147 lines
13 KiB
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147 lines
13 KiB
HTML
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<title>std::strstreambuf::overflow</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_strstreambuf_overflow skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::strstreambuf::</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-strstreambuf.html">strstreambuf</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 overflow <span class="br0">(</span>int_type c <span class="sy1">=</span> <a href="cpp-io-c.html"><span class="kw1882">EOF</span></a><span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>后附字符 <code>c</code> 到缓冲的放置区，若可能则重分配。</p>
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<div class="t-li1"><span class="t-li">1)</span> 若 <code>c==EOF</code> ，则不做任何事</div>
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<div class="t-li1"><span class="t-li">2)</span> 否则，若放置区拥有可用的写位置（ <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> ），则如同用 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>pptr<span class="br0">(</span><span class="br0">)</span><span class="sy2">++</span> <span class="sy1">=</span> c</span></span> 存储该字符</div>
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<div class="t-li1"><span class="t-li">3)</span> 否则，若流缓冲模式非动态，或流当前为冻结，则函数失败并返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-io-c.html"><span class="kw1882">EOF</span></a></span></span></div>
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<div class="t-li1"><span class="t-li">4)</span> 否则，函数重分配（或初始分配）足够大以保有当前动态数组（若存在）加至少一个额外写入位置的动态数组。若构造函数中使用了指向分配函数的指针 <code>palloc</code> ，则以 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span><span class="sy2">*</span>palloc<span class="br0">)</span><span class="br0">(</span>n<span class="br0">)</span></span></span> 调用该函数，否则用 <span class="t-c"><span class="mw-geshi cpp source-cpp">new <span class="kw4">char</span><span class="br0">[</span>n<span class="br0">]</span></span></span> ，其中 <code>n</code> 为要分配的字节数。若构造函数中使用了指向解分配函数的指针 <code>pfree</code> ，则以 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span><span class="sy2">*</span>pfree<span class="br0">)</span><span class="br0">(</span>p<span class="br0">)</span></span></span> 调用该函数分配先前的数组，否则用 <span class="t-c"><span class="mw-geshi cpp source-cpp">delete<span class="br0">[</span><span class="br0">]</span> p</span></span> ，若需要解分配。若分配失败，则函数失败并返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-io-c.html"><span class="kw1882">EOF</span></a></span></span> 。</div>
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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>c</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>若 <span class="t-c"><span class="mw-geshi cpp source-cpp">c<span class="sy1">==</span><a href="cpp-io-c.html"><span class="kw1882">EOF</span></a></span></span> ，则返回异于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-io-c.html"><span class="kw1882">EOF</span></a></span></span> 的某值。否则，成功时返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span><span class="kw4">unsigned</span> <span class="kw4">char</span><span class="br0">)</span><span class="br0">(</span>c<span class="br0">)</span></span></span> ，失败时返回 <span class="t-lc"><a href="cpp-io-c.html">EOF</a></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 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 <strstream></span>
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<span class="co2">#include <iostream></span>
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<span class="kw1">struct</span> mybuf <span class="sy4">:</span> <a href="cpp-io-strstreambuf.html"><span class="kw1752">std::<span class="me2">strstreambuf</span></span></a>
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<span class="br0">{</span>
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int_type overflow<span class="br0">(</span>int_type c<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">"Before overflow(): size of the put area is "</span> <span class="sy1"><<</span> epptr<span class="br0">(</span><span class="br0">)</span><span class="sy2">-</span>pbase<span class="br0">(</span><span class="br0">)</span>
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<span class="sy1"><<</span> <span class="st0">" with "</span> <span class="sy1"><<</span> epptr<span class="br0">(</span><span class="br0">)</span><span class="sy2">-</span>pptr<span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">" write positions available<span class="es1">\n</span>"</span><span class="sy4">;</span>
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int_type rc <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">strstreambuf</span><span class="sy4">::</span><span class="me2">overflow</span><span class="br0">(</span>c<span class="br0">)</span><span class="sy4">;</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 overflow(): size of the put area is "</span> <span class="sy1"><<</span> epptr<span class="br0">(</span><span class="br0">)</span><span class="sy2">-</span>pbase<span class="br0">(</span><span class="br0">)</span>
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<span class="sy1"><<</span> <span class="st0">" with "</span> <span class="sy1"><<</span> epptr<span class="br0">(</span><span class="br0">)</span><span class="sy2">-</span>pptr<span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">" write positions available<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="kw1">return</span> rc<span class="sy4">;</span>
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<span class="br0">}</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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mybuf sbuf<span class="sy4">;</span> <span class="co1">// 读写动态 strstreambuf</span>
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<a href="cpp-io-basic_iostream.html"><span class="kw1731">std::<span class="me2">iostream</span></span></a> stream<span class="br0">(</span><span class="sy3">&</span>sbuf<span class="br0">)</span><span class="sy4">;</span>
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stream <span class="sy1"><<</span> <span class="st0">"Sufficiently long string to overflow the initial allocation, at least "</span>
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<span class="sy1"><<</span> <span class="st0">" on some systems."</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>可能的输出：</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 overflow(): size of the put area is 16 with 0 write positions available
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After overflow(): size of the put area is 32 with 15 write positions available
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Before overflow(): size of the put area is 32 with 0 write positions available
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After overflow(): size of the put area is 64 with 31 write positions available
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Before overflow(): size of the put area is 64 with 0 write positions available
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After overflow(): size of the put area is 128 with 63 write positions available</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-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>从放置区写入字符到关联的输出序列<br />
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<span class="t-mark">(<code>std::basic_streambuf<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-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_streambuf-sputc.html"><span class="t-lines"><span>sputc</span></span></a></div>
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</div>
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</td>
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<td>写一个字符到放置区域，并令 next 指针前进<br />
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<span class="t-mark">(<code>std::basic_streambuf<CharT,Traits></code> 的公开成员函数)</span></td>
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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_ostream-put.html"><span class="t-lines"><span>put</span></span></a></div>
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</div>
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</td>
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<td>插入字符<br />
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<span class="t-mark">(<code>std::basic_ostream<CharT,Traits></code> 的公开成员函数)</span></td>
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