675 lines
40 KiB
HTML
675 lines
40 KiB
HTML
<!DOCTYPE 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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<head><meta http-equiv="x-ua-compatible" content="ie=edge">
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<title>std::unordered_map</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_container_unordered_map skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<div id="content"><a id="top"></a>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>unordered_map</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-container.html">container</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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<tbody>
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<td>
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<div>定义于头文件 <code><a href="cpp-header-unordered_map.html"><unordered_map></a></code></div>
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</td>
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<td></td>
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<td></td>
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<tr class="t-dcl t-since-cxx11">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span><br /></span>
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<p> <span class="kw1">class</span> Key,<br />
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<span class="kw1">class</span> T,<br />
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<span class="kw1">class</span> Hash <span class="sy1">=</span> <a href="cpp-utility-hash.html"><span class="kw1124">std::<span class="me2">hash</span></span></a><span class="sy1"><</span>Key<span class="sy1">></span>,<br />
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<span class="kw1">class</span> KeyEqual <span class="sy1">=</span> <a href="cpp-utility-functional-equal_to.html"><span class="kw1035">std::<span class="me2">equal_to</span></span></a><span class="sy1"><</span>Key<span class="sy1">></span>,<br />
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<span class="kw1">class</span> Allocator <span class="sy1">=</span> <a href="cpp-memory-allocator.html"><span class="kw700">std::<span class="me2">allocator</span></span></a><span class="sy1"><</span> <a href="cpp-utility-pair.html"><span class="kw1096">std::<span class="me2">pair</span></span></a><span class="sy1"><</span><span class="kw4">const</span> Key, T<span class="sy1">></span> <span class="sy1">></span><br /></p>
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<span class="sy1">></span> <span class="kw1">class</span> unordered_map<span class="sy4">;</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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<tr class="t-dcl t-since-cxx17">
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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">namespace</span> pmr <span class="br0">{</span><br /></span>
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<p> <span class="kw1">template</span> <span class="sy1"><</span><span class="kw1">class</span> Key,<br />
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<span class="kw1">class</span> T,<br />
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<span class="kw1">class</span> Hash <span class="sy1">=</span> <a href="cpp-utility-hash.html"><span class="kw1124">std::<span class="me2">hash</span></span></a><span class="sy1"><</span>Key<span class="sy1">></span>,<br />
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<span class="kw1">class</span> KeyEqual <span class="sy1">=</span> <a href="cpp-utility-functional-equal_to.html"><span class="kw1035">std::<span class="me2">equal_to</span></span></a><span class="sy1"><</span>Key<span class="sy1">>></span><br />
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<span class="kw1">using</span> unordered_map <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">unordered_map</span><span class="sy1"><</span>Key, T, Hash, Pred,<br />
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<a href="cpp-memory-polymorphic_allocator.html"><span class="kw707">std::<span class="me2">pmr</span><span class="sy4">::</span><span class="me2">polymorphic_allocator</span></span></a><span class="sy1"><</span><a href="cpp-utility-pair.html"><span class="kw1096">std::<span class="me2">pair</span></span></a><span class="sy1"><</span><span class="kw4">const</span> Key,T<span class="sy1">>>></span><span class="sy4">;</span><br /></p>
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<span class="br0">}</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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<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>unordered_map 是关联容器，含有带唯一键的键-值 pair 。搜索、插入和元素移除拥有平均常数时间复杂度。</p>
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<p>元素在内部不以任何特定顺序排序，而是组织进桶中。元素放进哪个桶完全依赖于其键的哈希。这允许对单独元素的快速访问，因为一旦计算哈希，则它准确指代元素所放进的桶。</p>
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<p><code>std::unordered_map</code> 满足<a href="cpp-named_req-Container.html"><span style="font-style:italic">容器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(Container)</span></a> 、<a href="cpp-named_req-AllocatorAwareContainer.html"><span style="font-style:italic">知分配器容器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(AllocatorAwareContainer)</span></a> 、<a href="cpp-named_req-UnorderedAssociativeContainer.html"><span style="font-style:italic">无序关联容器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(UnorderedAssociativeContainer)</span></a> 的要求。</p>
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<h3><span class="mw-headline" id=".E8.BF.AD.E4.BB.A3.E5.99.A8.E9.9D.9E.E6.B3.95.E5.8C.96">迭代器非法化</span></h3>
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<table class="dsctable" style="font-size:0.8em">
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<tr>
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<th>操作</th>
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<th>非法化</th>
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<tr>
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<td>所有只读操作、 <span class="t-lc"><a href="cpp-container-unordered_map-swap.html">swap</a></span> 、 <span class="t-lc"><a href="cpp-algorithm-swap.html">std::swap</a></span></td>
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<td>决不</td>
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<tr>
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<td><span class="t-lc"><a href="cpp-container-unordered_map-clear.html">clear</a></span> 、 <span class="t-lc"><a href="cpp-container-unordered_map-rehash.html">rehash</a></span> 、 <span class="t-lc"><a href="cpp-container-unordered_map-reserve.html">reserve</a></span> 、 <span class="t-lc"><a href="cpp-container-unordered_map-operator=.html">operator=</a></span></td>
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<td>始终</td>
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<td><span class="t-lc"><a href="cpp-container-unordered_map-insert.html">insert</a></span> 、 <span class="t-lc"><a href="cpp-container-unordered_map-emplace.html">emplace</a></span> 、 <span class="t-lc"><a href="cpp-container-unordered_map-emplace_hint.html">emplace_hint</a></span> 、 <span class="t-lc"><a href="cpp-container-unordered_map-operator_at.html">operator[]</a></span></td>
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<td>仅若重哈希导致</td>
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</tr>
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<tr>
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<td><span class="t-lc"><a href="cpp-container-unordered_map-erase.html">erase</a></span></td>
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<td>仅为指向被擦除元素者</td>
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</tr>
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</table>
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<h4><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h4>
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<ul>
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<li>swap 函数不非法化容器内的任何迭代器，但它们非法化标记交换区域结尾的迭代器。</li>
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</ul>
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<ul>
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<li>指向存储于容器中的关键或元素的引用和指针仅因擦除该元素才被非法化，即使在非法化对应迭代器时。</li>
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</ul>
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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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<table class="t-dsc-begin">
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<tr class="t-dsc-hitem">
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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>key_type</code></td>
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<td><code>Key</code></td>
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</tr>
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<tr class="t-dsc">
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<td><code>mapped_type</code></td>
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<td><code>T</code></td>
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</tr>
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<tr class="t-dsc">
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<td><code>value_type</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-pair.html"><span class="kw1096">std::<span class="me2">pair</span></span></a><span class="sy1"><</span><span class="kw4">const</span> Key, T<span class="sy1">></span></span></span></td>
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</tr>
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<tr class="t-dsc">
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<td><code>size_type</code></td>
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<td>无符号整数类型（通常是 <span class="t-lc"><a href="cpp-types-size_t.html">std::size_t</a></span> ）</td>
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</tr>
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<tr class="t-dsc">
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<td><code>difference_type</code></td>
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<td>有符号整数类型（通常是 <span class="t-lc"><a href="cpp-types-ptrdiff_t.html">std::ptrdiff_t</a></span> ）</td>
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</tr>
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<tr class="t-dsc">
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<td><code>hasher</code></td>
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<td><code>Hash</code></td>
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</tr>
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<tr class="t-dsc">
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<td><code>key_equal</code></td>
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<td><code>KeyEqual</code></td>
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</tr>
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<tr class="t-dsc">
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<td><code>allocator_type</code></td>
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<td><code>Allocator</code></td>
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</tr>
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<tr class="t-dsc">
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<td><code>reference</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">value_type<span class="sy3">&</span></span></span></td>
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</tr>
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<tr class="t-dsc">
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<td><code>const_reference</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> value_type<span class="sy3">&</span></span></span></td>
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</tr>
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<tr class="t-dsc">
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<td><code>pointer</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-memory-allocator_traits.html"><span class="kw701">std::<span class="me2">allocator_traits</span></span></a><span class="sy1"><</span>Allocator<span class="sy1">></span><span class="sy4">::</span><span class="me2">pointer</span></span></span></td>
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</tr>
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<tr class="t-dsc">
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<td><code>const_pointer</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-memory-allocator_traits.html"><span class="kw701">std::<span class="me2">allocator_traits</span></span></a><span class="sy1"><</span>Allocator<span class="sy1">></span><span class="sy4">::</span><span class="me2">const_pointer</span></span></span></td>
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</tr>
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<tr class="t-dsc">
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<td><code>iterator</code></td>
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<td>指向 <code>value_type</code> 的常<a href="cpp-named_req-ForwardIterator.html"><span style="font-style:italic">老式向前迭代器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LegacyForwardIterator)</span></a></td>
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</tr>
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<tr class="t-dsc">
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<td><code>const_iterator</code></td>
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<td>指向 <code>const value_type</code> 的<a href="cpp-named_req-ForwardIterator.html"><span style="font-style:italic">老式向前迭代器</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LegacyForwardIterator)</span></a></td>
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</tr>
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<tr class="t-dsc">
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<td><code>local_iterator</code></td>
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<td>类别、值、差、指针和引用类型都与 <code>iterator</code> 相同的迭代器类型。<br />
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能用此迭代器在单个桶迭代，但不能跨桶。</td>
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</tr>
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<tr class="t-dsc">
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<td><code>const_local_iterator</code></td>
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<td>类别、值、差、指针和引用类型都与 <code>const_iterator</code> 相同的迭代器类型。<br />
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能用此迭代器在单个桶迭代，但不能跨桶。</td>
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</tr>
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<tr class="t-dsc">
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<td><code>node_type</code><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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<td>表示容器结点的<a href="cpp-container-node_handle.html">结点把柄</a>特化</td>
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</tr>
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<tr class="t-dsc">
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<td><code>insert_return_type</code><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td>
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<td>描述插入 <code>node_type</code> 结果的类型，下列类型的特化
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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="kw1">template</span> <span class="sy1"><</span><span class="kw1">class</span> Iter, <span class="kw1">class</span> NodeType<span class="sy1">></span> <span class="kw1">struct</span> <span class="coMULTI">/*unspecified*/</span> <span class="br0">{</span>
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Iter position<span class="sy4">;</span>
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<span class="kw4">bool</span> inserted<span class="sy4">;</span>
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NodeType node<span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</span></pre></div>
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</div>
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，以模板实参 <code>iterator</code> 和 <code>node_type</code> 实例化。</td>
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</tr>
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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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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div t-dsc-member-nobold-div">
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<div><a href="cpp-container-unordered_map-unordered_map.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 <code>unordered_map</code><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 t-dsc-member-nobold-div">
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<div><a href="cpp-container-unordered_map-~unordered_map.html"><span class="t-lines"><span>(析构函数)</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>析构 <code>unordered_map</code><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-container-unordered_map-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>赋值给容器<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-container-unordered_map-get_allocator.html"><span class="t-lines"><span>get_allocator</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>返回相关的分配器<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>
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<td colspan="2">
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<h5><span class="mw-headline" id=".E8.BF.AD.E4.BB.A3.E5.99.A8">迭代器</span></h5>
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</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-container-unordered_map-begin.html"><span class="t-lines"><span>begin</span> <span>cbegin</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>返回指向起始的迭代器<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-container-unordered_map-end.html"><span class="t-lines"><span>end</span> <span>cend</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>返回指向末尾的迭代器<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>
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<td colspan="2">
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<h5><span class="mw-headline" id=".E5.AE.B9.E9.87.8F">容量</span></h5>
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</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-container-unordered_map-empty.html"><span class="t-lines"><span>empty</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>检查容器是否为空<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-container-unordered_map-size.html"><span class="t-lines"><span>size</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>返回容纳的元素数<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">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-max_size.html"><span class="t-lines"><span>max_size</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>返回可容纳的最大元素数<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr>
|
|
<td colspan="2">
|
|
<h5><span class="mw-headline" id=".E4.BF.AE.E6.94.B9.E5.99.A8">修改器</span></h5>
|
|
</td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-clear.html"><span class="t-lines"><span>clear</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>清除内容<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-insert.html"><span class="t-lines"><span>insert</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>插入元素<span class="t-rev-inl t-since-cxx17"><span>或结点</span> <span><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></span></span><br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-insert_or_assign.html"><span class="t-lines"><span>insert_or_assign</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>插入元素，或若键已存在则赋值给当前元素<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-emplace.html"><span class="t-lines"><span>emplace</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>原位构造元素<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-emplace_hint.html"><span class="t-lines"><span>emplace_hint</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>使用提示原位构造元素<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-try_emplace.html"><span class="t-lines"><span>try_emplace</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>若键不存在则原位插入，若键存在则不做任何事<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-erase.html"><span class="t-lines"><span>erase</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>擦除元素<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-swap.html"><span class="t-lines"><span>swap</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>交换内容<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-extract.html"><span class="t-lines"><span>extract</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>从另一容器释出结点<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-merge.html"><span class="t-lines"><span>merge</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>从另一容器接合结点<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr>
|
|
<td colspan="2">
|
|
<h5><span class="mw-headline" id=".E6.9F.A5.E6.89.BE">查找</span></h5>
|
|
</td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-at.html"><span class="t-lines"><span>at</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>访问指定的元素，同时进行越界检查<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-operator_at.html"><span class="t-lines"><span>operator[]</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>访问或插入指定的元素<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-count.html"><span class="t-lines"><span>count</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>返回匹配特定键的元素数量<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-find.html"><span class="t-lines"><span>find</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>寻找带有特定键的元素<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-contains.html"><span class="t-lines"><span>contains</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>检查容器是否含有带特定键的元素<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-equal_range.html"><span class="t-lines"><span>equal_range</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>返回匹配特定键的元素范围<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr>
|
|
<td colspan="2">
|
|
<h5><span class="mw-headline" id=".E6.A1.B6.E6.8E.A5.E5.8F.A3">桶接口</span></h5>
|
|
</td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-begin2.html"><span class="t-lines"><span>begin<span class="t-dsc-small">(size_type)</span></span> <span>cbegin<span class="t-dsc-small">(size_type)</span></span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>返回一个迭代器，指向指定的桶的开始<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-end2.html"><span class="t-lines"><span>end<span class="t-dsc-small">(size_type)</span></span> <span>cend<span class="t-dsc-small">(size_type)</span></span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>返回一个迭代器，指向指定的桶的末尾<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-bucket_count.html"><span class="t-lines"><span>bucket_count</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>返回桶数<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-max_bucket_count.html"><span class="t-lines"><span>max_bucket_count</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>返回桶的最大数量<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-bucket_size.html"><span class="t-lines"><span>bucket_size</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>返回在特定的桶中的元素数量<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-bucket.html"><span class="t-lines"><span>bucket</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>返回带有特定键的桶<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr>
|
|
<td colspan="2">
|
|
<h5><span class="mw-headline" id=".E5.93.88.E5.B8.8C.E7.AD.96.E7.95.A5">哈希策略</span></h5>
|
|
</td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-load_factor.html"><span class="t-lines"><span>load_factor</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>返回每个桶的平均元素数量<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-max_load_factor.html"><span class="t-lines"><span>max_load_factor</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>管理每个桶的平均元素数量的最大值<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-rehash.html"><span class="t-lines"><span>rehash</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>为至少为指定数量的桶预留存储空间并重新生成散列表<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-reserve.html"><span class="t-lines"><span>reserve</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>为至少为指定数量的元素预留存储空间并重新生成哈希表。<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr>
|
|
<td colspan="2">
|
|
<h5><span class="mw-headline" id=".E8.A7.82.E5.AF.9F.E5.99.A8">观察器</span></h5>
|
|
</td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-hash_function.html"><span class="t-lines"><span>hash_function</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>返回用于对键散列的函数<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-key_eq.html"><span class="t-lines"><span>key_eq</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>返回用于比较键的相等性的函数<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
</table>
|
|
<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>
|
|
<table class="t-dsc-begin">
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-operator_cmp.html"><span class="t-lines"><span>operator==</span><span>operator!=</span></span></a></div>
|
|
<div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 中移除)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>比较 unordered_map 中的值<br />
|
|
<span class="t-mark">(函数模板)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-container-unordered_map-swap2.html"><span class="t-lines"><span>std::swap<span class="t-dsc-small">(std::unordered_map)</span></span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>特化 <span class="t-lc"><a href="cpp-algorithm-swap.html">std::swap</a></span> 算法<br />
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<span class="t-mark">(函数模板)</span></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-container-unordered_map-erase_if.html"><span class="t-lines"><span>erase_if<span class="t-dsc-small">(std::unordered_map)</span></span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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</div>
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</td>
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<td>擦除所有满足特定判别标准的元素<br />
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<span class="t-mark">(函数模板)</span></td>
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</table>
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<h3><span class="mw-headline" id=".E6.8E.A8.E5.AF.BC.E6.8C.87.E5.BC.95.28C.2B.2B17_.E8.B5.B7.29"><a href="cpp-container-unordered_map-deduction_guides.html">推导指引</a><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></span></h3>
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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 <unordered_map></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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<span class="co1">// 创建三个 string 的 unordered_map （映射到 string ）</span>
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std<span class="sy4">::</span><span class="me2">unordered_map</span><span class="sy1"><</span><a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a>, <a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">></span> u <span class="sy1">=</span> <span class="br0">{</span>
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<span class="br0">{</span><span class="st0">"RED"</span>,<span class="st0">"#FF0000"</span><span class="br0">}</span>,
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<span class="br0">{</span><span class="st0">"GREEN"</span>,<span class="st0">"#00FF00"</span><span class="br0">}</span>,
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<span class="br0">{</span><span class="st0">"BLUE"</span>,<span class="st0">"#0000FF"</span><span class="br0">}</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="co1">// 迭代并打印 unordered_map 的关键和值</span>
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<span class="kw1">for</span><span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">auto</span><span class="sy3">&</span> n <span class="sy4">:</span> u <span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1756">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Key:["</span> <span class="sy1"><<</span> n.<span class="me1">first</span> <span class="sy1"><<</span> <span class="st0">"] Value:["</span> <span class="sy1"><<</span> n.<span class="me1">second</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="co1">// 添加新入口到 unordered_map</span>
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u<span class="br0">[</span><span class="st0">"BLACK"</span><span class="br0">]</span> <span class="sy1">=</span> <span class="st0">"#000000"</span><span class="sy4">;</span>
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u<span class="br0">[</span><span class="st0">"WHITE"</span><span class="br0">]</span> <span class="sy1">=</span> <span class="st0">"#FFFFFF"</span><span class="sy4">;</span>
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<span class="co1">// 用关键输出值</span>
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<a href="cpp-io-cout.html"><span class="kw1756">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"The HEX of color RED is:["</span> <span class="sy1"><<</span> u<span class="br0">[</span><span class="st0">"RED"</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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<a href="cpp-io-cout.html"><span class="kw1756">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"The HEX of color BLACK is:["</span> <span class="sy1"><<</span> u<span class="br0">[</span><span class="st0">"BLACK"</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="kw1">return</span> <span class="nu0">0</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>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">Key:[RED] Value:[#FF0000]
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Key:[BLUE] Value:[#0000FF]
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Key:[GREEN] Value:[#00FF00]
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The HEX of color RED is:[#FF0000]
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The HEX of color BLACK is:[#000000]</pre></div>
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</div>
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</div>
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