88 lines
8.4 KiB
HTML
88 lines
8.4 KiB
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<title>std::hash<std::unique_ptr></title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>hash<small><std::unique_ptr></small></h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-memory.html">memory</a>‎ | <a href="cpp-memory-unique_ptr.html">unique ptr</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T, <span class="kw1">class</span> Deleter<span class="sy1">></span> <span class="kw1">struct</span> hash<span class="sy1"><</span>unique_ptr<span class="sy1"><</span>T, Deleter<span class="sy1">>></span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<p><span class="t-lc"><a href="cpp-utility-hash.html">std::hash</a></span> 对 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-memory-unique_ptr.html"><span class="kw733">std::<span class="me2">unique_ptr</span></span></a><span class="sy1"><</span>T, Deleter<span class="sy1">></span></span></span> 的模板特化允许用户获得 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-memory-unique_ptr.html"><span class="kw733">std::<span class="me2">unique_ptr</span></span></a><span class="sy1"><</span>T, Deleter<span class="sy1">></span></span></span> 类型对象的散列值。</p>
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<p>若启用 <span class="t-lc">std::hash<typename std::unique_ptr<T,D>::pointer></span> ，则启用特化 <span class="t-lc">std::hash<std::unique_ptr<T,D>></span> （见 <span class="t-lc"><a href="cpp-utility-hash.html">std::hash</a></span> ），否则禁用它。</p>
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<p>启用时，对于给定的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-memory-unique_ptr.html"><span class="kw733">std::<span class="me2">unique_ptr</span></span></a><span class="sy1"><</span>T, D<span class="sy1">></span> p</span></span> ，此特化确保 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-hash.html"><span class="kw1124">std::<span class="me2">hash</span></span></a><span class="sy1"><</span><a href="cpp-memory-unique_ptr.html"><span class="kw733">std::<span class="me2">unique_ptr</span></span></a><span class="sy1"><</span>T, D<span class="sy1">>></span><span class="br0">(</span><span class="br0">)</span><span class="br0">(</span>p<span class="br0">)</span> <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><span class="kw1">typename</span> <a href="cpp-memory-unique_ptr.html"><span class="kw733">std::<span class="me2">unique_ptr</span></span></a><span class="sy1"><</span>T, D<span class="sy1">></span><span class="sy4">::</span><span class="me2">pointer</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">(</span>p.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 。</p>
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<p>此特化的成员函数不保证为 noexcept ，因为指针可能是缀饰指针且其散列函数可能抛出。</p>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <iostream></span>
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<span class="co2">#include <memory></span>
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<span class="co2">#include <functional></span>
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<span class="kw1">struct</span> Foo <span class="br0">{</span>
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Foo<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"Foo...<span class="es1">\n</span>"</span><span class="sy4">;</span> <span class="br0">}</span>
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~Foo<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span> <a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"~Foo...<span class="es1">\n</span><span class="es1">\n</span>"</span><span class="sy4">;</span> <span class="br0">}</span>
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<span class="br0">}</span><span class="sy4">;</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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Foo<span class="sy2">*</span> foo <span class="sy1">=</span> new Foo<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-memory-unique_ptr.html"><span class="kw733">std::<span class="me2">unique_ptr</span></span></a><span class="sy1"><</span>Foo<span class="sy1">></span> up<span class="br0">(</span>foo<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"hash(up): "</span> <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><a href="cpp-memory-unique_ptr.html"><span class="kw733">std::<span class="me2">unique_ptr</span></span></a><span class="sy1"><</span>Foo<span class="sy1">>></span><span class="br0">(</span><span class="br0">)</span><span class="br0">(</span>up<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="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"hash(foo): "</span> <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>Foo<span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">(</span>foo<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="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">Foo...
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hash(up): 3686401041
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hash(foo): 3686401041
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~Foo...</pre></div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<div class="t-dsc-member-div">
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<div><a href="cpp-utility-hash.html"><span class="t-lines"><span>hash</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>散列函数对象<br />
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<span class="t-mark">(类模板)</span></td>
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