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<h1 id="firstHeading" class="firstHeading">setvbuf</h1>
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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"><span class="kw4">int</span> setvbuf<span class="br0">(</span> <a href="c-io.html"><span class="kw883">FILE</span></a> <span class="sy2">*</span> &nbsp; &nbsp; &nbsp; &nbsp; stream, <span class="kw4">char</span> <span class="sy2">*</span> &nbsp; &nbsp; &nbsp; &nbsp; buffer,<br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span class="kw4">int</span> mode, <a href="c-types-size_t.html"><span class="kw100">size_t</span></a> size <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"><span class="kw4">int</span> setvbuf<span class="br0">(</span> <a href="c-io.html"><span class="kw883">FILE</span></a> <span class="sy2">*</span><span class="kw4">restrict</span> stream, <span class="kw4">char</span> <span class="sy2">*</span><span class="kw4">restrict</span> buffer,<br />
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;<span class="kw4">int</span> mode, <a href="c-types-size_t.html"><span class="kw100">size_t</span></a> size <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>&#20197; <code>mode</code> &#25152;&#25351;&#31034;&#20540;&#26356;&#25913;&#32473;&#23450;&#25991;&#20214;&#27969; <code>stream</code> &#30340;&#32531;&#20914;&#27169;&#24335;&#12290;&#21478;&#22806;&#65292;</p>
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<li>&#33509; <code>buffer</code> &#20026;&#31354;&#25351;&#38024;&#65292;&#21017;&#37325;&#35774;&#20869;&#37096;&#32531;&#20914;&#21306;&#22823;&#23567;&#20026; <code>size</code> &#12290;</li>
<li>&#33509; <code>buffer</code> &#19981;&#26159;&#31354;&#25351;&#38024;&#65292;&#21017;&#25351;&#31034;&#27969;&#20351;&#29992;&#22987;&#20110; <code>buffer</code> &#32780;&#22823;&#23567;&#20026; <code>size</code> &#30340;&#29992;&#25143;&#25552;&#20379;&#32531;&#20914;&#21306;&#12290;&#24517;&#39035;&#22312; <code>buffer</code> &#25152;&#25351;&#21521;&#30340;&#25968;&#32452;&#30340;<a href="cpp-language-lifetime.html">&#29983;&#23384;&#26399;</a>&#32467;&#26463;&#21069;&#65288;&#29992; <span class="t-lc"><a href="c-io-fclose.html">fclose</a></span> &#65289;&#20851;&#38381;&#27969;&#12290;&#25104;&#21151;&#35843;&#29992; <code>setvbuf</code> &#21518;&#65292;&#25968;&#32452;&#20869;&#23481;&#19981;&#30830;&#23450;&#65292;&#32780;&#20219;&#20309;&#20351;&#29992;&#23427;&#30340;&#23581;&#35797;&#26159;&#26410;&#23450;&#20041;&#34892;&#20026;&#12290;</li>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">&#21442;&#25968;</span></h3>
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<td>stream</td>
<td>-</td>
<td>&#35201;&#35774;&#32622;&#32531;&#20914;&#30340;&#25991;&#20214;&#27969;</td>
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<td>buffer</td>
<td>-</td>
<td>&#25351;&#21521;&#35201;&#20351;&#29992;&#30340;&#27969;&#32531;&#20914;&#21306;&#30340;&#25351;&#38024;&#65292;&#25110;&#33509;&#20165;&#26356;&#25913;&#22823;&#23567;&#21644;&#27169;&#24335;&#21017;&#20026;&#31354;&#25351;&#38024;</td>
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<td>mode</td>
<td>-</td>
<td>&#20351;&#29992;&#30340;&#32531;&#20914;&#27169;&#24335;&#12290;&#23427;&#33021;&#26159;&#19979;&#21015;&#20540;&#20043;&#19968;&#65306;
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<td><code>_IOFBF</code></td>
<td>&#20840;&#32531;&#20914;&#65306;&#24403;&#32531;&#20914;&#21306;&#20026;&#31354;&#26102;&#65292;&#20174;&#27969;&#35835;&#20837;&#25968;&#25454;&#12290;&#25110;&#32773;&#24403;&#32531;&#20914;&#21306;&#28385;&#26102;&#65292;&#21521;&#27969;&#20889;&#20837;&#25968;&#25454;&#12290;</td>
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<td><code>_IOLBF</code></td>
<td>&#34892;&#32531;&#20914;&#65306;&#27599;&#27425;&#20174;&#27969;&#20013;&#35835;&#20837;&#19968;&#34892;&#25968;&#25454;&#25110;&#21521;&#27969;&#20013;&#20889;&#20837;&#19968;&#34892;&#25968;&#25454;&#12290;</td>
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<td><code>_IONBF</code></td>
<td>&#26080;&#32531;&#20914;&#65306;&#30452;&#25509;&#20174;&#27969;&#20013;&#35835;&#20837;&#25968;&#25454;&#25110;&#30452;&#25509;&#21521;&#27969;&#20013;&#20889;&#20837;&#25968;&#25454;&#65292;&#32531;&#20914;&#35774;&#32622;&#26080;&#25928;&#12290;</td>
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<td>size</td>
<td>-</td>
<td>&#32531;&#20914;&#21306;&#30340;&#22823;&#23567;</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;&#26102;&#20026; <span class="t-c"><span class="mw-geshi c source-c">&#8203;<span class="nu0">0</span>&#8203;</span></span> &#65292;&#22833;&#36133;&#26102;&#20026;&#38750;&#38646;&#12290;</p>
<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">&#27880;&#24847;</span></h3>
<p>&#27492;&#20989;&#25968;&#20165;&#21487;&#22312;&#24050;&#23558; <code>stream</code> &#20851;&#32852;&#21040;&#25171;&#24320;&#30340;&#25991;&#20214;&#21518;&#65292;&#20294;&#35201;&#22312;&#20219;&#20309;&#20854;&#20182;&#25805;&#20316;&#65288;&#38500;&#20102;&#23545; <span class="t-lc"><a href="c-io-setbuf.html">setbuf</a></span>/<code>setvbuf</code> &#30340;&#22833;&#36133;&#35843;&#29992;&#65289;&#21069;&#20351;&#29992;&#12290;</p>
<p>&#19981;&#26159;&#25152;&#26377; <code>size</code> &#23383;&#33410;&#37117;&#38656;&#35201;&#29992;&#20110;&#32531;&#20914;&#65306;&#23454;&#38469;&#32531;&#20914;&#21306;&#22823;&#23567;&#36890;&#24120;&#21521;&#19979;&#21462;&#25972;&#21040; 2 &#30340;&#20493;&#25968;&#12289;&#39029;&#38754;&#22823;&#23567;&#30340;&#20493;&#25968;&#31561;&#12290;</p>
<p>&#22810;&#25968;&#23454;&#29616;&#19978;&#65292;&#34892;&#32531;&#20914;&#20165;&#23545;&#32456;&#31471;&#36755;&#20837;&#27969;&#21487;&#29992;&#12290;</p>
<p>&#19968;&#20010;&#24120;&#35265;&#38169;&#35823;&#26159;&#35774;&#32622; stdin &#25110; stdout &#30340;&#32531;&#20914;&#21306;&#20026;&#29983;&#23384;&#26399;&#22312;&#31243;&#24207;&#32456;&#27490;&#21069;&#32467;&#26463;&#30340;&#25968;&#32452;&#65306;</p>
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<div class="c source-c">
<pre class="de1"><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">char</span> buf<span class="br0">[</span><a href="c-io.html"><span class="kw891">BUFSIZ</span></a><span class="br0">]</span><span class="sy4">;</span>
<a href="c-io-setbuf.html"><span class="kw823">setbuf</span></a><span class="br0">(</span><a href="c-io.html"><span class="kw885">stdin</span></a>, buf<span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span> <span class="co1">// buf &#30340;&#29983;&#23384;&#26399;&#32467;&#26463;&#65292;&#26410;&#23450;&#20041;&#34892;&#20026;</span></pre></div>
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<p>&#26399;&#24453;&#40664;&#35748;&#32531;&#20914;&#21306;&#22823;&#23567; <span class="t-lc"><a href="c-io.html">BUFSIZ</a></span> &#20026;&#23454;&#29616;&#19978;&#25991;&#20214; I/O &#30340;&#26368;&#39640;&#25928;&#32531;&#20914;&#21306;&#22823;&#23567;&#65292;&#20294; POSIX <a rel="nofollow" class="external text" href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/fstat.html">fstat</a> &#32463;&#24120;&#25552;&#20379;&#26356;&#22909;&#30340;&#20272;&#35745;&#12290;</p>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">&#31034;&#20363;</span></h3>
<div class="t-example">
<p>&#22312;&#24050;&#30693;&#26356;&#22909;&#30340;&#22823;&#23567;&#26102;&#26356;&#25913;&#32531;&#20914;&#21306;&#22823;&#23567;&#30340;&#20351;&#29992;&#26679;&#20363;&#12290;</p>
<div class="t-example-live-link"></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;">
<div class="c source-c">
<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;sys/stat.h&gt;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>
<span class="br0">{</span>
<a href="c-io.html"><span class="kw883">FILE</span></a><span class="sy2">*</span> fp <span class="sy1">=</span> <a href="c-io-fopen.html"><span class="kw819">fopen</span></a><span class="br0">(</span><span class="st0">&quot;test.txt&quot;</span>, <span class="st0">&quot;r&quot;</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">if</span><span class="br0">(</span>fp <span class="sy1">==</span> <a href="c-types-NULL.html"><span class="kw103">NULL</span></a><span class="br0">)</span> <span class="br0">{</span>
<a href="c-io-perror.html"><span class="kw878">perror</span></a><span class="br0">(</span><span class="st0">&quot;fopen&quot;</span><span class="br0">)</span><span class="sy4">;</span> <span class="kw1">return</span> <span class="nu0">1</span><span class="sy4">;</span>
<span class="br0">}</span>
<span class="kw1">struct</span> stat stats<span class="sy4">;</span>
<span class="kw1">if</span><span class="br0">(</span>fstat<span class="br0">(</span>fileno<span class="br0">(</span>fp<span class="br0">)</span>, <span class="sy3">&amp;</span>stats<span class="br0">)</span> <span class="sy1">==</span> <span class="sy2">-</span><span class="nu0">1</span><span class="br0">)</span> <span class="br0">{</span> <span class="co1">// &#20165;&#38480; POSIX</span>
<a href="c-io-perror.html"><span class="kw878">perror</span></a><span class="br0">(</span><span class="st0">&quot;fstat&quot;</span><span class="br0">)</span><span class="sy4">;</span> <span class="kw1">return</span> <span class="nu0">1</span><span class="sy4">;</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;BUFSIZ is %d, but optimal block size is %ld<span class="es1">\n</span>&quot;</span>, <a href="c-io.html"><span class="kw891">BUFSIZ</span></a>, stats.<span class="me1">st_blksize</span><span class="br0">)</span><span class="sy4">;</span>
<span class="kw1">if</span><span class="br0">(</span>setvbuf<span class="br0">(</span>fp, <a href="c-types-NULL.html"><span class="kw103">NULL</span></a>, <a href="c-io.html"><span class="kw892">_IOFBF</span></a>, stats.<span class="me1">st_blksize</span><span class="br0">)</span> <span class="sy3">!</span><span class="sy1">=</span> <span class="nu0">0</span><span class="br0">)</span> <span class="br0">{</span>
<a href="c-io-perror.html"><span class="kw878">perror</span></a><span class="br0">(</span><span class="st0">&quot;setvbuf failed&quot;</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// POSIX &#29256;&#26412;&#35774;&#32622; errno</span>
<span class="kw1">return</span> <span class="nu0">1</span><span class="sy4">;</span>
<span class="br0">}</span>
<span class="kw4">int</span> ch<span class="sy4">;</span>
<span class="kw1">while</span><span class="br0">(</span><span class="br0">(</span>ch<span class="sy1">=</span><a href="c-io-fgetc.html"><span class="kw826">fgetc</span></a><span class="br0">(</span>fp<span class="br0">)</span><span class="br0">)</span> <span class="sy3">!</span><span class="sy1">=</span> <a href="c-io.html"><span class="kw888">EOF</span></a><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// &#35835;&#25972;&#20010;&#25991;&#20214;&#65306;&#29992; truss/strace &#35266;&#23519;</span>
<span class="co1">// &#20351;&#29992;&#30340; read(2) syscall</span>
<a href="c-io-fclose.html"><span class="kw822">fclose</span></a><span class="br0">(</span>fp<span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div>
</div>
<p>&#21487;&#33021;&#30340;&#36755;&#20986;&#65306;</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;">
<div class="text source-text">
<pre class="de1">BUFSIZ is 8192, but optimal block size is 65536</pre></div>
</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>
<dl>
<dd>
<ul>
<li>7.21.5.6 The setvbuf function (p: 308)</li>
</ul>
</dd>
</dl>
<div class="t-ref-std-c99">
<ul>
<li>C99 &#26631;&#20934;&#65288;ISO/IEC 9899:1999&#65289;&#65306;</li>
</ul>
<dl>
<dd>
<ul>
<li>7.19.5.6 The setvbuf function (p: 273-274)</li>
</ul>
</dd>
</dl>
<div class="t-ref-std-c89">
<ul>
<li>C89/C90 &#26631;&#20934;&#65288;ISO/IEC 9899:1990&#65289;&#65306;</li>
</ul>
<dl>
<dd>
<ul>
<li>4.9.5.6 The setvbuf function</li>
</ul>
</dd>
</dl>
</div>
<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-setbuf.html"><span class="t-lines"><span>setbuf</span></span></a></div>
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<td>&#20026;&#25991;&#20214;&#27969;&#35774;&#32622;&#32531;&#20914;&#21306;<br />
<span class="t-mark">(&#20989;&#25968;)</span></td>
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