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<title>sizeof &#36816;&#31639;&#31526;</title>
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<h1 id="firstHeading" class="firstHeading">sizeof &#36816;&#31639;&#31526;</h1>
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<div id="contentSub"><span class="subpages">&lt; <a href="cpp.html">cpp</a>&lrm; | <a href="cpp-language.html">language</a></span></div>
<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
<p>&#26597;&#35810;&#23545;&#35937;&#25110;&#31867;&#22411;&#30340;&#22823;&#23567;&#12290;</p>
<p>&#22312;&#38656;&#35201;&#30693;&#36947;&#23545;&#35937;&#30340;&#23454;&#38469;&#22823;&#23567;&#26102;&#20351;&#29992;&#12290;</p>
<h3><span class="mw-headline" id=".E8.AF.AD.E6.B3.95">&#35821;&#27861;</span></h3>
<table class="t-sdsc-begin">
<tr>
<td colspan="10" class="t-sdsc-sep"></td>
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<tr class="t-sdsc">
<td><code><b>sizeof(</b></code> <span class="t-spar">&#31867;&#22411;</span> <code><b>)</b></code></td>
<td>(1)</td>
<td class="t-sdsc-nopad"></td>
</tr>
<tr>
<td colspan="10" class="t-sdsc-sep"></td>
</tr>
<tr class="t-sdsc">
<td><code><b>sizeof</b></code> <span class="t-spar">&#34920;&#36798;&#24335;</span> <code></code></td>
<td>(2)</td>
<td class="t-sdsc-nopad"></td>
</tr>
<tr>
<td colspan="10" class="t-sdsc-sep"></td>
</tr>
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<p>&#20004;&#20010;&#29256;&#26412;&#37117;&#26159; <span class="t-lc"><a href="cpp-types-size_t.html">std::size_t</a></span> &#31867;&#22411;&#30340;&#24120;&#37327;&#34920;&#36798;&#24335;&#12290;</p>
<h3><span class="mw-headline" id=".E8.A7.A3.E9.87.8A">&#35299;&#37322;</span></h3>
<div class="t-li1"><span class="t-li">1)</span> &#20135;&#29983;<span class="t-spar">&#31867;&#22411;</span> &#30340;<a href="cpp-language-object.html">&#23545;&#35937;&#34920;&#31034;</a>&#30340;&#23383;&#33410;&#25968;&#12290;</div>
<div class="t-li1"><span class="t-li">2)</span> &#20135;&#29983;<span class="t-spar">&#34920;&#36798;&#24335;</span> &#30340;&#31867;&#22411;&#30340;&#23545;&#35937;&#34920;&#31034;&#30340;&#23383;&#33410;&#25968;&#65292;&#20551;&#22914;&#35813;&#34920;&#36798;&#24335;&#34987;&#27714;&#20540;&#12290;</div>
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">&#27880;&#35299;</span></h3>
<p>&#21462;&#20915;&#20110;&#35745;&#31639;&#26426;&#26550;&#26500;&#65292;<a href="https://en.wikipedia.org/wiki/Byte" class="extiw" title="enwiki:Byte">&#23383;&#33410;</a>&#21487;&#33021;&#20855;&#26377;8<i>&#25110;&#26356;&#22810;</i>&#20301;&#65292;&#31934;&#30830;&#30340;&#20301;&#25968;&#35760;&#24405;&#20110; <span class="t-lc"><a href="cpp-types-climits.html">CHAR_BIT</a></span>&#12290;</p>
<p>&#19979;&#21015; <code>sizeof</code> &#34920;&#36798;&#24335;&#24635;&#26159;&#27714;&#20540;&#20026; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="nu0">1</span></span></span>&#65306;</p>
<ul>
<li><span class="t-c"><span class="mw-geshi cpp source-cpp">sizeof<span class="br0">(</span><span class="kw4">char</span><span class="br0">)</span></span></span></li>
<li><span class="t-c"><span class="mw-geshi cpp source-cpp">sizeof<span class="br0">(</span><span class="kw4">signed</span> <span class="kw4">char</span><span class="br0">)</span></span></span></li>
<li><span class="t-c"><span class="mw-geshi cpp source-cpp">sizeof<span class="br0">(</span><span class="kw4">unsigned</span> <span class="kw4">char</span><span class="br0">)</span></span></span></li>
</ul>
<table class="t-rev-begin">
<tr class="t-rev t-since-cxx17">
<td>
<ul>
<li><span class="t-c"><span class="mw-geshi cpp source-cpp">sizeof<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">byte</span><span class="br0">)</span></span></span></li>
</ul>
</td>
<td><span class="t-mark-rev t-since-cxx17">(C++17 &#36215;)</span></td>
</tr>
</table>
<table class="t-rev-begin">
<tr class="t-rev t-since-cxx20">
<td>
<ul>
<li><span class="t-c"><span class="mw-geshi cpp source-cpp">sizeof<span class="br0">(</span>char8_t<span class="br0">)</span></span></span></li>
</ul>
</td>
<td><span class="t-mark-rev t-since-cxx20">(C++20 &#36215;)</span></td>
</tr>
</table>
<p>&#19981;&#33021;&#23545;&#20989;&#25968;&#31867;&#22411;&#12289;&#19981;&#23436;&#25972;&#31867;&#22411;&#25110;&#20301;&#22495;&#27867;&#24038;&#20540;&#20351;&#29992; <code>sizeof</code>&#12290;</p>
<p>&#24403;&#24212;&#29992;&#20110;&#24341;&#29992;&#31867;&#22411;&#26102;&#65292;&#32467;&#26524;&#26159;&#34987;&#24341;&#29992;&#31867;&#22411;&#30340;&#22823;&#23567;&#12290;</p>
<p>&#24403;&#24212;&#29992;&#20110;&#31867;&#31867;&#22411;&#26102;&#65292;&#32467;&#26524;&#26159;&#35813;&#31867;&#30340;&#23436;&#25972;&#23545;&#35937;&#25152;&#21344;&#25454;&#30340;&#23383;&#33410;&#25968;&#65292;&#21253;&#25324;&#36825;&#31181;&#23545;&#35937;&#25918;&#20837;&#25968;&#32452;&#26102;&#25152;&#38656;&#30340;&#20219;&#20309;&#39069;&#22806;&#22635;&#20805;&#12290;<a href="cpp-language-object.html#.E5.AD.90.E5.AF.B9.E8.B1.A1">&#28508;&#22312;&#37325;&#21472;&#30340;&#23376;&#23545;&#35937;</a>&#25152;&#21344;&#25454;&#30340;&#23383;&#33410;&#25968;&#21487;&#20197;&#23567;&#20110;&#35813;&#23545;&#35937;&#30340;&#22823;&#23567;&#12290;</p>
<p><code>sizeof</code> &#30340;&#32467;&#26524;&#22987;&#32456;&#38750;&#38646;&#65292;&#21363;&#20351;&#24212;&#29992;&#20110;&#31354;&#31867;&#12290;</p>
<p>&#24403;&#24212;&#29992;&#20110;&#26576;&#20010;&#34920;&#36798;&#24335;&#26102;&#65292;<code>sizeof</code> <a href="cpp-language-expressions.html#.E4.B8.8D.E6.B1.82.E5.80.BC.E8.A1.A8.E8.BE.BE.E5.BC.8F">&#24182;&#19981;&#23545;&#34920;&#36798;&#24335;&#36827;&#34892;&#27714;&#20540;</a>&#65292;&#24182;&#19988;&#21363;&#20415;&#34920;&#36798;&#24335;&#20195;&#34920;&#22810;&#24577;&#23545;&#35937;&#65292;&#20854;&#32467;&#26524;&#20063;&#26159;&#35813;&#34920;&#36798;&#24335;&#30340;&#38745;&#24577;&#31867;&#22411;&#30340;&#22823;&#23567;&#12290;&#19981;&#36827;&#34892;&#24038;&#20540;&#21521;&#21491;&#20540;&#12289;&#25968;&#32452;&#21521;&#25351;&#38024;&#21644;&#20989;&#25968;&#21521;&#25351;&#38024;&#36716;&#25442;&#12290;<span class="t-rev-inl t-since-cxx17"><span>&#19981;&#36807;&#65292;&#23427;&#22312;&#24418;&#24335;&#19978;&#23545;&#32431;&#21491;&#20540;&#23454;&#21442;&#36827;&#34892;<a href="cpp-language-implicit_conversion.html#.E4.B8.B4.E6.97.B6.E9.87.8F.E5.AE.9E.E8.B4.A8.E5.8C.96">&#20020;&#26102;&#37327;&#23454;&#36136;&#21270;</a>&#65306;&#33509;&#23454;&#21442;&#19981;&#21487;&#26512;&#26500;&#21017;&#31243;&#24207;&#38750;&#33391;&#26500;&#12290;</span> <span><span class="t-mark-rev t-since-cxx17">(C++17 &#36215;)</span></span></span></p>
<h3><span class="mw-headline" id=".E5.85.B3.E9.94.AE.E8.AF.8D">&#20851;&#38190;&#35789;</span></h3>
<p><a href="cpp-keyword-sizeof.html"><tt>sizeof</tt></a></p>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">&#31034;&#20363;</span></h3>
<div class="t-example">
<p>&#26412;&#31034;&#20363;&#30340;&#36755;&#20986;&#23545;&#24212;&#20110;&#20855;&#26377; 64 &#20301;&#25351;&#38024;&#21644; 32 &#20301; int &#30340;&#31995;&#32479;&#12290;</p>
<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;iostream&gt;</span>
<span class="kw1">struct</span> Empty <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">struct</span> Base <span class="br0">{</span> <span class="kw4">int</span> a<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">struct</span> Derived <span class="sy4">:</span> Base <span class="br0">{</span> <span class="kw4">int</span> b<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
<span class="kw1">struct</span> Bit <span class="br0">{</span> <span class="kw4">unsigned</span> bit<span class="sy4">:</span> <span class="nu0">1</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>
Empty e<span class="sy4">;</span>
Derived d<span class="sy4">;</span>
Base<span class="sy3">&amp;</span> b <span class="sy1">=</span> d<span class="sy4">;</span>
<span class="br0">[</span><span class="br0">[</span>maybe_unused<span class="br0">]</span><span class="br0">]</span> Bit bit<span class="sy4">;</span>
<span class="kw4">int</span> a<span class="br0">[</span><span class="nu0">10</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;&#31354;&#31867;&#30340;&#22823;&#23567;&#65306; &quot;</span> <span class="sy1">&lt;&lt;</span> sizeof e <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;<span class="es1">\n</span>&quot;</span>
<span class="sy1">&lt;&lt;</span> <span class="st0">&quot;&#25351;&#38024;&#30340;&#22823;&#23567;&#65306; &quot;</span> <span class="sy1">&lt;&lt;</span> sizeof <span class="sy3">&amp;</span>e <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;<span class="es1">\n</span>&quot;</span>
<span class="co1">// &lt;&lt; &quot;&#20989;&#25968;&#30340;&#22823;&#23567;&#65306; &quot; &lt;&lt; sizeof(void()) &lt;&lt; &quot;\n&quot; // &#38169;&#35823;</span>
<span class="co1">// &lt;&lt; &quot;&#19981;&#23436;&#25972;&#31867;&#22411;&#30340;&#22823;&#23567;&#65306; &quot; &lt;&lt; sizeof(int[]) &lt;&lt; &quot;\n&quot; // &#38169;&#35823;</span>
<span class="co1">// &lt;&lt; &quot;&#20301;&#22495;&#30340;&#22823;&#23567;&#65306; &quot; &lt;&lt; sizeof bit.bit &lt;&lt; &quot;\n&quot; // &#38169;&#35823;</span>
<span class="sy1">&lt;&lt;</span> <span class="st0">&quot;Bit &#31867;&#30340;&#22823;&#23567;&#65306; &quot;</span> <span class="sy1">&lt;&lt;</span> sizeof<span class="br0">(</span>Bit<span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">&#39;<span class="es1">\n</span>&#39;</span>
<span class="sy1">&lt;&lt;</span> <span class="st0">&quot;&#21547;&#26377;10&#20010; int &#30340;&#25968;&#32452;&#30340;&#22823;&#23567;&#65306; &quot;</span> <span class="sy1">&lt;&lt;</span> sizeof<span class="br0">(</span><span class="kw4">int</span><span class="br0">[</span><span class="nu0">10</span><span class="br0">]</span><span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;<span class="es1">\n</span>&quot;</span>
<span class="sy1">&lt;&lt;</span> <span class="st0">&quot;&#21547;&#26377;10&#20010; int &#30340;&#25968;&#32452;&#30340;&#22823;&#23567; (2)&#65306;&quot;</span> <span class="sy1">&lt;&lt;</span> sizeof a <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;<span class="es1">\n</span>&quot;</span>
<span class="sy1">&lt;&lt;</span> <span class="st0">&quot;&#21547;&#26377;10&#20010; int &#30340;&#25968;&#32452;&#30340;&#38271;&#24230;&#65306; &quot;</span> <span class="sy1">&lt;&lt;</span> <span class="br0">(</span><span class="br0">(</span>sizeof a<span class="br0">)</span> <span class="sy2">/</span> <span class="br0">(</span>sizeof <span class="sy2">*</span>a<span class="br0">)</span><span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;<span class="es1">\n</span>&quot;</span>
<span class="sy1">&lt;&lt;</span> <span class="st0">&quot;&#21547;&#26377;10&#20010; int &#30340;&#25968;&#32452;&#30340;&#38271;&#24230; (2)&#65306;&quot;</span> <span class="sy1">&lt;&lt;</span> <span class="br0">(</span><span class="br0">(</span>sizeof a<span class="br0">)</span> <span class="sy2">/</span> <span class="br0">(</span>sizeof a<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span><span class="br0">)</span><span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;<span class="es1">\n</span>&quot;</span>
<span class="sy1">&lt;&lt;</span> <span class="st0">&quot;Derived &#30340;&#22823;&#23567;: &quot;</span> <span class="sy1">&lt;&lt;</span> sizeof d <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;<span class="es1">\n</span>&quot;</span>
<span class="sy1">&lt;&lt;</span> <span class="st0">&quot;&#36890;&#36807; Base &#33719;&#21462; Derived &#30340;&#22823;&#23567;&#65306;&quot;</span> <span class="sy1">&lt;&lt;</span> sizeof b <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></pre></div>
</div>
<p>&#21487;&#33021;&#30340;&#36755;&#20986;&#65306;</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;">
<div class="text source-text">
<pre class="de1">&#31354;&#31867;&#30340;&#22823;&#23567;&#65306; 1
&#25351;&#38024;&#30340;&#22823;&#23567;&#65306; 8
Bit &#31867;&#30340;&#22823;&#23567;&#65306; 4
&#21547;&#26377;10&#20010; int &#30340;&#25968;&#32452;&#30340;&#22823;&#23567;&#65306; 40
&#21547;&#26377;10&#20010; int &#30340;&#25968;&#32452;&#30340;&#22823;&#23567; (2)&#65306;40
&#21547;&#26377;10&#20010; int &#30340;&#25968;&#32452;&#30340;&#38271;&#24230;&#65306; 10
&#21547;&#26377;10&#20010; int &#30340;&#25968;&#32452;&#30340;&#38271;&#24230; (2)&#65306;10
Derived &#30340;&#22823;&#23567;: 8
&#36890;&#36807; Base &#33719;&#21462; Derived &#30340;&#22823;&#23567;&#65306;4</pre></div>
</div>
</div>
<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><a href="cpp-language-alignof.html"><code>alignof</code> &#36816;&#31639;&#31526;</a><span class="t-mark-rev t-since-cxx11">(C++11)</span></td>
<td>&#26597;&#35810;&#31867;&#22411;&#30340;&#23545;&#40784;&#35201;&#27714;</td>
</tr>
<tr class="t-dsc">
<td><a href="cpp-language-sizeof....html"><code>sizeof...</code> operator</a><span class="t-mark-rev t-since-cxx11">(C++11)</span></td>
<td>&#26597;&#35810;<a href="cpp-language-parameter_pack.html">&#24418;&#21442;&#21253;</a>&#20013;&#30340;&#20803;&#32032;&#25968;</td>
</tr>
</table>
</div>
<div class="visualClear"></div>
</div>
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