241 lines
22 KiB
HTML
241 lines
22 KiB
HTML
<!DOCTYPE html>
|
|
<html lang="zh" dir="ltr" class="client-nojs" xmlns="http://www.w3.org/1999/xhtml" xml:lang="zh">
|
|
<head><meta http-equiv="x-ua-compatible" content="ie=edge">
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
|
<title>operator>>(std::basic_istream)</title>
|
|
<link rel="stylesheet" href="ext.css" />
|
|
<link rel="stylesheet" href="site_modules.css" />
|
|
</head>
|
|
<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_io_basic_istream_operator_gtgt2 skin-cppreference2 action-view cpp-navbar">
|
|
<div id="cpp-content-base">
|
|
<div id="content"><a id="top"></a>
|
|
<h1 id="firstHeading" class="firstHeading">operator>><span style="font-size:0.7em; line-height:130%">(std::basic_istream)</span></h1>
|
|
<div id="bodyContent">
|
|
<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>
|
|
<div id="mw-content-text" lang="zh" dir="ltr" class="mw-content-ltr" xml:lang="zh">
|
|
<table class="t-dcl-begin">
|
|
<tbody>
|
|
<tr class="t-dsc-header">
|
|
<td>
|
|
<div>定义于头文件 <code><a href="cpp-header-istream.html"><istream></a></code></div>
|
|
</td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
<tr class="t-dcl">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> CharT, <span class="kw1">class</span> Traits <span class="sy1">></span><br /></span>
|
|
<p>basic_istream<span class="sy1"><</span>CharT,Traits<span class="sy1">></span><span class="sy3">&</span> operator<span class="sy1">>></span><span class="br0">(</span> basic_istream<span class="sy1"><</span>CharT,Traits<span class="sy1">></span><span class="sy3">&</span> st, CharT<span class="sy3">&</span> ch <span class="br0">)</span><span class="sy4">;</span><br />
|
|
<br />
|
|
<span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> Traits <span class="sy1">></span><br />
|
|
basic_istream<span class="sy1"><</span><span class="kw4">char</span>,Traits<span class="sy1">></span><span class="sy3">&</span> operator<span class="sy1">>></span><span class="br0">(</span> basic_istream<span class="sy1"><</span><span class="kw4">char</span>,Traits<span class="sy1">></span><span class="sy3">&</span> st, <span class="kw4">signed</span> <span class="kw4">char</span><span class="sy3">&</span> ch <span class="br0">)</span><span class="sy4">;</span><br />
|
|
<br />
|
|
<span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> Traits <span class="sy1">></span><br /></p>
|
|
basic_istream<span class="sy1"><</span><span class="kw4">char</span>,Traits<span class="sy1">></span><span class="sy3">&</span> operator<span class="sy1">>></span><span class="br0">(</span> basic_istream<span class="sy1"><</span><span class="kw4">char</span>,Traits<span class="sy1">></span><span class="sy3">&</span> st, <span class="kw4">unsigned</span> <span class="kw4">char</span><span class="sy3">&</span> ch <span class="br0">)</span><span class="sy4">;</span></div>
|
|
</td>
|
|
<td>(1)</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
</tr>
|
|
</tbody>
|
|
<tbody class="t-dcl-rev t-dcl-rev-num">
|
|
<tr class="t-dcl-rev-aux">
|
|
<td></td>
|
|
<td rowspan="142">(2)</td>
|
|
<td></td>
|
|
</tr>
|
|
<tr class="t-dcl t-until-cxx20">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> CharT, <span class="kw1">class</span> Traits<span class="sy1">></span><br /></span>
|
|
<p>basic_istream<span class="sy1"><</span>CharT,Traits<span class="sy1">></span><span class="sy3">&</span> operator<span class="sy1">>></span><span class="br0">(</span> basic_istream<span class="sy1"><</span>CharT,Traits<span class="sy1">></span><span class="sy3">&</span> st, CharT<span class="sy2">*</span> s <span class="br0">)</span><span class="sy4">;</span><br />
|
|
<br />
|
|
<span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> Traits <span class="sy1">></span><br />
|
|
basic_istream<span class="sy1"><</span><span class="kw4">char</span>,Traits<span class="sy1">></span><span class="sy3">&</span> operator<span class="sy1">>></span><span class="br0">(</span> basic_istream<span class="sy1"><</span><span class="kw4">char</span>,Traits<span class="sy1">></span><span class="sy3">&</span> st, <span class="kw4">signed</span> <span class="kw4">char</span><span class="sy2">*</span> s <span class="br0">)</span><span class="sy4">;</span><br />
|
|
<br />
|
|
<span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> Traits <span class="sy1">></span><br /></p>
|
|
basic_istream<span class="sy1"><</span><span class="kw4">char</span>,Traits<span class="sy1">></span><span class="sy3">&</span> operator<span class="sy1">>></span><span class="br0">(</span> basic_istream<span class="sy1"><</span><span class="kw4">char</span>,Traits<span class="sy1">></span><span class="sy3">&</span> st, <span class="kw4">unsigned</span> <span class="kw4">char</span><span class="sy2">*</span> s <span class="br0">)</span><span class="sy4">;</span></div>
|
|
</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
<td><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl t-since-cxx20">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> CharT, <span class="kw1">class</span> Traits, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N <span class="sy1">></span><br /></span>
|
|
<p>basic_istream<span class="sy1"><</span>CharT,Traits<span class="sy1">></span><span class="sy3">&</span> operator<span class="sy1">>></span><span class="br0">(</span> basic_istream<span class="sy1"><</span>CharT,Traits<span class="sy1">></span><span class="sy3">&</span> st, CharT <span class="br0">(</span><span class="sy3">&</span>s<span class="br0">)</span><span class="br0">[</span>N<span class="br0">]</span> <span class="br0">)</span><span class="sy4">;</span><br />
|
|
<br />
|
|
<span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> Traits, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N <span class="sy1">></span><br />
|
|
basic_istream<span class="sy1"><</span><span class="kw4">char</span>,Traits<span class="sy1">></span><span class="sy3">&</span> operator<span class="sy1">>></span><span class="br0">(</span> basic_istream<span class="sy1"><</span><span class="kw4">char</span>,Traits<span class="sy1">></span><span class="sy3">&</span> st, <span class="kw4">signed</span> <span class="kw4">char</span> <span class="br0">(</span><span class="sy3">&</span>s<span class="br0">)</span><span class="br0">[</span>N<span class="br0">]</span> <span class="br0">)</span><span class="sy4">;</span><br />
|
|
<br />
|
|
<span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> Traits, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N <span class="sy1">></span><br /></p>
|
|
basic_istream<span class="sy1"><</span><span class="kw4">char</span>,Traits<span class="sy1">></span><span class="sy3">&</span> operator<span class="sy1">>></span><span class="br0">(</span> basic_istream<span class="sy1"><</span><span class="kw4">char</span>,Traits<span class="sy1">></span><span class="sy3">&</span> st, <span class="kw4">unsigned</span> <span class="kw4">char</span> <span class="br0">(</span><span class="sy3">&</span>s<span class="br0">)</span><span class="br0">[</span>N<span class="br0">]</span> <span class="br0">)</span><span class="sy4">;</span></div>
|
|
</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
</tbody>
|
|
<tbody>
|
|
<tr class="t-dcl t-since-cxx11">
|
|
<td>
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> Istream, <span class="kw1">class</span> T <span class="sy1">></span><br />
|
|
Istream<span class="sy3">&&</span> operator<span class="sy1">>></span><span class="br0">(</span> Istream<span class="sy3">&&</span> st, T<span class="sy3">&&</span> value <span class="br0">)</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td>(3)</td>
|
|
<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td>
|
|
</tr>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<p><br /></p>
|
|
<div class="t-li1"><span class="t-li">1-2)</span> 进行字符输入操作。</div>
|
|
<div class="t-li1"><span class="t-li">1)</span> 表现为<a href="cpp-named_req-FormattedInputFunction.html"><span style="font-style:italic">有格式输入函数</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(FormattedInputFunction)</span></a> 。在构造并检查 sentry 对象，因而可能跳过前导空白符后，释出一个字符并存储之到 <code>ch</code>。若无字符可用，则设置 <a href="cpp-io-ios_base-iostate.html"><tt>failbit</tt></a> （在<a href="cpp-named_req-FormattedInputFunction.html"><span style="font-style:italic">有格式输入函数</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(FormattedInputFunction)</span></a> 所要求的设置 <a href="cpp-io-ios_base-iostate.html"><tt>eofbit</tt></a> 外）。</div>
|
|
<div class="t-li1"><span class="t-li">2)</span> 表现为<a href="cpp-named_req-FormattedInputFunction.html"><span style="font-style:italic">有格式输入函数</span> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(FormattedInputFunction)</span></a> 。在构造并检查 sentry 对象，因而可能跳过前导空白后，释出相继字符，并存储它们到 <code>s</code> <span class="t-rev-inl t-until-cxx20"><span>指向其首元素的字符数组</span> <span><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></span></span>的相继位置。若满足下列条件之一，则释出停止：
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>找到空白字符（以 <a href="cpp-locale-ctype.html"><tt>ctype<CharT></tt></a> 平面确定）。不释出该空白字符。</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
<table class="t-rev-begin">
|
|
<tr class="t-rev t-until-cxx20">
|
|
<td>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>释出了 <span class="t-c"><span class="mw-geshi cpp source-cpp">st.<span class="me1">width</span><span class="br0">(</span><span class="br0">)</span> <span class="sy2">-</span> <span class="nu0">1</span></span></span> 个字符（若 <span class="t-c"><span class="mw-geshi cpp source-cpp">st.<span class="me1">width</span><span class="br0">(</span><span class="br0">)</span></span></span> 大于零）</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
</td>
|
|
<td><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td>
|
|
</tr>
|
|
<tr class="t-rev t-since-cxx20">
|
|
<td>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>释出了 <span class="t-c"><span class="mw-geshi cpp source-cpp">min<span class="br0">(</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a><span class="br0">(</span>st.<span class="me1">width</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span>, N<span class="br0">)</span> <span class="sy2">-</span> <span class="nu0">1</span></span></span> 个字符（若 <span class="t-c"><span class="mw-geshi cpp source-cpp">st.<span class="me1">width</span><span class="br0">(</span><span class="br0">)</span></span></span> 大于零）</li>
|
|
<li>否则为释出了 <span class="t-c"><span class="mw-geshi cpp source-cpp">N <span class="sy2">-</span> <span class="nu0">1</span></span></span> 个字符</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
</td>
|
|
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
|
|
</tr>
|
|
</table>
|
|
<dl>
|
|
<dd>
|
|
<ul>
|
|
<li>输入序列中出现文件尾（也会设置 <a href="cpp-io-ios_base-iostate.html"><tt>eofbit</tt></a> ）</li>
|
|
</ul>
|
|
</dd>
|
|
</dl>
|
|
任一情况下，存储额外的空字符值 <span class="t-c"><span class="mw-geshi cpp source-cpp">CharT<span class="br0">(</span><span class="br0">)</span></span></span> 于输出结尾。若未释出字符，则设置 <a href="cpp-io-ios_base-iostate.html"><tt>failbit</tt></a> （仍写入空字符到输出的首位置）。最后调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">st.<span class="me1">width</span><span class="br0">(</span><span class="nu0">0</span><span class="br0">)</span></span></span> 取消 <span class="t-lc"><a href="cpp-io-manip-setw.html">std::setw</a></span> 的效果，若存在。</div>
|
|
<div class="t-li1"><span class="t-li">3)</span> 给定到输入流对象的右值引用，调用适合的释出运算符（等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp">st <span class="sy1">>></span> <a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="br0">(</span>value<span class="br0">)</span></span></span> ）。此重载仅若表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">st <span class="sy1">>></span> <a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>T<span class="sy1">></span><span class="br0">(</span>value<span class="br0">)</span></span></span> 为良构且 <code>Istream</code> 为公开且无歧义派生自 <span class="t-lc"><a href="cpp-io-ios_base.html">std::ios_base</a></span> 的类类型才参与重载决议。</div>
|
|
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
|
|
<p>释出作为流的最末字符的单个字符不会设置 <code>eofbit</code> ：这异于有格式输入函数，例如以 <span class="t-c"><span class="mw-geshi cpp source-cpp">operator<span class="sy1">>></span></span></span> 释出最末的整数，但此行为匹配 <span class="t-lc"><a href="cpp-io-c-fscanf.html">std::scanf</a></span> 用 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="st0">"%c"</span></span></span> 格式指定符的行为。</p>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
|
|
<table class="t-par-begin">
|
|
<tr class="t-par">
|
|
<td>st</td>
|
|
<td>-</td>
|
|
<td>要自之释出数据的输入流</td>
|
|
</tr>
|
|
<tr class="t-par">
|
|
<td>ch</td>
|
|
<td>-</td>
|
|
<td>到要存储释出字符的字符的引用</td>
|
|
</tr>
|
|
<tr class="t-par">
|
|
<td>s</td>
|
|
<td>-</td>
|
|
<td><span class="t-rev-inl t-until-cxx20"><span>指针，指向</span> <span><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></span></span>要存储释出字符的字符数组</td>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
|
|
<p><code>st</code></p>
|
|
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
|
|
<div class="t-example">
|
|
<div class="t-example-live-link"></div>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="cpp source-cpp">
|
|
<pre class="de1"><span class="co2">#include <iostream></span>
|
|
<span class="co2">#include <iomanip></span>
|
|
<span class="co2">#include <sstream></span>
|
|
|
|
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<a href="cpp-string-basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> input <span class="sy1">=</span> <span class="st0">"n greetings"</span><span class="sy4">;</span>
|
|
<a href="cpp-io-basic_istringstream.html"><span class="kw1735">std::<span class="me2">istringstream</span></span></a> stream<span class="br0">(</span>input<span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw4">char</span> c<span class="sy4">;</span>
|
|
<span class="kw4">const</span> <span class="kw4">int</span> MAX <span class="sy1">=</span> <span class="nu0">6</span><span class="sy4">;</span>
|
|
<span class="kw4">char</span> cstr<span class="br0">[</span>MAX<span class="br0">]</span><span class="sy4">;</span>
|
|
|
|
stream <span class="sy1">>></span> c <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>MAX<span class="br0">)</span> <span class="sy1">>></span> cstr<span class="sy4">;</span>
|
|
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"c = "</span> <span class="sy1"><<</span> c <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span>
|
|
<span class="sy1"><<</span> <span class="st0">"cstr = "</span> <span class="sy1"><<</span> cstr <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
|
|
|
<span class="kw4">double</span> f<span class="sy4">;</span>
|
|
<a href="cpp-io-basic_istringstream.html"><span class="kw1735">std::<span class="me2">istringstream</span></span></a><span class="br0">(</span><span class="st0">"1.23"</span><span class="br0">)</span> <span class="sy1">>></span> f<span class="sy4">;</span> <span class="co1">// 右值流释出</span>
|
|
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="st0">"f = "</span> <span class="sy1"><<</span> f <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
|
<span class="br0">}</span></pre></div>
|
|
</div>
|
|
<p>输出：</p>
|
|
<div dir="ltr" class="mw-geshi" style="text-align: left;">
|
|
<div class="text source-text">
|
|
<pre class="de1">c = n
|
|
cstr = greet
|
|
f = 1.23</pre></div>
|
|
</div>
|
|
</div>
|
|
<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
|
|
<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。</p>
|
|
<table class="dsctable" style="font-size:0.8em">
|
|
<tr>
|
|
<th>DR</th>
|
|
<th>应用于</th>
|
|
<th>出版时的行为</th>
|
|
<th>正确行为</th>
|
|
</tr>
|
|
<tr>
|
|
<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue1203">LWG 1203</a></td>
|
|
<td>C++11</td>
|
|
<td>右值流的重载返回到基类的左值引用</td>
|
|
<td>返回到派生类的右值引用</td>
|
|
</tr>
|
|
<tr>
|
|
<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2328">LWG 2328</a></td>
|
|
<td>C++11</td>
|
|
<td>右值流的重载要求另一参数为左值</td>
|
|
<td>使之接受右值</td>
|
|
</tr>
|
|
<tr>
|
|
<td><a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2534">LWG 2534</a></td>
|
|
<td>C++11</td>
|
|
<td>右值流的重载未被制约</td>
|
|
<td>已制约</td>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
|
|
<table class="t-dsc-begin">
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-io-basic_istream-operator_gtgt.html"><span class="t-lines"><span>operator>></span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>提取带格式数据<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="visualClear"></div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html>
|