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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::ranges::</span>count, <span style="font-size:0.7em; line-height:130%">std::ranges::</span>count_if</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,<br /></span>
<p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span class="kw1">class</span> T, <span class="kw1">class</span> Proj <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">identity</span> <span class="sy1">&gt;</span><br />
requires std<span class="sy4">::</span><span class="me2">indirect_binary_predicate</span><span class="sy1">&lt;</span>ranges<span class="sy4">::</span><span class="me2">equal_to</span>, std<span class="sy4">::</span><span class="me2">projected</span><span class="sy1">&lt;</span>I, Proj<span class="sy1">&gt;</span>,<br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span class="kw4">const</span> T<span class="sy2">*</span><span class="sy1">&gt;</span><br />
<span class="kw4">constexpr</span> std<span class="sy4">::</span><span class="me2">iter_difference_t</span><span class="sy1">&lt;</span>I<span class="sy1">&gt;</span><br /></p>
&nbsp; count<span class="br0">(</span> I first, S last, <span class="kw4">const</span> T<span class="sy3">&amp;</span> value, 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> T, <span class="kw1">class</span> Proj <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">identity</span> <span class="sy1">&gt;</span><br /></span>
<p>requires std<span class="sy4">::</span><span class="me2">indirect_binary_predicate</span><span class="sy1">&lt;</span>ranges<span class="sy4">::</span><span class="me2">equal_to</span>,<br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 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;</span>,<br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span class="kw4">const</span> T<span class="sy2">*</span><span class="sy1">&gt;</span><br /></p>
<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">range_difference_t</span><span class="sy1">&lt;</span>R<span class="sy1">&gt;</span> count<span class="br0">(</span> R<span class="sy3">&amp;&amp;</span> r, <span class="kw4">const</span> T<span class="sy3">&amp;</span> value, 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><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,<br /></span>
<p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; <span class="kw1">class</span> Proj <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">identity</span>,<br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; std<span class="sy4">::</span><span class="me2">indirect_unary_predicate</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> Pred <span class="sy1">&gt;</span><br />
<span class="kw4">constexpr</span> std<span class="sy4">::</span><span class="me2">iter_difference_t</span><span class="sy1">&lt;</span>I<span class="sy1">&gt;</span><br /></p>
&nbsp; count_if<span class="br0">(</span> I first, S last, Pred pred <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span>, 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>(3)</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">indirect_unary_predicate</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> Pred <span class="sy1">&gt;</span><br />
<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">range_difference_t</span><span class="sy1">&lt;</span>R<span class="sy1">&gt;</span><br /></p>
&nbsp; count_if<span class="br0">(</span> R<span class="sy3">&amp;&amp;</span> r, Pred pred <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span>, 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>(4)</td>
<td><span class="t-mark-rev t-since-cxx20">(C++20 &#36215;)</span></td>
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<p>&#36820;&#22238;&#33539;&#22260; <code>[first, last)</code> &#20013;&#28385;&#36275;&#29305;&#23450;&#21028;&#21035;&#26631;&#20934;&#30340;&#30340;&#20803;&#32032;&#25968;&#12290;</p>
<div class="t-li1"><span class="t-li">1)</span> &#35745;&#25968;&#31561;&#20110; <code>value</code> &#30340;&#20803;&#32032;&#25968;&#12290;</div>
<div class="t-li1"><span class="t-li">3)</span> &#35745;&#25968;&#35859;&#35789; <code>p</code> &#23545;&#20854;&#36820;&#22238; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> &#30340;&#20803;&#32032;&#25968;&#12290;</div>
<div class="t-li1"><span class="t-li">2,4)</span> &#21516; <span class="t-v">(1,3)</span> &#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>&#27492;&#39029;&#38754;&#19978;&#25551;&#36848;&#30340;&#20223;&#20989;&#25968;&#23454;&#20307;&#26159; <i>niebloid</i> &#65292;&#21363;&#65306;</p>
<ul>
<li>&#35843;&#29992;&#23427;&#20204;&#20013;&#30340;&#20219;&#20309;&#19968;&#32773;&#26102;&#19981;&#21487;&#25351;&#23450;&#26174;&#24335;&#27169;&#26495;&#23454;&#21442;&#12290;</li>
<li>&#23427;&#20204;&#26080;&#19968;&#23545;<a href="cpp-language-adl.html">&#23454;&#21442;&#20381;&#36182;&#26597;&#25214;</a>&#21487;&#35265;&#12290;</li>
<li>&#22312;<a href="cpp-language-unqualified_lookup.html">&#36890;&#24120;&#26080;&#38480;&#23450;&#26597;&#25214;</a>&#23547;&#25214;&#20989;&#25968;&#35843;&#29992;&#36816;&#31639;&#31526;&#24038;&#20391;&#30340;&#21517;&#31216;&#25214;&#21040;&#23427;&#20204;&#20043;&#19968;&#26102;&#65292;&#23427;&#31105;&#27490;<a href="cpp-language-adl.html">&#23454;&#21442;&#20381;&#36182;&#26597;&#25214;</a>&#12290;</li>
</ul>
<p>&#23454;&#38469;&#19978;&#65292;&#23427;&#20204;&#33021;&#20197;&#20989;&#25968;&#23545;&#35937;&#65292;&#25110;&#20197;&#26576;&#20123;&#29305;&#27530;&#32534;&#35793;&#22120;&#25193;&#23637;&#23454;&#29616;&#12290;</p>
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">&#21442;&#25968;</span></h3>
<table class="t-par-begin">
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<td>first, last</td>
<td>-</td>
<td>&#35201;&#26816;&#39564;&#30340;&#20803;&#32032;&#33539;&#22260;</td>
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<tr class="t-par">
<td>r</td>
<td>-</td>
<td>&#35201;&#26816;&#39564;&#30340;&#20803;&#32032;&#33539;&#22260;</td>
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<tr class="t-par">
<td>value</td>
<td>-</td>
<td>&#35201;&#25628;&#32034;&#30340;&#20540;</td>
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<tr class="t-par">
<td>pred</td>
<td>-</td>
<td>&#24212;&#29992;&#21040;&#34987;&#25237;&#24433;&#20803;&#32032;&#30340;&#35859;&#35789;</td>
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<tr class="t-par">
<td>proj</td>
<td>-</td>
<td>&#24212;&#29992;&#21040;&#20803;&#32032;&#30340;&#25237;&#24433;</td>
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</table>
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">&#36820;&#22238;&#20540;</span></h3>
<p>&#33539;&#22260;&#20013;&#28385;&#36275;&#26465;&#20214;&#30340;&#20803;&#32032;&#25968;&#12290;</p>
<h3><span class="mw-headline" id=".E5.A4.8D.E6.9D.82.E5.BA.A6">&#22797;&#26434;&#24230;</span></h3>
<p>&#20934;&#30830;&#27604;&#36739;&#21644;&#24212;&#29992;&#25237;&#24433; <code>last</code> - <code>first</code> &#27425;&#12290;</p>
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">&#27880;&#35299;</span></h3>
<p>&#23545;&#20110;&#26080;&#20219;&#20309;&#21028;&#21035;&#26631;&#20934;&#30340;&#33539;&#22260;&#20013;&#30340;&#20803;&#32032;&#25968;&#65292;&#35265; <span class="t-lc">std::ranges::distance</span> &#12290;</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>
<table class="eq-fun-cpp-table">
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<th>&#29256;&#26412;&#19968;</th>
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<pre class="de1"><span class="kw1">struct</span> count_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> T, <span class="kw1">class</span> Proj <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">identity</span> <span class="sy1">&gt;</span>
requires std<span class="sy4">::</span><span class="me2">indirect_binary_predicate</span><span class="sy1">&lt;</span>ranges<span class="sy4">::</span><span class="me2">equal_to</span>, std<span class="sy4">::</span><span class="me2">projected</span><span class="sy1">&lt;</span>I, Proj<span class="sy1">&gt;</span>,
<span class="kw4">const</span> T<span class="sy2">*</span><span class="sy1">&gt;</span>
<span class="kw4">constexpr</span> std<span class="sy4">::</span><span class="me2">iter_difference_t</span><span class="sy1">&lt;</span>I<span class="sy1">&gt;</span>
operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span> I first, S last, <span class="kw4">const</span> T<span class="sy3">&amp;</span> value, 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>
std<span class="sy4">::</span><span class="me2">iter_difference_t</span><span class="sy1">&lt;</span>I<span class="sy1">&gt;</span> counter <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</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>
<span class="kw1">if</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>proj, <span class="sy2">*</span>first<span class="br0">)</span> <span class="sy1">==</span> value<span class="br0">)</span>
<span class="br0">{</span>
<span class="sy2">++</span>counter<span class="sy4">;</span>
<span class="br0">}</span>
<span class="br0">}</span>
<span class="kw1">return</span> counter<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> T, <span class="kw1">class</span> Proj <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">identity</span> <span class="sy1">&gt;</span>
requires std<span class="sy4">::</span><span class="me2">indirect_binary_predicate</span><span class="sy1">&lt;</span>ranges<span class="sy4">::</span><span class="me2">equal_to</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;</span>,
<span class="kw4">const</span> T<span class="sy2">*</span><span class="sy1">&gt;</span>
<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">range_difference_t</span><span class="sy1">&lt;</span>R<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, <span class="kw4">const</span> T<span class="sy3">&amp;</span> value, 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>, value, <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> count_fn count<span class="sy4">;</span></pre></div>
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<div class="cpp source-cpp">
<pre class="de1"><span class="kw1">struct</span> count_if_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">indirect_unary_predicate</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> Pred <span class="sy1">&gt;</span>
<span class="kw4">constexpr</span> std<span class="sy4">::</span><span class="me2">iter_difference_t</span><span class="sy1">&lt;</span>I<span class="sy1">&gt;</span>
operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span> I first, S last, Pred pred <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span>, 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>
std<span class="sy4">::</span><span class="me2">iter_difference_t</span><span class="sy1">&lt;</span>I<span class="sy1">&gt;</span> counter <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</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>
<span class="kw1">if</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>pred, <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="br0">)</span>
<span class="br0">{</span>
<span class="sy2">++</span>counter<span class="sy4">;</span>
<span class="br0">}</span>
<span class="br0">}</span>
<span class="kw1">return</span> counter<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">indirect_unary_predicate</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> Pred <span class="sy1">&gt;</span>
<span class="kw4">constexpr</span> ranges<span class="sy4">::</span><span class="me2">range_difference_t</span><span class="sy1">&lt;</span>R<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, Pred pred <span class="sy1">=</span> <span class="br0">{</span><span class="br0">}</span>, 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>,
<a href="cpp-utility-functional-ref.html"><span class="kw1069">std::<span class="me2">ref</span></span></a><span class="br0">(</span>pred<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> count_if_fn count_if<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">
<div class="t-example-live-link"></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;">
<div class="cpp source-cpp">
<pre class="de1"><span class="co2">#include &lt;algorithm&gt;</span>
<span class="co2">#include &lt;iostream&gt;</span>
<span class="co2">#include &lt;vector&gt;</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> 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="nu0">4</span>, <span class="nu0">3</span>, <span class="nu0">7</span>, <span class="nu0">8</span>, <span class="nu0">9</span>, <span class="nu0">10</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>
<span class="co1">// &#30830;&#23450; std::vector &#20013;&#26377;&#22810;&#23569;&#25972;&#25968;&#21305;&#37197;&#30446;&#26631;&#20540;&#12290;</span>
<span class="kw4">int</span> target1 <span class="sy1">=</span> <span class="nu0">3</span><span class="sy4">;</span>
<span class="kw4">int</span> target2 <span class="sy1">=</span> <span class="nu0">5</span><span class="sy4">;</span>
<span class="kw4">int</span> num_items1 <span class="sy1">=</span> ranges<span class="sy4">::</span><span class="me2">count</span><span class="br0">(</span>v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, v.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, target1<span class="br0">)</span><span class="sy4">;</span>
<span class="kw4">int</span> num_items2 <span class="sy1">=</span> ranges<span class="sy4">::</span><span class="me2">count</span><span class="br0">(</span>v, target2<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;number: &quot;</span> <span class="sy1">&lt;&lt;</span> target1 <span class="sy1">&lt;&lt;</span> <span class="st0">&quot; count: &quot;</span> <span class="sy1">&lt;&lt;</span> num_items1 <span class="sy1">&lt;&lt;</span> <span class="st0">&#39;<span class="es1">\n</span>&#39;</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;number: &quot;</span> <span class="sy1">&lt;&lt;</span> target2 <span class="sy1">&lt;&lt;</span> <span class="st0">&quot; count: &quot;</span> <span class="sy1">&lt;&lt;</span> num_items2 <span class="sy1">&lt;&lt;</span> <span class="st0">&#39;<span class="es1">\n</span>&#39;</span><span class="sy4">;</span>
<span class="co1">// &#29992; lambda &#34920;&#36798;&#24335;&#35745;&#25968;&#34987; 3 &#25972;&#38500;&#30340;&#20803;&#32032;&#12290;</span>
<span class="kw4">int</span> num_items3 <span class="sy1">=</span> ranges<span class="sy4">::</span><span class="me2">count_if</span><span class="br0">(</span>v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, v.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span>, <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">int</span> i<span class="br0">)</span><span class="br0">{</span><span class="kw1">return</span> i <span class="sy2">%</span> <span class="nu0">3</span> <span class="sy1">==</span> <span class="nu0">0</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;number divisible by three: &quot;</span> <span class="sy1">&lt;&lt;</span> num_items3 <span class="sy1">&lt;&lt;</span> <span class="st0">&#39;<span class="es1">\n</span>&#39;</span><span class="sy4">;</span>
<span class="co1">// &#29992; lambda &#34920;&#36798;&#24335;&#35745;&#25968;&#34987; 11 &#25972;&#38500;&#30340;&#20803;&#32032;&#12290;</span>
<span class="kw4">int</span> num_items11 <span class="sy1">=</span> ranges<span class="sy4">::</span><span class="me2">count_if</span><span class="br0">(</span>v, <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">int</span> i<span class="br0">)</span><span class="br0">{</span><span class="kw1">return</span> i <span class="sy2">%</span> <span class="nu0">11</span> <span class="sy1">==</span> <span class="nu0">0</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;number divisible by eleven: &quot;</span> <span class="sy1">&lt;&lt;</span> num_items11 <span class="sy1">&lt;&lt;</span> <span class="st0">&#39;<span class="es1">\n</span>&#39;</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div>
</div>
<p>&#36755;&#20986;&#65306;</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;">
<div class="text source-text">
<pre class="de1">number: 3 count: 2
number: 5 count: 0
number divisible by three: 3
number divisible by eleven: 0</pre></div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">&#21442;&#38405;</span></h3>
<table class="t-dsc-begin">
<tr class="t-dsc">
<td>
<div class="t-dsc-member-div">
<div><a href="cpp-iterator-ranges-distance.html"><span class="t-lines"><span>ranges::distance</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
</div>
</td>
<td>&#36820;&#22238;&#36845;&#20195;&#22120;&#19982;&#21736;&#20301;&#38388;&#30340;&#36317;&#31163;&#65292;&#25110;&#33539;&#22260;&#36215;&#22987;&#19982;&#32467;&#23614;&#38388;&#30340;&#36317;&#31163;<br />
<span class="t-mark">(niebloid)</span></td>
</tr>
<tr class="t-dsc">
<td>
<div class="t-dsc-member-div">
<div><a href="cpp-ranges-take_while_view.html"><span class="t-lines"><span>ranges::take_while_view</span><span>views::take_while</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
</div>
</td>
<td>&#30001;&#21478;&#19968; <a href="cpp-ranges-view.html"><code>view</code></a> &#30340;&#21040;&#39318;&#20010;&#35859;&#35789;&#36820;&#22238; <code>false</code> &#20026;&#27490;&#30340;&#36215;&#22987;&#20803;&#32032;&#32452;&#25104;&#30340; <a href="cpp-ranges-view.html"><code>view</code></a><br />
<span class="t-mark">(&#31867;&#27169;&#26495;)</span> <span class="t-mark">(&#33539;&#22260;&#36866;&#37197;&#22120;&#23545;&#35937;)</span></td>
</tr>
<tr class="t-dsc">
<td>
<div class="t-dsc-member-div">
<div><a href="cpp-algorithm-count.html"><span class="t-lines"><span>count</span><span>count_if</span></span></a></div>
</div>
</td>
<td>&#36820;&#22238;&#28385;&#36275;&#25351;&#23450;&#21028;&#21035;&#26631;&#20934;&#30340;&#20803;&#32032;&#25968;<br />
<span class="t-mark">(&#20989;&#25968;&#27169;&#26495;)</span></td>
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