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<title>std::basic_streambuf<CharT,Traits>::sputbackc</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::basic_streambuf<CharT,Traits>::</span>sputbackc</h1>
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-io.html">io</a>‎ | <a href="cpp-io-basic_streambuf.html">basic streambuf</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">int_type sputbackc<span class="br0">(</span> char_type c <span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>放回字符到获取区。</p>
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<p>若回放位置在获取区中可用（ <span class="t-c"><span class="mw-geshi cpp source-cpp">gptr<span class="br0">(</span><span class="br0">)</span> <span class="sy1">></span> eback<span class="br0">(</span><span class="br0">)</span></span></span> ），而字符 <code>c</code> 等于 <span class="t-lc"><a href="cpp-io-basic_streambuf-gptr.html">gptr()</a></span> 左一位置的字符（以 <span class="t-c"><span class="mw-geshi cpp source-cpp">Traits<span class="sy4">::</span><span class="me2">eq</span><span class="br0">(</span>c, gptr<span class="br0">(</span><span class="br0">)</span><span class="br0">[</span><span class="sy2">-</span><span class="nu0">1</span><span class="br0">]</span><span class="br0">)</span></span></span> 确定），则简单地减少下一位置指针（ <span class="t-lc"><a href="cpp-io-basic_streambuf-gptr.html">gptr()</a></span> ）。</p>
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<p>否则，调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">pbackfail<span class="br0">(</span>Traits<span class="sy4">::</span><span class="me2">to_int_type</span><span class="br0">(</span>c<span class="br0">)</span><span class="br0">)</span></span></span> 放回到获取区，或一同修改获取区和可能的关联字符序列。</p>
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<p>I/O 流函数 <a href="cpp-io-basic_istream-putback.html"><tt>basic_istream::putback</tt></a> 以此函数实现。</p>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<table class="t-par-begin">
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<td>c</td>
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<td>-</td>
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<td>要回放的字符</td>
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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>若回放位置可用，则返回下一位置指针现在指向的字符，以 <span class="t-c"><span class="mw-geshi cpp source-cpp">Traits<span class="sy4">::</span><span class="me2">to_int_type</span><span class="br0">(</span><span class="sy2">*</span>gptr<span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 转换为 <code>int_type</code> 。来自此 streambuf 的下个单字符输入将返回此字符。</p>
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<p>若回放位置不可用，则返回 <span class="t-lc"><a href="cpp-io-basic_streambuf-pbackfail.html">pbackfail()</a></span> 所返回者，在失败时为 <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> 。</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 <iostream></span>
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<span class="co2">#include <sstream></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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<a href="cpp-io-basic_stringstream.html"><span class="kw1737">std::<span class="me2">stringstream</span></span></a> s<span class="br0">(</span><span class="st0">"abcdef"</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// gptr() 指向 "abcdef" 中的 'a'</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> <span class="st0">"Before putback, string holds "</span> <span class="sy1"><<</span> s.<span class="me1">str</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 class="kw4">char</span> c1 <span class="sy1">=</span> s.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// c1 = 'a' ， gptr() 现在指向 "abcdef" 中的 'b'</span>
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<span class="kw4">char</span> c2 <span class="sy1">=</span> s.<span class="me1">rdbuf</span><span class="br0">(</span><span class="br0">)</span><span class="sy2">-</span><span class="sy1">></span>sputbackc<span class="br0">(</span><span class="st0">'z'</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 同 s.putback('z')</span>
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<span class="co1">// gptr() 现在指向 "zbcdef" 中的 'z'</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> <span class="st0">"After putback, string holds "</span> <span class="sy1"><<</span> s.<span class="me1">str</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 class="kw4">char</span> c3 <span class="sy1">=</span> s.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// c3 = 'z' ， gptr() 现在指向 "zbcdef" 中的 'b'</span>
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<span class="kw4">char</span> c4 <span class="sy1">=</span> s.<span class="me1">get</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// c4 = 'b' ， gptr() 现在指向 "zbcdef" 中的 'c'</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> c1 <span class="sy1"><<</span> c2 <span class="sy1"><<</span> c3 <span class="sy1"><<</span> c4 <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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s.<span class="me1">rdbuf</span><span class="br0">(</span><span class="br0">)</span><span class="sy2">-</span><span class="sy1">></span>sputbackc<span class="br0">(</span><span class="st0">'b'</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// gptr() 现在指向 "zbcdef" 中的 'b'</span>
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s.<span class="me1">rdbuf</span><span class="br0">(</span><span class="br0">)</span><span class="sy2">-</span><span class="sy1">></span>sputbackc<span class="br0">(</span><span class="st0">'z'</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// gptr() 现在指向 "zbcdef" 中的 'z'</span>
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<span class="kw4">int</span> eof <span class="sy1">=</span> s.<span class="me1">rdbuf</span><span class="br0">(</span><span class="br0">)</span><span class="sy2">-</span><span class="sy1">></span>sputbackc<span class="br0">(</span><span class="st0">'x'</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 无内容能反获取： pbackfail() 失败</span>
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<span class="kw1">if</span> <span class="br0">(</span>eof <span class="sy1">==</span> <a href="cpp-io-c.html"><span class="kw1882">EOF</span></a><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> <span class="st0">"No room to putback after 'z'<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></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">Before putback, string holds abcdef
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After putback, string holds zbcdef
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azzb
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No room to putback after 'z'</pre></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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<table class="t-dsc-begin">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-basic_streambuf-sungetc.html"><span class="t-lines"><span>sungetc</span></span></a></div>
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</div>
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<td>回移一位输出序列中的下一位置指针<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-basic_istream-putback.html"><span class="t-lines"><span>putback</span></span></a></div>
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</div>
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</td>
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<td>往输入流中退回一个字符<br />
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<span class="t-mark">(<code>std::basic_istream<CharT,Traits></code> 的公开成员函数)</span></td>
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<div class="visualClear"></div>
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