204 lines
15 KiB
HTML
204 lines
15 KiB
HTML
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<title>std::ios_base::setf</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_ios_base_setf 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::ios_base::</span>setf</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-ios_base.html">ios base</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">fmtflags setf<span class="br0">(</span> fmtflags flags <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(1)</td>
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<td class="t-dcl-nopad"></td>
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<div><span class="mw-geshi cpp source-cpp">fmtflags setf<span class="br0">(</span> fmtflags flags, fmtflags mask <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
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<td class="t-dcl-nopad"></td>
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<td></td>
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<td></td>
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<td></td>
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<p>设置格式化标志以指定设置。</p>
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<div class="t-li1"><span class="t-li">1)</span> 设置 <code>flags</code> 所标识的格式化标志。等效地进行下列操作: <span class="t-c"><span class="mw-geshi cpp source-cpp">fl <span class="sy1">=</span> fl <span class="sy3">|</span> flags</span></span> ,其中 <code>fl</code> 定义内部格式化标志的状态。</div>
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<div class="t-li1"><span class="t-li">2)</span> 清除 <code>mask</code> 下的格式化标志,并设置被清除的标志为 <code>flags</code> 所指定者。等效地进行下列操作: <span class="t-c"><span class="mw-geshi cpp source-cpp">fl <span class="sy1">=</span> <span class="br0">(</span>fl <span class="sy3">&</span> ~mask<span class="br0">)</span> <span class="sy3">|</span> <span class="br0">(</span>flags <span class="sy3">&</span> mask<span class="br0">)</span></span></span> ,其中 <code>fl</code> 定义格式化标志的内部状态。</div>
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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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<tr class="t-par">
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<td>flags, mask</td>
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<td>-</td>
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<td>新格式化设定。 <code>mask</code> 定义哪些标志可以改变, <code>flags</code> 定义要改变的标志中该设置那些(其他将被清除)。两个参数都能为下列常量的组合:
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<table class="t-dsc-begin">
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<td>常量</td>
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<td>解释</td>
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<td><a href="cpp-io-ios_base-fmtflags.html"><tt>dec</tt></a></td>
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<td>为整数 I/O 使用十进制底:见 <span class="t-lc"><a href="cpp-io-manip-hex.html">std::dec</a></span></td>
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<tr class="t-dsc">
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<td><a href="cpp-io-ios_base-fmtflags.html"><tt>oct</tt></a></td>
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<td>为整数 I/O 使用八进制底:见 <span class="t-lc"><a href="cpp-io-manip-hex.html">std::oct</a></span></td>
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<tr class="t-dsc">
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<td><a href="cpp-io-ios_base-fmtflags.html"><tt>hex</tt></a></td>
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<td>为整数 I/O 使用十六进制底:见 <span class="t-lc"><a href="cpp-io-manip-hex.html">std::hex</a></span></td>
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</tr>
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<tr class="t-dsc">
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<td><a href="cpp-io-ios_base-fmtflags.html"><tt>basefield</tt></a></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">dec<span class="sy3">|</span>oct<span class="sy3">|</span>hex</span></span> 。适用于掩码运算</td>
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<td><a href="cpp-io-ios_base-fmtflags.html"><tt>left</tt></a></td>
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<td>左校正(添加填充字符到右):见 <span class="t-lc"><a href="cpp-io-manip-left.html">std::left</a></span></td>
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<tr class="t-dsc">
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<td><a href="cpp-io-ios_base-fmtflags.html"><tt>right</tt></a></td>
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<td>右校正(添加填充字符到左):见 <span class="t-lc"><a href="cpp-io-manip-left.html">std::right</a></span></td>
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<td><a href="cpp-io-ios_base-fmtflags.html"><tt>internal</tt></a></td>
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<td>内部校正(添加填充字符到内部选定点):见 <span class="t-lc"><a href="cpp-io-manip-left.html">std::internal</a></span></td>
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<tr class="t-dsc">
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<td><a href="cpp-io-ios_base-fmtflags.html"><tt>adjustfield</tt></a></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">left<span class="sy3">|</span>right<span class="sy3">|</span>internal</span></span> 。适用于掩码运算</td>
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<tr class="t-dsc">
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<td><a href="cpp-io-ios_base-fmtflags.html"><tt>scientific</tt></a></td>
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<td>用科学记数法生成浮点类型,或若与 fixed 组合则用十六进制记法:见 <span class="t-lc"><a href="cpp-io-manip-fixed.html">std::scientific</a></span></td>
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<td><a href="cpp-io-ios_base-fmtflags.html"><tt>fixed</tt></a></td>
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<td>用定点记法生成浮点类型,或若与 scientific 组合则用十六进制记法:见 <span class="t-lc"><a href="cpp-io-manip-fixed.html">std::fixed</a></span></td>
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<td><a href="cpp-io-ios_base-fmtflags.html"><tt>floatfield</tt></a></td>
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<td><span class="t-c"><span class="mw-geshi cpp source-cpp">scientific<span class="sy3">|</span>fixed</span></span> 。适用于掩码运算</td>
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<tr class="t-dsc">
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<td><a href="cpp-io-ios_base-fmtflags.html"><tt>boolalpha</tt></a></td>
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<td>以字母数字格式插入并释出 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span></span></span> 类型:见 <span class="t-lc"><a href="cpp-io-manip-boolalpha.html">std::boolalpha</a></span></td>
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<td><a href="cpp-io-ios_base-fmtflags.html"><tt>showbase</tt></a></td>
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<td>生成为整数输出指示数字基底的前缀,货币 I/O 中要求现金指示器:见 <span class="t-lc"><a href="cpp-io-manip-showbase.html">std::showbase</a></span></td>
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<td><a href="cpp-io-ios_base-fmtflags.html"><tt>showpoint</tt></a></td>
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<td>无条件为浮点数输出生成小数点字符:见 <span class="t-lc"><a href="cpp-io-manip-showpoint.html">std::showpoint</a></span></td>
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<td><a href="cpp-io-ios_base-fmtflags.html"><tt>showpos</tt></a></td>
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<td>为非负数值输出生成 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">+</span></span></span> 字符,见 <span class="t-lc"><a href="cpp-io-manip-showpos.html">std::showpos</a></span></td>
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<td><a href="cpp-io-ios_base-fmtflags.html"><tt>skipws</tt></a></td>
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<td>在具体输入操作前跳过前导空白符:见 <span class="t-lc"><a href="cpp-io-manip-skipws.html">std::skipws</a></span></td>
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<td><a href="cpp-io-ios_base-fmtflags.html"><tt>unitbuf</tt></a></td>
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<td>在每次输出操作后冲入输出:见 <span class="t-lc"><a href="cpp-io-manip-unitbuf.html">std::unitbuf</a></span></td>
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<td><a href="cpp-io-ios_base-fmtflags.html"><tt>uppercase</tt></a></td>
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<td>在具体输出的输出操作中以大写等价替换小写字符:见 <span class="t-lc"><a href="cpp-io-manip-uppercase.html">std::uppercase</a></span></td>
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<p><br /></p>
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</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>调用函数前的格式化标志</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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<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 <iostream></span>
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<span class="co2">#include <iomanip></span>
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<span class="kw4">const</span> <span class="kw4">double</span> PI <span class="sy1">=</span> <span class="nu16">3.1415926535</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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<span class="kw4">const</span> <span class="kw4">int</span> WIDTH <span class="sy1">=</span> <span class="nu0">15</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="me1">setf</span><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">ios</span><span class="sy4">::</span><span class="me2">right</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 等价: cout << right;</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> <a href="cpp-io-manip-setw.html"><span class="kw1797">std::<span class="me2">setw</span></span></a><span class="br0">(</span>WIDTH<span class="sy2">/</span><span class="nu0">2</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">"radius"</span>
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<span class="sy1"><<</span> <a href="cpp-io-manip-setw.html"><span class="kw1797">std::<span class="me2">setw</span></span></a><span class="br0">(</span>WIDTH<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">"circumference"</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</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="me1">setf</span><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">ios</span><span class="sy4">::</span><span class="me2">fixed</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">double</span> radius <span class="sy1">=</span> <span class="nu0">1</span><span class="sy4">;</span> radius <span class="sy1"><=</span> <span class="nu0">6</span><span class="sy4">;</span> radius <span class="sy2">+</span><span class="sy1">=</span> <span class="nu16">0.5</span><span class="br0">)</span> <span class="br0">{</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> <a href="cpp-io-manip-setprecision.html"><span class="kw1796">std::<span class="me2">setprecision</span></span></a><span class="br0">(</span><span class="nu0">1</span><span class="br0">)</span> <span class="sy1"><<</span> <a href="cpp-io-manip-setw.html"><span class="kw1797">std::<span class="me2">setw</span></span></a><span class="br0">(</span>WIDTH<span class="sy2">/</span><span class="nu0">2</span><span class="br0">)</span>
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<span class="sy1"><<</span> radius
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<span class="sy1"><<</span> <a href="cpp-io-manip-setprecision.html"><span class="kw1796">std::<span class="me2">setprecision</span></span></a><span class="br0">(</span><span class="nu0">2</span><span class="br0">)</span> <span class="sy1"><<</span> <a href="cpp-io-manip-setw.html"><span class="kw1797">std::<span class="me2">setw</span></span></a><span class="br0">(</span>WIDTH<span class="br0">)</span>
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<span class="sy1"><<</span> <span class="br0">(</span><span class="nu0">2</span> <span class="sy2">*</span> PI <span class="sy2">*</span> radius<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>
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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">radius circumference
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1.0 6.28
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1.5 9.42
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2.0 12.57
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2.5 15.71
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3.0 18.85
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3.5 21.99
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4.0 25.13
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4.5 28.27
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5.0 31.42
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5.5 34.56
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6.0 37.70</pre></div>
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</div>
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</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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-ios_base-flags.html"><span class="t-lines"><span>flags</span></span></a></div>
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</div>
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</td>
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<td>管理格式标志<br />
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<span class="t-mark">(公开成员函数)</span></td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-ios_base-unsetf.html"><span class="t-lines"><span>unsetf</span></span></a></div>
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</div>
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</td>
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<td>清除特定格式的标志<br />
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<span class="t-mark">(公开成员函数)</span></td>
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</tr>
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</table>
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</div>
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<div class="visualClear"></div>
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</div>
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</body>
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