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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>any_cast</h1>
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<div id="contentSub"><span class="subpages">&lt; <a href="cpp.html">cpp</a>&lrm; | <a href="cpp-utility.html">utility</a>&lrm; | <a href="cpp-utility-any.html">any</a></span></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> T<span class="sy1">&gt;</span><br />
&nbsp; &nbsp; T any_cast<span class="br0">(</span><span class="kw4">const</span> any<span class="sy3">&amp;</span> operand<span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(1)</td>
<td><span class="t-mark-rev t-since-cxx17">(C++17 &#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><span class="kw1">class</span> T<span class="sy1">&gt;</span><br />
&nbsp; &nbsp; T any_cast<span class="br0">(</span>any<span class="sy3">&amp;</span> operand<span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
<td><span class="t-mark-rev t-since-cxx17">(C++17 &#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><span class="kw1">class</span> T<span class="sy1">&gt;</span><br />
&nbsp; &nbsp; T any_cast<span class="br0">(</span>any<span class="sy3">&amp;&amp;</span> operand<span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(3)</td>
<td><span class="t-mark-rev t-since-cxx17">(C++17 &#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><span class="kw1">class</span> T<span class="sy1">&gt;</span><br />
&nbsp; &nbsp; <span class="kw4">const</span> T<span class="sy2">*</span> any_cast<span class="br0">(</span><span class="kw4">const</span> any<span class="sy2">*</span> operand<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx17">(C++17 &#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><span class="kw1">class</span> T<span class="sy1">&gt;</span><br />
&nbsp; &nbsp; T<span class="sy2">*</span> any_cast<span class="br0">(</span>any<span class="sy2">*</span> operand<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td>(5)</td>
<td><span class="t-mark-rev t-since-cxx17">(C++17 &#36215;)</span></td>
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<p>&#36827;&#34892;&#23545;&#25152;&#21547;&#26377;&#23545;&#35937;&#30340;&#31867;&#22411;&#23433;&#20840;&#35775;&#38382;&#12290;</p>
<p>&#20196; <code>U</code> &#20026; <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-types-remove_cv.html"><span class="kw597">std::<span class="me2">remove_cv_t</span></span></a><span class="sy1">&lt;</span><a href="cpp-types-remove_reference.html"><span class="kw607">std::<span class="me2">remove_reference_t</span></span></a><span class="sy1">&lt;</span>T<span class="sy1">&gt;&gt;</span></span></span> &#12290;</p>
<div class="t-li1"><span class="t-li">1)</span> &#33509; <span class="t-c"><span class="mw-geshi cpp source-cpp">is_constructible_v<span class="sy1">&lt;</span>T, <span class="kw4">const</span> U<span class="sy3">&amp;</span><span class="sy1">&gt;</span></span></span> &#38750; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> &#21017;&#31243;&#24207;&#20026;&#30149;&#24335;&#12290;</div>
<div class="t-li1"><span class="t-li">2)</span> &#33509; <span class="t-c"><span class="mw-geshi cpp source-cpp">is_constructible_v<span class="sy1">&lt;</span>T, U<span class="sy3">&amp;</span><span class="sy1">&gt;</span></span></span> &#38750; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> &#21017;&#31243;&#24207;&#20026;&#30149;&#24335;&#12290;</div>
<div class="t-li1"><span class="t-li">3)</span> &#33509; <span class="t-c"><span class="mw-geshi cpp source-cpp">is_constructible_v<span class="sy1">&lt;</span>T, U<span class="sy1">&gt;</span></span></span> &#38750; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> &#21017;&#31243;&#24207;&#20026;&#30149;&#24335;&#12290;</div>
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">&#21442;&#25968;</span></h3>
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<td>operand</td>
<td>-</td>
<td>&#30446;&#26631; <code>any</code> &#23545;&#35937;</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>
<div class="t-li1"><span class="t-li">1-2)</span> &#36820;&#22238; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span><span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="br0">(</span><span class="sy2">*</span>std<span class="sy4">::</span><span class="me2">any_cast</span><span class="sy1">&lt;</span>U<span class="sy1">&gt;</span><span class="br0">(</span><span class="sy3">&amp;</span>operand<span class="br0">)</span><span class="br0">)</span></span></span> &#12290;</div>
<div class="t-li1"><span class="t-li">3)</span> &#36820;&#22238; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span><span class="sy1">&lt;</span>T<span class="sy1">&gt;</span><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span><span class="sy2">*</span>std<span class="sy4">::</span><span class="me2">any_cast</span><span class="sy1">&lt;</span>U<span class="sy1">&gt;</span><span class="br0">(</span><span class="sy3">&amp;</span>operand<span class="br0">)</span><span class="br0">)</span><span class="br0">)</span></span></span> &#12290;</div>
<div class="t-li1"><span class="t-li">4-5)</span> &#33509; <code>operand</code> &#19981;&#26159;&#31354;&#25351;&#38024;&#65292;&#19988;&#35831;&#27714;&#30340; <code>T</code> &#30340; <code>typeid</code> &#21305;&#37197; <code>operand</code> &#30340; <code>typeid</code> &#65292;&#21017;&#20026;&#25351;&#21521;&#25152;&#21547;&#20540;&#30340;&#25351;&#38024;&#65292;&#21542;&#21017;&#20026;&#31354;&#25351;&#38024;&#12290;</div>
<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">&#24322;&#24120;</span></h3>
<div class="t-li1"><span class="t-li">1-3)</span> &#33509;&#35831;&#27714;&#30340; <code>T</code> &#30340; <code>typeid</code> &#19981;&#21305;&#37197; <code>operand</code> &#20869;&#23481;&#30340; <code>typeid</code> &#65292;&#21017;&#25243;&#20986; <span class="t-lc"><a href="cpp-utility-any-bad_any_cast.html">std::bad_any_cast</a></span> &#12290;</div>
<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;string&gt;</span>
<span class="co2">#include &lt;iostream&gt;</span>
<span class="co2">#include &lt;any&gt;</span>
<span class="co2">#include &lt;utility&gt;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
<span class="co1">// &#31616;&#21333;&#31034;&#20363;</span>
<span class="kw4">auto</span> a <span class="sy1">=</span> <a href="cpp-utility-any.html"><span class="kw1071">std::<span class="me2">any</span></span></a><span class="br0">(</span><span class="nu0">12</span><span class="br0">)</span><span class="sy4">;</span>
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> std<span class="sy4">::</span><span class="me2">any_cast</span><span class="sy1">&lt;</span><span class="kw4">int</span><span class="sy1">&gt;</span><span class="br0">(</span>a<span class="br0">)</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">try</span> <span class="br0">{</span>
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> std<span class="sy4">::</span><span class="me2">any_cast</span><span class="sy1">&lt;</span><a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a><span class="sy1">&gt;</span><span class="br0">(</span>a<span class="br0">)</span> <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>
<span class="kw1">catch</span><span class="br0">(</span><span class="kw4">const</span> <a href="cpp-utility-any-bad_any_cast.html"><span class="kw1073">std::<span class="me2">bad_any_cast</span></span></a><span class="sy3">&amp;</span> e<span class="br0">)</span> <span class="br0">{</span>
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> e.<span class="me1">what</span><span class="br0">(</span><span class="br0">)</span> <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>
<span class="co1">// &#25351;&#38024;&#31034;&#20363;</span>
<span class="kw1">if</span> <span class="br0">(</span><span class="kw4">int</span><span class="sy2">*</span> i <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">any_cast</span><span class="sy1">&lt;</span><span class="kw4">int</span><span class="sy1">&gt;</span><span class="br0">(</span><span class="sy3">&amp;</span>a<span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span>
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;a is int: &quot;</span> <span class="sy1">&lt;&lt;</span> <span class="sy2">*</span>i <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> <span class="kw1">else</span> <span class="kw1">if</span> <span class="br0">(</span><a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a><span class="sy2">*</span> s <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">any_cast</span><span class="sy1">&lt;</span><a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a><span class="sy1">&gt;</span><span class="br0">(</span><span class="sy3">&amp;</span>a<span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span>
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;a is std::string: &quot;</span> <span class="sy1">&lt;&lt;</span> <span class="sy2">*</span>s <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> <span class="kw1">else</span> <span class="br0">{</span>
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;a is another type or unset<span class="es1">\n</span>&quot;</span><span class="sy4">;</span>
<span class="br0">}</span>
<span class="co1">// &#36827;&#38454;&#31034;&#20363;</span>
a <span class="sy1">=</span> <a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a><span class="br0">(</span><span class="st0">&quot;hello&quot;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw4">auto</span><span class="sy3">&amp;</span> ra <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">any_cast</span><span class="sy1">&lt;</span><a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a><span class="sy3">&amp;</span><span class="sy1">&gt;</span><span class="br0">(</span>a<span class="br0">)</span><span class="sy4">;</span> <span class="co1">//&lt; &#24341;&#29992;</span>
ra<span class="br0">[</span><span class="nu0">1</span><span class="br0">]</span> <span class="sy1">=</span> <span class="st0">&#39;o&#39;</span><span class="sy4">;</span>
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;a: &quot;</span>
<span class="sy1">&lt;&lt;</span> std<span class="sy4">::</span><span class="me2">any_cast</span><span class="sy1">&lt;</span><span class="kw4">const</span> <a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a><span class="sy3">&amp;</span><span class="sy1">&gt;</span><span class="br0">(</span>a<span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">&#39;<span class="es1">\n</span>&#39;</span><span class="sy4">;</span> <span class="co1">//&lt; const &#24341;&#29992;</span>
<span class="kw4">auto</span> b <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">any_cast</span><span class="sy1">&lt;</span><a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a><span class="sy3">&amp;&amp;</span><span class="sy1">&gt;</span><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>a<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">//&lt; &#21491;&#20540;&#24341;&#29992;</span>
<span class="co1">// &#27880;&#24847;&#65306; &#39;b&#39; &#26159;&#31227;&#21160;&#26500;&#36896;&#30340; std::string &#65292; &#39;a&#39; &#34987;&#32622;&#20110;&#21512;&#27861;&#20294;&#26410;&#25351;&#23450;&#30340;&#29366;&#24577;</span>
<a href="cpp-io-cout.html"><span class="kw1757">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;a: &quot;</span> <span class="sy1">&lt;&lt;</span> <span class="sy2">*</span>std<span class="sy4">::</span><span class="me2">any_cast</span><span class="sy1">&lt;</span><a href="cpp-string-basic_string.html"><span class="kw1229">std::<span class="me2">string</span></span></a><span class="sy1">&gt;</span><span class="br0">(</span><span class="sy3">&amp;</span>a<span class="br0">)</span> <span class="co1">//&lt; &#25351;&#38024;</span>
<span class="sy1">&lt;&lt;</span> <span class="st0">&quot;b: &quot;</span> <span class="sy1">&lt;&lt;</span> b <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>&#21487;&#33021;&#30340;&#36755;&#20986;&#65306;</p>
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<div class="text source-text">
<pre class="de1">12
bad any_cast
a is int: 12
a: hollo
a: b: hollo</pre></div>
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