143 lines
11 KiB
HTML
143 lines
11 KiB
HTML
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<title>std::fwrite</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_c_fwrite 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::</span>fwrite</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-c.html">c</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-cstdio.html"><cstdio></a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> fwrite<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">void</span><span class="sy2">*</span> buffer, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> size, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> count, <a href="cpp-io-c.html"><span class="kw1876">std::<span class="me2">FILE</span></span></a><span class="sy2">*</span> stream <span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>写 <code>count</code> 个来自给定数组 <code>buffer</code> 的对象到输出流<code>stream</code>。如同转译每个对象为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">char</span></span></span> 数组，并对每个对象调用 <code>size</code> 次 <span class="t-lc"><a href="cpp-io-c-fputc.html">std::fputc</a></span> 以将那些 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">unsigned</span> <span class="kw4">char</span></span></span> 按顺序写入 <code>stream</code> 一般写入。文件位置指示器前进写入的字节数。</p>
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<p>若对象不<a href="cpp-named_req-TriviallyCopyable.html"><span style="font-style:italic">可平凡复制</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(TriviallyCopyable)</span></a> ，则行为未定义。</p>
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<p>若出现错误，则文件位置指示器的结果值不确定。</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>buffer</td>
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<td>-</td>
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<td>指向数组中要被写入的首个对象的指针</td>
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<td>size</td>
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<td>-</td>
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<td>每个对象的大小</td>
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<td>count</td>
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<td>-</td>
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<td>要被写入的对象数</td>
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<td>stream</td>
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<td>-</td>
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<td>指向输出流的指针</td>
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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>成功写入的对象数，若错误发生则可能小于 <code>count</code> 。</p>
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<p>若 <code>size</code> 或 <code>count</code> 为零，则 <code>fwrite</code> 返回零并不进行其他行动。</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="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <cstdio></span>
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<span class="co2">#include <vector></span>
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<span class="co2">#include <array></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">// 写缓冲区到文件</span>
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<span class="kw1">if</span><span class="br0">(</span><a href="cpp-io-c.html"><span class="kw1876">std::<span class="me2">FILE</span></span></a><span class="sy2">*</span> f1 <span class="sy1">=</span> <a href="cpp-io-c-fopen.html"><span class="kw1813">std::<span class="me2">fopen</span></span></a><span class="br0">(</span><span class="st0">"file.bin"</span>, <span class="st0">"wb"</span><span class="br0">)</span><span class="br0">)</span> <span class="br0">{</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><span class="kw4">int</span>, <span class="nu0">3</span><span class="sy1">></span> v <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">42</span>, <span class="sy2">-</span><span class="nu0">1</span>, <span class="nu0">7</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// std::array 的底层存储为数组</span>
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std<span class="sy4">::</span><span class="me2">fwrite</span><span class="br0">(</span>v.<span class="me1">data</span><span class="br0">(</span><span class="br0">)</span>, sizeof v<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span>, v.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span>, f1<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-c-fclose.html"><span class="kw1816">std::<span class="me2">fclose</span></span></a><span class="br0">(</span>f1<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="co1">// 读取同一数据并打印它到标准输出</span>
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<span class="kw1">if</span><span class="br0">(</span><a href="cpp-io-c.html"><span class="kw1876">std::<span class="me2">FILE</span></span></a> <span class="sy2">*</span>f2 <span class="sy1">=</span> <a href="cpp-io-c-fopen.html"><span class="kw1813">std::<span class="me2">fopen</span></span></a><span class="br0">(</span><span class="st0">"file.bin"</span>, <span class="st0">"rb"</span><span class="br0">)</span><span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy1">></span> rbuf<span class="br0">(</span><span class="nu0">10</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// std::vector 的底层存储亦为数组</span>
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<a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> sz <span class="sy1">=</span> <a href="cpp-io-c-fread.html"><span class="kw1819">std::<span class="me2">fread</span></span></a><span class="br0">(</span>rbuf.<span class="me1">data</span><span class="br0">(</span><span class="br0">)</span>, sizeof rbuf<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span>, rbuf.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span>, f2<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-c-fclose.html"><span class="kw1816">std::<span class="me2">fclose</span></span></a><span class="br0">(</span>f2<span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">for</span><span class="br0">(</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> n <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> n <span class="sy1"><</span> sz<span class="sy4">;</span> <span class="sy2">++</span>n<span class="br0">)</span> <span class="br0">{</span>
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<a href="cpp-io-c-fprintf.html"><span class="kw1844">std::<span class="me2">printf</span></span></a><span class="br0">(</span><span class="st0">"%d<span class="es1">\n</span>"</span>, rbuf<span class="br0">[</span>n<span class="br0">]</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="br0">}</span>
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<span class="br0">}</span></pre></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">42
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-1
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7</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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<div class="t-dsc-member-div">
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<div><a href="cpp-io-c-fprintf.html"><span class="t-lines"><span>printf</span><span>fprintf</span><span>sprintf</span><span>snprintf</span></span></a></div>
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<div><span class="t-lines"><span></span><span></span><span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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</div>
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</td>
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<td>打印有格式输出到 <span class="t-lc"><a href="cpp-io-c.html">stdout</a></span>、文件流或缓冲区<br />
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<span class="t-mark">(函数)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-c-fputs.html"><span class="t-lines"><span>fputs</span></span></a></div>
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</div>
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</td>
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<td>写字符串到文件流<br />
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<span class="t-mark">(函数)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-c-fread.html"><span class="t-lines"><span>fread</span></span></a></div>
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<td>从文件读取<br />
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<span class="t-mark">(函数)</span></td>
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