189 lines
23 KiB
HTML
189 lines
23 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::ranges::swap</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_utility_ranges_swap 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::ranges::</span>swap</h1>
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<div id="bodyContent">
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-utility.html">utility</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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<table class="t-dcl-begin">
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<div>定义于头文件 <code><a href="cpp-header-concepts.html"><concepts></a></code></div>
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<td></td>
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<tr class="t-dcl t-since-cxx20">
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">inline</span> <span class="kw1">namespace</span> <span class="coMULTI">/* unspecified */</span> <span class="br0">{</span><br /></span>
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<p> <span class="kw1">inline</span> <span class="kw4">constexpr</span> <span class="coMULTI">/* unspecified */</span> swap <span class="sy1">=</span> <span class="coMULTI">/* unspecified */</span><span class="sy4">;</span><br /></p>
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<span class="br0">}</span></div>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span><br />
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<span class="t-mark">(定制点对象)</span></td>
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<div>调用签名</div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span> <span class="kw1">class</span> T, <span class="kw1">class</span> U <span class="sy1">></span><br /></span>
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<p> requires <span class="coMULTI">/* see below */</span><br /></p>
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<span class="kw4">constexpr</span> <span class="kw4">void</span> swap<span class="br0">(</span>T<span class="sy3">&&</span> t, U<span class="sy3">&&</span> u<span class="br0">)</span> <span class="kw1">noexcept</span><span class="br0">(</span><span class="coMULTI">/* see below */</span><span class="br0">)</span><span class="sy4">;</span></div>
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<td class="t-dcl-nopad"></td>
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</tbody>
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</table>
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<p>交换 <code>t</code> 和 <code>u</code> 所引用的值。</p>
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<p>调用 <code>ranges::swap</code> ：</p>
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<ol>
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<li>表达式等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>swap<span class="br0">(</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>t<span class="br0">)</span>, <a href="cpp-utility-forward.html"><span class="kw1117">std::<span class="me2">forward</span></span></a><span class="sy1"><</span>U<span class="sy1">></span><span class="br0">(</span>u<span class="br0">)</span><span class="br0">)</span></span></span> ，若以下列候选进行<a href="cpp-language-overload_resolution.html">重载决议</a>则该表达式合法：
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<ul>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T<span class="sy1">></span> <span class="kw4">void</span> swap<span class="br0">(</span>T<span class="sy3">&</span>, T<span class="sy3">&</span><span class="br0">)</span> <span class="sy1">=</span> delete<span class="sy4">;</span></span></span></li>
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<li><span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1"><</span><span class="kw1">class</span> T, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N<span class="sy1">></span> <span class="kw4">void</span> swap<span class="br0">(</span>T<span class="br0">(</span><span class="sy3">&</span><span class="br0">)</span><span class="br0">[</span>N<span class="br0">]</span>, T<span class="br0">(</span><span class="sy3">&</span><span class="br0">)</span><span class="br0">[</span>N<span class="br0">]</span><span class="br0">)</span> <span class="sy1">=</span> delete<span class="sy4">;</span></span></span></li>
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<li><a href="cpp-language-adl.html">实参依赖查找</a>所找到的任何 <code>swap</code> 的声明。</li>
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</ul>
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<dd>若重载决议所选择的函数不交换 <code>t</code> 和 <code>u</code> 所引用的值，则程序为谬构；不要求诊断。</dd>
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</dl>
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</li>
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<li>否则表达式等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="br0">(</span><span class="kw4">void</span><span class="br0">)</span>ranges<span class="sy4">::</span><span class="me2">swap_ranges</span><span class="br0">(</span>t, u<span class="br0">)</span></span></span> ，除了 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">noexcept</span><span class="br0">(</span>ranges<span class="sy4">::</span><span class="me2">swap</span><span class="br0">(</span>t<span class="br0">)</span>, ranges<span class="sy4">::</span><span class="me2">swap</span><span class="br0">(</span>u<span class="br0">)</span><span class="br0">)</span></span></span> 等于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">noexcept</span><span class="br0">(</span>ranges<span class="sy4">::</span><span class="me2">swap</span><span class="br0">(</span><span class="sy2">*</span>t, <span class="sy2">*</span>u<span class="br0">)</span><span class="br0">)</span></span></span> ，若 <code>T</code> 和 <code>U</code> 为到相等长度（但元素类型可能不同）的数组类型的左值引用，且 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">swap</span><span class="br0">(</span><span class="sy2">*</span>t, <span class="sy2">*</span>u<span class="br0">)</span></span></span> 为合法表达式；</li>
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<li>否则如同用 <span class="t-c"><span class="mw-geshi cpp source-cpp">V v<span class="br0">(</span>std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>t<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span> t <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>u<span class="br0">)</span><span class="sy4">;</span> u <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>v<span class="br0">)</span><span class="sy4">;</span></span></span> 交换其被引用值，若 <code>T</code> 与 <code>U</code> 均为 <code>V&</code> ，而 <code>V</code> 是满足 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">move_constructible</span><span class="sy1"><</span>V<span class="sy1">></span></span></span> 和 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">assignable_from</span><span class="sy1"><</span>V<span class="sy3">&</span>, V<span class="sy1">></span></span></span> 的某个类型，
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<ul>
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<li>调用是否为潜在抛出由上述操作指定。</li>
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<li>若上述操作与以交换 <code>u</code> 与 <code>v</code> 进行的上述操作均可用于常量求值，则调用为常量子表达式。</li>
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</ul>
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<dl>
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<dd>若任一概念未被实现，则程序为谬构；不要求诊断。</dd>
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</dl>
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</li>
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<li>所有其他情况下，对 <code>ranges::swap</code> 的调用为谬构，这能在 <span class="t-c"><span class="mw-geshi cpp source-cpp">ranges<span class="sy4">::</span><span class="me2">swap</span><span class="br0">(</span>t, u<span class="br0">)</span></span></span> 出现于模板实例化的立即语境时导致<a href="cpp-language-sfinae.html">替换失败</a>。</li>
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</ol>
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<h3><span class="mw-headline" id=".E8.A1.A8.E8.BE.BE.E5.BC.8F.E7.AD.89.E4.BB.B7">表达式等价</span></h3>
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<p>表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">e</span></span> <i>表达式等价</i>于表达式 <span class="t-c"><span class="mw-geshi cpp source-cpp">f</span></span> ，若 <span class="t-c"><span class="mw-geshi cpp source-cpp">e</span></span> 与 <span class="t-c"><span class="mw-geshi cpp source-cpp">f</span></span> 拥有相同效果，均为<a href="cpp-language-noexcept_spec.html">潜在抛出</a>或均非潜在抛出（即 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">noexcept</span><span class="br0">(</span>e<span class="br0">)</span> <span class="sy1">==</span> <span class="kw1">noexcept</span><span class="br0">(</span>f<span class="br0">)</span></span></span> ），且均为<a href="cpp-language-constant_expression.html">常量子表达式</a>或均非常量子表达式。</p>
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<h3><span class="mw-headline" id=".E5.AE.9A.E5.88.B6.E7.82.B9.E5.AF.B9.E8.B1.A1">定制点对象</span></h3>
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<p>名字 <code>ranges::swap</code> 代表一个<i>定制点对象</i>，它是<a href="cpp-named_req-LiteralType.html">字面</a> <a href="cpp-concepts-semiregular.html"><code>semiregular</code></a> 类类型的 const <a href="cpp-named_req-FunctionObject.html">函数对象</a>。为说明目的，以 <code><i>__swap_fn</i></code> 表示其类型的 cv 无限定版本。</p>
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<p><code><i>__swap_fn</i></code> 的所有实例均相等。在相同参数上调用类型 <code><i>__swap_fn</i></code> 的不同实例的效果是等价的，无关乎指代该实例的表达式是左值还是右值，以及是否为 const 限定（然而不要求 volatile 限定的实例可调用）。从而能自由地复制 <code>ranges::swap</code> 并且能彼此替代地使用其副本。</p>
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<p>给定类型集合 <code>Args...</code> ，若 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="cpp-utility-declval.html"><span class="kw1120">std::<span class="me2">declval</span></span></a><span class="sy1"><</span>Args<span class="sy1">></span><span class="br0">(</span><span class="br0">)</span>...</span></span> 满足上面对于 <code>ranges::swap</code> 的参数要求，则 <code><i>__swap_fn</i></code> 实现 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">invocable</span><span class="sy1"><</span>__swap_fn, Args...<span class="sy1">></span></span></span>、 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">invocable</span><span class="sy1"><</span><span class="kw4">const</span> __swap_fn, Args...<span class="sy1">></span></span></span>、 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">invocable</span><span class="sy1"><</span>__swap_fn<span class="sy3">&</span>, Args...<span class="sy1">></span></span></span> 及 <span class="t-c"><span class="mw-geshi cpp source-cpp">std<span class="sy4">::</span><span class="me2">invocable</span><span class="sy1"><</span><span class="kw4">const</span> __swap_fn<span class="sy3">&</span>, Args...<span class="sy1">></span></span></span> 。否则， <code><i>__swap_fn</i></code> 的函数调用运算符不参与重载决议。</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 <array></span>
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<span class="co2">#include <concepts></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <ranges></span>
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<span class="co2">#include <string_view></span>
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<span class="co2">#include <vector></span>
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<span class="kw4">void</span> print<span class="br0">(</span><a href="cpp-string-basic_string_view.html"><span class="kw1248">std::<span class="me2">string_view</span></span></a> <span class="kw4">const</span> name,
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std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">common_range</span> <span class="kw4">auto</span> <span class="kw4">const</span><span class="sy3">&</span> p,
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std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">common_range</span> <span class="kw4">auto</span> <span class="kw4">const</span><span class="sy3">&</span> q<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> name <span class="sy1"><<</span> <span class="st0">"1{ "</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">auto</span> <span class="kw4">const</span><span class="sy3">&</span> i <span class="sy4">:</span> p<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> i <span class="sy1"><<</span> <span class="st0">' '</span><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">"}, "</span> <span class="sy1"><<</span> name <span class="sy1"><<</span> <span class="st0">"2{ "</span><span class="sy4">;</span>
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<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">auto</span> <span class="kw4">const</span><span class="sy3">&</span> i <span class="sy4">:</span> q<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> i <span class="sy1"><<</span> <span class="st0">' '</span><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">"}<span class="es1">\n</span>"</span><span class="sy4">;</span>
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<span class="br0">}</span>
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<span class="kw4">void</span> print<span class="br0">(</span><a href="cpp-string-basic_string_view.html"><span class="kw1248">std::<span class="me2">string_view</span></span></a> <span class="kw4">const</span> name, <span class="kw4">int</span> p, <span class="kw4">int</span> q<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> name <span class="sy1"><<</span> <span class="st0">"1 = "</span> <span class="sy1"><<</span> p <span class="sy1"><<</span> <span class="st0">", "</span> <span class="sy1"><<</span> name <span class="sy1"><<</span> <span class="st0">"2 = "</span> <span class="sy1"><<</span> q <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="br0">}</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-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a> a1<span class="br0">{</span><span class="nu0">10</span>,<span class="nu0">11</span>,<span class="nu0">12</span><span class="br0">}</span>, a2<span class="br0">{</span><span class="nu0">13</span>,<span class="nu0">14</span><span class="br0">}</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">swap</span><span class="br0">(</span>a1, a2<span class="br0">)</span><span class="sy4">;</span>
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print<span class="br0">(</span><span class="st0">"a"</span>, a1, a2<span class="br0">)</span><span class="sy4">;</span>
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<a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a> b1<span class="br0">{</span><span class="nu0">15</span>,<span class="nu0">16</span>,<span class="nu0">17</span><span class="br0">}</span>, b2<span class="br0">{</span><span class="nu0">18</span>,<span class="nu0">19</span>,<span class="nu0">20</span><span class="br0">}</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">swap</span><span class="br0">(</span>b1, b2<span class="br0">)</span><span class="sy4">;</span>
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print<span class="br0">(</span><span class="st0">"b"</span>, b1, b2<span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// std::array c1{1,2,3}; std::array c2{4,5};</span>
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<span class="co1">// std::ranges::swap(c1, c2); // 错误：类型不匹配</span>
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<span class="kw4">int</span> d1<span class="br0">[</span><span class="br0">]</span><span class="br0">{</span><span class="nu0">21</span>,<span class="nu0">22</span>,<span class="nu0">23</span><span class="br0">}</span>, d2<span class="br0">[</span><span class="br0">]</span><span class="br0">{</span><span class="nu0">24</span>,<span class="nu0">25</span>,<span class="nu0">26</span><span class="br0">}</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">swap</span><span class="br0">(</span>d1, d2<span class="br0">)</span><span class="sy4">;</span>
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print<span class="br0">(</span><span class="st0">"d"</span>, d1, d2<span class="br0">)</span><span class="sy4">;</span>
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<span class="co1">// int e1[]{1,2,3}, e2[]{4,5};</span>
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<span class="co1">// std::ranges::swap(e1, e2); // 错误：类型不匹配</span>
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<span class="co1">// char f1[]{1,2,3};</span>
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<span class="co1">// int f2[]{4,5,6};</span>
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<span class="co1">// std::ranges::swap(f1, f2); // 错误：类型不匹配</span>
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<span class="kw4">int</span> g1<span class="br0">{</span><span class="nu0">27</span><span class="br0">}</span>, g2<span class="br0">{</span><span class="nu0">28</span><span class="br0">}</span><span class="sy4">;</span>
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std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">swap</span><span class="br0">(</span>g1, g2<span class="br0">)</span><span class="sy4">;</span>
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print<span class="br0">(</span><span class="st0">"g"</span>, g1, g2<span class="br0">)</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">a1{ 13 14 }, a2{ 10 11 12 }
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b1{ 18 19 20 }, b2{ 15 16 17 }
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d1{ 24 25 26 }, d2{ 21 22 23 }
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g1 = 28, g2 = 27</pre></div>
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</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-concepts-swappable.html"><span class="t-lines"><span>swappable</span><span>swappable_with</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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</div>
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</td>
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<td>指定一个类型能进行交换，或两个类型能彼此交换<br />
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<span class="t-mark">(概念)</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-algorithm-swap.html"><span class="t-lines"><span>swap</span></span></a></div>
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</div>
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</td>
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<td>交换两个对象的值<br />
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<span class="t-mark">(函数模板)</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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</div>
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</body>
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</html>
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