91 lines
6.2 KiB
HTML
91 lines
6.2 KiB
HTML
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<title>std::shared_ptr<T>::operator bool</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_memory_shared_ptr_operator_bool 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::shared_ptr<T>::</span>operator bool</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-memory.html">memory</a>‎ | <a href="cpp-memory-shared_ptr.html">shared ptr</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">explicit</span> operator <span class="kw4">bool</span><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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<p>检查 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 是否存储非空指针，即是否有 <span class="t-c"><span class="mw-geshi cpp source-cpp">get<span class="br0">(</span><span class="br0">)</span> <span class="sy3">!</span><span class="sy1">=</span> nullptr</span></span> 。</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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<p>（无）</p>
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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>若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 存储非空指针则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> ，否则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> 。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h3>
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<p>空 shared_ptr （其中 <span class="t-c"><span class="mw-geshi cpp source-cpp">use_count<span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> <span class="nu0">0</span></span></span> ）可能存储能以 <code>get()</code> 访问的非空指针，例如若它以别名使用构造函数创建。</p>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <iostream></span>
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<span class="co2">#include <memory></span>
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<span class="kw4">void</span> report<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"><</span><span class="kw4">int</span><span class="sy1">></span> ptr<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">if</span> <span class="br0">(</span>ptr<span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"*ptr="</span> <span class="sy1"><<</span> <span class="sy2">*</span>ptr <span class="sy1"><<</span> <span class="st0">"<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span> <span class="kw1">else</span> <span class="br0">{</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"ptr is not a valid pointer.<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<a href="cpp-memory-shared_ptr.html"><span class="kw734">std::<span class="me2">shared_ptr</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> ptr<span class="sy4">;</span>
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report<span class="br0">(</span>ptr<span class="br0">)</span><span class="sy4">;</span>
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ptr <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"><</span><span class="kw4">int</span><span class="sy1">></span><span class="br0">(</span><span class="nu0">7</span><span class="br0">)</span><span class="sy4">;</span>
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report<span class="br0">(</span>ptr<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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<p>输出：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="text source-text">
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<pre class="de1">ptr is not a valid pointer.
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*ptr=7</pre></div>
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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-memory-shared_ptr-get.html"><span class="t-lines"><span>get</span></span></a></div>
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<td>返回存储的指针<br />
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<span class="t-mark">(公开成员函数)</span></td>
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