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<title>fwrite</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-c_io_fwrite skin-cppreference2 action-view cpp-navbar">
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<div id="contentSub"><span class="subpages">&lt; <a href="c.html">c</a>&lrm; | <a href="c-io.html">io</a></span></div>
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<div>&#23450;&#20041;&#20110;&#22836;&#25991;&#20214; <code>&lt;stdio.h&gt;</code></div>
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<div><span class="mw-geshi c source-c"><a href="c-types-size_t.html"><span class="kw100">size_t</span></a> fwrite<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">void</span> <span class="sy2">*</span>buffer, <a href="c-types-size_t.html"><span class="kw100">size_t</span></a> size, <a href="c-types-size_t.html"><span class="kw100">size_t</span></a> count,<br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<a href="c-io.html"><span class="kw883">FILE</span></a> <span class="sy2">*</span>stream <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-until-c99">(C99 &#21069;)</span></td>
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<div><span class="mw-geshi c source-c"><a href="c-types-size_t.html"><span class="kw100">size_t</span></a> fwrite<span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">void</span> <span class="sy2">*</span><span class="kw4">restrict</span> buffer, <a href="c-types-size_t.html"><span class="kw100">size_t</span></a> size, <a href="c-types-size_t.html"><span class="kw100">size_t</span></a> count,<br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<a href="c-io.html"><span class="kw883">FILE</span></a> <span class="sy2">*</span><span class="kw4">restrict</span> stream <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-c99">(C99 &#36215;)</span></td>
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<p>&#20889; <code>count</code> &#20010;&#26469;&#33258;&#32473;&#23450;&#25968;&#32452; <code>buffer</code> &#30340;&#23545;&#35937;&#21040;&#36755;&#20986;&#27969;<code>stream</code>&#12290;&#22914;&#21516;&#36716;&#35793;&#27599;&#20010;&#23545;&#35937;&#20026; <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">char</span></span></span> &#25968;&#32452;&#65292;&#24182;&#23545;&#27599;&#20010;&#23545;&#35937;&#35843;&#29992; <code>size</code> &#27425; <span class="t-lc"><a href="c-io-fputc.html">fputc</a></span> &#20197;&#23558;&#37027;&#20123; <span class="t-c"><span class="mw-geshi c source-c"><span class="kw4">unsigned</span> <span class="kw4">char</span></span></span> &#25353;&#39034;&#24207;&#20889;&#20837; <code>stream</code> &#19968;&#33324;&#20889;&#20837;&#12290;&#25991;&#20214;&#20301;&#32622;&#25351;&#31034;&#22120;&#21069;&#36827;&#20889;&#20837;&#30340;&#23383;&#33410;&#25968;&#12290;</p>
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">&#21442;&#25968;</span></h3>
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<td>buffer</td>
<td>-</td>
<td>&#25351;&#21521;&#25968;&#32452;&#20013;&#35201;&#34987;&#20889;&#20837;&#30340;&#39318;&#20010;&#23545;&#35937;&#30340;&#25351;&#38024;</td>
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<td>size</td>
<td>-</td>
<td>&#27599;&#20010;&#23545;&#35937;&#30340;&#22823;&#23567;</td>
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<td>count</td>
<td>-</td>
<td>&#35201;&#34987;&#20889;&#20837;&#30340;&#23545;&#35937;&#25968;</td>
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<td>stream</td>
<td>-</td>
<td>&#25351;&#21521;&#36755;&#20986;&#27969;&#30340;&#25351;&#38024;</td>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">&#36820;&#22238;&#20540;</span></h3>
<p>&#25104;&#21151;&#20889;&#20837;&#30340;&#23545;&#35937;&#25968;&#65292;&#33509;&#38169;&#35823;&#21457;&#29983;&#21017;&#21487;&#33021;&#23567;&#20110; <code>count</code> &#12290;</p>
<p>&#33509; <code>size</code> &#25110; <code>count</code> &#20026;&#38646;&#65292;&#21017; <code>fwrite</code> &#36820;&#22238;&#38646;&#24182;&#19981;&#36827;&#34892;&#20854;&#20182;&#34892;&#21160;&#12290;</p>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">&#31034;&#20363;</span></h3>
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<pre class="de1"><span class="co2">#include &lt;stdio.h&gt;</span>
<span class="co2">#include &lt;stdlib.h&gt;</span>
<span class="co2">#include &lt;assert.h&gt;</span>
<span class="kw2">enum</span> <span class="br0">{</span> SIZE <span class="sy1">=</span> <span class="nu0">5</span> <span class="br0">}</span><span class="sy4">;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
<span class="kw4">double</span> a<span class="br0">[</span>SIZE<span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span><span class="nu0">1</span>, <span class="nu0">2</span>, <span class="nu0">3</span>, <span class="nu0">4</span>, <span class="nu0">5</span><span class="br0">}</span><span class="sy4">;</span>
<a href="c-io.html"><span class="kw883">FILE</span></a> <span class="sy2">*</span>f1 <span class="sy1">=</span> <a href="c-io-fopen.html"><span class="kw819">fopen</span></a><span class="br0">(</span><span class="st0">&quot;file.bin&quot;</span>, <span class="st0">&quot;wb&quot;</span><span class="br0">)</span><span class="sy4">;</span>
<a href="c-error-assert.html"><span class="kw407">assert</span></a><span class="br0">(</span>f1<span class="br0">)</span><span class="sy4">;</span>
<a href="c-types-size_t.html"><span class="kw100">size_t</span></a> r1 <span class="sy1">=</span> fwrite<span class="br0">(</span>a, <span class="kw4">sizeof</span> a<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span>, SIZE, f1<span class="br0">)</span><span class="sy4">;</span>
<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">&quot;wrote %zu elements out of %d requested<span class="es1">\n</span>&quot;</span>, r1, SIZE<span class="br0">)</span><span class="sy4">;</span>
<a href="c-io-fclose.html"><span class="kw822">fclose</span></a><span class="br0">(</span>f1<span class="br0">)</span><span class="sy4">;</span>
<span class="kw4">double</span> b<span class="br0">[</span>SIZE<span class="br0">]</span><span class="sy4">;</span>
<a href="c-io.html"><span class="kw883">FILE</span></a> <span class="sy2">*</span>f2 <span class="sy1">=</span> <a href="c-io-fopen.html"><span class="kw819">fopen</span></a><span class="br0">(</span><span class="st0">&quot;file.bin&quot;</span>, <span class="st0">&quot;rb&quot;</span><span class="br0">)</span><span class="sy4">;</span>
<a href="c-types-size_t.html"><span class="kw100">size_t</span></a> r2 <span class="sy1">=</span> <a href="c-io-fread.html"><span class="kw825">fread</span></a><span class="br0">(</span>b, <span class="kw4">sizeof</span> b<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span>, SIZE, f2<span class="br0">)</span><span class="sy4">;</span>
<a href="c-io-fclose.html"><span class="kw822">fclose</span></a><span class="br0">(</span>f2<span class="br0">)</span><span class="sy4">;</span>
<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">&quot;read back: &quot;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">for</span><span class="br0">(</span><a href="c-types-size_t.html"><span class="kw100">size_t</span></a> i <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> i <span class="sy1">&lt;</span> r2<span class="sy4">;</span> i<span class="sy2">++</span><span class="br0">)</span>
<a href="c-io-fprintf.html"><span class="kw850">printf</span></a><span class="br0">(</span><span class="st0">&quot;%0.2f &quot;</span>, b<span class="br0">[</span>i<span class="br0">]</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div>
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<p>&#36755;&#20986;&#65306;</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;">
<div class="text source-text">
<pre class="de1">wrote 5 elements out of 5 requested
read back: 1.00 2.00 3.00 4.00 5.00</pre></div>
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<h3><span class="mw-headline" id=".E5.BC.95.E7.94.A8">&#24341;&#29992;</span></h3>
<div class="t-ref-std-11">
<ul>
<li>C11 &#26631;&#20934;&#65288;ISO/IEC 9899:2011&#65289;&#65306;</li>
</ul>
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<dd>
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<li>7.21.8.2 The fwrite function (p: 335-336)</li>
</ul>
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<div class="t-ref-std-c99">
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<li>C99 &#26631;&#20934;&#65288;ISO/IEC 9899:1999&#65289;&#65306;</li>
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<li>7.19.8.2 The fwrite function (p: 301-302)</li>
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<div class="t-ref-std-c89">
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<li>C89/C90 &#26631;&#20934;&#65288;ISO/IEC 9899:1990&#65289;&#65306;</li>
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<li>4.9.8.2 The fwrite function</li>
</ul>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">&#21442;&#38405;</span></h3>
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<div><a href="c-io-fprintf.html"><span class="t-lines"><span>printf</span><span>fprintf</span><span>sprintf</span><span>snprintf</span><span>printf_s</span><span>fprintf_s</span><span>sprintf_s</span><span>snprintf_s</span></span></a></div>
<div><span class="t-lines"><span></span><span></span><span></span><span><span class="t-mark-rev t-since-c99">(C99)</span></span><span><span class="t-mark-rev t-since-c11">(C11)</span></span><span><span class="t-mark-rev t-since-c11">(C11)</span></span><span><span class="t-mark-rev t-since-c11">(C11)</span></span><span><span class="t-mark-rev t-since-c11">(C11)</span></span></span></div>
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<td>&#25171;&#21360;&#26684;&#24335;&#21270;&#36755;&#20986;&#21040; <span class="t-lc"><a href="c-io.html">stdout</a></span> &#12289;&#25991;&#20214;&#27969;&#25110;&#32531;&#20914;&#21306;<br />
<span class="t-mark">(&#20989;&#25968;)</span></td>
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<div class="t-dsc-member-div">
<div><a href="c-io-fputs.html"><span class="t-lines"><span>fputs</span></span></a></div>
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<td>&#23558;&#19968;&#20010;&#23383;&#31526;&#20018;&#20889;&#20837;&#25991;&#20214;&#27969;<br />
<span class="t-mark">(&#20989;&#25968;)</span></td>
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<div><a href="c-io-fread.html"><span class="t-lines"><span>fread</span></span></a></div>
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<td>&#20174;&#25991;&#20214;&#35835;&#21462;<br />
<span class="t-mark">(&#20989;&#25968;)</span></td>
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