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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::unordered_map<Key,T,Hash,KeyEqual,Allocator>::</span>unordered_map</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-unordered_map.html">unordered map</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">unordered_map<span class="br0">(</span><span class="br0">)</span> <span class="sy4">:</span> unordered_map<span class="br0">(</span> size_type<span class="br0">(</span><span class="coMULTI">/*implementation-defined*/</span><span class="br0">)</span> <span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span><br /></span>
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<p><span class="kw1">explicit</span> unordered_map<span class="br0">(</span> size_type bucket_count,<br />
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<span class="kw4">const</span> Hash<span class="sy3">&</span> hash <span class="sy1">=</span> Hash<span class="br0">(</span><span class="br0">)</span>,<br />
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<span class="kw4">const</span> key_equal<span class="sy3">&</span> equal <span class="sy1">=</span> key_equal<span class="br0">(</span><span class="br0">)</span>,<br /></p>
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<span class="kw4">const</span> Allocator<span class="sy3">&</span> alloc <span class="sy1">=</span> Allocator<span class="br0">(</span><span class="br0">)</span> <span class="br0">)</span><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>
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<tr class="t-dcl t-since-cxx14">
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<div><span class="mw-geshi cpp source-cpp">unordered_map<span class="br0">(</span> size_type bucket_count,<br /></span>
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<p> <span class="kw4">const</span> Allocator<span class="sy3">&</span> alloc <span class="br0">)</span><br />
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<span class="sy4">:</span> unordered_map<span class="br0">(</span>bucket_count, Hash<span class="br0">(</span><span class="br0">)</span>, key_equal<span class="br0">(</span><span class="br0">)</span>, alloc<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span><br />
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unordered_map<span class="br0">(</span> size_type bucket_count,<br />
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<span class="kw4">const</span> Hash<span class="sy3">&</span> hash,<br />
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<span class="kw4">const</span> Allocator<span class="sy3">&</span> alloc <span class="br0">)</span><br /></p>
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<span class="sy4">:</span> unordered_map<span class="br0">(</span>bucket_count, hash, key_equal<span class="br0">(</span><span class="br0">)</span>, alloc<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</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-cxx14">(C++14 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx11">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">explicit</span> unordered_map<span class="br0">(</span> <span class="kw4">const</span> Allocator<span class="sy3">&</span> alloc <span class="br0">)</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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</tr>
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<tr class="t-dcl t-since-cxx11">
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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 /></span>
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<p>unordered_map<span class="br0">(</span> InputIt first, InputIt last,<br />
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size_type bucket_count <span class="sy1">=</span> <span class="coMULTI">/*implementation-defined*/</span>,<br />
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<span class="kw4">const</span> Hash<span class="sy3">&</span> hash <span class="sy1">=</span> Hash<span class="br0">(</span><span class="br0">)</span>,<br />
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<span class="kw4">const</span> key_equal<span class="sy3">&</span> equal <span class="sy1">=</span> key_equal<span class="br0">(</span><span class="br0">)</span>,<br /></p>
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<span class="kw4">const</span> Allocator<span class="sy3">&</span> alloc <span class="sy1">=</span> Allocator<span class="br0">(</span><span class="br0">)</span> <span class="br0">)</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-cxx11">(C++11 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx14">
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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> <span class="kw1">class</span> InputIt <span class="sy1">></span><br /></span>
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<p>unordered_map<span class="br0">(</span> InputIt first, InputIt last,<br />
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size_type bucket_count,<br />
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<span class="kw4">const</span> Allocator<span class="sy3">&</span> alloc <span class="br0">)</span><br />
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<span class="sy4">:</span> unordered_map<span class="br0">(</span>first, last,<br /></p>
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bucket_count, Hash<span class="br0">(</span><span class="br0">)</span>, key_equal<span class="br0">(</span><span class="br0">)</span>, alloc<span class="br0">)</span> <span class="br0">{</span><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-cxx14">(C++14 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx14">
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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> <span class="kw1">class</span> InputIt <span class="sy1">></span><br /></span>
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<p>unordered_map<span class="br0">(</span> InputIt first, InputIt last,<br />
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size_type bucket_count,<br />
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<span class="kw4">const</span> Hash<span class="sy3">&</span> hash,<br />
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<span class="kw4">const</span> Allocator<span class="sy3">&</span> alloc <span class="br0">)</span><br />
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<span class="sy4">:</span> unordered_map<span class="br0">(</span>first, last,<br /></p>
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bucket_count, hash, key_equal<span class="br0">(</span><span class="br0">)</span>, alloc<span class="br0">)</span> <span class="br0">{</span><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-cxx14">(C++14 起)</span></td>
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</tr>
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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">unordered_map<span class="br0">(</span> <span class="kw4">const</span> unordered_map<span class="sy3">&</span> other <span class="br0">)</span><span class="sy4">;</span></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-cxx11">(C++11 起)</span></td>
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</tr>
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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">unordered_map<span class="br0">(</span> <span class="kw4">const</span> unordered_map<span class="sy3">&</span> other, <span class="kw4">const</span> Allocator<span class="sy3">&</span> alloc <span class="br0">)</span><span class="sy4">;</span></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-cxx11">(C++11 起)</span></td>
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</tr>
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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">unordered_map<span class="br0">(</span> unordered_map<span class="sy3">&&</span> other <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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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>
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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">unordered_map<span class="br0">(</span> unordered_map<span class="sy3">&&</span> other, <span class="kw4">const</span> Allocator<span class="sy3">&</span> alloc <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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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>
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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">unordered_map<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>value_type<span class="sy1">></span> init,<br /></span>
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<p> size_type bucket_count <span class="sy1">=</span> <span class="coMULTI">/*implementation-defined*/</span>,<br />
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<span class="kw4">const</span> Hash<span class="sy3">&</span> hash <span class="sy1">=</span> Hash<span class="br0">(</span><span class="br0">)</span>,<br />
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<span class="kw4">const</span> key_equal<span class="sy3">&</span> equal <span class="sy1">=</span> key_equal<span class="br0">(</span><span class="br0">)</span>,<br /></p>
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<span class="kw4">const</span> Allocator<span class="sy3">&</span> alloc <span class="sy1">=</span> Allocator<span class="br0">(</span><span class="br0">)</span> <span class="br0">)</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-cxx11">(C++11 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx14">
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<td>
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<div><span class="mw-geshi cpp source-cpp">unordered_map<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>value_type<span class="sy1">></span> init,<br /></span>
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<p> size_type bucket_count,<br />
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<span class="kw4">const</span> Allocator<span class="sy3">&</span> alloc <span class="br0">)</span><br />
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<span class="sy4">:</span> unordered_map<span class="br0">(</span>init, bucket_count,<br /></p>
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Hash<span class="br0">(</span><span class="br0">)</span>, key_equal<span class="br0">(</span><span class="br0">)</span>, alloc<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</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-cxx14">(C++14 起)</span></td>
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</tr>
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<tr class="t-dcl t-since-cxx14">
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<td>
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<div><span class="mw-geshi cpp source-cpp">unordered_map<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>value_type<span class="sy1">></span> init,<br /></span>
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<p> size_type bucket_count,<br />
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<span class="kw4">const</span> Hash<span class="sy3">&</span> hash,<br />
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<span class="kw4">const</span> Allocator<span class="sy3">&</span> alloc <span class="br0">)</span><br />
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<span class="sy4">:</span> unordered_map<span class="br0">(</span>init, bucket_count,<br /></p>
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hash, key_equal<span class="br0">(</span><span class="br0">)</span>, alloc<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</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-cxx14">(C++14 起)</span></td>
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</tr>
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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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</tr>
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</tbody>
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</table>
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<p>从各种数据源构造新容器。可选的以用户提供的 <code>bucket_count</code> 为用于创建的最小桶数，以 <code>hash</code> 为哈希函数，以 <code>equal</code> 为比较关键的函数，和以 <code>alloc</code> 为分配器。</p>
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<div class="t-li1"><span class="t-li">1)</span> 构造空容器。设置 <code>max_load_factor()</code> 为 1.0 。对于默认构造函数，桶数是实现定义的。</div>
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<div class="t-li1"><span class="t-li">2)</span> 构造拥有范围 <code>[first, last)</code> 的内容的容器。设置 <code>max_load_factor()</code> 为 1.0 。若范围中的多个元素拥有比较等价的关键，则插入哪个元素是未指定的（待决的 <a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2844">LWG2844</a> ）。</div>
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<div class="t-li1"><span class="t-li">3)</span> 复制构造函数。构造拥有 <code>other</code> 内容副本的容器，一同复制加载因子、谓词和哈希函数。若不提供 <code>alloc</code> ，则通过调用 <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_type<span class="sy1">></span><span class="sy4">::</span><span class="me2">select_on_container_copy_construction</span><span class="br0">(</span>other.<span class="me1">get_allocator</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 获得分配器。
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<table class="t-rev-begin">
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<tr class="t-rev t-since-cxx23">
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<td>
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<p>在用于<a href="cpp-language-class_template_argument_deduction.html">类模板实参推导</a>时，仅从首个实参推导模板形参 <code>Allocator</code> 。</p>
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</td>
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<td><span class="t-mark-rev t-since-cxx23">(C++23 起)</span></td>
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</tr>
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</table>
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</div>
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<div class="t-li1"><span class="t-li">4)</span> 移动构造函数。用移动语义构造拥有 <code>other</code> 内容的容器。若不提供 <code>alloc</code> ，则通过从属于 <code>other</code> 的分配器移动构造获得分配器。
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<table class="t-rev-begin">
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<tr class="t-rev t-since-cxx23">
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<td>
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<p>在用于<a href="cpp-language-class_template_argument_deduction.html">类模板实参推导</a>时，仅从首个实参推导模板形参 <code>Allocator</code> 。</p>
|
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</td>
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<td><span class="t-mark-rev t-since-cxx23">(C++23 起)</span></td>
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</tr>
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</table>
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</div>
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<div class="t-li1"><span class="t-li">5)</span> 构造拥有 initializer_list <code>init</code> 内容的容器，同 <span class="t-c"><span class="mw-geshi cpp source-cpp">unordered_map<span class="br0">(</span>init.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, init.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 。</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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<tr class="t-par">
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<td>alloc</td>
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<td>-</td>
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<td>用于此容器所有内存分配器的分配器</td>
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</tr>
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<tr class="t-par">
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<td>bucket_count</td>
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<td>-</td>
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<td>初始化时用的最小桶数。若不指定，则使用实现定义的默认值</td>
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</tr>
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<tr class="t-par">
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<td>hash</td>
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<td>-</td>
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<td>要用的哈希函数</td>
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</tr>
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<tr class="t-par">
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<td>equal</td>
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<td>-</td>
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<td>用于此容器所有关键比较的比较函数</td>
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</tr>
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<tr class="t-par">
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<td>first, last</td>
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<td>-</td>
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<td>复制元素来源的范围</td>
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</tr>
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<tr class="t-par">
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<td>other</td>
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<td>-</td>
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<td>用作源以初始化容器元素的另一容器</td>
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</tr>
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<tr class="t-par">
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<td>init</td>
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<td>-</td>
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<td>用以初始化容器元素的 initializer_list</td>
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</tr>
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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>
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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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</tr>
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</table>
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<h3><span class="mw-headline" id=".E5.A4.8D.E6.9D.82.E5.BA.A6">复杂度</span></h3>
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<div class="t-li1"><span class="t-li">1)</span> 常数</div>
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<div class="t-li1"><span class="t-li">2)</span> 平均情况与 <code>first</code> 和 <code>last</code> 间的距离成线性，最坏情况成平方。</div>
|
||||
<div class="t-li1"><span class="t-li">3)</span> 与 <code>other</code> 的大小成线性。</div>
|
||||
<div class="t-li1"><span class="t-li">4)</span> 常数。若给定 <code>alloc</code> 且 <span class="t-c"><span class="mw-geshi cpp source-cpp">alloc <span class="sy3">!</span><span class="sy1">=</span> other.<span class="me1">get_allocator</span><span class="br0">(</span><span class="br0">)</span></span></span> 则为线性。</div>
|
||||
<div class="t-li1"><span class="t-li">5)</span> 平均情况与 <code>init</code> 的大小成线性，最坏情况成平方。</div>
|
||||
<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
|
||||
<p>对 <code>Allocator::allocate</code> 的调用可能抛出。</p>
|
||||
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
|
||||
<div class="t-template-editlink" style=""></div>
|
||||
在容器移动构造（重载 <span class="t-v">(4)</span> ）后，指向 <code>other</code> 的引用及迭代器（除了尾迭代器）保持合法，但指代现于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 中的元素。当前标准由 <a rel="nofollow" class="external text" href="https://eel.is/c++draft/container.requirements.general#12">[container.requirements.general]/12</a> 中的总括陈述作出此保证，而 <a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2321">LWG 2321</a> 正在考虑更严格的保证。
|
||||
<p>尽管在 C++23 前未正式要求，一些实现已经在较早的模式中将 <code>Allocator</code> 放入<a href="cpp-language-template_argument_deduction.html#.E9.9D.9E.E6.8E.A8.E5.AF.BC.E8.AF.AD.E5.A2.83">非推导语境</a>。</p>
|
||||
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
|
||||
<div class="t-example">
|
||||
<div class="t-example-live-link"></div>
|
||||
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
||||
<div class="cpp source-cpp">
|
||||
<pre class="de1"><span class="co2">#include <unordered_map></span>
|
||||
<span class="co2">#include <vector></span>
|
||||
<span class="co2">#include <bitset></span>
|
||||
<span class="co2">#include <string></span>
|
||||
<span class="co2">#include <utility></span>
|
||||
|
||||
<span class="kw1">struct</span> Key <span class="br0">{</span>
|
||||
<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> first<span class="sy4">;</span>
|
||||
<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> second<span class="sy4">;</span>
|
||||
<span class="br0">}</span><span class="sy4">;</span>
|
||||
|
||||
<span class="kw1">struct</span> KeyHash <span class="br0">{</span>
|
||||
<a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span><span class="kw4">const</span> Key<span class="sy3">&</span> k<span class="br0">)</span> <span class="kw4">const</span>
|
||||
<span class="br0">{</span>
|
||||
<span class="kw1">return</span> <a href="cpp-utility-hash.html"><span class="kw1124">std::<span class="me2">hash</span></span></a><span class="sy1"><</span><a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">(</span>k.<span class="me1">first</span><span class="br0">)</span> <span class="sy3">^</span>
|
||||
<span class="br0">(</span><a href="cpp-utility-hash.html"><span class="kw1124">std::<span class="me2">hash</span></span></a><span class="sy1"><</span><a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">(</span>k.<span class="me1">second</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="nu0">1</span><span class="br0">)</span><span class="sy4">;</span>
|
||||
<span class="br0">}</span>
|
||||
<span class="br0">}</span><span class="sy4">;</span>
|
||||
|
||||
<span class="kw1">struct</span> KeyEqual <span class="br0">{</span>
|
||||
<span class="kw4">bool</span> operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span><span class="kw4">const</span> Key<span class="sy3">&</span> lhs, <span class="kw4">const</span> Key<span class="sy3">&</span> rhs<span class="br0">)</span> <span class="kw4">const</span>
|
||||
<span class="br0">{</span>
|
||||
<span class="kw1">return</span> lhs.<span class="me1">first</span> <span class="sy1">==</span> rhs.<span class="me1">first</span> <span class="sy3">&&</span> lhs.<span class="me1">second</span> <span class="sy1">==</span> rhs.<span class="me1">second</span><span class="sy4">;</span>
|
||||
<span class="br0">}</span>
|
||||
<span class="br0">}</span><span class="sy4">;</span>
|
||||
|
||||
<span class="kw1">struct</span> Foo <span class="br0">{</span>
|
||||
Foo<span class="br0">(</span><span class="kw4">int</span> val_<span class="br0">)</span> <span class="sy4">:</span> val<span class="br0">(</span>val_<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span>
|
||||
<span class="kw4">int</span> val<span class="sy4">;</span>
|
||||
<span class="kw4">bool</span> operator<span class="sy1">==</span><span class="br0">(</span><span class="kw4">const</span> Foo <span class="sy3">&</span>rhs<span class="br0">)</span> <span class="kw4">const</span> <span class="br0">{</span> <span class="kw1">return</span> val <span class="sy1">==</span> rhs.<span class="me1">val</span><span class="sy4">;</span> <span class="br0">}</span>
|
||||
<span class="br0">}</span><span class="sy4">;</span>
|
||||
|
||||
<span class="kw1">namespace</span> std <span class="br0">{</span>
|
||||
<span class="kw1">template</span><span class="sy1"><></span> <span class="kw1">struct</span> hash<span class="sy1"><</span>Foo<span class="sy1">></span> <span class="br0">{</span>
|
||||
<a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span><span class="kw4">const</span> Foo <span class="sy3">&</span>f<span class="br0">)</span> <span class="kw4">const</span> <span class="br0">{</span>
|
||||
<span class="kw1">return</span> <a href="cpp-utility-hash.html"><span class="kw1124">std::<span class="me2">hash</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span><span class="br0">{</span><span class="br0">}</span><span class="br0">(</span>f.<span class="me1">val</span><span class="br0">)</span><span class="sy4">;</span>
|
||||
<span class="br0">}</span>
|
||||
<span class="br0">}</span><span class="sy4">;</span>
|
||||
<span class="br0">}</span>
|
||||
|
||||
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
|
||||
<span class="br0">{</span>
|
||||
<span class="co1">// 默认构造函数：空 unordered_map</span>
|
||||
<a href="cpp-container-unordered_map.html"><span class="kw1293">std::<span class="me2">unordered_map</span></span></a><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> m1<span class="sy4">;</span>
|
||||
|
||||
<span class="co1">// 列表构造函数</span>
|
||||
<a href="cpp-container-unordered_map.html"><span class="kw1293">std::<span class="me2">unordered_map</span></span></a><span class="sy1"><</span><span class="kw4">int</span>, <a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">></span> m2 <span class="sy1">=</span>
|
||||
<span class="br0">{</span>
|
||||
<span class="br0">{</span><span class="nu0">1</span>, <span class="st0">"foo"</span><span class="br0">}</span>,
|
||||
<span class="br0">{</span><span class="nu0">3</span>, <span class="st0">"bar"</span><span class="br0">}</span>,
|
||||
<span class="br0">{</span><span class="nu0">2</span>, <span class="st0">"baz"</span><span class="br0">}</span>,
|
||||
<span class="br0">}</span><span class="sy4">;</span>
|
||||
|
||||
<span class="co1">// 复制构造函数</span>
|
||||
<a href="cpp-container-unordered_map.html"><span class="kw1293">std::<span class="me2">unordered_map</span></span></a><span class="sy1"><</span><span class="kw4">int</span>, <a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">></span> m3 <span class="sy1">=</span> m2<span class="sy4">;</span>
|
||||
|
||||
<span class="co1">// 移动构造函数</span>
|
||||
<a href="cpp-container-unordered_map.html"><span class="kw1293">std::<span class="me2">unordered_map</span></span></a><span class="sy1"><</span><span class="kw4">int</span>, <a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">></span> m4 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>m2<span class="br0">)</span><span class="sy4">;</span>
|
||||
|
||||
<span class="co1">// 范围构造函数</span>
|
||||
<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</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><a href="cpp-utility-bitset.html"><span class="kw1027">std::<span class="me2">bitset</span></span></a><span class="sy1"><</span><span class="nu0">8</span><span class="sy1">></span>, <span class="kw4">int</span><span class="sy1">>></span> v <span class="sy1">=</span> <span class="br0">{</span> <span class="br0">{</span><span class="nu12">0x12</span>, <span class="nu0">1</span><span class="br0">}</span>, <span class="br0">{</span><span class="nu12">0x01</span>,<span class="sy2">-</span><span class="nu0">1</span><span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span>
|
||||
<a href="cpp-container-unordered_map.html"><span class="kw1293">std::<span class="me2">unordered_map</span></span></a><span class="sy1"><</span><a href="cpp-utility-bitset.html"><span class="kw1027">std::<span class="me2">bitset</span></span></a><span class="sy1"><</span><span class="nu0">8</span><span class="sy1">></span>, <span class="kw4">double</span><span class="sy1">></span> m5<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">// 带定制 Key 类型的构造函数的选项 1</span>
|
||||
<span class="co1">// 定义 KeyHash 与 KeyEqual 结构体并在模板中使用它们</span>
|
||||
<a href="cpp-container-unordered_map.html"><span class="kw1293">std::<span class="me2">unordered_map</span></span></a><span class="sy1"><</span>Key, <a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a>, KeyHash, KeyEqual<span class="sy1">></span> m6 <span class="sy1">=</span> <span class="br0">{</span>
|
||||
<span class="br0">{</span> <span class="br0">{</span><span class="st0">"John"</span>, <span class="st0">"Doe"</span><span class="br0">}</span>, <span class="st0">"example"</span><span class="br0">}</span>,
|
||||
<span class="br0">{</span> <span class="br0">{</span><span class="st0">"Mary"</span>, <span class="st0">"Sue"</span><span class="br0">}</span>, <span class="st0">"another"</span><span class="br0">}</span>
|
||||
<span class="br0">}</span><span class="sy4">;</span>
|
||||
|
||||
<span class="co1">// 带定制 Key 类型的构造函数的选项 2</span>
|
||||
<span class="co1">// 为 class/struct 定义 const == 运算符并于 std 命名空间特化 std::hash 结构体</span>
|
||||
<a href="cpp-container-unordered_map.html"><span class="kw1293">std::<span class="me2">unordered_map</span></span></a><span class="sy1"><</span>Foo, <a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">></span> m7 <span class="sy1">=</span> <span class="br0">{</span>
|
||||
<span class="br0">{</span> Foo<span class="br0">(</span><span class="nu0">1</span><span class="br0">)</span>, <span class="st0">"One"</span><span class="br0">}</span>, <span class="br0">{</span> <span class="nu0">2</span>, <span class="st0">"Two"</span><span class="br0">}</span>, <span class="br0">{</span> <span class="nu0">3</span>, <span class="st0">"Three"</span><span class="br0">}</span>
|
||||
<span class="br0">}</span><span class="sy4">;</span>
|
||||
|
||||
<span class="co1">// 选项 3 ：用 lambdas</span>
|
||||
<span class="co1">// 注意必须将初始桶数传递给构造函数</span>
|
||||
<span class="kw1">struct</span> Goo <span class="br0">{</span><span class="kw4">int</span> val<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
|
||||
<span class="kw4">auto</span> hash <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">const</span> Goo <span class="sy3">&</span>g<span class="br0">)</span><span class="br0">{</span> <span class="kw1">return</span> <a href="cpp-utility-hash.html"><span class="kw1124">std::<span class="me2">hash</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span><span class="br0">{</span><span class="br0">}</span><span class="br0">(</span>g.<span class="me1">val</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
|
||||
<span class="kw4">auto</span> comp <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">const</span> Goo <span class="sy3">&</span>l, <span class="kw4">const</span> Goo <span class="sy3">&</span>r<span class="br0">)</span><span class="br0">{</span> <span class="kw1">return</span> l.<span class="me1">val</span> <span class="sy1">==</span> r.<span class="me1">val</span><span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
|
||||
<a href="cpp-container-unordered_map.html"><span class="kw1293">std::<span class="me2">unordered_map</span></span></a><span class="sy1"><</span>Goo, <span class="kw4">double</span>, decltype<span class="br0">(</span>hash<span class="br0">)</span>, decltype<span class="br0">(</span>comp<span class="br0">)</span><span class="sy1">></span> m8<span class="br0">(</span><span class="nu0">10</span>, hash, comp<span class="br0">)</span><span class="sy4">;</span>
|
||||
<span class="br0">}</span></pre></div>
|
||||
</div>
|
||||
</div>
|
||||
<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
|
||||
<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>
|
||||
<table class="dsctable" style="font-size:0.8em">
|
||||
<tr>
|
||||
<th>DR</th>
|
||||
<th>应用于</th>
|
||||
<th>出版时的行为</th>
|
||||
<th>正确行为</th>
|
||||
</tr>
|
||||
<tr>
|
||||
<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2193">LWG 2193</a></td>
|
||||
<td>C++11</td>
|
||||
<td>默认构造函数为 explicit</td>
|
||||
<td>使之为非 explicit</td>
|
||||
</tr>
|
||||
</table>
|
||||
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</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=.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>赋值给容器<br />
|
||||
<span class="t-mark">(公开成员函数)</span></td>
|
||||
</tr>
|
||||
</table>
|
||||
</div>
|
||||
<div class="visualClear"></div>
|
||||
</div>
|
||||
</div>
|
||||
</div>
|
||||
</body>
|
||||
</html>
|
||||
Reference in New Issue
Block a user