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<!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 `offset_of` macro in crate `memoffset`."><meta name="keywords" content="rust, rustlang, rust-lang, offset_of"><title>memoffset::offset_of - Rust</title><link rel="stylesheet" type="text/css" href="../normalize.css"><link rel="stylesheet" type="text/css" href="../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../dark.css"><link rel="stylesheet" type="text/css" href="../light.css" id="themeStyle"><script src="../storage.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="shortcut icon" href="../favicon.ico"><style type="text/css">#crate-search{background-image:url("../down-arrow.svg");}</style></head><body class="rustdoc macro"><!--[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='../memoffset/index.html'><div class='logo-container'><img src='../rust-logo.png' alt='logo'></div></a><div class="sidebar-elems"><p class='location'><a href='index.html'>memoffset</a></p><script>window.sidebarCurrent = {name: 'offset_of', ty: 'macro', 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="../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../theme.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="../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><span class='out-of-band'><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/memoffset/offset_of.rs.html#68-83' title='goto source code'>[src]</a></span><span class='in-band'>Macro <a href='index.html'>memoffset</a>::<wbr><a class="macro" href=''>offset_of</a></span></h1><div class="docblock type-decl hidden-by-usual-hider"><div class="example-wrap"><pre class="rust macro">
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<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">offset_of</span> {
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(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">father</span>:<span class="ident">ty</span>, $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">field</span>:<span class="ident">tt</span>)<span class="op">+</span>) <span class="op">=</span><span class="op">></span> { ... };
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}</pre></div>
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</div><div class='docblock'><p>Calculates the offset of the specified field from the start of the struct.
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This macro supports arbitrary amount of subscripts and recursive member-accesses.</p>
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<p><em>Note</em>: This macro may not make much sense when used on structs that are not <code>#[repr(C, packed)]</code></p>
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<h2 id="examples---simple" class="section-header"><a href="#examples---simple">Examples - Simple</a></h2>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="attribute">#[<span class="ident">macro_use</span>]</span>
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<span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">memoffset</span>;
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<span class="attribute">#[<span class="ident">repr</span>(<span class="ident">C</span>, <span class="ident">packed</span>)]</span>
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<span class="kw">struct</span> <span class="ident">Foo</span> {
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<span class="ident">a</span>: <span class="ident">u32</span>,
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<span class="ident">b</span>: <span class="ident">u64</span>,
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<span class="ident">c</span>: [<span class="ident">u8</span>; <span class="number">5</span>]
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}
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<span class="kw">fn</span> <span class="ident">main</span>() {
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="macro">offset_of</span><span class="macro">!</span>(<span class="ident">Foo</span>, <span class="ident">a</span>), <span class="number">0</span>);
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="macro">offset_of</span><span class="macro">!</span>(<span class="ident">Foo</span>, <span class="ident">b</span>), <span class="number">4</span>);
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="macro">offset_of</span><span class="macro">!</span>(<span class="ident">Foo</span>, <span class="ident">c</span>[<span class="number">2</span>]), <span class="number">14</span>);
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}</pre></div>
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<h2 id="examples---advanced" class="section-header"><a href="#examples---advanced">Examples - Advanced</a></h2>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="attribute">#[<span class="ident">macro_use</span>]</span>
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<span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">memoffset</span>;
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<span class="attribute">#[<span class="ident">repr</span>(<span class="ident">C</span>, <span class="ident">packed</span>)]</span>
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<span class="kw">struct</span> <span class="ident">UnnecessarilyComplicatedStruct</span> {
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<span class="ident">member</span>: [<span class="ident">UnnecessarilyComplexStruct</span>; <span class="number">12</span>]
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}
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<span class="attribute">#[<span class="ident">repr</span>(<span class="ident">C</span>, <span class="ident">packed</span>)]</span>
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<span class="kw">struct</span> <span class="ident">UnnecessarilyComplexStruct</span> {
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<span class="ident">a</span>: <span class="ident">u32</span>,
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<span class="ident">b</span>: <span class="ident">u64</span>,
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<span class="ident">c</span>: [<span class="ident">u8</span>; <span class="number">5</span>]
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}
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<span class="kw">fn</span> <span class="ident">main</span>() {
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="macro">offset_of</span><span class="macro">!</span>(<span class="ident">UnnecessarilyComplicatedStruct</span>, <span class="ident">member</span>[<span class="number">3</span>].<span class="ident">c</span>[<span class="number">3</span>]), <span class="number">66</span>);
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}</pre></div>
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