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<title>std::basic_string&lt;CharT,Traits,Allocator&gt;::substr</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>substr</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">basic_string substr<span class="br0">(</span> size_type pos <span class="sy1">=</span> <span class="nu0">0</span>, size_type count <span class="sy1">=</span> npos <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-until-cxx20">(C++20 &#21069;)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> basic_string substr<span class="br0">(</span> size_type pos <span class="sy1">=</span> <span class="nu0">0</span>, size_type count <span class="sy1">=</span> npos <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>&#36820;&#22238;&#23376;&#20018; <code>[pos, pos+count)</code> &#12290;&#33509;&#35831;&#27714;&#30340;&#23383;&#20018;&#36234;&#36807;&#23383;&#31526;&#20018;&#30340;&#32467;&#23614;&#65292;&#21363; <code>count</code> &#22823;&#20110; <span class="t-c"><span class="mw-geshi cpp source-cpp">size<span class="br0">(</span><span class="br0">)</span> <span class="sy2">-</span> pos</span></span> &#65288;&#20363;&#22914;&#33509; <span class="t-c"><span class="mw-geshi cpp source-cpp">count <span class="sy1">==</span> npos</span></span> &#65289;&#65292;&#21017;&#36820;&#22238;&#30340;&#23376;&#20018;&#20026; <code>[pos, <a href="cpp-string-basic_string-size.html">size()</a>)</code> &#12290;</p>
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">&#21442;&#25968;</span></h3>
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<td>pos</td>
<td>-</td>
<td>&#35201;&#21253;&#21547;&#30340;&#39318;&#20010;&#23383;&#31526;&#30340;&#20301;&#32622;</td>
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<td>count</td>
<td>-</td>
<td>&#23376;&#20018;&#30340;&#38271;&#24230;</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>&#21547;&#23376;&#20018; <code>[pos, pos+count)</code> &#25110; <code>[pos, <a href="cpp-string-basic_string-size.html">size()</a>)</code> &#30340; string &#12290;</p>
<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">&#24322;&#24120;</span></h3>
<p>&#33509; <code>pos &gt; <a href="cpp-string-basic_string-size.html">size()</a></code> &#21017;&#20026; <span class="t-lc"><a href="cpp-error-out_of_range.html">std::out_of_range</a></span> &#12290;</p>
<h3><span class="mw-headline" id=".E5.A4.8D.E6.9D.82.E5.BA.A6">&#22797;&#26434;&#24230;</span></h3>
<p>&#19982; <code>count</code> &#25104;&#32447;&#24615;&#12290;</p>
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">&#27880;&#35299;</span></h3>
<p>&#22914;&#21516;&#20197; <span class="t-c"><span class="mw-geshi cpp source-cpp">basic_string<span class="br0">(</span>data<span class="br0">(</span><span class="br0">)</span><span class="sy2">+</span>pos, count<span class="br0">)</span></span></span> &#26500;&#36896;&#36820;&#22238;&#30340; string &#65292;&#36825;&#38544;&#21547;&#23558;&#20250;&#40664;&#35748;&#26500;&#36896;&#36820;&#22238;&#30340; string &#30340;&#20998;&#37197;&#22120;&mdash;&mdash;&#26032;&#20998;&#37197;&#22120;&#23558;<i>&#19981;</i>&#26159; <code>this-&gt;<a href="cpp-string-basic_string-get_allocator.html">get_allocator()</a></code> &#30340;&#21103;&#26412;&#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;string&gt;</span>
<span class="co2">#include &lt;iostream&gt;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> a <span class="sy1">=</span> <span class="st0">&quot;0123456789abcdefghij&quot;</span><span class="sy4">;</span>
<span class="co1">// count &#20026; npos &#65292;&#36820;&#22238; [pos, size())</span>
<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> sub1 <span class="sy1">=</span> a.<span class="me1">substr</span><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> sub1 <span class="sy1">&lt;&lt;</span> <span class="st0">&#39;<span class="es1">\n</span>&#39;</span><span class="sy4">;</span>
<span class="co1">// pos &#21644; pos+count &#37117;&#22312;&#36793;&#30028;&#20869;&#65292;&#36820;&#22238; [pos, pos+count)</span>
<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> sub2 <span class="sy1">=</span> a.<span class="me1">substr</span><span class="br0">(</span><span class="nu0">5</span>, <span class="nu0">3</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> sub2 <span class="sy1">&lt;&lt;</span> <span class="st0">&#39;<span class="es1">\n</span>&#39;</span><span class="sy4">;</span>
<span class="co1">// pos &#22312;&#36793;&#30028;&#20869;&#65292; pos+count &#19981;&#22312;&#65292;&#36820;&#22238; [pos, size()) </span>
<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> sub4 <span class="sy1">=</span> a.<span class="me1">substr</span><span class="br0">(</span>a.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span><span class="sy2">-</span><span class="nu0">3</span>, <span class="nu0">50</span><span class="br0">)</span><span class="sy4">;</span>
<span class="co1">// &#36825;&#31561;&#25928;&#20110;</span>
<span class="co1">// std::string sub4 = a.substr(17, 3);</span>
<span class="co1">// &#22240;&#20026; a.size() == 20 &#65292; pos == a.size()-3 == 17 &#32780; a.size()-pos == 3</span>
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> sub4 <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>
<span class="co1">// pos &#22312;&#36793;&#30028;&#22806;&#65292;&#25243;&#20986;</span>
<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> sub5 <span class="sy1">=</span> a.<span class="me1">substr</span><span class="br0">(</span>a.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span><span class="sy2">+</span><span class="nu0">3</span>, <span class="nu0">50</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> sub5 <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-error-out_of_range.html"><span class="kw768">std::<span class="me2">out_of_range</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="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;pos exceeds string size<span class="es1">\n</span>&quot;</span><span class="sy4">;</span>
<span class="br0">}</span>
<span class="br0">}</span></pre></div>
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<p>&#36755;&#20986;&#65306;</p>
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<pre class="de1">abcdefghij
567
hij
pos exceeds string size</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-copy.html"><span class="t-lines"><span>copy</span></span></a></div>
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<td>&#22797;&#21046;&#23383;&#31526;<br />
<span class="t-mark">(&#20844;&#24320;&#25104;&#21592;&#20989;&#25968;)</span></td>
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<div><a href="cpp-string-basic_string-size.html"><span class="t-lines"><span>size</span><span>length</span></span></a></div>
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<td>&#36820;&#22238;&#23383;&#31526;&#25968;<br />
<span class="t-mark">(&#20844;&#24320;&#25104;&#21592;&#20989;&#25968;)</span></td>
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<div><a href="cpp-string-basic_string-find.html"><span class="t-lines"><span>find</span></span></a></div>
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<td>&#20110;&#23383;&#31526;&#20018;&#20013;&#23547;&#25214;&#23383;&#31526;<br />
<span class="t-mark">(&#20844;&#24320;&#25104;&#21592;&#20989;&#25968;)</span></td>
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<div><a href="cpp-string-basic_string-npos.html"><span class="t-lines"><span>npos</span></span></a></div>
<div><span class="t-lines"><span><span class="t-cmark">[&#38745;&#24577;]</span></span></span></div>
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<td>&#29305;&#27530;&#20540;&#12290;&#20934;&#30830;&#21547;&#20041;&#20381;&#36182;&#35821;&#22659;<br />
<span class="t-mark">(&#20844;&#24320;&#38745;&#24577;&#25104;&#21592;&#24120;&#37327;)</span></td>
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