113 lines
8.8 KiB
HTML
113 lines
8.8 KiB
HTML
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<title>std::basic_streambuf<CharT,Traits>::pbackfail</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>pbackfail</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"><span class="kw1">protected</span><span class="sy4">:</span><br />
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<span class="kw1">virtual</span> int_type pbackfail<span class="br0">(</span> int_type c <span class="sy1">=</span> Traits<span class="sy4">::</span><span class="me2">eof</span><span class="br0">(</span><span class="br0">)</span> <span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>在下列情况之一时，此受保护虚函数为公开成员函数 <span class="t-lc"><a href="cpp-io-basic_streambuf-sungetc.html">sungetc()</a></span> 和 <span class="t-lc"><a href="cpp-io-basic_streambuf-sputbackc.html">sputbackc()</a></span> 所调用（它们继而为 <a href="cpp-io-basic_istream-unget.html"><tt>basic_istream::unget</tt></a> 和 <a href="cpp-io-basic_istream-putback.html"><tt>basic_istream::putback</tt></a> 所调用）：</p>
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<div class="t-li1"><span class="t-li">1)</span> 获取区中无回放位置（以无参数调用 <code>pbackfail()</code> ）。此情形中， <code>pbackfail()</code> 的目的是令获取区后备一个字符，若关联字符序列允许（例如文件支持的 streambuf 可以在提前一个字符的位置，从文件重新加载缓冲区）。</div>
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<div class="t-li1"><span class="t-li">2)</span> 调用方试图回放异于先前取得字符的另一字符（以需要回放的字符调用 <code>pbackfail()</code> ）。此情形中， <code>pbackfail()</code> 的目的是将字符 <code>c</code> 置于获取区中刚好前于 <a href="cpp-io-basic_streambuf-gptr.html"><tt>basic_streambuf::gptr()</tt></a> 的位置，以及若可能则修改关联字符序列以反映此更改。这可能涉及如在第一变体中一般的后备获取区。</div>
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<p>此函数的默认基类版本不做任何事并于所有情形返回 <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> 。导出类覆写此函数： <a href="cpp-io-basic_stringbuf-pbackfail.html"><tt>basic_stringbuf::pbackfail</tt></a> 、 <a href="cpp-io-basic_filebuf-pbackfail.html"><tt>basic_filebuf::pbackfail</tt></a> 、 <a href="cpp-io-strstreambuf-pbackfail.html"><tt>strstreambuf::pbackfail</tt></a> ，而且期待用户定义和第三方库流类也覆写此函数。</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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<td>ch</td>
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<td>要回放的字符，或若只请求放弃则为 <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></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>失败情况下为 <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> ，某个不同值指示成功。基类版本始终失败。</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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<td class="mbox-text" style="">本节未完成<br />
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原因：暂无示例</td>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<div><a href="cpp-io-basic_filebuf-pbackfail.html"><span class="t-lines"><span>pbackfail</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-cmark">[虚]</span></span></span></div>
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</td>
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<td>回退输出序列以放回字符，不影响关联文件<br />
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<span class="t-mark">(<code>std::basic_filebuf<CharT,Traits></code> 的虚受保护成员函数)</span></td>
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<div><a href="cpp-io-basic_stringbuf-pbackfail.html"><span class="t-lines"><span>pbackfail</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-cmark">[虚]</span></span></span></div>
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<td>回放字符到输出序列中<br />
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<span class="t-mark">(<code>std::basic_stringbuf<CharT,Traits,Allocator></code> 的虚受保护成员函数)</span></td>
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<div><a href="cpp-io-strstreambuf-pbackfail.html"><span class="t-lines"><span>pbackfail</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-cmark">[虚]</span></span></span></div>
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<td>回退输入序列以反获取一个字符<br />
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<span class="t-mark">(<code>std::strstreambuf</code> 的虚受保护成员函数)</span></td>
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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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<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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<div><a href="cpp-io-basic_streambuf-sputbackc.html"><span class="t-lines"><span>sputbackc</span></span></a></div>
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<td>在输入序列中放回一个字符<br />
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<span class="t-mark">(公开成员函数)</span></td>
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