76 lines
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76 lines
8.0 KiB
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<title>std::input_iterator</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_iterator_input_iterator 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>input_iterator</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-iterator.html">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><span class="kw1">class</span> I<span class="sy1">></span><br /></span>
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<p> concept input_iterator <span class="sy1">=</span><br />
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std<span class="sy4">::</span><span class="me2">input_or_output_iterator</span><span class="sy1"><</span>I<span class="sy1">></span> <span class="sy3">&&</span><br />
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std<span class="sy4">::</span><span class="me2">indirectly_readable</span><span class="sy1"><</span>I<span class="sy1">></span> <span class="sy3">&&</span><br />
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requires <span class="br0">{</span> <span class="kw1">typename</span> <span class="coMULTI">/*ITER_CONCEPT*/</span><span class="sy1"><</span>I<span class="sy1">></span><span class="sy4">;</span> <span class="br0">}</span> <span class="sy3">&&</span><br /></p>
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std<span class="sy4">::</span><span class="me2">derived_from</span><span class="sy1"><</span><span class="coMULTI">/*ITER_CONCEPT*/</span><span class="sy1"><</span>I<span class="sy1">></span>, <a href="cpp-iterator-iterator_tags.html"><span class="kw652">std::<span class="me2">input_iterator_tag</span></span></a><span class="sy1">></span><span class="sy4">;</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><code>input_iterator</code> 概念是 <a href="cpp-iterator-input_or_output_iterator.html"><code>input_or_output_iterator</code></a> 的细化，添加能读取被引用值的要求（经由 <a href="cpp-iterator-indirectly_readable.html"><code>indirectly_readable</code></a> ）和迭代器概念标签存在的要求。</p>
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<h3><span class="mw-headline" id=".E8.BF.AD.E4.BB.A3.E5.99.A8.E6.A6.82.E5.BF.B5.E7.A1.AE.E5.AE.9A">迭代器概念确定</span></h3>
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<p>此概念的定义通过仅用于阐释的别名模板 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*ITER_CONCEPT*/</span></span></span> 说明。</p>
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<p>为确定 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*ITER_CONCEPT*/</span><span class="sy1"><</span>I<span class="sy1">></span></span></span> ，令 <span class="t-c"><span class="mw-geshi cpp source-cpp">ITER_TRAITS<span class="sy1"><</span>I<span class="sy1">></span></span></span> 若特化 <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></span> 从主模板生成则指代 <span class="t-c"><span class="mw-geshi cpp source-cpp">I</span></span> ，否则指代 <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></span> ：</p>
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<ul>
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<li>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">ITER_TRAITS<span class="sy1"><</span>I<span class="sy1">></span><span class="sy4">::</span><span class="me2">iterator_concept</span></span></span> 合法并指名类型，则 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*ITER_CONCEPT*/</span><span class="sy1"><</span>I<span class="sy1">></span></span></span> 指代该类型。</li>
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<li>否则，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">ITER_TRAITS<span class="sy1"><</span>I<span class="sy1">></span><span class="sy4">::</span><span class="me2">iterator_category</span></span></span> 合法并指名类型，则 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*ITER_CONCEPT*/</span><span class="sy1"><</span>I<span class="sy1">></span></span></span> 指代该类型。</li>
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<li>否则，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></span> 从主模板生成，则 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*ITER_CONCEPT*/</span><span class="sy1"><</span>I<span class="sy1">></span></span></span> 指代 <span class="t-lc"><a href="cpp-iterator-iterator_tags.html">std::random_access_iterator_tag</a></span> 。</li>
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<li>否则 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*ITER_CONCEPT*/</span><span class="sy1"><</span>I<span class="sy1">></span></span></span> 不指代类型并导致替换失败。</li>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>不同于<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> 要求， <code>input_iterator</code> 概念不要求 <a href="cpp-concepts-equality_comparable.html"><code>equality_comparable</code></a> ，因为输入迭代器常与哨位比较。</p>
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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><a href="cpp-iterator-input_or_output_iterator.html"><span class="t-lines"><span>input_or_output_iterator</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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<td>指定该类型对象可以自增且可以解引用<br />
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<span class="t-mark">(概念)</span></td>
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