97 lines
6.6 KiB
HTML
97 lines
6.6 KiB
HTML
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<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
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<title>std::basic_filebuf<CharT,Traits>::showmanyc</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_basic_filebuf_showmanyc 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_filebuf<CharT,Traits>::</span>showmanyc</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-basic_filebuf.html">basic filebuf</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">protected</span><span class="sy4">:</span><br />
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<span class="kw1">virtual</span> <a href="cpp-io-streamsize.html"><span class="kw1804">std::<span class="me2">streamsize</span></span></a> showmanyc<span class="br0">(</span><span class="br0">)</span></span></div>
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<p>若实现，则返回从文件留待读取的字符数。</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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<p>（无）</p>
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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>可从文件读取的字符数，或若抵达文件尾则为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">-</span><span class="nu0">1</span></span></span> 。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h3>
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<p>此函数为可选。若不实现，则此函数返回 <span class="t-c"><span class="mw-geshi cpp source-cpp">​<span class="nu0">0</span>​</span></span> （因为基类版本 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">basic_streambuf</span><span class="sy4">::</span><span class="me2">showmanyc</span></span></span> 得到调用）。</p>
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<p>无论是否实现，若获取区为空，则此函数为 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">basic_streambuf</span><span class="sy4">::</span><span class="me2">in_avail</span></span></span> 所正常调用。</p>
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<p>此函数的名称表示“流：多少字符？”，故它读作“ S how many C ”，而不是“ show many C ”。</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>查看是否为 filebuf 实现 showmanyc() 的实现测试</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 <fstream></span>
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<span class="co2">#include <iostream></span>
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<span class="kw1">struct</span> mybuf <span class="sy4">:</span> <a href="cpp-io-basic_filebuf.html"><span class="kw1725">std::<span class="me2">filebuf</span></span></a>
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<span class="br0">{</span>
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<span class="kw1">using</span> std<span class="sy4">::</span><span class="me2">filebuf</span><span class="sy4">::</span><span class="me2">showmanyc</span><span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</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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mybuf fin<span class="sy4">;</span>
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fin.<span class="me1">open</span><span class="br0">(</span><span class="st0">"main.cpp"</span>, <a href="cpp-io-ios_base-openmode.html"><span class="kw1674">std::<span class="me2">ios_base</span><span class="sy4">::</span><span class="me2">in</span></span></a><span class="br0">)</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="sy1"><<</span> <span class="st0">"showmanyc() returns "</span> <span class="sy1"><<</span> fin.<span class="me1">showmanyc</span><span class="br0">(</span><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="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">showmanyc() returns 267</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-basic_streambuf-in_avail.html"><span class="t-lines"><span>in_avail</span></span></a></div>
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</div>
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</td>
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<td>获得获取区中立即可用的字符数<br />
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<span class="t-mark">(<code>std::basic_streambuf<CharT,Traits></code> 的公开成员函数)</span></td>
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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_istream-readsome.html"><span class="t-lines"><span>readsome</span></span></a></div>
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</div>
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</td>
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<td>读并取走已经可用的字符块<br />
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<span class="t-mark">(<code>std::basic_istream<CharT,Traits></code> 的公开成员函数)</span></td>
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