134 lines
9.9 KiB
HTML
134 lines
9.9 KiB
HTML
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<title>std::basic_istream<CharT,Traits>::tellg</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::basic_istream<CharT,Traits>::</span>tellg</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_istream.html">basic istream</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">pos_type tellg<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>返回当前关联的 <code>streambuf</code> 对象的输入位置指示器。</p>
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<p>表现为<a href="cpp-named_req-UnformattedInputFunction.html"><span style="font-style:italic">无格式输入函数</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(UnformattedInputFunction)</span></a> ，除了不影响 <span class="t-lc"><a href="cpp-io-basic_istream-gcount.html">gcount()</a></span> 。构造并检查 sentry 对象后，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">fail<span class="br0">(</span><span class="br0">)</span> <span class="sy1">==</span> <span class="kw2">true</span></span></span> ，则返回 <span class="t-c"><span class="mw-geshi cpp source-cpp">pos_type<span class="br0">(</span><span class="sy2">-</span><span class="nu0">1</span><span class="br0">)</span></span></span> 。否则，返回 <span class="t-c"><span class="mw-geshi cpp source-cpp">rdbuf<span class="br0">(</span><span class="br0">)</span><span class="sy2">-</span><span class="sy1">></span>pubseekoff<span class="br0">(</span><span class="nu0">0</span>, <a href="cpp-io-ios_base-seekdir.html"><span class="kw1704">std::<span class="me2">ios_base</span><span class="sy4">::</span><span class="me2">cur</span></span></a>, <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></span> 。</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>成功时为获取指针的当前位置，失败时为 <span class="t-c"><span class="mw-geshi cpp source-cpp">pos_type<span class="br0">(</span><span class="sy2">-</span><span class="nu0">1</span><span class="br0">)</span></span></span> 。</p>
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<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
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<div class="t-template-editlink" style=""></div>
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若出现错误（错误状态标志不是 <span class="t-lc"><a href="cpp-io-ios_base-iostate.html">goodbit</a></span> ）并且设置了 <span class="t-lc"><a href="cpp-io-basic_ios-exceptions.html">exceptions()</a></span> 为对该状态抛出则为 <span class="t-lc"><a href="cpp-io-ios_base-failure.html">failure</a></span> 。
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<p>若内部操作抛出异常，则捕获它并设置 <span class="t-lc"><a href="cpp-io-ios_base-iostate.html">badbit</a></span> 。若对 <code>badbit</code> 设置了 <span class="t-lc"><a href="cpp-io-basic_ios-exceptions.html">exceptions()</a></span> ，则重抛该异常。</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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<pre class="de1"><span class="co2">#include <iostream></span>
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<span class="co2">#include <string></span>
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<span class="co2">#include <sstream></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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<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> str <span class="sy1">=</span> <span class="st0">"Hello, world"</span><span class="sy4">;</span>
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<a href="cpp-io-basic_istringstream.html"><span class="kw1735">std::<span class="me2">istringstream</span></span></a> in<span class="br0">(</span>str<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> word<span class="sy4">;</span>
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in <span class="sy1">>></span> word<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">"After reading the word <span class="es1">\"</span>"</span> <span class="sy1"><<</span> word
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<span class="sy1"><<</span> <span class="st0">"<span class="es1">\"</span> tellg() returns "</span> <span class="sy1"><<</span> in.<span class="me1">tellg</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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<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">After reading the word "Hello," tellg() returns 6</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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<table class="t-dsc-begin">
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-basic_filebuf-seekoff.html"><span class="t-lines"><span>seekoff</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-cmark">[虚]</span></span></span></div>
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</div>
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</td>
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<td>用相对寻址重寻位文件位置<br />
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<span class="t-mark">(<code>std::basic_filebuf<CharT,Traits></code> 的虚受保护成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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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_stringbuf-seekoff.html"><span class="t-lines"><span>seekoff</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-cmark">[虚]</span></span></span></div>
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</div>
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</td>
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<td>用相对寻址，重定位输入序列、输出序列或两者中的下一位置指针<br />
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<span class="t-mark">(<code>std::basic_stringbuf<CharT,Traits,Allocator></code> 的虚受保护成员函数)</span></td>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-strstreambuf-seekoff.html"><span class="t-lines"><span>seekoff</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-cmark">[虚]</span></span></span></div>
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</div>
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</td>
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<td>用相对寻址重寻位输入序列、输出序列或两者中的下一位置指针<br />
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<span class="t-mark">(<code>std::strstreambuf</code> 的虚受保护成员函数)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-basic_istream-seekg.html"><span class="t-lines"><span>seekg</span></span></a></div>
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</div>
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</td>
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<td>设置输入位置指示器<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-basic_ostream-tellp.html"><span class="t-lines"><span>tellp</span></span></a></div>
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</div>
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</td>
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<td>返回输出位置指示器<br />
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<span class="t-mark">(<code>std::basic_ostream<CharT,Traits></code> 的公开成员函数)</span></td>
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</tr>
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<tr class="t-dsc">
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-basic_ostream-seekp.html"><span class="t-lines"><span>seekp</span></span></a></div>
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</div>
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</td>
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<td>设置输出位置指示器<br />
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<span class="t-mark">(<code>std::basic_ostream<CharT,Traits></code> 的公开成员函数)</span></td>
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