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<title>std::basic_istream&lt;CharT,Traits&gt;::putback</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::basic_istream&lt;CharT,Traits&gt;::</span>putback</h1>
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<div id="contentSub"><span class="subpages">&lt; <a href="cpp.html">cpp</a>&lrm; | <a href="cpp-io.html">io</a>&lrm; | <a href="cpp-io-basic_istream.html">basic istream</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">basic_istream<span class="sy3">&amp;</span> putback<span class="br0">(</span> char_type ch <span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>&#22238;&#25918;&#23383;&#31526; <code>ch</code> &#21040;&#36755;&#20837;&#27969;&#65292;&#20174;&#20351;&#24471;&#19979;&#20010;&#37322;&#20986;&#30340;&#23383;&#31526;&#23558;&#20026; <code>ch</code> &#12290;</p>
<p>&#39318;&#20808;&#28165;&#38500; <code>eofbit</code> &#65292;&#28982;&#21518;&#34920;&#29616;&#20026;<a href="cpp-named_req-UnformattedInputFunction.html"><span style="font-style:italic">&#26080;&#26684;&#24335;&#36755;&#20837;&#20989;&#25968;</span> <span style="font-family: Georgia, &#39;DejaVu Serif&#39;, serif; font-style:italic">(UnformattedInputFunction)</span></a> &#12290;&#26500;&#36896;&#24182;&#26816;&#26597; sentry &#23545;&#35937;&#21518;&#65292;&#33509; <code>rdbuf()</code> &#38750;&#31354;&#65292;&#21017;&#35843;&#29992; <span class="t-c"><span class="mw-geshi cpp source-cpp">rdbuf<span class="br0">(</span><span class="br0">)</span><span class="sy2">-</span><span class="sy1">&gt;</span>sputbackc<span class="br0">(</span>ch<span class="br0">)</span></span></span> &#65292;&#33509; <code>ch</code> &#19981;&#31561;&#20110;&#26368;&#36817;&#36755;&#20986;&#30340;&#23383;&#31526;&#65292;&#21017;&#23427;&#35843;&#29992; <span class="t-c"><span class="mw-geshi cpp source-cpp">rdbuf<span class="br0">(</span><span class="br0">)</span><span class="sy2">-</span><span class="sy1">&gt;</span>pbackfail<span class="br0">(</span>ch<span class="br0">)</span></span></span> &#12290;</p>
<p>&#33509; <code>rdbuf()</code> &#20026;&#31354;&#25110;&#33509; <span class="t-c"><span class="mw-geshi cpp source-cpp">rdbuf<span class="sy2">-</span><span class="sy1">&gt;</span>sputbackc<span class="br0">(</span>ch<span class="br0">)</span></span></span> &#36820;&#22238; <span class="t-c"><span class="mw-geshi cpp source-cpp">Traits<span class="sy4">::</span><span class="me2">eof</span><span class="br0">(</span><span class="br0">)</span></span></span> &#65292;&#21017;&#35843;&#29992; <span class="t-c"><span class="mw-geshi cpp source-cpp">setstate<span class="br0">(</span>badbit<span class="br0">)</span></span></span> &#12290;</p>
<p>&#20219;&#20309;&#24773;&#20917;&#19979;&#65292;&#35774;&#32622; <code>gcount()</code> &#35745;&#25968;&#22120;&#20026;&#38646;&#12290;</p>
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">&#21442;&#25968;</span></h3>
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<td>ch</td>
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<td>&#35201;&#25918;&#20837;&#36755;&#20837;&#27969;&#30340;&#23383;&#31526;</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><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span></p>
<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">&#24322;&#24120;</span></h3>
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&#33509;&#20986;&#29616;&#38169;&#35823;&#65288;&#38169;&#35823;&#29366;&#24577;&#26631;&#24535;&#19981;&#26159; <span class="t-lc"><a href="cpp-io-ios_base-iostate.html">goodbit</a></span> &#65289;&#24182;&#19988;&#35774;&#32622;&#20102; <span class="t-lc"><a href="cpp-io-basic_ios-exceptions.html">exceptions()</a></span> &#20026;&#23545;&#35813;&#29366;&#24577;&#25243;&#20986;&#21017;&#20026; <span class="t-lc"><a href="cpp-io-ios_base-failure.html">failure</a></span> &#12290;
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">&#31034;&#20363;</span></h3>
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<p>&#28436;&#31034;&#20462;&#25913;&#21644;&#38750;&#20462;&#25913; putback() &#38388;&#30340;&#24046;&#24322;</p>
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<pre class="de1"><span class="co2">#include &lt;sstream&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-io-basic_stringstream.html"><span class="kw1737">std::<span class="me2">stringstream</span></span></a> s1<span class="br0">(</span><span class="st0">&quot;Hello, world&quot;</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// IO &#27969;</span>
s1.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">if</span> <span class="br0">(</span>s1.<span class="me1">putback</span><span class="br0">(</span><span class="st0">&#39;Y&#39;</span><span class="br0">)</span><span class="br0">)</span> <span class="co1">// &#20462;&#25913;&#32531;&#20914;&#21306;</span>
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> s1.<span class="me1">rdbuf</span><span class="br0">(</span><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="kw1">else</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;putback failed<span class="es1">\n</span>&quot;</span><span class="sy4">;</span>
<a href="cpp-io-basic_istringstream.html"><span class="kw1735">std::<span class="me2">istringstream</span></span></a> s2<span class="br0">(</span><span class="st0">&quot;Hello, world&quot;</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// &#20165;&#36755;&#20837;&#27969;</span>
s2.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">if</span> <span class="br0">(</span>s2.<span class="me1">putback</span><span class="br0">(</span><span class="st0">&#39;Y&#39;</span><span class="br0">)</span><span class="br0">)</span> <span class="co1">// cannot modify input-only buffer</span>
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> s2.<span class="me1">rdbuf</span><span class="br0">(</span><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="kw1">else</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;putback failed<span class="es1">\n</span>&quot;</span><span class="sy4">;</span>
s2.<span class="me1">clear</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">if</span> <span class="br0">(</span>s2.<span class="me1">putback</span><span class="br0">(</span><span class="st0">&#39;H&#39;</span><span class="br0">)</span><span class="br0">)</span> <span class="co1">// &#38750;&#20462;&#25913;&#22238;&#25918;</span>
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> s2.<span class="me1">rdbuf</span><span class="br0">(</span><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="kw1">else</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;putback failed<span class="es1">\n</span>&quot;</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">Yello, world
putback failed
Hello, world</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-io-basic_streambuf-sputbackc.html"><span class="t-lines"><span>sputbackc</span></span></a></div>
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<td>&#22312;&#36755;&#20837;&#24207;&#21015;&#20013;&#25918;&#22238;&#19968;&#20010;&#23383;&#31526;<br />
<span class="t-mark">(<code>std::basic_streambuf&lt;CharT,Traits&gt;</code> &#30340;&#20844;&#24320;&#25104;&#21592;&#20989;&#25968;)</span></td>
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<div><a href="cpp-io-basic_istream-unget.html"><span class="t-lines"><span>unget</span></span></a></div>
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<td>&#25764;&#38144;&#27969;&#20013;&#21018;&#21462;&#36208;&#65288;&#31227;&#38500;&#65292;&#31867;&#20284;&#25351;&#38024;&#21521;&#21518;&#36864;&#22238;&#19968;&#20010;&#20301;&#32622;&#65289;&#30340;&#23383;&#31526;<br />
<span class="t-mark">(&#20844;&#24320;&#25104;&#21592;&#20989;&#25968;)</span></td>
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<div><a href="cpp-io-basic_istream-peek.html"><span class="t-lines"><span>peek</span></span></a></div>
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<td>&#20165;&#35835;&#20986;&#20294;&#19981;&#21462;&#36208;&#65288;&#19981;&#31227;&#38500;&#31867;&#20284;&#25351;&#38024;&#24182;&#26410;&#31227;&#21160;&#65289;&#19968;&#20010;&#23383;&#31526;<br />
<span class="t-mark">(&#20844;&#24320;&#25104;&#21592;&#20989;&#25968;)</span></td>
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