190 lines
17 KiB
HTML
190 lines
17 KiB
HTML
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<title>std::basic_streambuf<CharT,Traits>::overflow</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>overflow</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">virtual</span> int_type overflow<span class="br0">(</span> int_type ch <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>通过保存始于 <span class="t-lc"><a href="cpp-io-basic_streambuf-pptr.html">pbase()</a></span> 的某个起始字符子序列到输入序列，并更新放置区（若需要），确保<a href="cpp-io-basic_streambuf.html">放置区</a>有至少一个字符的空间。若 <code>ch</code> 不是 <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> （即 <span class="t-c"><span class="mw-geshi cpp source-cpp">Traits<span class="sy4">::</span><span class="me2">eq_int_type</span><span class="br0">(</span>ch, Traits<span class="sy4">::</span><span class="me2">eof</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <span class="sy3">!</span><span class="sy1">=</span> <span class="kw2">true</span></span></span> ），则将它放到放置区或直接保存到输出序列。</p>
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<p>函数可以更新 <code>pptr</code> 、 <code>epptr</code> 和 <code>pbase</code> 指针以定义要写入更多数据的位置。失败时，函数确保 <span class="t-c"><span class="mw-geshi cpp source-cpp">pptr<span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> nullptr</span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp">pptr<span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> epptr</span></span> 。</p>
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<p>函数的基类版本不做任何事。允许此函数的导出类版本在耗尽的情况下更新放置区。</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>ch</td>
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<td>-</td>
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<td>要存储于放置区的字符</td>
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</tr>
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</table>
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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>成功时返回不等于 <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> 的未指定值，失败时返回 <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> 。</p>
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<p>此函数的基类版本返回 <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> 。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h3>
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<p><span class="t-lc"><a href="cpp-io-basic_streambuf-sputc.html">sputc()</a></span> 和 <span class="t-lc"><a href="cpp-io-basic_streambuf-sputn.html">sputn()</a></span> 在可能上溢的情况（ <span class="t-c"><span class="mw-geshi cpp source-cpp">pptr<span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> nullptr</span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp">pptr<span class="br0">(</span><span class="br0">)</span> <span class="sy1">>=</span> epptr<span class="br0">(</span><span class="br0">)</span></span></span> ）下调用此函数。</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 <array></span>
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<span class="co1">// 以 std::array 实现的 std::ostream 缓冲区</span>
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<span class="kw1">template</span><span class="sy1"><</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> SIZE, <span class="kw1">class</span> CharT <span class="sy1">=</span> <span class="kw4">char</span><span class="sy1">></span>
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<span class="kw1">class</span> ArrayedStreamBuffer <span class="sy4">:</span> <span class="kw1">public</span> <a href="cpp-io-basic_streambuf.html"><span class="kw1666">std::<span class="me2">basic_streambuf</span></span></a><span class="sy1"><</span>CharT<span class="sy1">></span> <span class="br0">{</span>
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<span class="kw1">public</span><span class="sy4">:</span>
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<span class="kw1">using</span> Base <span class="sy1">=</span> <a href="cpp-io-basic_streambuf.html"><span class="kw1666">std::<span class="me2">basic_streambuf</span></span></a><span class="sy1"><</span>CharT<span class="sy1">></span><span class="sy4">;</span>
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<span class="kw1">using</span> char_type <span class="sy1">=</span> <span class="kw1">typename</span> Base<span class="sy4">::</span><span class="me2">char_type</span><span class="sy4">;</span>
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<span class="kw1">using</span> int_type <span class="sy1">=</span> <span class="kw1">typename</span> Base<span class="sy4">::</span><span class="me2">int_type</span><span class="sy4">;</span>
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ArrayedStreamBuffer<span class="br0">(</span><span class="br0">)</span> <span class="sy4">:</span> buffer_<span class="br0">{</span><span class="br0">}</span> <span class="co1">// 值初始化 buffer_ 为全零</span>
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<span class="br0">{</span>
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Base<span class="sy4">::</span><span class="me2">setp</span><span class="br0">(</span>buffer_.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, buffer_.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 设置 std::basic_streambuf</span>
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<span class="co1">// 放置区指针以 'buffer_' 工作</span>
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<span class="br0">}</span>
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int_type overflow<span class="br0">(</span>int_type ch<span class="br0">)</span>
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<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">"overflow<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="kw1">return</span> Base<span class="sy4">::</span><span class="me2">overflow</span><span class="br0">(</span>ch<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw4">void</span> print_buffer<span class="br0">(</span><span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">const</span> <span class="kw4">auto</span><span class="sy3">&</span> i<span class="sy4">:</span> buffer_<span class="br0">)</span> <span class="br0">{</span>
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<span class="kw1">if</span> <span class="br0">(</span>i <span class="sy1">==</span> <span class="nu0">0</span><span class="br0">)</span> <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">"NULL"</span><span class="sy4">;</span>
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<span class="br0">}</span> <span class="kw1">else</span> <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> i<span class="sy4">;</span>
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<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">" "</span><span class="sy4">;</span>
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<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">"<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw1">private</span><span class="sy4">:</span>
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<a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a><span class="sy1"><</span>char_type, SIZE<span class="sy1">></span> buffer_<span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</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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ArrayedStreamBuffer<span class="sy1"><</span><span class="nu0">10</span><span class="sy1">></span> streambuf<span class="sy4">;</span>
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<a href="cpp-io-basic_ostream.html"><span class="kw1729">std::<span class="me2">ostream</span></span></a> stream<span class="br0">(</span><span class="sy3">&</span>streambuf<span class="br0">)</span><span class="sy4">;</span>
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stream <span class="sy1"><<</span> <span class="st0">"hello"</span><span class="sy4">;</span>
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streambuf.<span class="me1">print_buffer</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span>stream.<span class="me1">good</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <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">"stream is good<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span>
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stream <span class="sy1"><<</span> <span class="st0">"world"</span><span class="sy4">;</span>
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streambuf.<span class="me1">print_buffer</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span>stream.<span class="me1">good</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <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">"stream is good<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span>
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stream <span class="sy1"><<</span> <span class="st0">"!"</span><span class="sy4">;</span>
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streambuf.<span class="me1">print_buffer</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">if</span> <span class="br0">(</span><span class="sy3">!</span>stream.<span class="me1">good</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span> <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">"stream is not good<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span></pre></div>
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</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">h e l l o NULL NULL NULL NULL NULL
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stream is good
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h e l l o w o r l d
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stream is good
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overflow
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h e l l o w o r l d
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stream is not good</pre></div>
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</div>
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</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-uflow.html"><span class="t-lines"><span>uflow</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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</div>
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</td>
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<td>从输入序列读取字符到获取区，并令下一位置指针前进<br />
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<span class="t-mark">(虚受保护成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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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-underflow.html"><span class="t-lines"><span>underflow</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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</div>
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</td>
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<td>从关联输入序列读取字符到获取区<br />
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<span class="t-mark">(虚受保护成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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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_filebuf-overflow.html"><span class="t-lines"><span>overflow</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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</div>
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</td>
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<td>从放置区写字符到关联的文件<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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</tr>
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<tr class="t-dsc">
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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_stringbuf-overflow.html"><span class="t-lines"><span>overflow</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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</div>
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</td>
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<td>后附字符到输出序列<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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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-strstreambuf-overflow.html"><span class="t-lines"><span>overflow</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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</div>
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</td>
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<td>后附字符到输出序列，可能重分配或初始地分配缓冲区，若它为动态且未被冻结<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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</tr>
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</table>
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</div>
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<div class="visualClear"></div>
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</div>
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