101 lines
9.5 KiB
HTML
101 lines
9.5 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::weakly_incrementable</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_iterator_weakly_incrementable 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::</span>weakly_incrementable</h1>
|
|
<div id="bodyContent">
|
|
<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-iterator.html">iterator</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-iterator.html"><iterator></a></code></div>
|
|
</td>
|
|
<td></td>
|
|
<td></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> I<span class="sy1">></span><br /></span>
|
|
<p> concept weakly_incrementable <span class="sy1">=</span><br />
|
|
std<span class="sy4">::</span><span class="me2">default_initializable</span><span class="sy1"><</span>I<span class="sy1">></span> <span class="sy3">&&</span> std<span class="sy4">::</span><span class="me2">movable</span><span class="sy1"><</span>I<span class="sy1">></span> <span class="sy3">&&</span><br />
|
|
requires<span class="br0">(</span>I i<span class="br0">)</span> <span class="br0">{</span><br />
|
|
<span class="kw1">typename</span> std<span class="sy4">::</span><span class="me2">iter_difference_t</span><span class="sy1"><</span>I<span class="sy1">></span><span class="sy4">;</span><br />
|
|
requires <span class="coMULTI">/*is-signed-integer-like*/</span><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">iter_difference_t</span><span class="sy1"><</span>I<span class="sy1">>></span><span class="sy4">;</span><br />
|
|
<span class="br0">{</span> <span class="sy2">++</span>i <span class="br0">}</span> <span class="sy2">-</span><span class="sy1">></span> std<span class="sy4">::</span><span class="me2">same_as</span><span class="sy1"><</span>I<span class="sy3">&</span><span class="sy1">></span><span class="sy4">;</span> <span class="co1">// 不要求保持相等性</span><br />
|
|
i<span class="sy2">++</span><span class="sy4">;</span> <span class="co1">// 不要求保持相等性</span><br /></p>
|
|
<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>
|
|
<tr class="t-dcl-sep">
|
|
<td></td>
|
|
<td></td>
|
|
<td></td>
|
|
</tr>
|
|
</tbody>
|
|
</table>
|
|
<p>其中 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*is-signed-integer-like*/</span><span class="sy1"><</span>I<span class="sy1">></span></span></span> 当且仅当 <code>I</code> 为有符号整数式类型（见后述）。</p>
|
|
<p>此概念指定能以前后自增运算符自增的类型上的要求，不过这些自增运算不要求保持相等性，而且不要求类型自身为 <span class="t-lc">std::equality_comparable</span> 。</p>
|
|
<p>对于 <code>std::weakly_incrementable</code> 类型， <span class="t-c"><span class="mw-geshi cpp source-cpp">a <span class="sy1">==</span> b</span></span> 不蕴含 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">++</span>a <span class="sy1">==</span> <span class="sy2">++</span>b</span></span> 。弱可自增类型上的算法必须是单趟算法。这些算法能通过 <span class="t-lc"><a href="cpp-iterator-istream_iterator.html">std::istream_iterator</a></span> 用于作为输入数据源的 <code>istream</code> 。</p>
|
|
<h3><span class="mw-headline" id=".E8.AF.AD.E4.B9.89.E8.A6.81.E6.B1.82">语义要求</span></h3>
|
|
<p>给定类型 <code>I</code> 的任何对象 <code>i</code> ， <code>I</code> 仅若满足下列条件才实现 <code>std::weakly_incrementable</code></p>
|
|
<ul>
|
|
<li>表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">++</span>i</span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">i<span class="sy2">++</span></span></span> 拥有相同定义域</li>
|
|
<li>若 <code>i</code> 可自增，则 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">++</span>i</span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">i<span class="sy2">++</span></span></span> 均增加 <code>i</code></li>
|
|
<li>若 <code>i</code> 可自增，则 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-memory-addressof.html"><span class="kw757">std::<span class="me2">addressof</span></span></a><span class="br0">(</span><span class="sy2">++</span>i<span class="br0">)</span> <span class="sy1">==</span> <a href="cpp-memory-addressof.html"><span class="kw757">std::<span class="me2">addressof</span></span></a><span class="br0">(</span>i<span class="br0">)</span></span></span></li>
|
|
</ul>
|
|
<h3><span class="mw-headline" id=".E6.95.B4.E6.95.B0.E5.BC.8F.E7.B1.BB.E5.9E.8B">整数式类型</span></h3>
|
|
<p>一个整数式类型是（可有 cv 限定的）整数类型（除了 <i>cv</i> <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span></span></span> ）或一个实现提供（非用户提供）的表现同整数类型的类，包括所有运算符、隐式转换及 <span class="t-lc"><a href="cpp-types-numeric_limits.html">std::numeric_limits</a></span> 特化。若一个整数式类型仅表示非负值，则它为无符号整数式，否则它为有符号整数式。</p>
|
|
<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/issue3467">LWG 3467</a></td>
|
|
<td>C++20</td>
|
|
<td><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">bool</span></span></span> 被认为是整数类型</td>
|
|
<td>已排除</td>
|
|
</tr>
|
|
<tr>
|
|
<td><a rel="nofollow" class="external text" href="https://wg21.link/P2325R3">P2325R3</a></td>
|
|
<td>C++20</td>
|
|
<td>要求 <a href="cpp-concepts-default_initializable.html"><code>default_initializable</code></a></td>
|
|
<td>不要求</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-iterator-incrementable.html"><span class="t-lines"><span>incrementable</span></span></a></div>
|
|
<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
|
|
</div>
|
|
</td>
|
|
<td>指定 <strong class="selflink"><code>weakly_incrementable</code></strong> 类型上的自增操作保持相等性，而且该类型为 <a href="cpp-concepts-equality_comparable.html"><code>equality_comparable</code></a><br />
|
|
<span class="t-mark">(概念)</span></td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="visualClear"></div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html>
|