136 lines
15 KiB
HTML
136 lines
15 KiB
HTML
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<title>std::collate<CharT>::hash, std::collate<CharT>::do_hash</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::collate<CharT>::</span>hash, <span style="font-size:0.7em; line-height:130%">std::collate<CharT>::</span>do_hash</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-locale.html">locale</a>‎ | <a href="cpp-locale-collate.html">collate</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-locale.html"><locale></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">public</span><span class="sy4">:</span><br />
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<span class="kw4">long</span> hash<span class="br0">(</span> <span class="kw4">const</span> CharT<span class="sy2">*</span> beg, <span class="kw4">const</span> CharT<span class="sy2">*</span> end <span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<td>(1)</td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">protected</span><span class="sy4">:</span><br />
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<span class="kw1">virtual</span> <span class="kw4">long</span> do_hash<span class="br0">(</span> <span class="kw4">const</span> CharT<span class="sy2">*</span> beg, <span class="kw4">const</span> CharT<span class="sy2">*</span> end <span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
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<div class="t-li1"><span class="t-li">1)</span> 公开成员函数，调用最终导出类的受保护虚成员函数 <code>do_hash</code> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 转换字符序列 <code>[beg, end)</code> 为整数值，该值对所有此本地环境中对照等价（ <span class="t-lc"><a href="cpp-locale-collate-compare.html">compare()</a></span> 返回 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> ）的字符串相同。对于二个不对照等价的字符串，其哈希相等的概率要非常小，近似 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu16">1.0</span><span class="sy2">/</span><a href="cpp-types-numeric_limits.html"><span class="kw344">std::<span class="me2">numeric_limits</span></span></a><span class="sy1"><</span><span class="kw4">unsigned</span> <span class="kw4">long</span><span class="sy1">></span><span class="sy4">::</span><span class="me2">max</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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<td>beg</td>
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<td>-</td>
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<td>指向要哈希的序列中首字符的指针</td>
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</tr>
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<td>end</td>
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<td>-</td>
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<td>要哈西的序列的尾后一位置指针</td>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
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<p>相对于对照顺序的哈希值。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h3>
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<p>若 <a href="cpp-string-basic_string-operator_cmp.html"><tt>basic_string::operator==</tt></a> 返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> ，则系统提供的本地环正常地不对照二个字符串为等价（ <span class="t-lc"><a href="cpp-locale-collate-compare.html">compare()</a></span> 不返回 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> ），但用户安装的 <span class="t-lc"><a href="cpp-locale-collate.html">std::collate</a></span> 平面可提供不同的对照规则，例如，它可以若字符串拥有相同的 Unicode 正常化形式，则对待字符串为等价。</p>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<p>演示具本地环境的无序容器</p>
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<div class="t-example-live-link"></div>
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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 <locale></span>
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<span class="co2">#include <unordered_set></span>
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<span class="kw1">struct</span> CollateHash <span class="br0">{</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">typename</span> CharT<span class="sy1">></span>
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<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> <a href="cpp-string-basic_string.html"><span class="kw1228">std::<span class="me2">basic_string</span></span></a><span class="sy1"><</span>CharT<span class="sy1">></span><span class="sy3">&</span> s<span class="br0">)</span> <span class="kw4">const</span>
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<span class="br0">{</span>
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<span class="kw1">return</span> <a href="cpp-locale-use_facet.html"><span class="kw1897">std::<span class="me2">use_facet</span></span></a><span class="sy1"><</span><a href="cpp-locale-collate.html"><span class="kw1943">std::<span class="me2">collate</span></span></a><span class="sy1"><</span>CharT<span class="sy1">>></span><span class="br0">(</span><a href="cpp-locale-locale.html"><span class="kw1894">std::<span class="me2">locale</span></span></a><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span>.<span class="me1">hash</span><span class="br0">(</span>
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<span class="sy3">&</span>s<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span>, <span class="sy3">&</span>s<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span> <span class="sy2">+</span> s.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span>
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<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">struct</span> CollateEq <span class="br0">{</span>
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<span class="kw1">template</span><span class="sy1"><</span><span class="kw1">typename</span> CharT<span class="sy1">></span>
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<span class="kw4">bool</span> operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span><span class="kw4">const</span> <a href="cpp-string-basic_string.html"><span class="kw1228">std::<span class="me2">basic_string</span></span></a><span class="sy1"><</span>CharT<span class="sy1">></span><span class="sy3">&</span> s1,
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<span class="kw4">const</span> <a href="cpp-string-basic_string.html"><span class="kw1228">std::<span class="me2">basic_string</span></span></a><span class="sy1"><</span>CharT<span class="sy1">></span><span class="sy3">&</span> s2<span class="br0">)</span> <span class="kw4">const</span>
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<span class="br0">{</span>
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<span class="kw1">return</span> <a href="cpp-locale-use_facet.html"><span class="kw1897">std::<span class="me2">use_facet</span></span></a><span class="sy1"><</span><a href="cpp-locale-collate.html"><span class="kw1943">std::<span class="me2">collate</span></span></a><span class="sy1"><</span>CharT<span class="sy1">>></span><span class="br0">(</span><a href="cpp-locale-locale.html"><span class="kw1894">std::<span class="me2">locale</span></span></a><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span>.<span class="me1">compare</span><span class="br0">(</span>
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<span class="sy3">&</span>s1<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span>, <span class="sy3">&</span>s1<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span> <span class="sy2">+</span> s1.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span>,
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<span class="sy3">&</span>s2<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span>, <span class="sy3">&</span>s2<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span> <span class="sy2">+</span> s2.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span>
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<span class="br0">)</span> <span class="sy1">==</span> <span class="nu0">0</span><span class="sy4">;</span>
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<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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std<span class="sy4">::</span><span class="me2">locale</span><span class="sy4">::</span><span class="me2">global</span><span class="br0">(</span><a href="cpp-locale-locale.html"><span class="kw1894">std::<span class="me2">locale</span></span></a><span class="br0">(</span><span class="st0">"en_US.utf8"</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1759">std::<span class="me2">wcout</span></span></a>.<span class="me1">imbue</span><span class="br0">(</span><a href="cpp-locale-locale.html"><span class="kw1894">std::<span class="me2">locale</span></span></a><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-container-unordered_set.html"><span class="kw1289">std::<span class="me2">unordered_set</span></span></a><span class="sy1"><</span><a href="cpp-string-basic_string.html"><span class="kw1232">std::<span class="me2">wstring</span></span></a>, CollateHash, CollateEq<span class="sy1">></span> s2 <span class="sy1">=</span> <span class="br0">{</span>L<span class="st0">"Foo"</span>, L<span class="st0">"Bar"</span><span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">for</span><span class="br0">(</span><span class="kw4">auto</span><span class="sy3">&</span> str<span class="sy4">:</span> s2<span class="br0">)</span>
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<a href="cpp-io-cout.html"><span class="kw1759">std::<span class="me2">wcout</span></span></a> <span class="sy1"><<</span> str <span class="sy1"><<</span> <span class="st0">' '</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">'<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>可能的输出：</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">Bar Foo</pre></div>
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</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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<table class="t-dsc-begin">
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<div class="t-dsc-member-div">
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<div><a href="cpp-string-basic_string-hash.html"><span class="t-lines"><span>std::hash<span class="t-dsc-small"><std::string></span></span><span>std::hash<span class="t-dsc-small"><std::u8string></span></span><span>std::hash<span class="t-dsc-small"><std::u16string></span></span><span>std::hash<span class="t-dsc-small"><std::u32string></span></span><span>std::hash<span class="t-dsc-small"><std::wstring></span></span><span>std::hash<span class="t-dsc-small"><std::pmr::string></span></span><span>std::hash<span class="t-dsc-small"><std::pmr::u8string></span></span><span>std::hash<span class="t-dsc-small"><std::pmr::u16string></span></span><span>std::hash<span class="t-dsc-small"><std::pmr::u32string></span></span><span>std::hash<span class="t-dsc-small"><std::pmr::wstring></span></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><span class="t-mark-rev t-since-cxx20">(C++20)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
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</div>
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<td>string 的散列支持<br />
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<span class="t-mark">(类模板特化)</span></td>
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</div>
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<div class="visualClear"></div>
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