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<title>std::basic_string&lt;CharT,Traits,Allocator&gt;::starts_with</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::basic_string&lt;CharT,Traits,Allocator&gt;::</span>starts_with</h1>
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<div id="contentSub"><span class="subpages">&lt; <a href="cpp.html">cpp</a>&lrm; | <a href="cpp-string.html">string</a>&lrm; | <a href="cpp-string-basic_string.html">basic string</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw4">bool</span> starts_with<span class="br0">(</span> <a href="cpp-string-basic_string_view.html"><span class="kw1246">std::<span class="me2">basic_string_view</span></span></a><span class="sy1">&lt;</span>CharT,Traits<span class="sy1">&gt;</span> sv <span class="br0">)</span><br />
&nbsp; &nbsp; <span class="kw4">const</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td>(1)</td>
<td><span class="t-mark-rev t-since-cxx20">(C++20 &#36215;)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw4">bool</span> starts_with<span class="br0">(</span> CharT c <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>(2)</td>
<td><span class="t-mark-rev t-since-cxx20">(C++20 &#36215;)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw4">bool</span> starts_with<span class="br0">(</span> <span class="kw4">const</span> CharT<span class="sy2">*</span> s <span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 &#36215;)</span></td>
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<p>&#26816;&#26597; string &#26159;&#21542;&#22987;&#20110;&#32473;&#23450;&#21069;&#32512;&#12290;&#21069;&#32512;&#21487;&#20026;&#20197;&#19979;&#20043;&#19968;&#65306;</p>
<div class="t-li1"><span class="t-li">1)</span> string_view <code>sv</code> &#65288;&#21487;&#20197;&#26159;&#20174;&#21478;&#19968; <code>std::basic_string</code> &#38544;&#24335;&#36716;&#25442;&#30340;&#32467;&#26524;&#65289;&#12290;</div>
<div class="t-li1"><span class="t-li">2)</span> &#21333;&#20010;&#23383;&#31526; <code>c</code></div>
<div class="t-li1"><span class="t-li">3)</span> &#31354;&#32456;&#27490;&#23383;&#31526;&#20018; <code>s</code></div>
<p>&#25152;&#26377;&#19977;&#20010;&#37325;&#36733;&#31561;&#25928;&#22320;&#36820;&#22238; <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-string-basic_string_view.html"><span class="kw1246">std::<span class="me2">basic_string_view</span></span></a><span class="sy1">&lt;</span>CharT, Traits<span class="sy1">&gt;</span><span class="br0">(</span>data<span class="br0">(</span><span class="br0">)</span>, size<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span>.<span class="me1">starts_with</span><span class="br0">(</span>x<span class="br0">)</span></span></span> &#65292;&#20854;&#20013; <code>x</code> &#26159;&#21442;&#25968;&#12290;</p>
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">&#21442;&#25968;</span></h3>
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<td>sv</td>
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<td>string_view &#65292;&#21487;&#20026;&#20174;&#21478;&#19968; <code>std::basic_string</code> &#38544;&#24335;&#36716;&#25442;&#30340;&#32467;&#26524;</td>
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<td>c</td>
<td>-</td>
<td>&#21333;&#20010;&#23383;&#31526;</td>
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<td>s</td>
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<td>&#31354;&#32456;&#27490;&#23383;&#31526;&#20018;</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>
<p>&#33509; string &#22987;&#20110;&#21069;&#32512;&#36215;&#22987;&#21017;&#20026; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> &#65292;&#21542;&#21017;&#20026; <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">false</span></span></span> &#12290;</p>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">&#31034;&#20363;</span></h3>
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<pre class="de1"><span class="co2">#include &lt;iostream&gt;</span>
<span class="co2">#include &lt;string_view&gt;</span>
<span class="co2">#include &lt;string&gt;</span>
<span class="kw1">template</span> <span class="sy1">&lt;</span><span class="kw1">typename</span> PrefixType<span class="sy1">&gt;</span>
<span class="kw4">void</span> test_prefix_print<span class="br0">(</span><span class="kw4">const</span> <a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy3">&amp;</span> str, PrefixType prefix<span class="br0">)</span>
<span class="br0">{</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">&#39;<span class="es1">\&#39;</span>&#39;</span> <span class="sy1">&lt;&lt;</span> str <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;&#39; starts with &#39;&quot;</span> <span class="sy1">&lt;&lt;</span> prefix <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;&#39;: &quot;</span> <span class="sy1">&lt;&lt;</span>
str.<span class="me1">starts_with</span><span class="br0">(</span>prefix<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="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
<a href="cpp-io-manip-boolalpha.html"><span class="kw1764">std::<span class="me2">boolalpha</span></span></a><span class="br0">(</span><a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a><span class="br0">)</span><span class="sy4">;</span>
<span class="kw4">auto</span> helloWorld <span class="sy1">=</span> <a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="br0">(</span><span class="st0">&quot;hello world&quot;</span><span class="br0">)</span><span class="sy4">;</span>
test_prefix_print<span class="br0">(</span>helloWorld, <a href="cpp-string-basic_string_view.html"><span class="kw1248">std::<span class="me2">string_view</span></span></a><span class="br0">(</span><span class="st0">&quot;hello&quot;</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
test_prefix_print<span class="br0">(</span>helloWorld, <a href="cpp-string-basic_string_view.html"><span class="kw1248">std::<span class="me2">string_view</span></span></a><span class="br0">(</span><span class="st0">&quot;goodbye&quot;</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
test_prefix_print<span class="br0">(</span>helloWorld, <span class="st0">&#39;h&#39;</span><span class="br0">)</span><span class="sy4">;</span>
test_prefix_print<span class="br0">(</span>helloWorld, <span class="st0">&#39;x&#39;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div>
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<p>&#36755;&#20986;&#65306;</p>
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<pre class="de1">&#39;hello world&#39; starts with &#39;hello&#39;: true
&#39;hello world&#39; starts with &#39;goodby&#39;: false
&#39;hello world&#39; starts with &#39;h&#39;: true
&#39;hello world&#39; starts with &#39;x&#39;: false</pre></div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">&#21442;&#38405;</span></h3>
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<div><a href="cpp-string-basic_string-ends_with.html"><span class="t-lines"><span>ends_with</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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<td>&#26816;&#26597; string &#26159;&#21542;&#32456;&#20110;&#32473;&#23450;&#21518;&#32512;<br />
<span class="t-mark">(&#20844;&#24320;&#25104;&#21592;&#20989;&#25968;)</span></td>
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<div class="t-dsc-member-div">
<div><a href="cpp-string-basic_string_view-starts_with.html"><span class="t-lines"><span>starts_with</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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<td>&#26816;&#26597; string_view &#26159;&#21542;&#22987;&#20110;&#32473;&#23450;&#21069;&#32512;<br />
<span class="t-mark">(<code>std::basic_string_view&lt;CharT,Traits&gt;</code> &#30340;&#20844;&#24320;&#25104;&#21592;&#20989;&#25968;)</span></td>
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<div class="t-dsc-member-div">
<div><a href="cpp-string-basic_string_view-ends_with.html"><span class="t-lines"><span>ends_with</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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<td>&#26816;&#26597; string_view &#26159;&#21542;&#32456;&#20110;&#32473;&#23450;&#21518;&#32512;<br />
<span class="t-mark">(<code>std::basic_string_view&lt;CharT,Traits&gt;</code> &#30340;&#20844;&#24320;&#25104;&#21592;&#20989;&#25968;)</span></td>
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<div><a href="cpp-string-basic_string-contains.html"><span class="t-lines"><span>contains</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx23">(C++23)</span></span></span></div>
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<td>&#26816;&#26597;&#23383;&#31526;&#20018;&#26159;&#21542;&#21547;&#26377;&#32473;&#23450;&#30340;&#23376;&#20018;&#25110;&#23383;&#31526;<br />
<span class="t-mark">(&#20844;&#24320;&#25104;&#21592;&#20989;&#25968;)</span></td>
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<div class="t-dsc-member-div">
<div><a href="cpp-string-basic_string_view-contains.html"><span class="t-lines"><span>contains</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx23">(C++23)</span></span></span></div>
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<td>&#26816;&#26597;&#23383;&#31526;&#20018;&#35270;&#22270;&#26159;&#21542;&#21547;&#26377;&#32473;&#23450;&#30340;&#23376;&#20018;&#25110;&#23383;&#31526;<br />
<span class="t-mark">(<code>std::basic_string_view&lt;CharT,Traits&gt;</code> &#30340;&#20844;&#24320;&#25104;&#21592;&#20989;&#25968;)</span></td>
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<div><a href="cpp-string-basic_string-compare.html"><span class="t-lines"><span>compare</span></span></a></div>
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<td>&#27604;&#36739;&#20108;&#20010;&#23383;&#31526;&#20018;<br />
<span class="t-mark">(&#20844;&#24320;&#25104;&#21592;&#20989;&#25968;)</span></td>
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<div class="t-dsc-member-div">
<div><a href="cpp-string-basic_string-substr.html"><span class="t-lines"><span>substr</span></span></a></div>
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<td>&#36820;&#22238;&#23376;&#20018;<br />
<span class="t-mark">(&#20844;&#24320;&#25104;&#21592;&#20989;&#25968;)</span></td>
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