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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::ranges::</span>for_each</h1>
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<div id="contentSub"><span class="subpages">&lt; <a href="cpp.html">cpp</a>&lrm; | <a href="cpp-algorithm.html">algorithm</a>&lrm; | <a href="cpp-algorithm-ranges.html">ranges</a></span></div>
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<div>&#23450;&#20041;&#20110;&#22836;&#25991;&#20214; <code><a href="cpp-header-algorithm.html">&lt;algorithm&gt;</a></code></div>
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<div>&#35843;&#29992;&#31614;&#21517;</div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1">&lt;</span> std<span class="sy4">::</span><span class="me2">input_iterator</span> I, std<span class="sy4">::</span><span class="me2">sentinel_for</span><span class="sy1">&lt;</span>I<span class="sy1">&gt;</span> S, <span class="kw1">class</span> Proj <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">identity</span>,<br /></span>
<p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; std<span class="sy4">::</span><span class="me2">indirectly_unary_invocable</span><span class="sy1">&lt;</span>std<span class="sy4">::</span><span class="me2">projected</span><span class="sy1">&lt;</span>I, Proj<span class="sy1">&gt;&gt;</span> Fun <span class="sy1">&gt;</span><br /></p>
<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">for_each_result</span><span class="sy1">&lt;</span>I, Fun<span class="sy1">&gt;</span> for_each<span class="br0">(</span> I first, S last, Fun f, Proj proj <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span> <span class="br0">)</span><span class="sy4">;</span></div>
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<td>(1)</td>
<td><span class="t-mark-rev t-since-cxx20">(C++20 &#36215;)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1">&lt;</span> ranges<span class="sy4">::</span><span class="me2">input_range</span> R, <span class="kw1">class</span> Proj <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">identity</span>,<br /></span>
<p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; std<span class="sy4">::</span><span class="me2">indirectly_unary_invocable</span><span class="sy1">&lt;</span>std<span class="sy4">::</span><span class="me2">projected</span><span class="sy1">&lt;</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1">&lt;</span>R<span class="sy1">&gt;</span>, Proj<span class="sy1">&gt;&gt;</span> Fun <span class="sy1">&gt;</span><br />
<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">for_each_result</span><span class="sy1">&lt;</span>ranges<span class="sy4">::</span><span class="me2">borrowed_iterator_t</span><span class="sy1">&lt;</span>R<span class="sy1">&gt;</span>, Fun<span class="sy1">&gt;</span><br /></p>
for_each<span class="br0">(</span> R<span class="sy3">&amp;&amp;</span> r, Fun f, Proj proj <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span> <span class="br0">)</span><span class="sy4">;</span></div>
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<td>(2)</td>
<td><span class="t-mark-rev t-since-cxx20">(C++20 &#36215;)</span></td>
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<div>&#36741;&#21161;&#31867;&#22411;</div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1">&lt;</span> <span class="kw1">class</span> I, <span class="kw1">class</span> F <span class="sy1">&gt;</span><br />
<span class="kw1">using</span> for_each_result <span class="sy1">=</span> ranges<span class="sy4">::</span><span class="me2">in_fun_result</span><span class="sy1">&lt;</span>I, F<span class="sy1">&gt;</span><span class="sy4">;</span></span></div>
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<td>(3)</td>
<td><span class="t-mark-rev t-since-cxx20">(C++20 &#36215;)</span></td>
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<div class="t-li1"><span class="t-li">1)</span> &#23558;&#32473;&#23450;&#30340;&#20989;&#25968;&#23545;&#35937; <code>f</code> &#24212;&#29992;&#20110;&#33539;&#22260; <code>[first, last)</code> &#20013;&#27599;&#20010;&#36845;&#20195;&#22120;&#25237;&#24433;&#30340;&#20540;&#30340;&#32467;&#26524;&#65292;&#25353;&#39034;&#24207;&#25490;&#21015;&#12290;</div>
<div class="t-li1"><span class="t-li">2)</span> &#19982; <span class="t-v">(1)</span> &#30456;&#21516;&#65292;&#20294;&#20197; <code>r</code> &#20026;&#28304;&#33539;&#22260;&#65292;&#22914;&#21516;&#20197; <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> &#20026; <code>first</code> &#24182;&#20197; <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> &#20026; <code>last</code> &#12290;</div>
<p>&#23545;&#20110;&#20004;&#20010;&#37325;&#36733;&#65292;&#22914;&#26524;&#36845;&#20195;&#22120;&#30340;&#31867;&#22411;&#26159;&#21487;&#21464;&#30340;&#65292;&#21017; <code>f</code> &#21487;&#33021;&#20250;&#35299;&#24341;&#29992;&#30340;&#36845;&#20195;&#22120;&#21435;&#20462;&#25913;&#33539;&#22260;&#20013;&#30340;&#20803;&#32032;&#12290;&#22914;&#26524; <code>f</code> &#20250;&#36820;&#22238;&#32467;&#26524;&#65292;&#21017;&#24573;&#30053;&#27492;&#32467;&#26524;&#12290;</p>
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">&#21442;&#25968;</span></h3>
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<td>first, last</td>
<td>-</td>
<td>&#20195;&#34920;&#35201;&#24212;&#29992;&#20989;&#25968;&#21040;&#30340;&#33539;&#22260;&#30340;&#36845;&#20195;&#22120;-&#21736;&#20301;&#23545;</td>
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<td>r</td>
<td>-</td>
<td>&#35201;&#23558;&#20989;&#25968;&#24212;&#29992;&#21040;&#30340;&#20803;&#32032;&#33539;&#22260;</td>
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<td>f</td>
<td>-</td>
<td>&#24212;&#29992;&#21040;&#25237;&#24433;&#21518;&#33539;&#22260;&#30340;&#20803;&#32032;</td>
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<td>proj</td>
<td>-</td>
<td>&#24212;&#29992;&#33539;&#22260;&#30340;&#25237;&#24433;</td>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">&#36820;&#22238;&#20540;</span></h3>
<p><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">{</span>std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">next</span><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>first<span class="br0">)</span>, last<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></span></p>
<h3><span class="mw-headline" id=".E5.A4.8D.E6.9D.82.E5.BA.A6">&#22797;&#26434;&#24230;</span></h3>
<p>&#20934;&#30830;&#24212;&#29992; <code>last</code> - <code>first</code> &#27425; <code>f</code> &#21644; <code>proj</code></p>
<h3><span class="mw-headline" id=".E5.8F.AF.E8.83.BD.E7.9A.84.E5.AE.9E.E7.8E.B0">&#21487;&#33021;&#30340;&#23454;&#29616;</span></h3>
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<pre class="de1"><span class="kw1">struct</span> for_each_fn <span class="br0">{</span>
<span class="kw1">template</span><span class="sy1">&lt;</span>std<span class="sy4">::</span><span class="me2">input_iterator</span> I, std<span class="sy4">::</span><span class="me2">sentinel_for</span><span class="sy1">&lt;</span>I<span class="sy1">&gt;</span> S, <span class="kw1">class</span> Proj <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">identity</span>,
std<span class="sy4">::</span><span class="me2">indirectly_unary_invocable</span><span class="sy1">&lt;</span>std<span class="sy4">::</span><span class="me2">projected</span><span class="sy1">&lt;</span>I, Proj<span class="sy1">&gt;&gt;</span> Fun<span class="sy1">&gt;</span>
<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">for_each_result</span><span class="sy1">&lt;</span>I, Fun<span class="sy1">&gt;</span>
operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span>I first, S last, Fun f, Proj proj <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span><span class="br0">)</span> <span class="kw4">const</span>
<span class="br0">{</span>
<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>
<a href="cpp-utility-functional-invoke.html"><span class="kw1058">std::<span class="me2">invoke</span></span></a><span class="br0">(</span>f, <a href="cpp-utility-functional-invoke.html"><span class="kw1058">std::<span class="me2">invoke</span></span></a><span class="br0">(</span>proj, <span class="sy2">*</span>first<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span>
<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>
<span class="br0">}</span>
<span class="kw1">template</span><span class="sy1">&lt;</span>ranges<span class="sy4">::</span><span class="me2">input_range</span> R, <span class="kw1">class</span> Proj <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">identity</span>,
std<span class="sy4">::</span><span class="me2">indirectly_unary_invocable</span><span class="sy1">&lt;</span>std<span class="sy4">::</span><span class="me2">projected</span><span class="sy1">&lt;</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1">&lt;</span>R<span class="sy1">&gt;</span>, Proj<span class="sy1">&gt;&gt;</span> Fun<span class="sy1">&gt;</span>
<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">for_each_result</span><span class="sy1">&lt;</span>ranges<span class="sy4">::</span><span class="me2">borrowed_iterator_t</span><span class="sy1">&lt;</span>R<span class="sy1">&gt;</span>, Fun<span class="sy1">&gt;</span>
operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span>R<span class="sy3">&amp;&amp;</span> r, Fun f, Proj proj <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span><span class="br0">)</span> <span class="kw4">const</span>
<span class="br0">{</span>
<span class="kw1">return</span> <span class="br0">(</span><span class="sy2">*</span>this<span class="br0">)</span><span class="br0">(</span>ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>r<span class="br0">)</span>, ranges<span class="sy4">::</span><span class="me2">end</span><span class="br0">(</span>r<span class="br0">)</span>, std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>f<span class="br0">)</span>, <a href="cpp-utility-functional-ref.html"><span class="kw1069">std::<span class="me2">ref</span></span></a><span class="br0">(</span>proj<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span>
<span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">inline</span> <span class="kw4">constexpr</span> for_each_fn for_each<span class="sy4">;</span></pre></div>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">&#31034;&#20363;</span></h3>
<div class="t-example">
<p>&#19979;&#36848;&#30340;&#31034;&#20363;&#29992; <a href="cpp-language-lambda.html">lambda &#34920;&#36798;&#24335;</a>&#36882;&#22686; <code>vector</code> &#25152;&#26377;&#30340;&#20803;&#32032;&#65292;&#28982;&#21518;&#29992;&#20989;&#25968;&#23545;&#35937;&#20013;&#37325;&#36733;&#30340; <code>operator()</code> &#35745;&#31639;&#23427;&#20204;&#30340;&#21644;&#12290;&#27880;&#24847;&#65292;&#35201;&#35745;&#31639;&#24635;&#21644;&#30340;&#35805;&#65292;&#24314;&#35758;&#20351;&#29992;&#19987;&#29992;&#30340;&#31639;&#27861; <span class="t-lc"><a href="cpp-algorithm-accumulate.html">std::accumulate</a></span> &#12290;</p>
<div class="t-example-live-link"></div>
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<div class="cpp source-cpp">
<pre class="de1"><span class="co2">#include &lt;algorithm&gt;</span>
<span class="co2">#include &lt;cassert&gt;</span>
<span class="co2">#include &lt;iostream&gt;</span>
<span class="co2">#include &lt;string&gt;</span>
<span class="co2">#include &lt;utility&gt;</span>
<span class="co2">#include &lt;vector&gt;</span>
<span class="kw1">struct</span> Sum
<span class="br0">{</span>
<span class="kw4">void</span> operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span><span class="kw4">int</span> n<span class="br0">)</span> <span class="br0">{</span> sum <span class="sy2">+</span><span class="sy1">=</span> n<span class="sy4">;</span> <span class="br0">}</span>
<span class="kw4">int</span> sum<span class="br0">{</span><span class="nu0">0</span><span class="br0">}</span><span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1">&lt;</span><span class="kw4">int</span><span class="sy1">&gt;</span> nums<span class="br0">{</span><span class="nu0">3</span>, <span class="nu0">4</span>, <span class="nu0">2</span>, <span class="nu0">8</span>, <span class="nu0">15</span>, <span class="nu0">267</span><span class="br0">}</span><span class="sy4">;</span>
<span class="kw4">auto</span> print <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">const</span> <span class="kw4">auto</span><span class="sy3">&amp;</span> n<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">&lt;&lt;</span> <span class="st0">&#39; &#39;</span> <span class="sy1">&lt;&lt;</span> n<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">namespace</span> ranges <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">;</span>
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;before:&quot;</span><span class="sy4">;</span>
ranges<span class="sy4">::</span><span class="me2">for_each</span><span class="br0">(</span><a href="cpp-utility-as_const.html"><span class="kw1121">std::<span class="me2">as_const</span></span></a><span class="br0">(</span>nums<span class="br0">)</span>, print<span class="br0">)</span><span class="sy4">;</span>
print<span class="br0">(</span><span class="st0">&#39;<span class="es1">\n</span>&#39;</span><span class="br0">)</span><span class="sy4">;</span>
ranges<span class="sy4">::</span><span class="me2">for_each</span><span class="br0">(</span>nums, <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">int</span><span class="sy3">&amp;</span> n<span class="br0">)</span><span class="br0">{</span> <span class="sy2">++</span>n<span class="sy4">;</span> <span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
<span class="co1">// &#23545;&#27599;&#20010;&#25968;&#35843;&#29992; Sum::operator()</span>
<span class="kw4">auto</span> <span class="br0">[</span>i, s<span class="br0">]</span> <span class="sy1">=</span> ranges<span class="sy4">::</span><span class="me2">for_each</span><span class="br0">(</span>nums.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, nums.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, Sum<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
<a href="cpp-error-assert.html"><span class="kw774">assert</span></a><span class="br0">(</span>i <span class="sy1">==</span> nums.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;after: &quot;</span><span class="sy4">;</span>
ranges<span class="sy4">::</span><span class="me2">for_each</span><span class="br0">(</span>nums.<span class="me1">cbegin</span><span class="br0">(</span><span class="br0">)</span>, nums.<span class="me1">cend</span><span class="br0">(</span><span class="br0">)</span>, print<span class="br0">)</span><span class="sy4">;</span>
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;<span class="es1">\n</span>&quot;</span> <span class="st0">&quot;sum: &quot;</span> <span class="sy1">&lt;&lt;</span> s.<span class="me1">sum</span> <span class="sy1">&lt;&lt;</span> <span class="st0">&#39;<span class="es1">\n</span>&#39;</span><span class="sy4">;</span>
<span class="kw1">using</span> pair <span class="sy1">=</span> <a href="cpp-utility-pair.html"><span class="kw1096">std::<span class="me2">pair</span></span></a><span class="sy1">&lt;</span><span class="kw4">int</span>, <a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">&gt;</span><span class="sy4">;</span>
<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1">&lt;</span>pair<span class="sy1">&gt;</span> pairs<span class="br0">{</span><span class="br0">{</span><span class="nu0">1</span>,<span class="st0">&quot;one&quot;</span><span class="br0">}</span>, <span class="br0">{</span><span class="nu0">2</span>,<span class="st0">&quot;two&quot;</span><span class="br0">}</span>, <span class="br0">{</span><span class="nu0">3</span>,<span class="st0">&quot;three&quot;</span><span class="br0">}</span><span class="br0">}</span><span class="sy4">;</span>
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;project the pair::first: &quot;</span><span class="sy4">;</span>
ranges<span class="sy4">::</span><span class="me2">for_each</span><span class="br0">(</span>pairs, print, <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">const</span> pair<span class="sy3">&amp;</span> p<span class="br0">)</span> <span class="br0">{</span> <span class="kw1">return</span> p.<span class="me1">first</span><span class="sy4">;</span> <span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;<span class="es1">\n</span>&quot;</span> <span class="st0">&quot;project the pair::second:&quot;</span><span class="sy4">;</span>
ranges<span class="sy4">::</span><span class="me2">for_each</span><span class="br0">(</span>pairs, print, <span class="sy3">&amp;</span>pair<span class="sy4">::</span><span class="me2">second</span><span class="br0">)</span><span class="sy4">;</span>
print<span class="br0">(</span><span class="st0">&#39;<span class="es1">\n</span>&#39;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div>
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<p>&#36755;&#20986;&#65306;</p>
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<pre class="de1">before: 3 4 2 8 15 267
after: 4 5 3 9 16 268
sum: 305
project the pair::first: 1 2 3
project the pair::second: one two tree</pre></div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">&#21442;&#38405;</span></h3>
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<td><a href="cpp-language-range-for.html">&#33539;&#22260; <code>for</code> &#24490;&#29615;</a><span class="t-mark-rev t-since-cxx11">(C++11)</span></td>
<td>&#25191;&#34892;&#33539;&#22260;&#19978;&#30340;&#24490;&#29615;</td>
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<td>
<div class="t-dsc-member-div">
<div><a href="cpp-algorithm-ranges-transform.html"><span class="t-lines"><span>ranges::transform</span></span></a></div>
<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>
<td>&#23558;&#19968;&#20010;&#20989;&#25968;&#24212;&#29992;&#20110;&#26576;&#19968;&#33539;&#22260;&#30340;&#21508;&#20010;&#20803;&#32032;<br />
<span class="t-mark">(niebloid)</span></td>
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<td>
<div class="t-dsc-member-div">
<div><a href="cpp-algorithm-ranges-for_each_n.html"><span class="t-lines"><span>ranges::for_each_n</span></span></a></div>
<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>
<td>&#24212;&#29992;&#20989;&#25968;&#23545;&#35937;&#21040;&#24207;&#21015;&#30340;&#39318; n &#20010;&#20803;&#32032;<br />
<span class="t-mark">(niebloid)</span></td>
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<tr class="t-dsc">
<td>
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<div><a href="cpp-algorithm-for_each.html"><span class="t-lines"><span>for_each</span></span></a></div>
</div>
</td>
<td>&#24212;&#29992;&#20989;&#25968;&#21040;&#33539;&#22260;&#20013;&#30340;&#20803;&#32032;<br />
<span class="t-mark">(&#20989;&#25968;&#27169;&#26495;)</span></td>
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