179 lines
19 KiB
HTML
179 lines
19 KiB
HTML
<!DOCTYPE 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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<head><meta http-equiv="x-ua-compatible" content="ie=edge">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<title>std::ios_base::width</title>
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<link rel="stylesheet" href="ext.css" />
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<link rel="stylesheet" href="site_modules.css" />
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</head>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_ios_base_width skin-cppreference2 action-view cpp-navbar">
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<div id="cpp-content-base">
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<div id="content"><a id="top"></a>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::ios_base::</span>width</h1>
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<div id="bodyContent">
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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 id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<table class="t-dcl-begin">
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<tbody>
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<tr class="t-dcl">
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<td>
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<div><span class="mw-geshi cpp source-cpp">streamsize width<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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</td>
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<td>(1)</td>
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<td class="t-dcl-nopad"></td>
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</tr>
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<tr class="t-dcl">
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<td>
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<div><span class="mw-geshi cpp source-cpp">streamsize width<span class="br0">(</span> streamsize new_width <span class="br0">)</span><span class="sy4">;</span></span></div>
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</td>
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<td>(2)</td>
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<td class="t-dcl-nopad"></td>
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</tr>
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<tr class="t-dcl-sep">
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<td></td>
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<td></td>
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<td></td>
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</tr>
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</tbody>
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</table>
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<p>管理某些输出操作时生成的最小字符数，和某些输出操作时生成的最大字符数。</p>
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<div class="t-li1"><span class="t-li">1)</span> 返回当前域宽。</div>
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<div class="t-li1"><span class="t-li">2)</span> 设置域宽为给定值。返回先前的位宽。</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>new_width</td>
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<td>-</td>
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<td>设置的新域宽</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>调用函数前的域宽</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>一些 I/O 函数在返回前调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">width<span class="br0">(</span><span class="nu0">0</span><span class="br0">)</span></span></span> ，见 <span class="t-lc"><a href="cpp-io-manip-setw.html">std::setw</a></span> （这导致此域仅在下次 I/O 函数，而不再任何后继 I/O 时有效）。</p>
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<p>此修改器在输入和输出上拥有的准确效果在单独的 I/O 函数之间有别，效果单独描述于每个 <code>operator<<</code> 和 <code>operator>></code> 重载的页面。</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 <array></span>
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<span class="co2">#include <tuple></span>
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<span class="co2">#include <ctime></span>
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<span class="co2">#include <string></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <sstream></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="kw4">auto</span> str_time <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">int</span> year, <span class="kw4">int</span> mon, <span class="kw4">int</span> day<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">constexpr</span> <a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a><span class="sy1"><</span><span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span>, <span class="nu0">7</span><span class="sy1">></span> week_day<span class="br0">{</span> <span class="br0">{</span>
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<span class="st0">"Sunday"</span>, <span class="st0">"Monday"</span>, <span class="st0">"Tuesday"</span>, <span class="st0">"Wednesday"</span>, <span class="st0">"Thursday"</span>, <span class="st0">"Friday"</span>, <span class="st0">"Saturday"</span>
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<span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span>
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<a href="cpp-chrono-c-tm.html"><span class="kw1023">std::<span class="me2">tm</span></span></a> tm<span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
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tm.<span class="me1">tm_year</span> <span class="sy1">=</span> year <span class="sy2">-</span> <span class="nu0">1900</span><span class="sy4">;</span>
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tm.<span class="me1">tm_mon</span> <span class="sy1">=</span> mon <span class="sy2">-</span> <span class="nu0">1</span><span class="sy4">;</span>
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tm.<span class="me1">tm_mday</span> <span class="sy1">=</span> day<span class="sy4">;</span>
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day <span class="sy2">+</span><span class="sy1">=</span> mon <span class="sy1"><</span> <span class="nu0">3</span> <span class="sy4">?</span> year<span class="sy2">--</span> <span class="sy4">:</span> year <span class="sy2">-</span> <span class="nu0">2</span><span class="sy4">;</span>
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tm.<span class="me1">tm_wday</span> <span class="sy1">=</span> <span class="br0">(</span><span class="nu0">23</span> <span class="sy2">*</span> mon <span class="sy2">/</span> <span class="nu0">9</span> <span class="sy2">+</span> day <span class="sy2">+</span> <span class="nu0">4</span> <span class="sy2">+</span> year <span class="sy2">/</span> <span class="nu0">4</span> <span class="sy2">-</span> year <span class="sy2">/</span> <span class="nu0">100</span> <span class="sy2">+</span> year <span class="sy2">/</span> <span class="nu0">400</span><span class="br0">)</span> <span class="sy2">%</span> <span class="nu0">7</span><span class="sy4">;</span>
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<a href="cpp-io-basic_ostringstream.html"><span class="kw1736">std::<span class="me2">ostringstream</span></span></a> out<span class="sy4">;</span>
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out <span class="sy1"><<</span> week_day<span class="br0">[</span>tm.<span class="me1">tm_wday</span><span class="br0">]</span> <span class="sy1"><<</span> <span class="st0">", "</span> <span class="sy1"><<</span> <a href="cpp-io-manip-put_time.html"><span class="kw1801">std::<span class="me2">put_time</span></span></a><span class="br0">(</span><span class="sy3">&</span>tm, <span class="st0">"%B %d, %Y"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw1">return</span> out.<span class="me1">str</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">constexpr</span> <span class="kw4">int</span> column_size <span class="sy1">=</span> <span class="nu0">4</span><span class="sy4">;</span>
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<span class="kw1">using</span> table_t <span class="sy1">=</span> <a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a><span class="sy1"><</span><a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a>, column_size<span class="sy1">></span><span class="sy4">;</span>
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table_t headers<span class="br0">{</span> <span class="br0">{</span> <span class="st0">"Name"</span>, <span class="st0">"Birthdate"</span>, <span class="st0">"Death date"</span>, <span class="st0">"Language Created"</span> <span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span>
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<a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a><span class="sy1"><</span>table_t, <span class="nu0">5</span><span class="sy1">></span> data<span class="br0">{</span> <span class="br0">{</span>
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<span class="br0">{</span> <span class="br0">{</span> <span class="st0">"Dennis MacAlistair Ritchie"</span>, str_time<span class="br0">(</span><span class="nu0">1941</span>, <span class="nu0">9</span>, <span class="nu0">9</span><span class="br0">)</span>, str_time<span class="br0">(</span><span class="nu0">2011</span>, <span class="nu0">10</span>, <span class="nu0">12</span><span class="br0">)</span>, <span class="st0">"C"</span> <span class="br0">}</span> <span class="br0">}</span>,
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<span class="br0">{</span> <span class="br0">{</span> <span class="st0">"Bjarne Stroustrup"</span>, str_time<span class="br0">(</span><span class="nu0">1950</span>, <span class="nu0">12</span>, <span class="nu0">30</span><span class="br0">)</span>, <span class="st0">""</span>, <span class="st0">"C++"</span> <span class="br0">}</span> <span class="br0">}</span>,
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<span class="br0">{</span> <span class="br0">{</span> <span class="st0">"Anders Hejlsberg"</span>, str_time<span class="br0">(</span><span class="nu0">1960</span>, <span class="nu0">12</span>, <span class="nu0">2</span><span class="br0">)</span>, <span class="st0">""</span>, <span class="st0">"C#"</span> <span class="br0">}</span> <span class="br0">}</span>,
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<span class="br0">{</span> <span class="br0">{</span> <span class="st0">"Guido van Rossum"</span>, str_time<span class="br0">(</span><span class="nu0">1956</span>, <span class="nu0">1</span>, <span class="nu0">31</span><span class="br0">)</span>, <span class="st0">""</span>, <span class="st0">"Python"</span> <span class="br0">}</span> <span class="br0">}</span>,
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<span class="br0">{</span> <span class="br0">{</span> <span class="st0">"Brendan Eich"</span>, str_time<span class="br0">(</span><span class="nu0">1961</span>, <span class="nu0">7</span>, <span class="nu0">4</span><span class="br0">)</span>, <span class="st0">""</span>, <span class="st0">"Javascript"</span> <span class="br0">}</span> <span class="br0">}</span>
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<span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">constexpr</span> <span class="kw4">int</span> name_wid <span class="sy1">=</span> <span class="nu0">30</span><span class="sy4">;</span>
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<span class="kw4">constexpr</span> <span class="kw4">int</span> birth_wid <span class="sy1">=</span> <span class="nu0">30</span><span class="sy4">;</span>
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<span class="kw4">constexpr</span> <span class="kw4">int</span> death_wid <span class="sy1">=</span> <span class="nu0">30</span><span class="sy4">;</span>
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<span class="kw4">constexpr</span> <span class="kw4">int</span> lang_wid <span class="sy1">=</span> <span class="nu0">18</span><span class="sy4">;</span>
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<span class="kw4">auto</span> print_line <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span>table_t <span class="kw4">const</span> <span class="sy3">&</span>tbl<span class="br0">)</span>
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<span class="br0">{</span>
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<span class="kw4">auto</span> <span class="kw4">const</span> <span class="sy3">&</span><span class="br0">[</span>Name, Birthdate, DeathDate, LanguageCreated<span class="br0">]</span> <span class="sy1">=</span> tbl<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">width</span><span class="br0">(</span>name_wid<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="br0">(</span><span class="st0">"| "</span> <span class="sy2">+</span> Name<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'|'</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">width</span><span class="br0">(</span>birth_wid<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="br0">(</span><span class="st0">' '</span> <span class="sy2">+</span> Birthdate<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'|'</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">width</span><span class="br0">(</span>death_wid<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="br0">(</span><span class="st0">' '</span> <span class="sy2">+</span> DeathDate<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'|'</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">width</span><span class="br0">(</span>lang_wid<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="br0">(</span><span class="st0">' '</span> <span class="sy2">+</span> LanguageCreated<span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'|'</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">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">constexpr</span> <span class="kw4">int</span> total_wid <span class="sy1">=</span> name_wid <span class="sy2">+</span> birth_wid <span class="sy2">+</span> death_wid <span class="sy2">+</span> lang_wid <span class="sy2">+</span> column_size<span class="sy4">;</span>
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<span class="kw4">auto</span> print_break <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span>
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<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="me1">width</span><span class="br0">(</span>total_wid<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="me1">fill</span><span class="br0">(</span><span class="st0">'-'</span><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">'-'</span> <span class="sy1"><<</span> <a href="cpp-io-manip-endl.html"><span class="kw1791">std::<span class="me2">endl</span></span></a><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">fill</span><span class="br0">(</span><span class="st0">' '</span><span class="br0">)</span><span class="sy4">;</span>
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<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="me1">setf</span><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">ios</span><span class="sy4">::</span><span class="me2">left</span>, std<span class="sy4">::</span><span class="me2">ios</span><span class="sy4">::</span><span class="me2">adjustfield</span><span class="br0">)</span><span class="sy4">;</span>
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print_break<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
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print_line<span class="br0">(</span>headers<span class="br0">)</span><span class="sy4">;</span>
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print_break<span class="br0">(</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">auto</span> <span class="kw4">const</span> <span class="sy3">&</span>entry <span class="sy4">:</span> data<span class="br0">)</span>
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print_line<span class="br0">(</span>entry<span class="br0">)</span><span class="sy4">;</span>
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print_break<span class="br0">(</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">----------------------------------------------------------------------------------------------------------------
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| Name | Birthdate | Death date | Language Created |
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----------------------------------------------------------------------------------------------------------------
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| Dennis MacAlistair Ritchie | Tuesday, September 09, 1941 | Wednesday, October 12, 2011 | C |
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| Bjarne Stroustrup | Saturday, December 30, 1950 | | C++ |
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| Anders Hejlsberg | Friday, December 02, 1960 | | C# |
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| Guido van Rossum | Tuesday, January 31, 1956 | | Python |
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| Brendan Eich | Tuesday, July 04, 1961 | | Javascript |
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----------------------------------------------------------------------------------------------------------------</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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<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-ios_base-precision.html"><span class="t-lines"><span>precision</span></span></a></div>
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</div>
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</td>
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<td>管理浮点操作的精度<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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</div>
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</div>
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</body>
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</html>
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