107 lines
11 KiB
HTML
107 lines
11 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::iterator_traits<std::counted_iterator></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_counted_iterator_iterator_traits 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>iterator_traits<small><std::counted_iterator></small></h1>
|
|
<div id="bodyContent">
|
|
<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-iterator.html">iterator</a>‎ | <a href="cpp-iterator-counted_iterator.html">counted 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> std<span class="sy4">::</span><span class="me2">input_iterator</span> I <span class="sy1">></span><br /></span>
|
|
<p> requires <span class="coMULTI">/* see below */</span><br />
|
|
<span class="kw1">struct</span> iterator_traits<span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">counted_iterator</span><span class="sy1"><</span>I<span class="sy1">>></span> <span class="sy4">:</span> <a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>I<span class="sy1">></span> <span class="br0">{</span><br />
|
|
<span class="kw1">using</span> pointer <span class="sy1">=</span> <a href="cpp-types-conditional.html"><span class="kw634">std::<span class="me2">conditional_t</span></span></a><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">contiguous_iterator</span><span class="sy1"><</span>I<span class="sy1">></span>,<br />
|
|
<a href="cpp-types-add_pointer.html"><span class="kw615">std::<span class="me2">add_pointer_t</span></span></a><span class="sy1"><</span>std<span class="sy4">::</span><span class="me2">iter_reference_t</span><span class="sy1"><</span>I<span class="sy1">>></span>,<br />
|
|
<span class="kw4">void</span><span class="sy1">></span><span class="sy4">;</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>从定制（从标准部分特化或程序定义特化生成）的 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>I<span class="sy1">></span></span></span> 继承属性，调整成员类型 <code>pointer</code> ，其中 <code>I</code> 实现 <a href="cpp-iterator-input_iterator.html"><code>input_iterator</code></a> 。</p>
|
|
<p>值得注意的是， <code>iterator_concept</code> （若存在）和 <code>iterator_category</code> （若存在）从 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>I<span class="sy1">></span></span></span> 继承。</p>
|
|
<p>requires 子句中的条件为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw2">true</span></span></span> 当且仅当 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>I<span class="sy1">></span></span></span> 不从主模板生成。</p>
|
|
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
|
|
<p><a rel="nofollow" class="external text" href="https://wg21.link/P2259R1">P2259R1</a> 前，即使 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>I<span class="sy1">></span></span></span> 从主模板生成也使用此特化。结果在针对迭代器概念（例如 <a href="cpp-iterator-forward_iterator.html"><code>forward_iterator</code></a> ）测试 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">counted_iterator</span><span class="sy1"><</span>I<span class="sy1">></span></span></span> 时， <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="coMULTI">/*ITER_CONCEPT*/</span></span></span> 的确定过程不考虑 <code>I::iterator_concept</code> ，从而 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">counted_iterator</span><span class="sy1"><</span>I<span class="sy1">></span></span></span> 有时错误地表现为它无法实现该概念。此错误行为在 10.4 前的 libstdc++ 与 VS 2022 17.0 Preview 3 前的 MSVC STL 中实现。</p>
|
|
<p>标准库对指针类型、 <span class="t-lc">std::counted_iterator</span> 及 <span class="t-lc">std::common_iterator</span> 提供 <span class="t-lc"><a href="cpp-iterator-iterator_traits.html">std::iterator_traits</a></span> 的部分特化。</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 <iterator></span>
|
|
<span class="co2">#include <type_traits></span>
|
|
<span class="co2">#include <list></span>
|
|
<span class="co2">#include <vector></span>
|
|
|
|
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
|
|
<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a> v<span class="br0">{</span><span class="nu0">1</span>,<span class="nu0">2</span>,<span class="nu0">3</span>,<span class="nu0">4</span><span class="br0">}</span><span class="sy4">;</span>
|
|
<a href="cpp-container-list.html"><span class="kw1275">std::<span class="me2">list</span></span></a> l<span class="br0">{</span><span class="nu0">1</span>,<span class="nu0">2</span>,<span class="nu0">3</span>,<span class="nu0">4</span><span class="br0">}</span><span class="sy4">;</span>
|
|
std<span class="sy4">::</span><span class="me2">counted_iterator</span> iv<span class="br0">{</span>v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, <span class="nu0">3</span><span class="br0">}</span><span class="sy4">;</span>
|
|
std<span class="sy4">::</span><span class="me2">counted_iterator</span> il<span class="br0">{</span>l.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, <span class="nu0">3</span><span class="br0">}</span><span class="sy4">;</span>
|
|
static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw588">std::<span class="me2">is_same</span></span></a><span class="sy1"><</span><span class="kw4">int</span><span class="sy2">*</span>, <a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>decltype<span class="br0">(</span>iv<span class="br0">)</span><span class="sy1">></span><span class="sy4">::</span><span class="me2">pointer</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
|
|
static_assert<span class="br0">(</span><a href="cpp-types-is_same.html"><span class="kw588">std::<span class="me2">is_same</span></span></a><span class="sy1"><</span><span class="kw4">void</span>, <a href="cpp-iterator-iterator_traits.html"><span class="kw651">std::<span class="me2">iterator_traits</span></span></a><span class="sy1"><</span>decltype<span class="br0">(</span>il<span class="br0">)</span><span class="sy1">></span><span class="sy4">::</span><span class="me2">pointer</span><span class="sy1">></span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
|
|
<span class="br0">}</span></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://wg21.link/P2259R1">P2259R1</a></td>
|
|
<td>C++20</td>
|
|
<td>无 requires 子句<br />
|
|
无条件定义 <code>pointer</code> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span></td>
|
|
<td>添加约束</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-iterator_traits.html"><span class="t-lines"><span>iterator_traits</span></span></a></div>
|
|
</div>
|
|
</td>
|
|
<td>为迭代器各项性质提供统一接口<br />
|
|
<span class="t-mark">(类模板)</span></td>
|
|
</tr>
|
|
</table>
|
|
</div>
|
|
<div class="visualClear"></div>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html>
|