114 lines
8.4 KiB
HTML
114 lines
8.4 KiB
HTML
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<title>std::setbuf</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_c_setbuf 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>setbuf</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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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span> setbuf<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> stream, <span class="kw4">char</span><span class="sy2">*</span> buffer <span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>为 C 流 <code>stream</code> 上进行的 I/O 操作设置内部缓冲区。</p>
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<p>若 <code>buffer</code> 非空，则等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-io-c-setvbuf.html"><span class="kw1817">std::<span class="me2">setvbuf</span></span></a><span class="br0">(</span>stream, buffer, <a href="cpp-io-c.html"><span class="kw1885">_IOFBF</span></a>, <a href="cpp-io-c.html"><span class="kw1884">BUFSIZ</span></a><span class="br0">)</span></span></span> 。</p>
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<p>若 <code>buffer</code> 为空，则等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-io-c-setvbuf.html"><span class="kw1817">std::<span class="me2">setvbuf</span></span></a><span class="br0">(</span>stream, <a href="cpp-types-NULL.html"><span class="kw103">NULL</span></a>, <a href="cpp-io-c.html"><span class="kw1887">_IONBF</span></a>, <span class="nu0">0</span><span class="br0">)</span></span></span> ，这会关闭缓冲。</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>stream</td>
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<td>-</td>
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<td>要设置缓冲区的文件流</td>
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</tr>
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<tr class="t-par">
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<td>buffer</td>
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<td>-</td>
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<td>指向文件流所用的缓冲区的指针。若提供空指针，则关闭缓冲。若它非空，则数组必须足以保有至少 <code>BUFSIZ</code> 个字符</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>（无）</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>若 <span class="t-lc"><a href="cpp-io-c.html">BUFSIZ</a></span> 不是适合的缓冲区大小，则能用 <span class="t-lc"><a href="cpp-io-c-setvbuf.html">std::setvbuf</a></span> 更改它。</p>
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<p><span class="t-lc"><a href="cpp-io-c-setvbuf.html">std::setvbuf</a></span> 亦应当用于检测错误，因为 <code>std::setbuf</code> 不指示成功或失败。</p>
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<p>此函数仅可在已将 <code>stream</code> 关联到打开的文件后，但要在任何其他操作（除了对 <span class="t-lc"><strong class="selflink">std::setbuf</strong></span>/<code>std::setvbuf</code> 的失败调用）前使用。</p>
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<p>一个常见错误是设置 stdin 或 stdout 的缓冲区为生存期在程序终止前结束的数组：</p>
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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="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="kw4">char</span> buf<span class="br0">[</span><a href="cpp-io-c.html"><span class="kw1884">BUFSIZ</span></a><span class="br0">]</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">setbuf</span><span class="br0">(</span><span class="kw2">stdin</span>, buf<span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span> <span class="co1">// buf 的生存期结束，未定义行为</span></pre></div>
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</div>
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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>setbuf 可用于禁用要求立即输出的流上的缓冲</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 <cstdio></span>
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<span class="co2">#include <thread></span>
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<span class="co2">#include <chrono></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="kw1">using</span> <span class="kw1">namespace</span> std<span class="sy4">::</span><span class="me2">chrono_literals</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">setbuf</span><span class="br0">(</span><span class="kw2">stdout</span>, <a href="cpp-types-NULL.html"><span class="kw103">NULL</span></a><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 无缓冲的 stdout</span>
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<a href="cpp-io-c-putchar.html"><span class="kw1828">std::<span class="me2">putchar</span></span></a><span class="br0">(</span><span class="st0">'a'</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 在无缓冲的流上立即显现</span>
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<a href="cpp-thread-sleep_for.html"><span class="kw2148">std::<span class="me2">this_thread</span><span class="sy4">::</span><span class="me2">sleep_for</span></span></a><span class="br0">(</span>1s<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-io-c-putchar.html"><span class="kw1828">std::<span class="me2">putchar</span></span></a><span class="br0">(</span><span class="st0">'b'</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>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">ab</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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-c-setvbuf.html"><span class="t-lines"><span>setvbuf</span></span></a></div>
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</div>
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</td>
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<td>为文件流设置缓冲区与其大小<br />
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<span class="t-mark">(函数)</span></td>
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