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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>empty</h1>
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<div id="contentSub"><span class="subpages">&lt; <a href="cpp.html">cpp</a>&lrm; | <a href="cpp-iterator.html">iterator</a></span></div>
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<div>&#23450;&#20041;&#20110;&#22836;&#25991;&#20214; <code><a href="cpp-header-array.html">&lt;array&gt;</a></code></div>
</td>
<td></td>
<td></td>
</tr>
<tr class="t-dsc-header">
<td>
<div>&#23450;&#20041;&#20110;&#22836;&#25991;&#20214; <code><a href="cpp-header-deque.html">&lt;deque&gt;</a></code></div>
</td>
<td></td>
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<div>&#23450;&#20041;&#20110;&#22836;&#25991;&#20214; <code><a href="cpp-header-forward_list.html">&lt;forward_list&gt;</a></code></div>
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<div>&#23450;&#20041;&#20110;&#22836;&#25991;&#20214; <code><a href="cpp-header-iterator.html">&lt;iterator&gt;</a></code></div>
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<td></td>
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<div>&#23450;&#20041;&#20110;&#22836;&#25991;&#20214; <code><a href="cpp-header-list.html">&lt;list&gt;</a></code></div>
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<td></td>
<td></td>
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<div>&#23450;&#20041;&#20110;&#22836;&#25991;&#20214; <code><a href="cpp-header-map.html">&lt;map&gt;</a></code></div>
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<div>&#23450;&#20041;&#20110;&#22836;&#25991;&#20214; <code><a href="cpp-header-regex.html">&lt;regex&gt;</a></code></div>
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<div>&#23450;&#20041;&#20110;&#22836;&#25991;&#20214; <code><a href="cpp-header-set.html">&lt;set&gt;</a></code></div>
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<td></td>
<td></td>
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<div>&#23450;&#20041;&#20110;&#22836;&#25991;&#20214; <code><a href="cpp-header-span.html">&lt;span&gt;</a></code></div>
</td>
<td></td>
<td>
<div><span class="t-mark-rev t-since-cxx20">(C++20 &#36215;)</span></div>
</td>
</tr>
<tr class="t-dsc-header">
<td>
<div>&#23450;&#20041;&#20110;&#22836;&#25991;&#20214; <code><a href="cpp-header-string.html">&lt;string&gt;</a></code></div>
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<div>&#23450;&#20041;&#20110;&#22836;&#25991;&#20214; <code><a href="cpp-header-string_view.html">&lt;string_view&gt;</a></code></div>
</td>
<td></td>
<td>
<div><span class="t-mark-rev t-since-cxx17">(C++17 &#36215;)</span></div>
</td>
</tr>
<tr class="t-dsc-header">
<td>
<div>&#23450;&#20041;&#20110;&#22836;&#25991;&#20214; <code><a href="cpp-header-unordered_map.html">&lt;unordered_map&gt;</a></code></div>
</td>
<td></td>
<td></td>
</tr>
<tr class="t-dsc-header">
<td>
<div>&#23450;&#20041;&#20110;&#22836;&#25991;&#20214; <code><a href="cpp-header-unordered_set.html">&lt;unordered_set&gt;</a></code></div>
</td>
<td></td>
<td></td>
</tr>
<tr class="t-dsc-header">
<td>
<div>&#23450;&#20041;&#20110;&#22836;&#25991;&#20214; <code><a href="cpp-header-vector.html">&lt;vector&gt;</a></code></div>
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<tbody class="t-dcl-rev t-dcl-rev-num">
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<td rowspan="142">(1)</td>
<td></td>
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<tr class="t-dcl t-since-cxx17 t-until-cxx20">
<td>
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> C<span class="sy1">&gt;</span><br />
<span class="kw4">constexpr</span> <span class="kw4">auto</span> empty<span class="br0">(</span><span class="kw4">const</span> C<span class="sy3">&amp;</span> c<span class="br0">)</span> <span class="sy2">-</span><span class="sy1">&gt;</span> decltype<span class="br0">(</span>c.<span class="me1">empty</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span></span></div>
</td>
<td class="t-dcl-nopad"></td>
<td><span class="t-mark-rev t-since-cxx17">(C++17 &#36215;)</span><br />
<span class="t-mark-rev t-until-cxx20">(C++20 &#21069;)</span></td>
</tr>
<tr class="t-dcl t-since-cxx20">
<td>
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> C<span class="sy1">&gt;</span><br />
<span class="br0">[</span><span class="br0">[</span>nodiscard<span class="br0">]</span><span class="br0">]</span> <span class="kw4">constexpr</span> <span class="kw4">auto</span> empty<span class="br0">(</span><span class="kw4">const</span> C<span class="sy3">&amp;</span> c<span class="br0">)</span> <span class="sy2">-</span><span class="sy1">&gt;</span> decltype<span class="br0">(</span>c.<span class="me1">empty</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span></span></div>
</td>
<td class="t-dcl-nopad"></td>
<td><span class="t-mark-rev t-since-cxx20">(C++20 &#36215;)</span></td>
</tr>
</tbody>
<tbody></tbody>
<tbody class="t-dcl-rev t-dcl-rev-num">
<tr class="t-dcl-rev-aux">
<td></td>
<td rowspan="142">(2)</td>
<td></td>
</tr>
<tr class="t-dcl t-since-cxx17 t-until-cxx20">
<td>
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N<span class="sy1">&gt;</span><br />
<span class="kw4">constexpr</span> <span class="kw4">bool</span> empty<span class="br0">(</span><span class="kw4">const</span> T <span class="br0">(</span><span class="sy3">&amp;</span>array<span class="br0">)</span><span class="br0">[</span>N<span class="br0">]</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
</td>
<td class="t-dcl-nopad"></td>
<td><span class="t-mark-rev t-since-cxx17">(C++17 &#36215;)</span><br />
<span class="t-mark-rev t-until-cxx20">(C++20 &#21069;)</span></td>
</tr>
<tr class="t-dcl t-since-cxx20">
<td>
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N<span class="sy1">&gt;</span><br />
<span class="br0">[</span><span class="br0">[</span>nodiscard<span class="br0">]</span><span class="br0">]</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> empty<span class="br0">(</span><span class="kw4">const</span> T <span class="br0">(</span><span class="sy3">&amp;</span>array<span class="br0">)</span><span class="br0">[</span>N<span class="br0">]</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
</td>
<td class="t-dcl-nopad"></td>
<td><span class="t-mark-rev t-since-cxx20">(C++20 &#36215;)</span></td>
</tr>
</tbody>
<tbody></tbody>
<tbody class="t-dcl-rev t-dcl-rev-num">
<tr class="t-dcl-rev-aux">
<td></td>
<td rowspan="142">(3)</td>
<td></td>
</tr>
<tr class="t-dcl t-since-cxx17 t-until-cxx20">
<td>
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> E<span class="sy1">&gt;</span><br />
<span class="kw4">constexpr</span> <span class="kw4">bool</span> empty<span class="br0">(</span><a href="cpp-utility-initializer_list.html"><span class="kw959">std::<span class="me2">initializer_list</span></span></a><span class="sy1">&lt;</span>E<span class="sy1">&gt;</span> il<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
</td>
<td class="t-dcl-nopad"></td>
<td><span class="t-mark-rev t-since-cxx17">(C++17 &#36215;)</span><br />
<span class="t-mark-rev t-until-cxx20">(C++20 &#21069;)</span></td>
</tr>
<tr class="t-dcl t-since-cxx20">
<td>
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> E<span class="sy1">&gt;</span><br />
<span class="br0">[</span><span class="br0">[</span>nodiscard<span class="br0">]</span><span class="br0">]</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> empty<span class="br0">(</span><a href="cpp-utility-initializer_list.html"><span class="kw959">std::<span class="me2">initializer_list</span></span></a><span class="sy1">&lt;</span>E<span class="sy1">&gt;</span> il<span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
</td>
<td class="t-dcl-nopad"></td>
<td><span class="t-mark-rev t-since-cxx20">(C++20 &#36215;)</span></td>
</tr>
</tbody>
<tbody>
<tr class="t-dcl-sep">
<td></td>
<td></td>
<td></td>
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</table>
<p>&#36820;&#22238;&#32473;&#23450;&#30340;&#33539;&#22260;&#26159;&#21542;&#20026;&#31354;&#12290;</p>
<div class="t-li1"><span class="t-li">1)</span> &#36820;&#22238; <span class="t-c"><span class="mw-geshi cpp source-cpp">c.<span class="me1">empty</span><span class="br0">(</span><span class="br0">)</span></span></span></div>
<div class="t-li1"><span class="t-li">2)</span> &#36820;&#22238; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span></div>
<div class="t-li1"><span class="t-li">3)</span> &#36820;&#22238; <span class="t-c"><span class="mw-geshi cpp source-cpp">il.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> <span class="nu0">0</span></span></span></div>
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">&#21442;&#25968;</span></h3>
<table class="t-par-begin">
<tr class="t-par">
<td>c</td>
<td>-</td>
<td>&#25317;&#26377; <code>empty</code> &#25104;&#21592;&#20989;&#25968;&#30340;&#23481;&#22120;&#25110;&#35270;&#22270;</td>
</tr>
<tr class="t-par">
<td>array</td>
<td>-</td>
<td>&#20219;&#24847;&#31867;&#22411;&#30340;&#25968;&#32452;</td>
</tr>
<tr class="t-par">
<td>il</td>
<td>-</td>
<td>&#19968;&#20010; initializer_list</td>
</tr>
</table>
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">&#36820;&#22238;&#20540;</span></h3>
<p>&#33509;&#33539;&#22260;&#19981;&#21547;&#26377;&#20219;&#20309;&#20803;&#32032;&#21017;&#20026; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> &#12290;</p>
<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)</span> &#21487;&#33021;&#25243;&#20986;&#23454;&#29616;&#23450;&#20041;&#30340;&#24322;&#24120;&#12290;</div>
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">&#27880;&#35299;</span></h3>
<p>&#38656;&#35201;&#23545; <span class="t-lc"><a href="cpp-utility-initializer_list.html">std::initializer_list</a></span> &#30340;&#37325;&#36733;&#65292;&#22240;&#20026;&#23427;&#26080;&#25104;&#21592;&#20989;&#25968; <code>empty</code> &#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">
<tr>
<th>&#29256;&#26412;&#19968;</th>
</tr>
<tr>
<td>
<div dir="ltr" class="mw-geshi" style="text-align: left;">
<div class="cpp source-cpp">
<pre class="de1"><span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> C<span class="sy1">&gt;</span>
<span class="br0">[</span><span class="br0">[</span>nodiscard<span class="br0">]</span><span class="br0">]</span> <span class="kw4">constexpr</span> <span class="kw4">auto</span> empty<span class="br0">(</span><span class="kw4">const</span> C<span class="sy3">&amp;</span> c<span class="br0">)</span> <span class="sy2">-</span><span class="sy1">&gt;</span> decltype<span class="br0">(</span>c.<span class="me1">empty</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span>
<span class="br0">{</span>
<span class="kw1">return</span> c.<span class="me1">empty</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div>
</div>
</td>
</tr>
<tr>
<th>&#29256;&#26412;&#20108;</th>
</tr>
<tr>
<td>
<div dir="ltr" class="mw-geshi" style="text-align: left;">
<div class="cpp source-cpp">
<pre class="de1"><span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N<span class="sy1">&gt;</span>
<span class="br0">[</span><span class="br0">[</span>nodiscard<span class="br0">]</span><span class="br0">]</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> empty<span class="br0">(</span><span class="kw4">const</span> T <span class="br0">(</span><span class="sy3">&amp;</span>array<span class="br0">)</span><span class="br0">[</span>N<span class="br0">]</span><span class="br0">)</span> <span class="kw1">noexcept</span>
<span class="br0">{</span>
<span class="kw1">return</span> <span class="kw2">false</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div>
</div>
</td>
</tr>
<tr>
<th>&#29256;&#26412;&#19977;</th>
</tr>
<tr>
<td>
<div dir="ltr" class="mw-geshi" style="text-align: left;">
<div class="cpp source-cpp">
<pre class="de1"><span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> E<span class="sy1">&gt;</span>
<span class="br0">[</span><span class="br0">[</span>nodiscard<span class="br0">]</span><span class="br0">]</span> <span class="kw4">constexpr</span> <span class="kw4">bool</span> empty<span class="br0">(</span><a href="cpp-utility-initializer_list.html"><span class="kw959">std::<span class="me2">initializer_list</span></span></a><span class="sy1">&lt;</span>E<span class="sy1">&gt;</span> il<span class="br0">)</span> <span class="kw1">noexcept</span>
<span class="br0">{</span>
<span class="kw1">return</span> il.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> <span class="nu0">0</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div>
</div>
</td>
</tr>
</table>
<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;iostream&gt;</span>
<span class="co2">#include &lt;vector&gt;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> T<span class="sy1">&gt;</span>
<span class="kw4">void</span> print<span class="br0">(</span><span class="kw4">const</span> T<span class="sy3">&amp;</span> container<span class="br0">)</span>
<span class="br0">{</span>
<span class="kw1">if</span> <span class="br0">(</span> <span class="sy3">!</span>std<span class="sy4">::</span><span class="me2">empty</span><span class="br0">(</span>container<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;Elements:<span class="es1">\n</span>&quot;</span><span class="sy4">;</span>
<span class="kw1">for</span> <span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">auto</span><span class="sy3">&amp;</span> element <span class="sy4">:</span> container <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> element <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;Empty<span class="es1">\n</span>&quot;</span><span class="sy4">;</span>
<span class="br0">}</span>
<span class="br0">}</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="kw1268">std::<span class="me2">vector</span></span></a><span class="sy1">&lt;</span><span class="kw4">int</span><span class="sy1">&gt;</span> c <span class="sy1">=</span> <span class="br0">{</span> <span class="nu0">1</span>, <span class="nu0">2</span>, <span class="nu0">3</span> <span class="br0">}</span><span class="sy4">;</span>
print<span class="br0">(</span>c<span class="br0">)</span><span class="sy4">;</span>
c.<span class="me1">clear</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
print<span class="br0">(</span>c<span class="br0">)</span><span class="sy4">;</span>
<span class="kw4">int</span> array<span class="br0">[</span><span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span> <span class="nu0">4</span>, <span class="nu0">5</span>, <span class="nu0">6</span> <span class="br0">}</span><span class="sy4">;</span>
print<span class="br0">(</span>array<span class="br0">)</span><span class="sy4">;</span>
<span class="kw4">auto</span> il <span class="sy1">=</span> <span class="br0">{</span> <span class="nu0">7</span>, <span class="nu0">8</span>, <span class="nu0">9</span> <span class="br0">}</span><span class="sy4">;</span>
print<span class="br0">(</span>il<span class="br0">)</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">Elements:
1
2
3
Empty
Elements:
4
5
6
Elements:
7
8
9</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>
<div class="t-dsc-member-div">
<div><a href="cpp-ranges-empty.html"><span class="t-lines"><span>ranges::empty</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>&#26816;&#26597;&#33539;&#22260;&#26159;&#21542;&#20026;&#31354;<br />
<span class="t-mark">(&#23450;&#21046;&#28857;&#23545;&#35937;)</span></td>
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