<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="API documentation for the Rust `swap` fn in crate `std`."><meta name="keywords" content="rust, rustlang, rust-lang, swap"><title>std::ptr::swap - Rust</title><link rel="stylesheet" type="text/css" href="../../normalize1.35.0.css"><link rel="stylesheet" type="text/css" href="../../rustdoc1.35.0.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../dark1.35.0.css"><link rel="stylesheet" type="text/css" href="../../light1.35.0.css" id="themeStyle"><script src="../../storage1.35.0.js"></script><noscript><link rel="stylesheet" href="../../noscript1.35.0.css"></noscript><link rel="shortcut icon" href="../../favicon1.35.0.ico"><style type="text/css">#crate-search{background-image:url("../../down-arrow1.35.0.svg");}</style></head><body class="rustdoc fn"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">☰</div><a href='../../std/index.html'><img src='../../rust-logo1.35.0.png' alt='logo' width='100'></a><div class="sidebar-elems"><p class='location'><a href='../index.html'>std</a>::<wbr><a href='index.html'>ptr</a></p><script>window.sidebarCurrent = {name: 'swap', ty: 'fn', relpath: ''};</script><script defer src="sidebar-items.js"></script></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../../brush1.35.0.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../../theme1.35.0.js"></script><nav class="sub"><form class="search-form js-only"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><a id="settings-menu" href="../../settings.html"><img src="../../wheel1.35.0.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><span class='out-of-band'><span class='since' title='Stable since Rust version 1.0.0'>1.0.0</span><span id='render-detail'><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class='inner'>−</span>]</a></span><a class='srclink' href='../../src/core/ptr.rs.html#296-305' title='goto source code'>[src]</a></span><span class='in-band'>Function <a href='../index.html'>std</a>::<wbr><a href='index.html'>ptr</a>::<wbr><a class="fn" href=''>swap</a></span></h1><pre class='rust fn'>pub unsafe fn swap<T>(x: <a class="primitive" href="../primitive.pointer.html">*mut T</a>, y: <a class="primitive" href="../primitive.pointer.html">*mut T</a>)</pre><div class='docblock'><p>Swaps the values at two mutable locations of the same type, without
deinitializing either.</p>
<p>But for the following two exceptions, this function is semantically
equivalent to <a href="../mem/fn.swap.html"><code>mem::swap</code></a>:</p>
<ul>
<li>
<p>It operates on raw pointers instead of references. When references are
available, <a href="../mem/fn.swap.html"><code>mem::swap</code></a> should be preferred.</p>
</li>
<li>
<p>The two pointed-to values may overlap. If the values do overlap, then the
overlapping region of memory from <code>x</code> will be used. This is demonstrated
in the second example below.</p>
</li>
</ul>
<h1 id="safety" class="section-header"><a href="#safety">Safety</a></h1>
<p>Behavior is undefined if any of the following conditions are violated:</p>
<ul>
<li>
<p>Both <code>x</code> and <code>y</code> must be <a href="../ptr/index.html#safety">valid</a> for reads and writes.</p>
</li>
<li>
<p>Both <code>x</code> and <code>y</code> must be properly aligned.</p>
</li>
</ul>
<p>Note that even if <code>T</code> has size <code>0</code>, the pointers must be non-NULL and properly aligned.</p>
<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
<p>Swapping two non-overlapping regions:</p>
<div class="example-wrap"><pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">ptr</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">array</span> <span class="op">=</span> [<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>];
<span class="kw">let</span> <span class="ident">x</span> <span class="op">=</span> <span class="ident">array</span>[<span class="number">0</span>..].<span class="ident">as_mut_ptr</span>() <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> [<span class="ident">u32</span>; <span class="number">2</span>]; <span class="comment">// this is `array[0..2]`</span>
<span class="kw">let</span> <span class="ident">y</span> <span class="op">=</span> <span class="ident">array</span>[<span class="number">2</span>..].<span class="ident">as_mut_ptr</span>() <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> [<span class="ident">u32</span>; <span class="number">2</span>]; <span class="comment">// this is `array[2..4]`</span>
<span class="kw">unsafe</span> {
<span class="ident">ptr</span>::<span class="ident">swap</span>(<span class="ident">x</span>, <span class="ident">y</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>([<span class="number">2</span>, <span class="number">3</span>, <span class="number">0</span>, <span class="number">1</span>], <span class="ident">array</span>);
}<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0Ause%20std%3A%3Aptr%3B%0A%0Alet%20mut%20array%20%3D%20%5B0%2C%201%2C%202%2C%203%5D%3B%0A%0Alet%20x%20%3D%20array%5B0..%5D.as_mut_ptr()%20as%20*mut%20%5Bu32%3B%202%5D%3B%20%2F%2F%20this%20is%20%60array%5B0..2%5D%60%0Alet%20y%20%3D%20array%5B2..%5D.as_mut_ptr()%20as%20*mut%20%5Bu32%3B%202%5D%3B%20%2F%2F%20this%20is%20%60array%5B2..4%5D%60%0A%0Aunsafe%20%7B%0A%20%20%20%20ptr%3A%3Aswap(x%2C%20y)%3B%0A%20%20%20%20assert_eq!(%5B2%2C%203%2C%200%2C%201%5D%2C%20array)%3B%0A%7D%0A%7D">Run</a></pre></div>
<p>Swapping two overlapping regions:</p>
<div class="example-wrap"><pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">ptr</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">array</span> <span class="op">=</span> [<span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>];
<span class="kw">let</span> <span class="ident">x</span> <span class="op">=</span> <span class="ident">array</span>[<span class="number">0</span>..].<span class="ident">as_mut_ptr</span>() <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> [<span class="ident">u32</span>; <span class="number">3</span>]; <span class="comment">// this is `array[0..3]`</span>
<span class="kw">let</span> <span class="ident">y</span> <span class="op">=</span> <span class="ident">array</span>[<span class="number">1</span>..].<span class="ident">as_mut_ptr</span>() <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> [<span class="ident">u32</span>; <span class="number">3</span>]; <span class="comment">// this is `array[1..4]`</span>
<span class="kw">unsafe</span> {
<span class="ident">ptr</span>::<span class="ident">swap</span>(<span class="ident">x</span>, <span class="ident">y</span>);
<span class="comment">// The indices `1..3` of the slice overlap between `x` and `y`.</span>
<span class="comment">// Reasonable results would be for to them be `[2, 3]`, so that indices `0..3` are</span>
<span class="comment">// `[1, 2, 3]` (matching `y` before the `swap`); or for them to be `[0, 1]`</span>
<span class="comment">// so that indices `1..4` are `[0, 1, 2]` (matching `x` before the `swap`).</span>
<span class="comment">// This implementation is defined to make the latter choice.</span>
<span class="macro">assert_eq</span><span class="macro">!</span>([<span class="number">1</span>, <span class="number">0</span>, <span class="number">1</span>, <span class="number">2</span>], <span class="ident">array</span>);
}<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0Ause%20std%3A%3Aptr%3B%0A%0Alet%20mut%20array%20%3D%20%5B0%2C%201%2C%202%2C%203%5D%3B%0A%0Alet%20x%20%3D%20array%5B0..%5D.as_mut_ptr()%20as%20*mut%20%5Bu32%3B%203%5D%3B%20%2F%2F%20this%20is%20%60array%5B0..3%5D%60%0Alet%20y%20%3D%20array%5B1..%5D.as_mut_ptr()%20as%20*mut%20%5Bu32%3B%203%5D%3B%20%2F%2F%20this%20is%20%60array%5B1..4%5D%60%0A%0Aunsafe%20%7B%0A%20%20%20%20ptr%3A%3Aswap(x%2C%20y)%3B%0A%20%20%20%20%2F%2F%20The%20indices%20%601..3%60%20of%20the%20slice%20overlap%20between%20%60x%60%20and%20%60y%60.%0A%20%20%20%20%2F%2F%20Reasonable%20results%20would%20be%20for%20to%20them%20be%20%60%5B2%2C%203%5D%60%2C%20so%20that%20indices%20%600..3%60%20are%0A%20%20%20%20%2F%2F%20%60%5B1%2C%202%2C%203%5D%60%20(matching%20%60y%60%20before%20the%20%60swap%60)%3B%20or%20for%20them%20to%20be%20%60%5B0%2C%201%5D%60%0A%20%20%20%20%2F%2F%20so%20that%20indices%20%601..4%60%20are%20%60%5B0%2C%201%2C%202%5D%60%20(matching%20%60x%60%20before%20the%20%60swap%60).%0A%20%20%20%20%2F%2F%20This%20implementation%20is%20defined%20to%20make%20the%20latter%20choice.%0A%20%20%20%20assert_eq!(%5B1%2C%200%2C%201%2C%202%5D%2C%20array)%3B%0A%7D%0A%7D">Run</a></pre></div>
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