140 lines
16 KiB
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140 lines
16 KiB
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<title>std::priority_queue 的推导指引</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_container_priority_queue_deduction_guides skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><code>std::priority_queue</code> 的推导指引</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-container.html">container</a>‎ | <a href="cpp-container-priority_queue.html">priority queue</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-queue.html"><queue></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> Comp, <span class="kw1">class</span> Container<span class="sy1">></span><br /></span>
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<p>priority_queue<span class="br0">(</span>Comp, Container<span class="br0">)</span><br /></p>
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<span class="sy2">-</span><span class="sy1">></span> priority_queue<span class="sy1"><</span><span class="kw1">typename</span> Container<span class="sy4">::</span><span class="me2">value_type</span>, Container, Comp<span class="sy1">></span><span class="sy4">;</span></div>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 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,<br /></span>
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<p> <span class="kw1">class</span> Comp <span class="sy1">=</span> <a href="cpp-utility-functional-less.html"><span class="kw1039">std::<span class="me2">less</span></span></a><span class="sy1"><</span><span class="coMULTI">/*iter-value-type*/</span><span class="sy1"><</span>InputIt<span class="sy1">>></span>,<br />
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<span class="kw1">class</span> Container <span class="sy1">=</span> <a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><span class="coMULTI">/*iter-value-type*/</span><span class="sy1"><</span>InputIt<span class="sy1">>></span><br />
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priority_queue<span class="br0">(</span>InputIt, InputIt, Comp <span class="sy1">=</span> Comp<span class="br0">(</span><span class="br0">)</span>, Container <span class="sy1">=</span> Container<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><br /></p>
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<span class="sy2">-</span><span class="sy1">></span> priority_queue<span class="sy1"><</span><span class="coMULTI">/*iter-value-type*/</span><span class="sy1"><</span>InputIt<span class="sy1">></span>, Container, Comp<span class="sy1">></span><span class="sy4">;</span></div>
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</td>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 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> Comp, <span class="kw1">class</span> Container, <span class="kw1">class</span> Alloc<span class="sy1">></span><br /></span>
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<p>priority_queue<span class="br0">(</span>Comp, Container, Alloc<span class="br0">)</span><br /></p>
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<span class="sy2">-</span><span class="sy1">></span> priority_queue<span class="sy1"><</span><span class="kw1">typename</span> Container<span class="sy4">::</span><span class="me2">value_type</span>, Container, Comp<span class="sy1">></span><span class="sy4">;</span></div>
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</td>
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<td>(3)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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<tr class="t-dcl t-since-cxx17">
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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="kw1">class</span> Alloc<span class="sy1">></span><br /></span>
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<p>priority_queue<span class="br0">(</span>InputIt, InputIt, Alloc<span class="br0">)</span><br />
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<span class="sy2">-</span><span class="sy1">></span> priority_queue<span class="sy1"><</span><span class="coMULTI">/*iter-value-type*/</span><span class="sy1"><</span>InputIt<span class="sy1">></span>,<br />
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<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><span class="coMULTI">/*iter-value-type*/</span><span class="sy1"><</span>InputIt<span class="sy1">></span>, Alloc<span class="sy1">></span>,<br /></p>
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<a href="cpp-utility-functional-less.html"><span class="kw1039">std::<span class="me2">less</span></span></a><span class="sy1"><</span><span class="coMULTI">/*iter-value-type*/</span><span class="sy1"><</span>InputIt<span class="sy1">>>></span><span class="sy4">;</span></div>
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<td>(4)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx17">
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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="kw1">class</span> Comp, <span class="kw1">class</span> Alloc<span class="sy1">></span><br /></span>
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<p>priority_queue<span class="br0">(</span>InputIt, InputIt, Comp, Alloc<span class="br0">)</span><br />
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<span class="sy2">-</span><span class="sy1">></span> priority_queue<span class="sy1"><</span><span class="coMULTI">/*iter-value-type*/</span><span class="sy1"><</span>InputIt<span class="sy1">></span>,<br /></p>
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<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><span class="coMULTI">/*iter-value-type*/</span><span class="sy1"><</span>InputIt<span class="sy1">></span>, Alloc<span class="sy1">></span>, Comp<span class="sy1">></span><span class="sy4">;</span></div>
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</td>
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<td>(5)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx17">
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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="kw1">class</span> Comp, <span class="kw1">class</span> Container, <span class="kw1">class</span> Alloc<span class="sy1">></span><br /></span>
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<p>priority_queue<span class="br0">(</span>InputIt, InputIt, Comp, Container, Alloc<span class="br0">)</span><br /></p>
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<span class="sy2">-</span><span class="sy1">></span> priority_queue<span class="sy1"><</span><span class="kw1">typename</span> Container<span class="sy4">::</span><span class="me2">value_type</span>, Container, Comp<span class="sy1">></span><span class="sy4">;</span></div>
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<td>(6)</td>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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<tr class="t-dcl-sep">
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<p>为 <span class="t-lc"><a href="cpp-container-priority_queue.html">std::priority_queue</a></span> 提供这些<a href="cpp-language-class_template_argument_deduction.html">推导指引</a>以允许从底层容器类型以及从迭代器范围推导。对任何类型 <code>It</code> ， <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*iter-value-type*/</span><span class="sy1"><</span>It<span class="sy1">></span></span></span> 指代 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">typename</span> <a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>It<span class="sy1">></span><span class="sy4">::</span><span class="me2">value_type</span></span></span> 。</p>
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<p>这些重载仅若</p>
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<ul>
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<li><code>InputIt</code> 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> 、</li>
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<li><code>Comp</code> 不满足<a href="cpp-named_req-Allocator.html"><span style="font-style:italic">分配器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Allocator)</span></a> 、</li>
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<li><code>Container</code> 不满足<a href="cpp-named_req-Allocator.html"><span style="font-style:italic">分配器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Allocator)</span></a> ，</li>
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<li><span class="t-rev-inl t-since-cxx23"><span>对于重载 <span class="t-v">(4)</span> 与 <span class="t-v">(5)</span> ，</span> <span><span class="t-mark-rev t-since-cxx23">(C++23 起)</span></span></span> <code>Alloc</code> 满足<a href="cpp-named_req-Allocator.html"><span style="font-style:italic">分配器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Allocator)</span></a> ，并且</li>
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<li>对于重载 <span class="t-v">(3)</span> 与 <span class="t-v">(6)</span> ， <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-memory-uses_allocator.html"><span class="kw705">std::<span class="me2">uses_allocator_v</span></span></a><span class="sy1"><</span>Container, Alloc<span class="sy1">></span></span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 才参与重载决议。</li>
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</ul>
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<p>注意：库确定类型是否满足<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> 的程度是未指定的，除了最低要求是整数类型不具备输入迭代器的条件。类似地，确定类型是否满足<a href="cpp-named_req-Allocator.html"><span style="font-style:italic">分配器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Allocator)</span></a> 是未指定的，除了最低要求是成员类型 <code>Alloc::value_type</code> 必须存在，且表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-declval.html"><span class="kw1120">std::<span class="me2">declval</span></span></a><span class="sy1"><</span>Alloc<span class="sy3">&</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span>.<span class="me1">allocate</span><span class="br0">(</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a><span class="br0">{</span><span class="br0">}</span><span class="br0">)</span></span></span> 在作为不求值操作数时必须为良构。</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 <vector></span>
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<span class="co2">#include <queue></span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> v <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="br0">}</span><span class="sy4">;</span>
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<a href="cpp-container-priority_queue.html"><span class="kw1299">std::<span class="me2">priority_queue</span></span></a> pq1<span class="br0">{</span><a href="cpp-utility-functional-greater.html"><span class="kw1037">std::<span class="me2">greater</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span><span class="br0">{</span><span class="br0">}</span>, v<span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 推导 std::priority_queue<</span>
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<span class="co1">// int, std::vector<int>,</span>
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<span class="co1">// std::greater<int>></span>
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<a href="cpp-container-priority_queue.html"><span class="kw1299">std::<span class="me2">priority_queue</span></span></a> pq2<span class="br0">{</span>v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, v.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// 推导 std::priority_queue<int></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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</tr>
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<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue3506">LWG 3506</a></td>
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<td>C++17</td>
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<td>缺少源自迭代器和分配器的推导指引</td>
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<td>已添加</td>
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</table>
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</div>
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<div class="visualClear"></div>
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