112 lines
8.6 KiB
HTML
112 lines
8.6 KiB
HTML
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<title>std::basic_ostream<CharT,Traits>::write</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_basic_ostream_write 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::basic_ostream<CharT,Traits>::</span>write</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-basic_ostream.html">basic ostream</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">basic_ostream<span class="sy3">&</span> write<span class="br0">(</span> <span class="kw4">const</span> char_type<span class="sy2">*</span> s, <a href="cpp-io-streamsize.html"><span class="kw1804">std::<span class="me2">streamsize</span></span></a> count <span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>表现为<a href="cpp-named_req-UnformattedOutputFunction.html"><span style="font-style:italic">无格式输出函数</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(UnformattedOutputFunction)</span></a> 。构造并检查 sentry 对象后，输出来自首元素为 <code>s</code> 所指向的字符数组中的相继位置的字符。插入字符到输出序列，直至出现下列条件之一：</p>
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<ul>
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<li>准确插入了 <code>count</code> 个字符</li>
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<li>插入到输出序列失败（该情况下调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">setstate<span class="br0">(</span>badbit<span class="br0">)</span></span></span> ）</li>
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</ul>
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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>指向要写入的字符串的指针</td>
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</tr>
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<tr class="t-par">
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<td>count</td>
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<td>-</td>
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<td>要写入的字符数</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><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span></p>
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<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<div class="t-template-editlink" style=""></div>
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若出现错误（错误状态标志不是 <span class="t-lc"><a href="cpp-io-ios_base-iostate.html">goodbit</a></span> ）并且设置了 <span class="t-lc"><a href="cpp-io-basic_ios-exceptions.html">exceptions()</a></span> 为对该状态抛出则为 <span class="t-lc"><a href="cpp-io-ios_base-failure.html">failure</a></span> 。
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<p>若内部操作抛出异常，则捕获它并设置 <span class="t-lc"><a href="cpp-io-ios_base-iostate.html">badbit</a></span> 。若对 <code>badbit</code> 设置了 <span class="t-lc"><a href="cpp-io-basic_ios-exceptions.html">exceptions()</a></span> ，则重抛该异常。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>此函数不对 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">signed</span> <span class="kw4">char</span></span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">char</span></span></span> 类型重载，不同于有格式的 <a href="cpp-io-basic_ostream-operator_ltlt2.html">operator<<</a> 。</p>
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<p>而且，不同于有格式输出函数，此函数在失败时不设置 <code>failbit</code> 。</p>
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<p>使用非转换本地环境（默认本地环境为非转换）时， <span class="t-lc"><a href="cpp-io-basic_ofstream.html">std::basic_ofstream</a></span> 中此函数的覆写者可为零复制大块 I/O 优化（通过覆写 <span class="t-lc"><a href="cpp-io-basic_streambuf-sputn.html">std::streambuf::xsputn</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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<p>此函数可用于输出对象表示，即二进制输出</p>
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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="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="kw4">int</span> n <span class="sy1">=</span> <span class="nu12">0x41424344</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="me1">write</span><span class="br0">(</span><span class="kw1">reinterpret_cast</span><span class="sy1"><</span><span class="kw4">char</span><span class="sy2">*</span><span class="sy1">></span><span class="br0">(</span><span class="sy3">&</span>n<span class="br0">)</span>, sizeof n<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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<span class="kw4">char</span> c<span class="br0">[</span><span class="br0">]</span><span class="sy1">=</span><span class="st0">"This is sample text."</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="me1">write</span><span class="br0">(</span>c, <span class="nu0">4</span><span class="br0">)</span>.<span class="me1">write</span><span class="br0">(</span><span class="st0">"!<span class="es1">\n</span>"</span>, <span class="nu0">2</span><span class="br0">)</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">DCBA
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This</pre></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_ostream-operator_ltlt2.html"><span class="t-lines"><span>operator<<<span class="t-dsc-small">(std::basic_ostream)</span></span></span></a></div>
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</div>
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</td>
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<td>插入字符数据<br />
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<span class="t-mark">(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_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">(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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