126 lines
11 KiB
HTML
126 lines
11 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::showbase, std::noshowbase</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_manip_showbase 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>showbase, <span style="font-size:0.7em; line-height:130%">std::</span>noshowbase</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-manip.html">manip</a></span></div>
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<div>定义于头文件 <code><a href="cpp-header-ios.html"><ios></a></code></div>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><a href="cpp-io-ios_base.html"><span class="kw1669">std::<span class="me2">ios_base</span></span></a><span class="sy3">&</span> showbase<span class="br0">(</span> <a href="cpp-io-ios_base.html"><span class="kw1669">std::<span class="me2">ios_base</span></span></a><span class="sy3">&</span> str <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(1)</td>
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<div><span class="mw-geshi cpp source-cpp"><a href="cpp-io-ios_base.html"><span class="kw1669">std::<span class="me2">ios_base</span></span></a><span class="sy3">&</span> noshowbase<span class="br0">(</span> <a href="cpp-io-ios_base.html"><span class="kw1669">std::<span class="me2">ios_base</span></span></a><span class="sy3">&</span> str <span class="br0">)</span><span class="sy4">;</span></span></div>
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<td>(2)</td>
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<p>1) 如同以调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">str.<span class="me1">setf</span><span class="br0">(</span><a href="cpp-io-ios_base-fmtflags.html"><span class="kw1691">std::<span class="me2">ios_base</span><span class="sy4">::</span><span class="me2">showbase</span></span></a><span class="br0">)</span></span></span> 启用流 <code>str</code> 中的 <code>showbase</code> 标志</p>
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<p>2) 如同以调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">str.<span class="me1">unsetf</span><span class="br0">(</span><a href="cpp-io-ios_base-fmtflags.html"><span class="kw1691">std::<span class="me2">ios_base</span><span class="sy4">::</span><span class="me2">showbase</span></span></a><span class="br0">)</span></span></span> 禁用流 <code>str</code> 中的 <code>showbase</code> 标志</p>
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<p>这是 I/O 操纵符，可用如 <span class="t-c"><span class="mw-geshi cpp source-cpp">out <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">showbase</span></span></span> 的表达式对任何 <span class="t-lc"><a href="cpp-io-basic_ostream.html">std::basic_ostream</a></span> 类型 <code>out</code> 的，或用如 <span class="t-c"><span class="mw-geshi cpp source-cpp">in <span class="sy1">>></span> std<span class="sy4">::</span><span class="me2">showbase</span></span></span> 的表达式对任何 <span class="t-lc"><a href="cpp-io-basic_istream.html">std::basic_istream</a></span> 类型的 <code>in</code> 调用。</p>
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<p><code>showbase</code> 标志影响整数输出（见 <span class="t-lc"><a href="cpp-locale-num_put-put.html">std::num_put::put</a></span> ）、货币输入（见 <span class="t-lc"><a href="cpp-locale-money_get-get.html">std::money_get::get</a></span> ）和货币输出（见 <span class="t-lc"><a href="cpp-locale-money_put-put.html">std::money_put::put</a></span> ）的行为。</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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<tr class="t-par">
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<td>str</td>
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<td>-</td>
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<td>到 I/O 流的引用</td>
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</tr>
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</table>
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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><code>str</code> （到操纵后的流的引用）</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>按 <span class="t-lc"><a href="cpp-locale-num_put-put.html">std::num_put::put</a></span> 中指定，整数输出中的 showbase 标志表现类似 <span class="t-lc"><a href="cpp-io-c-fprintf.html">std::printf</a></span> 中的 # 格式指定符，这表示输出值为零时<i>不</i>添加数值底前缀。</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 <sstream></span>
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<span class="co2">#include <locale></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <iomanip></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="co1">// showbase 影响八进制和十六进制的输出</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-hex.html"><span class="kw1780">std::<span class="me2">hex</span></span></a>
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<span class="sy1"><<</span> <span class="st0">"showbase: "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">showbase</span> <span class="sy1"><<</span> <span class="nu0">42</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
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<span class="sy1"><<</span> <span class="st0">"noshowbase: "</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">noshowbase</span> <span class="sy1"><<</span> <span class="nu0">42</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="co1">// 及货币值的输入和输出</span>
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std<span class="sy4">::</span><span class="me2">locale</span><span class="sy4">::</span><span class="me2">global</span><span class="br0">(</span><a href="cpp-locale-locale.html"><span class="kw1892">std::<span class="me2">locale</span></span></a><span class="br0">(</span><span class="st0">"en_US.utf8"</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">long</span> <span class="kw4">double</span> val <span class="sy1">=</span> <span class="nu0">0</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> is<span class="br0">(</span><span class="st0">"3.14"</span><span class="br0">)</span><span class="sy4">;</span>
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is <span class="sy1">>></span> std<span class="sy4">::</span><span class="me2">showbase</span> <span class="sy1">>></span> <a href="cpp-io-manip-get_money.html"><span class="kw1796">std::<span class="me2">get_money</span></span></a><span class="br0">(</span>val<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">"With showbase, parsing 3.14 as money gives "</span> <span class="sy1"><<</span> val <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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is.<span class="me1">seekg</span><span class="br0">(</span><span class="nu0">0</span><span class="br0">)</span><span class="sy4">;</span>
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is <span class="sy1">>></span> std<span class="sy4">::</span><span class="me2">noshowbase</span> <span class="sy1">>></span> <a href="cpp-io-manip-get_money.html"><span class="kw1796">std::<span class="me2">get_money</span></span></a><span class="br0">(</span>val<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">"Without showbase, parsing 3.14 as money gives "</span> <span class="sy1"><<</span> val <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>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">showbase: 0x2a
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noshowbase: 2a
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With showbase, parsing 3.14 as money gives 0
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Without showbase, parsing 3.14 as money gives 314</pre></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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<div class="t-dsc-member-div">
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<div><a href="cpp-io-manip-resetiosflags.html"><span class="t-lines"><span>resetiosflags</span></span></a></div>
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</div>
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</td>
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<td>清除指定的 ios_base 标志<br />
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<span class="t-mark">(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-manip-setiosflags.html"><span class="t-lines"><span>setiosflags</span></span></a></div>
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</div>
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</td>
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<td>设置指定的 ios_base 标志<br />
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<span class="t-mark">(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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