>
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<div class="visualClear"></div>
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