85 lines
4.9 KiB
HTML
85 lines
4.9 KiB
HTML
<!DOCTYPE html>
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<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
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<head><meta http-equiv="x-ua-compatible" content="ie=edge">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>std::span<T,Extent>::empty</title>
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<link rel="stylesheet" href="ext.css" />
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_container_span_empty skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::span<T,Extent>::</span>empty</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-container.html">container</a>‎ | <a href="cpp-container-span.html">span</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><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="br0">)</span> <span class="kw4">const</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td></td>
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<td></td>
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<td></td>
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</tr>
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</tbody>
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</table>
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<p>检查 span 是否为空。</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 为空（即 <span class="t-c"><span class="mw-geshi cpp source-cpp">size<span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> <span class="nu0">0</span></span></span> ）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=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<div class="t-example-live-link"></div>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <span></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <iomanip></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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std<span class="sy4">::</span><span class="me2">span</span><span class="sy1"><</span><span class="kw4">const</span> <span class="kw4">char</span><span class="sy1">></span> span<span class="br0">{</span> <span class="st0">"ABCDEF"</span> <span class="br0">}</span><span class="sy4">;</span>
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<span class="kw1">while</span> <span class="br0">(</span><span class="sy3">!</span>span.<span class="me1">empty</span><span class="br0">(</span><span class="br0">)</span><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> <a href="cpp-io-manip-quoted.html"><span class="kw1802">std::<span class="me2">quoted</span></span></a><span class="br0">(</span>span.<span class="me1">data</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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span <span class="sy1">=</span> span.<span class="me1">last</span><span class="br0">(</span>span.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span> <span class="sy2">-</span> <span class="nu0">1</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span></pre></div>
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</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">"ABCDEF"
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"BCDEF"
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"CDEF"
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"DEF"
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"EF"
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"F"
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""</pre></div>
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</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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-container-span-size.html"><span class="t-lines"><span>size</span></span></a></div>
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</div>
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</td>
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<td>返回序列中的元素数<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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</table>
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</div>
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</div>
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</div>
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</div>
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