284 lines
24 KiB
HTML
284 lines
24 KiB
HTML
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<title>std::unordered_set<Key,Hash,KeyEqual,Allocator>::unordered_set</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::unordered_set<Key,Hash,KeyEqual,Allocator>::</span>unordered_set</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>‎ | <a href="cpp-container-unordered_set.html">unordered set</a></span></div>
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<div class="t-page-template" style="">
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<p></p>
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<table class="t-dcl-begin">
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<tbody>
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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_set<span class="br0">(</span><span class="br0">)</span> <span class="sy4">:</span> unordered_set<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_set<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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<td>
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<div><span class="mw-geshi cpp source-cpp">unordered_set<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_set<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_set<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_set<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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<td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">explicit</span> unordered_set<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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<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_set<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_set<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_set<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_set<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_set<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_set<span class="br0">(</span> <span class="kw4">const</span> unordered_set<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_set<span class="br0">(</span> <span class="kw4">const</span> unordered_set<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_set<span class="br0">(</span> unordered_set<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_set<span class="br0">(</span> unordered_set<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_set<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_set<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_set<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_set<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_set<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_set<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>
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<div class="t-li1"><span class="t-li">3)</span> 与 <code>other</code> 的大小成线性。</div>
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<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>
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<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>
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<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<p>对 <code>Allocator::allocate</code> 的调用可能抛出。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<div class="t-template-editlink" style=""></div>
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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。
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<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>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style="">
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<tr>
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<td class="mbox-empty-cell"></td>
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<td class="mbox-text" style="">本节未完成<br />
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原因：暂无示例</td>
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</tr>
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</table>
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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>
|
|
<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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<tr>
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<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2193">LWG 2193</a></td>
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<td>C++11</td>
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|
<td>默认构造函数为 explicit</td>
|
|
<td>使之为非 explicit</td>
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|
</tr>
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</table>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</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">
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|
<div><a href="cpp-container-unordered_set-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>
|
|
<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>
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</div>
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</div>
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</body>
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</html>
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