138 lines
15 KiB
HTML
138 lines
15 KiB
HTML
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<title>std::iterator_traits<std::common_iterator></title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_iterator_common_iterator_iterator_traits skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>iterator_traits<small><std::common_iterator></small></h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-iterator.html">iterator</a>‎ | <a href="cpp-iterator-common_iterator.html">common iterator</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-iterator.html"><iterator></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> std<span class="sy4">::</span><span class="me2">input_iterator</span> I, <span class="kw1">class</span> S <span class="sy1">></span><br />
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<span class="kw1">struct</span> iterator_traits<span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">common_iterator</span><span class="sy1"><</span>I, S<span class="sy1">>></span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<p>提供对于 <span class="t-lc">std::common_iterator</span> 类型的属性的统一接口。</p>
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<h3><span class="mw-headline" id=".E6.88.90.E5.91.98.E7.B1.BB.E5.9E.8B">成员类型</span></h3>
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<td>成员类型</td>
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<td>定义</td>
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<td><code>iterator_concept</code></td>
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<td><span class="t-lc"><a href="cpp-iterator-iterator_tags.html">std::forward_iterator_tag</a></span> ，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">I</span></span> 实现 <span class="t-lc">std::forward_iterator</span> ；<br />
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否则为 <span class="t-lc"><a href="cpp-iterator-iterator_tags.html">std::input_iterator_tag</a></span></td>
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<td><code>iterator_category</code></td>
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<td><span class="t-lc"><a href="cpp-iterator-iterator_tags.html">std::forward_iterator_tag</a></span> ，若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>I<span class="sy1">></span>​<span class="sy4">::</span>​iterator_category</span></span> 合法并指代实现 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">derived_from</span><span class="sy1"><</span><a href="cpp-iterator-iterator_tags.html"><span class="kw654">std::<span class="me2">forward_iterator_tag</span></span></a><span class="sy1">></span></span></span> 的类型；<br />
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否则为 <span class="t-lc"><a href="cpp-iterator-iterator_tags.html">std::input_iterator_tag</a></span></td>
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<td><code>value_type</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">iter_value_t</span><span class="sy1"><</span>I<span class="sy1">></span></span></span></td>
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<td><code>difference_type</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">iter_difference_t</span><span class="sy1"><</span>I<span class="sy1">></span></span></span></td>
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<td><code>pointer</code></td>
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<td>表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">c.<span class="me1">operator</span><span class="sy2">-</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span></span></span> 的类型，若它为良构，其中 <span class="t-c"><span class="mw-geshi cpp source-cpp">c</span></span> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">const</span> std<span class="sy4">::</span><span class="me2">common_iterator</span><span class="sy1"><</span>I, S<span class="sy1">></span></span></span> 类型左值；<br />
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否则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span></td>
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<td><code>reference</code></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">iter_reference_t</span><span class="sy1"><</span>I<span class="sy1">></span></span></span></td>
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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-live-link"></div>
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <vector></span>
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<span class="co2">#include <iterator></span>
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<span class="co2">#include <type_traits></span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a> v<span class="br0">{</span><span class="nu0">1</span>,<span class="nu0">2</span>,<span class="nu0">3</span>,<span class="nu0">4</span><span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">using</span> CV <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">common_iterator</span><span class="sy1"><</span>
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std<span class="sy4">::</span><span class="me2">counted_iterator</span><span class="sy1"><</span><a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span><span class="sy4">::</span><span class="me2">iterator</span><span class="sy1">></span>,
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std<span class="sy4">::</span><span class="me2">default_sentinel_t</span><span class="sy1">></span><span class="sy4">;</span>
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CV i <span class="br0">{</span> std<span class="sy4">::</span><span class="me2">counted_iterator</span> <span class="br0">{</span> v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, <span class="nu0">3</span> <span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">using</span> TRCV <span class="sy1">=</span> <a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>decltype<span class="br0">(</span>i<span class="br0">)</span><span class="sy1">></span><span class="sy4">;</span>
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static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw588">std::<span class="me2">is_same</span></span></a><span class="sy1"><</span>TRCV<span class="sy4">::</span><span class="me2">iterator_concept</span>, <a href="cpp-iterator-iterator_tags.html"><span class="kw654">std::<span class="me2">forward_iterator_tag</span></span></a><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw588">std::<span class="me2">is_same</span></span></a><span class="sy1"><</span>TRCV<span class="sy4">::</span><span class="me2">iterator_category</span>, <a href="cpp-iterator-iterator_tags.html"><span class="kw654">std::<span class="me2">forward_iterator_tag</span></span></a><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw588">std::<span class="me2">is_same</span></span></a><span class="sy1"><</span>TRCV<span class="sy4">::</span><span class="me2">value_type</span>, <span class="kw4">int</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw588">std::<span class="me2">is_same</span></span></a><span class="sy1"><</span>TRCV<span class="sy4">::</span><span class="me2">difference_type</span>, <a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span><span class="sy4">::</span><span class="me2">difference_type</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw588">std::<span class="me2">is_same</span></span></a><span class="sy1"><</span>TRCV<span class="sy4">::</span><span class="me2">pointer</span>, decltype<span class="br0">(</span>i.<span class="me1">operator</span><span class="sy2">-</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw588">std::<span class="me2">is_same</span></span></a><span class="sy1"><</span>TRCV<span class="sy4">::</span><span class="me2">reference</span>, <span class="kw4">int</span><span class="sy3">&</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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CV s <span class="br0">{</span> std<span class="sy4">::</span><span class="me2">default_sentinel</span> <span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">using</span> TRCS <span class="sy1">=</span> <a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>decltype<span class="br0">(</span>s<span class="br0">)</span><span class="sy1">></span><span class="sy4">;</span>
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static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw588">std::<span class="me2">is_same</span></span></a><span class="sy1"><</span>TRCS<span class="sy4">::</span><span class="me2">iterator_concept</span>, <a href="cpp-iterator-iterator_tags.html"><span class="kw654">std::<span class="me2">forward_iterator_tag</span></span></a><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw588">std::<span class="me2">is_same</span></span></a><span class="sy1"><</span>TRCS<span class="sy4">::</span><span class="me2">iterator_category</span>, <a href="cpp-iterator-iterator_tags.html"><span class="kw654">std::<span class="me2">forward_iterator_tag</span></span></a><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw588">std::<span class="me2">is_same</span></span></a><span class="sy1"><</span>TRCS<span class="sy4">::</span><span class="me2">value_type</span>, <span class="kw4">int</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw588">std::<span class="me2">is_same</span></span></a><span class="sy1"><</span>TRCS<span class="sy4">::</span><span class="me2">difference_type</span>, <a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span><span class="sy4">::</span><span class="me2">difference_type</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw588">std::<span class="me2">is_same</span></span></a><span class="sy1"><</span>TRCS<span class="sy4">::</span><span class="me2">pointer</span>, decltype<span class="br0">(</span>s.<span class="me1">operator</span><span class="sy2">-</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw588">std::<span class="me2">is_same</span></span></a><span class="sy1"><</span>TRCS<span class="sy4">::</span><span class="me2">reference</span>, <span class="kw4">int</span><span class="sy3">&</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span></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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-iterator-iterator_traits.html"><span class="t-lines"><span>iterator_traits</span></span></a></div>
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</div>
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</td>
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<td>为迭代器各项性质提供统一接口<br />
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<span class="t-mark">(类模板)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-iterator-common_iterator-incrementable_traits.html"><span class="t-lines"><span>std::incrementable_traits<span class="t-dsc-small"><std::common_iterator></span></span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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</div>
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</td>
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<td>计算 <span class="t-lc">std::common_iterator</span> 类型的关联差类型<br />
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<span class="t-mark">(类模板特化)</span></td>
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