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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::weak_ptr&lt;T&gt;::</span>use_count</h1>
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<div id="contentSub"><span class="subpages">&lt; <a href="cpp.html">cpp</a>&lrm; | <a href="cpp-memory.html">memory</a>&lrm; | <a href="cpp-memory-weak_ptr.html">weak ptr</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span> use_count<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 &#36215;)</span></td>
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<p>&#36820;&#22238;&#20849;&#20139;&#34987;&#31649;&#29702;&#23545;&#35937;&#25152;&#26377;&#26435;&#30340; <code>shared_ptr</code> &#23454;&#20363;&#25968;&#37327;&#65292;&#25110; <span class="t-c"><span class="mw-geshi cpp source-cpp">&#8203;<span class="nu0">0</span>&#8203;</span></span> &#65292;&#33509;&#34987;&#31649;&#29702;&#23545;&#35937;&#24050;&#34987;&#21024;&#38500;&#65292;&#21363; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> &#20026;&#31354;&#12290;</p>
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">&#21442;&#25968;</span></h3>
<p>&#65288;&#26080;&#65289;</p>
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">&#36820;&#22238;&#20540;</span></h3>
<p>&#22312;&#35843;&#29992;&#30340;&#30636;&#38388;&#20849;&#20139;&#34987;&#31649;&#29702;&#23545;&#35937;&#25152;&#26377;&#26435;&#30340; <code>shared_ptr</code> &#23454;&#20363;&#25968;&#37327;&#12290;</p>
<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">&#27880;&#24847;</span></h3>
<p><span class="t-lc"><a href="cpp-memory-weak_ptr-expired.html">expired()</a></span> &#21487;&#33021;&#24555;&#20110; <code>use_count()</code> &#12290;&#27492;&#20989;&#25968;&#22266;&#26377;&#22320;&#26377;&#19981;&#31283;&#65292;&#33509;&#34987;&#31649;&#29702;&#23545;&#35937;&#22312;&#21487;&#33021;&#21019;&#24314;&#24182;&#38144;&#27585; <code>shared_ptr</code> &#21103;&#26412;&#30340;&#32447;&#31243;&#38388;&#20849;&#20139;&#65306;&#21017;&#32467;&#26524;&#20165;&#33509;&#21305;&#37197;&#35843;&#29992;&#26041;&#32447;&#31243;&#25152;&#29420;&#21344;&#30340;&#21103;&#26412;&#25968;&#25110;&#38646;&#25165;&#21487;&#38752;&#65307;&#20219;&#20309;&#20854;&#20182;&#20540;&#21487;&#33021;&#22312;&#33021;&#20351;&#29992;&#21069;&#23601;&#21464;&#24471;&#36807;&#26102;&#20102;&#12290;</p>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">&#31034;&#20363;</span></h3>
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<pre class="de1"><span class="co2">#include &lt;iostream&gt;</span>
<span class="co2">#include &lt;memory&gt;</span>
<a href="cpp-memory-weak_ptr.html"><span class="kw741">std::<span class="me2">weak_ptr</span></span></a><span class="sy1">&lt;</span><span class="kw4">int</span><span class="sy1">&gt;</span> gwp<span class="sy4">;</span>
<span class="kw4">void</span> observe_gwp<span class="br0">(</span><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">&quot;use_count(): &quot;</span> <span class="sy1">&lt;&lt;</span> gwp.<span class="me1">use_count</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;<span class="es1">\t</span> id: &quot;</span><span class="sy4">;</span>
<span class="kw1">if</span> <span class="br0">(</span><span class="kw4">auto</span> sp <span class="sy1">=</span> gwp.<span class="me1">lock</span><span class="br0">(</span><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="sy2">*</span>sp <span class="sy1">&lt;&lt;</span> <span class="st0">&#39;<span class="es1">\n</span>&#39;</span><span class="sy4">;</span>
<span class="kw1">else</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="sy4">;</span>
<span class="br0">}</span>
<span class="kw4">void</span> share_recursively<span class="br0">(</span><a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1">&lt;</span><span class="kw4">int</span><span class="sy1">&gt;</span> sp, <span class="kw4">int</span> depth<span class="br0">)</span> <span class="br0">{</span>
observe_gwp<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// : 2 3 4</span>
<span class="kw1">if</span> <span class="br0">(</span><span class="nu0">1</span> <span class="sy1">&lt;</span> depth<span class="br0">)</span>
share_recursively<span class="br0">(</span>sp, depth <span class="sy2">-</span> <span class="nu0">1</span><span class="br0">)</span><span class="sy4">;</span>
observe_gwp<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// : 4 3 2</span>
<span class="br0">}</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
observe_gwp<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">{</span>
<span class="kw4">auto</span> sp <span class="sy1">=</span> <a href="cpp-memory-shared_ptr-make_shared.html"><span class="kw736">std::<span class="me2">make_shared</span></span></a><span class="sy1">&lt;</span><span class="kw4">int</span><span class="sy1">&gt;</span><span class="br0">(</span><span class="nu0">42</span><span class="br0">)</span><span class="sy4">;</span>
gwp <span class="sy1">=</span> sp<span class="sy4">;</span>
observe_gwp<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// : 1</span>
share_recursively<span class="br0">(</span>sp, <span class="nu0">3</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// : 2 3 4 4 3 2</span>
observe_gwp<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// : 1</span>
<span class="br0">}</span>
observe_gwp<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// : 0</span>
<span class="br0">}</span></pre></div>
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<p>&#36755;&#20986;&#65306;</p>
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<pre class="de1">use_count(): 0 id: ??
use_count(): 1 id: 42
use_count(): 2 id: 42
use_count(): 3 id: 42
use_count(): 4 id: 42
use_count(): 4 id: 42
use_count(): 3 id: 42
use_count(): 2 id: 42
use_count(): 1 id: 42
use_count(): 0 id: ??</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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<div><a href="cpp-memory-weak_ptr-expired.html"><span class="t-lines"><span>expired</span></span></a></div>
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<td>&#26816;&#26597;&#34987;&#24341;&#29992;&#30340;&#23545;&#35937;&#26159;&#21542;&#24050;&#21024;&#38500;<br />
<span class="t-mark">(&#20844;&#24320;&#25104;&#21592;&#20989;&#25968;)</span></td>
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