146 lines
10 KiB
HTML
146 lines
10 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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<title>std::setw</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_manip_setw 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>setw</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 id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
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<div>定义于头文件 <code><a href="cpp-header-iomanip.html"><iomanip></a></code></div>
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<td></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*unspecified*/</span> setw<span class="br0">(</span> <span class="kw4">int</span> n <span class="br0">)</span><span class="sy4">;</span></span></div>
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<p>用于表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">out <span class="sy1"><<</span> setw<span class="br0">(</span>n<span class="br0">)</span></span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp">in <span class="sy1">>></span> setw<span class="br0">(</span>n<span class="br0">)</span></span></span> 时，设置流 <code>out</code> 或 <code>in</code> 的 <code>width</code> 参数准确为 <code>n</code> 。</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>n</td>
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<td>-</td>
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<td>width 的新值</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>返回未指定类型对象，满足若 <code>str</code> 是 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-io-basic_ostream.html"><span class="kw1715">std::<span class="me2">basic_ostream</span></span></a><span class="sy1"><</span>CharT, Traits<span class="sy1">></span></span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-io-basic_istream.html"><span class="kw1713">std::<span class="me2">basic_istream</span></span></a><span class="sy1"><</span>CharT, Traits<span class="sy1">></span></span></span> 类型流的名称，则表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">str <span class="sy1"><<</span> setw<span class="br0">(</span>n<span class="br0">)</span></span></span> 或 <span class="t-c"><span class="mw-geshi cpp source-cpp">str <span class="sy1">>></span> setw<span class="br0">(</span>n<span class="br0">)</span></span></span> 表现为如同执行下列代码：</p>
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<p><span class="t-c"><span class="mw-geshi cpp source-cpp">str.<span class="me1">width</span><span class="br0">(</span>n<span class="br0">)</span><span class="sy4">;</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>若调用任何下列函数，则流的宽度属性将被设为零（表示“不指定”）：</p>
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<ul>
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<li>输入</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li><a href="cpp-string-basic_string-operator_ltltgtgt.html"><tt>operator>>(basic_istream&, basic_string&)</tt></a></li>
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<li><a href="cpp-io-basic_istream-operator_gtgt2.html"><tt>operator>>(basic_istream&, char*)</tt></a></li>
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</ul>
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</dd>
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</dl>
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<ul>
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<li>输出</li>
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</ul>
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<dl>
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<dd>
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<ul>
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<li><a href="cpp-io-basic_ostream-operator_ltlt.html"><tt>basic_ostream::operator<<()</tt></a> 的重载 1-7 （在 <a href="cpp-locale-num_put-put.html"><tt>num_put::put()</tt></a> 的阶段 3 ）</li>
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<li><a href="cpp-io-basic_ostream-operator_ltlt2.html"><tt>operator<<(basic_ostream&, char)</tt></a> 和 <a href="cpp-io-basic_ostream-operator_ltlt2.html"><tt>operator<<(basic_ostream&, char*)</tt></a></li>
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<li><a href="cpp-string-basic_string-operator_ltltgtgt.html"><tt>operator<<(basic_ostream&, basic_string&)</tt></a></li>
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<li><span class="t-lc"><a href="cpp-io-manip-put_money.html">std::put_money</a></span> （在 <a href="cpp-locale-money_put-put.html"><tt>money_put::put()</tt></a> 内）</li>
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<li><span class="t-lc"><a href="cpp-io-manip-quoted.html">std::quoted</a></span> （以输出流使用时）</li>
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</ul>
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</dd>
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</dl>
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<p>此修改器在输入与输出上的准确效果在单独的 I/O 函数间有别，单独地描述于每个 <code>operator<<</code> 各 <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 <sstream></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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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"no setw:"</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">"setw(6):"</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">setw</span><span class="br0">(</span><span class="nu0">6</span><span class="br0">)</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">"setw(6), several elements: "</span> <span class="sy1"><<</span> <span class="nu0">89</span> <span class="sy1"><<</span> std<span class="sy4">::</span><span class="me2">setw</span><span class="br0">(</span><span class="nu0">6</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="nu0">12</span> <span class="sy1"><<</span> <span class="nu0">34</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-basic_istringstream.html"><span class="kw1735">std::<span class="me2">istringstream</span></span></a> is<span class="br0">(</span><span class="st0">"hello, world"</span><span class="br0">)</span><span class="sy4">;</span>
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<span class="kw4">char</span> arr<span class="br0">[</span><span class="nu0">10</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">setw</span><span class="br0">(</span><span class="nu0">6</span><span class="br0">)</span> <span class="sy1">>></span> arr<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">"Input from <span class="es1">\"</span>"</span> <span class="sy1"><<</span> is.<span class="me1">str</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">"<span class="es1">\"</span> with setw(6) gave <span class="es1">\"</span>"</span>
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<span class="sy1"><<</span> arr <span class="sy1"><<</span> <span class="st0">"<span class="es1">\"</span><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">no setw:42
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setw(6): 42
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setw(6), several elements: 89 1234
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Input from "hello, world" with setw(6) gave "hello"</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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<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-width.html"><span class="t-lines"><span>width</span></span></a></div>
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</div>
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</td>
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<td>管理域的宽度<br />
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<span class="t-mark">(<code>std::ios_base</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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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-io-manip-setfill.html"><span class="t-lines"><span>setfill</span></span></a></div>
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</div>
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</td>
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<td>更改填充字符<br />
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<span class="t-mark">(函数模板)</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-manip-left.html"><span class="t-lines"><span>internal</span><span>left</span><span>right</span></span></a></div>
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</div>
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</td>
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<td>设置填充字符的布置<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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</div>
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</body>
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