<!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 `copy` fn in crate `std`."><meta name="keywords" content="rust, rustlang, rust-lang, copy"><title>std::ptr::copy - 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: 'copy', 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/intrinsics.rs.html#1478-1480' 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=''>copy</a></span></h1><pre class='rust fn'>pub unsafe fn copy<T>(src: <a class="primitive" href="../primitive.pointer.html">*const T</a>, dst: <a class="primitive" href="../primitive.pointer.html">*mut T</a>, count: <a class="primitive" href="../primitive.usize.html">usize</a>)</pre><div class='docblock'><p>Copies <code>count * size_of::<T>()</code> bytes from <code>src</code> to <code>dst</code>. The source
and destination may overlap.</p>
<p>If the source and destination will <em>never</em> overlap,
<a href="./fn.copy_nonoverlapping.html"><code>copy_nonoverlapping</code></a> can be used instead.</p>
<p><code>copy</code> is semantically equivalent to C's <a href="https://en.cppreference.com/w/c/string/byte/memmove"><code>memmove</code></a>, but with the argument
order swapped. Copying takes place as if the bytes were copied from <code>src</code>
to a temporary array and then copied from the array to <code>dst</code>.</p>
<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><code>src</code> must be <a href="../ptr/index.html#safety">valid</a> for reads of <code>count * size_of::<T>()</code> bytes.</p>
</li>
<li>
<p><code>dst</code> must be <a href="../ptr/index.html#safety">valid</a> for writes of <code>count * size_of::<T>()</code> bytes.</p>
</li>
<li>
<p>Both <code>src</code> and <code>dst</code> must be properly aligned.</p>
</li>
</ul>
<p>Like <a href="../ptr/fn.read.html"><code>read</code></a>, <code>copy</code> creates a bitwise copy of <code>T</code>, regardless of
whether <code>T</code> is <a href="../marker/trait.Copy.html"><code>Copy</code></a>. If <code>T</code> is not <a href="../marker/trait.Copy.html"><code>Copy</code></a>, using both the values
in the region beginning at <code>*src</code> and the region beginning at <code>*dst</code> can
<a href="../ptr/fn.read.html#ownership-of-the-returned-value">violate memory safety</a>.</p>
<p>Note that even if the effectively copied size (<code>count * size_of::<T>()</code>) is
<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>Efficiently create a Rust vector from an unsafe buffer:</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">unsafe</span> <span class="kw">fn</span> <span class="ident">from_buf_raw</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="ident">ptr</span>: <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">T</span>, <span class="ident">elts</span>: <span class="ident">usize</span>) <span class="op">-></span> <span class="ident">Vec</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">dst</span> <span class="op">=</span> <span class="ident">Vec</span>::<span class="ident">with_capacity</span>(<span class="ident">elts</span>);
<span class="ident">dst</span>.<span class="ident">set_len</span>(<span class="ident">elts</span>);
<span class="ident">ptr</span>::<span class="ident">copy</span>(<span class="ident">ptr</span>, <span class="ident">dst</span>.<span class="ident">as_mut_ptr</span>(), <span class="ident">elts</span>);
<span class="ident">dst</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%0A%23%5Ballow(dead_code)%5D%0Aunsafe%20fn%20from_buf_raw%3CT%3E(ptr%3A%20*const%20T%2C%20elts%3A%20usize)%20-%3E%20Vec%3CT%3E%20%7B%0A%20%20%20%20let%20mut%20dst%20%3D%20Vec%3A%3Awith_capacity(elts)%3B%0A%20%20%20%20dst.set_len(elts)%3B%0A%20%20%20%20ptr%3A%3Acopy(ptr%2C%20dst.as_mut_ptr()%2C%20elts)%3B%0A%20%20%20%20dst%0A%7D%0A%7D">Run</a></pre></div>
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