140 lines
14 KiB
HTML
140 lines
14 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>std::ios_base::pword</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_ios_base_pword skin-cppreference2 action-view cpp-navbar">
|
|
<div id="cpp-content-base">
|
|
<div id="content"><a id="top"></a>
|
|
<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::ios_base::</span>pword</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-ios_base.html">ios base</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-dcl">
|
|
<td class="t-dcl-nopad">
|
|
<div><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">*</span><span class="sy3">&</span> pword<span class="br0">(</span> <span class="kw4">int</span> index <span class="br0">)</span><span class="sy4">;</span></span></div>
|
|
</td>
|
|
<td class="t-dcl-nopad"></td>
|
|
<td class="t-dcl-nopad"></td>
|
|
</tr>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<p>首先，充分地分配或重置私有存储（ <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">*</span></span></span> 的动态数组或另一可索引数据结构）以确保 <code>index</code> 是合法下标，然后返回到带下标 <code>index</code> 的私有存储 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span><span class="sy2">*</span></span></span> 元素。</p>
|
|
<p>引用可能被此 <code>ios_base</code> 对象上任何其他操作非法化，包含另一对 <code>pword()</code> 的调用，但维持返回值，使得以相同下标从 <span class="t-c"><span class="mw-geshi cpp source-cpp">pword<span class="br0">(</span>index<span class="br0">)</span></span></span> 读取将产生相同值（直至下次到 <span class="t-c"><span class="mw-geshi cpp source-cpp">copyfmt<span class="br0">(</span><span class="br0">)</span></span></span> 的调用）。值能用于任何目的。元素下标必须由 <span class="t-lc"><a href="cpp-io-ios_base-xalloc.html">xalloc()</a></span> 获得，否则行为未定义。初始化新元素为空指针。</p>
|
|
<p>若分配失败，则调用可能抛出 <span class="t-lc"><a href="cpp-io-ios_base-failure.html">std::ios_base::failure</a></span> 的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-io-basic_ios.html"><span class="kw1712">std::<span class="me2">basic_ios</span></span></a><span class="sy1"><></span><span class="sy4">::</span><span class="me2">setstate</span><span class="br0">(</span>badbit<span class="br0">)</span></span></span> 。</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>index</td>
|
|
<td>-</td>
|
|
<td>元素的下标值</td>
|
|
</tr>
|
|
</table>
|
|
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
|
|
<p>到该元素的引用。</p>
|
|
<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
|
|
<p>设置 badbit 时可能抛出 <span class="t-lc"><a href="cpp-io-ios_base-failure.html">std::ios_base::failure</a></span> 。</p>
|
|
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
|
|
<p>若存储于 <code>pword</code> 的指针要求管理，则可用 <span class="t-lc"><a href="cpp-io-ios_base-register_callback.html">register_callback()</a></span> 安装按需执行深复制或解分配的处理函数。</p>
|
|
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
|
|
<div class="t-template-editlink" style=""></div>
|
|
<div class="t-example">
|
|
<p>将基类 pword 存储用于导出的流对象的运行时类型鉴别。</p>
|
|
<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="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> charT, <span class="kw1">class</span> traits <span class="sy1">=</span> <a href="cpp-string-char_traits.html"><span class="kw1267">std::<span class="me2">char_traits</span></span></a><span class="sy1"><</span>charT<span class="sy1">></span> <span class="sy1">></span>
|
|
<span class="kw1">class</span> mystream <span class="sy4">:</span> <span class="kw1">public</span> <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 class="br0">{</span>
|
|
<span class="kw1">public</span><span class="sy4">:</span>
|
|
<span class="kw4">static</span> <span class="kw4">const</span> <span class="kw4">int</span> xindex<span class="sy4">;</span>
|
|
mystream<span class="br0">(</span><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 class="sy3">&</span> ostr<span class="br0">)</span> <span class="sy4">:</span>
|
|
<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 class="br0">(</span>ostr.<span class="me1">rdbuf</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
this<span class="sy2">-</span><span class="sy1">></span>pword<span class="br0">(</span>xindex<span class="br0">)</span> <span class="sy1">=</span> this<span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
|
|
<span class="kw4">void</span> myfn<span class="br0">(</span><span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<span class="sy2">*</span>this <span class="sy1"><<</span> <span class="st0">"[special handling for mystream]"</span><span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
<span class="br0">}</span><span class="sy4">;</span>
|
|
|
|
<span class="co1">// 每个 mystream 特化从 xalloc() 获得独有的下标</span>
|
|
<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>
|
|
<span class="kw4">const</span> <span class="kw4">int</span> mystream<span class="sy1"><</span>charT, traits<span class="sy1">></span><span class="sy4">::</span><span class="me2">xindex</span> <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">ios_base</span><span class="sy4">::</span><span class="me2">xalloc</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
|
|
|
<span class="co1">// 此 I/O 操纵符将能用于辨识身为 mystream 的 ostream</span>
|
|
<span class="co1">// 通过查找存储于 pword 的指针</span>
|
|
<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>
|
|
<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 class="sy3">&</span> mymanip<span class="br0">(</span><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 class="sy3">&</span> os<span class="br0">)</span>
|
|
<span class="br0">{</span>
|
|
<span class="kw1">if</span> <span class="br0">(</span>os.<span class="me1">pword</span><span class="br0">(</span>mystream<span class="sy1"><</span>charT,traits<span class="sy1">></span><span class="sy4">::</span><span class="me2">xindex</span><span class="br0">)</span> <span class="sy1">==</span> <span class="sy3">&</span>os<span class="br0">)</span>
|
|
<span class="kw1">static_cast</span><span class="sy1"><</span>mystream<span class="sy1"><</span>charT,traits<span class="sy1">></span><span class="sy3">&</span><span class="sy1">></span><span class="br0">(</span>os<span class="br0">)</span>.<span class="me1">myfn</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="kw1">return</span> os<span class="sy4">;</span>
|
|
<span class="br0">}</span>
|
|
|
|
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
|
|
<span class="br0">{</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">"cout, narrow-character test "</span> <span class="sy1"><<</span> mymanip <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
|
|
|
mystream<span class="sy1"><</span><span class="kw4">char</span><span class="sy1">></span> myout<span class="br0">(</span><a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a><span class="br0">)</span><span class="sy4">;</span>
|
|
myout <span class="sy1"><<</span> <span class="st0">"myout, narrow-character test "</span> <span class="sy1"><<</span> mymanip <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
|
|
|
<a href="cpp-io-cout.html"><span class="kw1759">std::<span class="me2">wcout</span></span></a> <span class="sy1"><<</span> <span class="st0">"wcout, wide-character test "</span> <span class="sy1"><<</span> mymanip <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
|
|
|
|
mystream<span class="sy1"><</span><span class="kw4">wchar_t</span><span class="sy1">></span> mywout<span class="br0">(</span><a href="cpp-io-cout.html"><span class="kw1759">std::<span class="me2">wcout</span></span></a><span class="br0">)</span><span class="sy4">;</span>
|
|
mywout <span class="sy1"><<</span> <span class="st0">"mywout, wide-character test "</span> <span class="sy1"><<</span> mymanip <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">cout, narrow-character test
|
|
myout, narrow-character test [special handling for mystream]
|
|
wcout, wide-character test
|
|
mywout, wide-character test [special handling for mystream]</pre></div>
|
|
</div>
|
|
</div>
|
|
<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-ios_base-iword.html"><span class="t-lines"><span>iword</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>如果有必要的话，调整私有存储的大小，并且访问位于提供的下标的<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">long</span></span></span>元素<br />
|
|
<span class="t-mark">(公开成员函数)</span></td>
|
|
</tr>
|
|
<tr class="t-dsc">
|
|
<td>
|
|
<div class="t-dsc-member-div">
|
|
<div><a href="cpp-io-ios_base-xalloc.html"><span class="t-lines"><span>xalloc</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-cmark">[静态]</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>返回能安全用作 pword() 和 iword() 下标的程序范围内独有的整数<br />
|
|
<span class="t-mark">(公开静态成员函数)</span></td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="visualClear"></div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html>
|