212 lines
18 KiB
HTML
212 lines
18 KiB
HTML
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<title>std::strstreambuf::strstreambuf</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_strstreambuf_strstreambuf 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>strstreambuf</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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<td rowspan="142">(1)</td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">explicit</span> strstreambuf<span class="br0">(</span> <a href="cpp-io-streamsize.html"><span class="kw1804">std::<span class="me2">streamsize</span></span></a> alsize <span class="sy1">=</span> <span class="nu0">0</span> <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-until-cxx11">(C++11 前)</span></td>
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<div><span class="mw-geshi cpp source-cpp">strstreambuf<span class="br0">(</span><span class="br0">)</span> <span class="sy4">:</span> strstreambuf<span class="br0">(</span><span class="nu0">0</span><span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span><br />
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<span class="kw1">explicit</span> strstreambuf<span class="br0">(</span> <a href="cpp-io-streamsize.html"><span class="kw1804">std::<span class="me2">streamsize</span></span></a> alsize <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp">strstreambuf<span class="br0">(</span> <span class="kw4">void</span><span class="sy2">*</span> <span class="br0">(</span><span class="sy2">*</span>palloc<span class="br0">)</span><span class="br0">(</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a><span class="br0">)</span>, <span class="kw4">void</span> <span class="br0">(</span><span class="sy2">*</span>pfree<span class="br0">)</span><span class="br0">(</span><span class="kw4">void</span><span class="sy2">*</span><span class="br0">)</span> <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
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<div><span class="mw-geshi cpp source-cpp">strstreambuf<span class="br0">(</span> <span class="kw4">char</span><span class="sy2">*</span> gnext, <a href="cpp-io-streamsize.html"><span class="kw1804">std::<span class="me2">streamsize</span></span></a> n, <span class="kw4">char</span><span class="sy2">*</span> pbeg <span class="sy1">=</span> <span class="nu0">0</span> <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(3)</td>
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<div><span class="mw-geshi cpp source-cpp">strstreambuf<span class="br0">(</span> <span class="kw4">signed</span> <span class="kw4">char</span><span class="sy2">*</span> gnext, <a href="cpp-io-streamsize.html"><span class="kw1804">std::<span class="me2">streamsize</span></span></a> n, <span class="kw4">signed</span> <span class="kw4">char</span><span class="sy2">*</span> pbeg <span class="sy1">=</span> <span class="nu0">0</span> <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(4)</td>
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<div><span class="mw-geshi cpp source-cpp">strstreambuf<span class="br0">(</span> <span class="kw4">unsigned</span> <span class="kw4">char</span><span class="sy2">*</span> gnext, <a href="cpp-io-streamsize.html"><span class="kw1804">std::<span class="me2">streamsize</span></span></a> n, <span class="kw4">unsigned</span> <span class="kw4">char</span><span class="sy2">*</span> pbeg <span class="sy1">=</span> <span class="nu0">0</span> <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(5)</td>
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<div><span class="mw-geshi cpp source-cpp">strstreambuf<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> gnext, <a href="cpp-io-streamsize.html"><span class="kw1804">std::<span class="me2">streamsize</span></span></a> n <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(6)</td>
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<div><span class="mw-geshi cpp source-cpp">strstreambuf<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">signed</span> <span class="kw4">char</span><span class="sy2">*</span> gnext, <a href="cpp-io-streamsize.html"><span class="kw1804">std::<span class="me2">streamsize</span></span></a> n<span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(7)</td>
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<div><span class="mw-geshi cpp source-cpp">strstreambuf<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">unsigned</span> <span class="kw4">char</span><span class="sy2">*</span> gnext, <a href="cpp-io-streamsize.html"><span class="kw1804">std::<span class="me2">streamsize</span></span></a> n <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(8)</td>
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<div class="t-li1"><span class="t-li">1)</span> 构造 <code>std::strstreambuf</code> 对象:通过调用 <span class="t-lc"><a href="cpp-io-basic_streambuf.html">std::streambuf</a></span> 的默认构造函数初始化基类,初始化缓冲状态为“动态”(将按需分配缓冲区),初始化已分配大小为提供的 <code>alsize</code> ,初始化分配和解分配函数为空值(将使用 <span class="t-c"><span class="mw-geshi cpp source-cpp">new<span class="br0">[</span><span class="br0">]</span></span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">delete<span class="br0">[</span><span class="br0">]</span></span></span> )。</div>
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<div class="t-li1"><span class="t-li">2)</span> 构造 <code>std::strstreambuf</code> 对象:通过调用 <span class="t-lc"><a href="cpp-io-basic_streambuf.html">std::streambuf</a></span> 的默认构造函数初始化基类,初始化缓冲状态为“动态”(将按需分配缓冲区),初始化已分配大小为未指定值,初始化分配函数为 <code>palloc</code> ,解分配函数为 <code>pfree</code> 。</div>
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<div class="t-li1"><span class="t-li">3-5)</span> 依下列步骤构造 <code>std::strstreambuf</code> 对象:</div>
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<div class="t-li2"><span class="t-li">a)</span> 通过调用 <span class="t-lc"><a href="cpp-io-basic_streambuf.html">std::streambuf</a></span> 的默认构造函数初始化基类</div>
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<div class="t-li2"><span class="t-li">b)</span> 初始化缓冲状态为“冻结”(缓冲区为用户提供的固定大小缓冲区)</div>
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<div class="t-li2"><span class="t-li">c)</span> 以下列方式确定用户提供的数组中的元素数:若 <code>n</code> 大于零,则使用 <code>n</code> 。若 <code>n</code> 为,则执行 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-string-byte-strlen.html"><span class="kw1145">std::<span class="me2">strlen</span></span></a><span class="br0">(</span>gnext<span class="br0">)</span></span></span> 确定缓冲区大小。若 <code>n</code> 为负,则使用 <span class="t-lc"><a href="cpp-types-climits.html">INT_MAX</a></span> 。</div>
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<div class="t-li2"><span class="t-li">d)</span> 以下列方式配置 <span class="t-lc"><a href="cpp-io-basic_streambuf.html">std::basic_streambuf</a></span> 的指针:若 <code>pbeg</code> 为空指针,则调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">setg<span class="br0">(</span>gnext, gnext, gnext <span class="sy2">+</span> N<span class="br0">)</span></span></span> 。若 <code>pbeg</code> 不是空指针,则执行 <span class="t-c"><span class="mw-geshi cpp source-cpp">setg<span class="br0">(</span>gnext, gnext, pbeg<span class="br0">)</span></span></span> 和 <span class="t-c"><span class="mw-geshi cpp source-cpp">setp<span class="br0">(</span>pbeg, pbeg<span class="sy2">+</span>N<span class="br0">)</span></span></span> ,其中 N 是之前确定的数组中的元素数。</div>
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<div class="t-li1"><span class="t-li">6-8)</span> 同 <span class="t-c"><span class="mw-geshi cpp source-cpp">strstreambuf<span class="br0">(</span><span class="br0">(</span><span class="kw4">char</span><span class="sy2">*</span><span class="br0">)</span>gnext, n<span class="br0">)</span></span></span> ,除了在缓冲状态位掩码中设置“常量”(不允许输出到此缓冲区)。</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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<table class="t-par-begin">
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<tr class="t-par">
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<td>alsize</td>
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<td>-</td>
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<td>动态分配的缓冲区的初始大小</td>
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</tr>
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<tr class="t-par">
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<td>palloc</td>
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<td>-</td>
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<td>指向用户提供的分配函数的指针</td>
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</tr>
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<tr class="t-par">
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<td>pfree</td>
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<td>-</td>
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<td>指向用户提供的解分配函数的指针</td>
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</tr>
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<tr class="t-par">
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<td>gnext</td>
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<td>-</td>
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<td>指向用户提供的数组中获取区起始的指针</td>
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</tr>
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<tr class="t-par">
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<td>pbeg</td>
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<td>-</td>
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<td>指向用户提供的数组中放置区起始的指针</td>
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</tr>
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<tr class="t-par">
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<td>n</td>
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<td>-</td>
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<td>用户提供数组的获取区(若 pbeg 为空)或放置区(若 pbeg 非空)中的字节数</td>
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</tr>
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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>这些构造函数常为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-io-strstream.html"><span class="kw1755">std::<span class="me2">strstream</span></span></a></span></span> 的构造函数所调用</p>
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<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
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<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。</p>
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<table class="dsctable" style="font-size:0.8em">
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<tr>
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<th>DR</th>
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<th>应用于</th>
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<th>出版时的行为</th>
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<th>正确行为</th>
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</tr>
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<tr>
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<td><a rel="nofollow" class="external text" href="https://wg21.link/P0935R0">P0935R0</a></td>
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<td>C++11</td>
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<td>默认构造函数曾为 explicit</td>
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<td>使之为隐式</td>
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</tr>
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</table>
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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 <strstream></span>
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<span class="co2">#include <iostream></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-strstreambuf.html"><span class="kw1752">std::<span class="me2">strstreambuf</span></span></a> dyn<span class="sy4">;</span> <span class="co1">// 动态</span>
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<a href="cpp-io-strstream.html"><span class="kw1755">std::<span class="me2">strstream</span></span></a> dyn_s<span class="sy4">;</span> <span class="co1">// 等价的流</span>
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dyn_s <span class="sy1"><<</span> <span class="nu16">1.23</span> <span class="sy1"><<</span> <a href="cpp-io-manip-ends.html"><span class="kw1789">std::<span class="me2">ends</span></span></a><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> dyn_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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dyn_s.<span class="me1">freeze</span><span class="br0">(</span><span class="kw2">false</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">char</span> buf<span class="br0">[</span><span class="nu0">10</span><span class="br0">]</span><span class="sy4">;</span>
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<a href="cpp-io-strstreambuf.html"><span class="kw1752">std::<span class="me2">strstreambuf</span></span></a> user<span class="br0">(</span>buf, <span class="nu0">10</span>, buf<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 用户提供的输出缓冲区</span>
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<a href="cpp-io-ostrstream.html"><span class="kw1754">std::<span class="me2">ostrstream</span></span></a> user_s<span class="br0">(</span>buf, <span class="nu0">10</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 等价的流</span>
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user_s <span class="sy1"><<</span> <span class="nu16">1.23</span> <span class="sy1"><<</span> <a href="cpp-io-manip-ends.html"><span class="kw1789">std::<span class="me2">ends</span></span></a><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> buf <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<a href="cpp-io-strstreambuf.html"><span class="kw1752">std::<span class="me2">strstreambuf</span></span></a> lit<span class="br0">(</span><span class="st0">"1 2 3"</span>, <span class="nu0">5</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 常量</span>
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<a href="cpp-io-istrstream.html"><span class="kw1753">std::<span class="me2">istrstream</span></span></a> lit_s<span class="br0">(</span><span class="st0">"1 2 3"</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 等价的流</span>
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<span class="kw4">int</span> i, j, k<span class="sy4">;</span>
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lit_s <span class="sy1">>></span> i <span class="sy1">>></span> j <span class="sy1">>></span> k<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> i <span class="sy1"><<</span> <span class="st0">' '</span> <span class="sy1"><<</span> j <span class="sy1"><<</span> <span class="st0">' '</span> <span class="sy1"><<</span> k <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></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">1.23
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1.23
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1 2 3</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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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div t-dsc-member-nobold-div">
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<div><a href="cpp-io-strstream-strstream.html"><span class="t-lines"><span>(构造函数)</span></span></a></div>
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</div>
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</td>
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<td>构造 strstream ,可选地分配缓冲区<br />
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<span class="t-mark">(<code>std::strstream</code> 的公开成员函数)</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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</div>
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</div>
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</body>
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</html>
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