175 lines
13 KiB
HTML
175 lines
13 KiB
HTML
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<title>std::strstream::strstream</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_strstream_strstream skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<div id="content"><a id="top"></a>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::strstream::</span>strstream</h1>
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<div id="bodyContent">
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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-strstream.html">strstream</a></span></div>
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<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<table class="t-dcl-begin">
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<td>
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<div><span class="mw-geshi cpp source-cpp">strstream<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td class="t-dcl-nopad"></td>
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<div><span class="mw-geshi cpp source-cpp">strstream<span class="br0">(</span><span class="kw4">char</span><span class="sy2">*</span> s, <span class="kw4">int</span> n, <a href="cpp-io-ios_base-openmode.html"><span class="kw1671">std::<span class="me2">ios_base</span><span class="sy4">::</span><span class="me2">openmode</span></span></a> mode<br />
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<span class="sy1">=</span> <a href="cpp-io-ios_base-openmode.html"><span class="kw1674">std::<span class="me2">ios_base</span><span class="sy4">::</span><span class="me2">in</span></span></a> <span class="sy3">|</span> <a href="cpp-io-ios_base-openmode.html"><span class="kw1675">std::<span class="me2">ios_base</span><span class="sy4">::</span><span class="me2">out</span></span></a><span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
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<td class="t-dcl-nopad"></td>
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<td></td>
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<td></td>
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<td></td>
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<p>构造新的输入/输出 strstream 及其底层 <span class="t-lc"><a href="cpp-io-strstreambuf.html">std::strstreambuf</a></span> 。</p>
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<div class="t-li1"><span class="t-li">1)</span> 默认构造底层 <span class="t-lc"><a href="cpp-io-strstreambuf.html">std::strstreambuf</a></span> ，这创建动态成长的缓冲区，并以该 strstreambuf 成员的地址初始化基类。</div>
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<div class="t-li1"><span class="t-li">2)</span> 以底层 <span class="t-lc"><a href="cpp-io-strstreambuf.html">std::strstreambuf</a></span> 成员的地址初始化基类，该成员以二种可能方式之一初始化，两者都使用用户提供的数组：</div>
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<div class="t-li2"><span class="t-li">a)</span> 若 <code>mode</code> 中未设置 <code>app</code> 位，则通过调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">strstreambuf<span class="br0">(</span>s, n, s<span class="br0">)</span></span></span> 构造缓冲。若首元素为 <code>s</code> 所指向的数组中元素少于 <code>n</code> 个，则行为未定义。</div>
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<div class="t-li2"><span class="t-li">b)</span> 若 <code>mode</code> 中设置了 <code>app</code> 位，则通过调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">strstreambuf<span class="br0">(</span>s, n, s <span class="sy2">+</span> <a href="cpp-string-byte-strlen.html"><span class="kw1145">std::<span class="me2">strlen</span></span></a><span class="br0">(</span>s<span class="br0">)</span><span class="br0">)</span></span></span> 构造缓冲。若首元素为 <code>s</code> 所指向的数组中元素少于 <code>n</code> 个，或若数组不含合法的空终止字符序列，则行为未定义。</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>s</td>
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<td>-</td>
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<td>用作输出缓冲区的 char 数组</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>用作输出缓冲区的数组大小</td>
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</tr>
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<tr class="t-par">
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<td>mode</td>
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<td>-</td>
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<td>指定流打开模式。它是位掩码类型，定义下列常量（尽管只使用 <code>app</code> ）：
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<table class="t-dsc-begin">
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<tr class="t-dsc-hitem">
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<td>常量</td>
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<td>解释</td>
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<tr class="t-dsc">
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<td><a href="cpp-io-ios_base-openmode.html"><tt>app</tt></a></td>
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<td>每次写入前寻位到流结尾</td>
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</tr>
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<tr class="t-dsc">
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<td><a href="cpp-io-ios_base-openmode.html"><tt>binary</tt></a></td>
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<td>以<a href="cpp-io-c-FILE.html#.E4.BA.8C.E8.BF.9B.E5.88.B6.E4.B8.8E.E6.96.87.E6.9C.AC.E6.A8.A1.E5.BC.8F">二进制模式</a>打开</td>
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</tr>
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<tr class="t-dsc">
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<td><a href="cpp-io-ios_base-openmode.html"><tt>in</tt></a></td>
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<td>为读打开</td>
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</tr>
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<tr class="t-dsc">
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<td><a href="cpp-io-ios_base-openmode.html"><tt>out</tt></a></td>
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<td>为写打开</td>
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</tr>
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<tr class="t-dsc">
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<td><a href="cpp-io-ios_base-openmode.html"><tt>trunc</tt></a></td>
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<td>在打开时舍弃流的内容</td>
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</tr>
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<tr class="t-dsc">
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<td><a href="cpp-io-ios_base-openmode.html"><tt>ate</tt></a></td>
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<td>打开后立即寻位到流结尾</td>
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</tr>
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</table>
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</td>
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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 <iostream></span>
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<span class="co2">#include <strstream></span>
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<span class="co2">#include <string></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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<span class="co1">// dynamic buffer</span>
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<a href="cpp-io-strstream.html"><span class="kw1755">std::<span class="me2">strstream</span></span></a> s1<span class="sy4">;</span> <span class="co1">// 动态缓冲区</span>
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s1 <span class="sy1"><<</span> <span class="nu0">1</span> <span class="sy1"><<</span> <span class="st0">' '</span> <span class="sy1"><<</span> <span class="nu16">3.14</span> <span class="sy1"><<</span> <span class="st0">" example"</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> <span class="st0">"buffer holds '"</span> <span class="sy1"><<</span> s1.<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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s1.<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">int</span> n<span class="sy4">;</span> <span class="kw4">double</span> d<span class="sy4">;</span>
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<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> w<span class="sy4">;</span>
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s1 <span class="sy1">>></span> n <span class="sy1">>></span> d <span class="sy1">>></span> w<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">"Read back: n = "</span> <span class="sy1"><<</span> n
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<span class="sy1"><<</span> <span class="st0">" d = "</span> <span class="sy1"><<</span> d
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<span class="sy1"><<</span> <span class="st0">" w = '"</span> <span class="sy1"><<</span> w <span class="sy1"><<</span> <span class="st0">"'<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="co1">// 静态缓冲区</span>
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<span class="kw4">char</span> arr<span class="br0">[</span><span class="nu0">20</span><span class="br0">]</span> <span class="sy1">=</span> <span class="st0">"-1 -3.14 "</span><span class="sy4">;</span>
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<a href="cpp-io-strstream.html"><span class="kw1755">std::<span class="me2">strstream</span></span></a> s2<span class="br0">(</span>arr, sizeof arr, <a href="cpp-io-ios_base-openmode.html"><span class="kw1672">std::<span class="me2">ios_base</span><span class="sy4">::</span><span class="me2">app</span></span></a><span class="br0">)</span><span class="sy4">;</span>
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s2 <span class="sy1"><<</span> <span class="st0">"another"</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> <span class="st0">"buffer holds: '"</span> <span class="sy1"><<</span> s2.<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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s2 <span class="sy1">>></span> n <span class="sy1">>></span> d <span class="sy1">>></span> w<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">"Read back: n = "</span> <span class="sy1"><<</span> n
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<span class="sy1"><<</span> <span class="st0">" d = "</span> <span class="sy1"><<</span> d
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<span class="sy1"><<</span> <span class="st0">" w = '"</span> <span class="sy1"><<</span> w <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">buffer holds '1 3.14 example'
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Read back: n = 1 d = 3.14 w = 'example'
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buffer holds: '-1 -3.14 another'
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Read back: n = -1 d = -3.14 w = 'another'</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 t-dsc-member-nobold-div">
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<div><a href="cpp-io-strstreambuf-strstreambuf.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 strstreambuf 对象<br />
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<span class="t-mark">(<code>std::strstreambuf</code> 的公开成员函数)</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 t-dsc-member-nobold-div">
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<div><a href="cpp-io-istrstream-istrstream.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::istrstream</code> 的公开成员函数)</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 t-dsc-member-nobold-div">
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<div><a href="cpp-io-ostrstream-ostrstream.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::ostrstream</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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</body>
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