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<title>std::experimental::ranges::for_each</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_experimental_ranges_algorithm_for_each 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::experimental::ranges::</span>for_each</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-experimental.html">experimental</a>‎ | <a href="cpp-experimental-ranges.html">ranges</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-experimental-ranges-algorithm.html"><experimental/ranges/algorithm></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> InputIterator I, Sentinel<span class="sy1"><</span>I<span class="sy1">></span> S, <span class="kw1">class</span> Proj <span class="sy1">=</span> ranges<span class="sy4">::</span><span class="me2">identity</span>,<br /></span>
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<p> IndirectUnaryInvocable<span class="sy1"><</span>projected<span class="sy1"><</span>I, Proj<span class="sy1">>></span> Fun <span class="sy1">></span><br />
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ranges<span class="sy4">::</span><span class="me2">tagged_pair</span><span class="sy1"><</span>tag<span class="sy4">::</span><span class="me2">in</span><span class="br0">(</span>I<span class="br0">)</span>, tag<span class="sy4">::</span><span class="me2">fun</span><span class="br0">(</span>Fun<span class="br0">)</span><span class="sy1">></span><br /></p>
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for_each<span class="br0">(</span>I first, S last, Fun f, Proj proj <span class="sy1">=</span> Proj<span class="br0">{</span><span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span></div>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-ranges-ts t-mark-ts">(范围 TS)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> InputRange R, <span class="kw1">class</span> Proj <span class="sy1">=</span> ranges<span class="sy4">::</span><span class="me2">identity</span>,<br /></span>
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<p> IndirectUnaryInvocable<span class="sy1"><</span>projected<span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span>R<span class="sy1">></span>, Proj<span class="sy1">>></span> Fun <span class="sy1">></span><br />
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ranges<span class="sy4">::</span><span class="me2">tagged_pair</span><span class="sy1"><</span>tag<span class="sy4">::</span><span class="me2">in</span><span class="br0">(</span>ranges<span class="sy4">::</span><span class="me2">safe_iterator_t</span><span class="sy1"><</span>R<span class="sy1">></span><span class="br0">)</span>, tag<span class="sy4">::</span><span class="me2">fun</span><span class="br0">(</span>Fun<span class="br0">)</span><span class="sy1">></span><br /></p>
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for_each<span class="br0">(</span>R<span class="sy3">&&</span> r, Fun f, Proj proj <span class="sy1">=</span> Proj<span class="br0">{</span><span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span></div>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-ranges-ts t-mark-ts">(范围 TS)</span></td>
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<div class="t-li1"><span class="t-li">1)</span> 按顺序，调用给定的函数对象 <code>f</code> 到在解引用范围 <code>[first, last)</code> 中的每个迭代器时调用的投影 <code>proj</code> 的结果（即 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">invoke</span><span class="br0">(</span>f, ranges<span class="sy4">::</span><span class="me2">invoke</span><span class="br0">(</span>proj, <span class="sy2">*</span>i<span class="br0">)</span><span class="br0">)</span></span></span> ）。</div>
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<div class="t-li1"><span class="t-li">2)</span> 同 <span class="t-v">(1)</span> ，但以 <code>r</code> 为源范围，如同以 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>r<span class="br0">)</span></span></span> 为 <code>first</code> 并以 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">end</span><span class="br0">(</span>r<span class="br0">)</span></span></span> 为 <code>last</code> 。</div>
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<p>对于两个重载，若迭代器类型可变，则 <code>f</code> 可以通过解引用后的迭代器修改范围的元素。若 <code>f</code> 返回结果，则湖绿结果。</p>
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<p>不同于另外的算法，不允许 <code>for_each</code> 复制序列中的元素，即使它们为可平凡复制。</p>
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<p>不同于 <span class="t-lc"><a href="cpp-algorithm-for_each.html">std::for_each</a></span> （它只要求<a href="cpp-named_req-MoveConstructible.html"><span style="font-style:italic">可移动构造</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(MoveConstructible)</span></a> ），这些函数要求 <code>Fun</code> 实现 <a href="cpp-experimental-ranges-concepts-CopyConstructible.html"><code>CopyConstructible</code></a> 。</p>
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<p>尽管声明描述如上，算法声明的模板形参的实际数量和顺序是未指定的。从而若在调用算法时使用显式模板实参，则程序很可能不可移植。</p>
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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>first, last</td>
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<td>-</td>
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<td>要应用函数到的范围</td>
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<tr class="t-par">
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<td>r</td>
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<td>-</td>
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<td>要应用函数到的范围</td>
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<td>f</td>
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<td>-</td>
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<td>应用到每个投影后的范围中元素的可调用对象</td>
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<tr class="t-par">
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<td>proj</td>
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<td>-</td>
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<td>应用到元素的投影</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>含有列二个成员的 <code>tagged_pair</code> ：</p>
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<ul>
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<li>第一成员带标签 <code>tag::in</code> ，是源范围的尾后迭代器（即比较等于哨位 <code>last</code> 的 <code>I</code> 类型迭代器）。</li>
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<li>第二成员带标签 <code>tag::fun</code> ，（在该函数对象的所有应用后）从 <code>std::move(f)</code> 初始化。</li>
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</ul>
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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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<p>准确应用 <code>last</code> - <code>first</code> 次 <code>f</code> 和 <code>proj</code> 。</p>
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<h3><span class="mw-headline" id=".E5.8F.AF.E8.83.BD.E7.9A.84.E5.AE.9E.E7.8E.B0">可能的实现</span></h3>
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<div class="cpp source-cpp">
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<pre class="de1"><span class="kw1">template</span><span class="sy1"><</span> InputIterator I, Sentinel<span class="sy1"><</span>I<span class="sy1">></span> S, <span class="kw1">class</span> Proj <span class="sy1">=</span> ranges<span class="sy4">::</span><span class="me2">identity</span>,
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IndirectUnaryInvocable<span class="sy1"><</span><a href="cpp-experimental-ranges-iterator-projected.html"><span class="kw2597">ranges::<span class="me2">projected</span></span></a><span class="sy1"><</span>I, Proj<span class="sy1">>></span> Fun <span class="sy1">></span>
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<span class="kw4">auto</span> for_each<span class="br0">(</span>I first, S last, Fun f, Proj proj <span class="sy1">=</span> Proj<span class="br0">{</span><span class="br0">}</span><span class="br0">)</span>
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<span class="sy2">-</span><span class="sy1">></span> ranges<span class="sy4">::</span><span class="me2">tagged_pair</span><span class="sy1"><</span>tag<span class="sy4">::</span><span class="me2">in</span><span class="br0">(</span>I<span class="br0">)</span>, tag<span class="sy4">::</span><span class="me2">fun</span><span class="br0">(</span>Fun<span class="br0">)</span><span class="sy1">></span>
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<span class="br0">{</span>
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<span class="kw1">for</span><span class="br0">(</span><span class="sy4">;</span> first <span class="sy3">!</span><span class="sy1">=</span> last<span class="sy4">;</span> <span class="sy2">++</span>first<span class="br0">)</span> <span class="br0">{</span>
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ranges<span class="sy4">::</span><span class="me2">invoke</span><span class="br0">(</span>f, ranges<span class="sy4">::</span><span class="me2">invoke</span><span class="br0">(</span>proj, <span class="sy2">*</span>first<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw1">return</span> <span class="br0">{</span>std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>first<span class="br0">)</span>, std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>f<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=".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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<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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<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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<td>
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<div class="t-dsc-member-div">
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<div><a href="https://zh.cppreference.com/mwiki/index.php?title=cpp/experimental/ranges/algorithm/transform&action=edit&redlink=1" class="new" title="cpp/experimental/ranges/algorithm/transform（页面不存在）"><span class="t-lines"><span>transform</span></span></a></div>
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</div>
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<td>应用一个函数到元素范围<br />
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<span class="t-mark">(函数模板)</span></td>
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<td><a href="cpp-language-range-for.html">范围 <code>for</code> 循环</a><span class="t-mark-rev t-since-cxx11">(C++11)</span></td>
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<td>执行范围上的循环</td>
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</tr>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-algorithm-for_each.html"><span class="t-lines"><span>for_each</span></span></a></div>
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</div>
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</td>
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<td>应用函数到范围中的元素<br />
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<span class="t-mark">(函数模板)</span></td>
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</tr>
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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-algorithm-for_each_n.html"><span class="t-lines"><span>for_each_n</span></span></a></div>
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<div><span class="t-lines"><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>
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<td>应用一个函数对象到序列的前 n 个元素<br />
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<span class="t-mark">(函数模板)</span></td>
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<div class="visualClear"></div>
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