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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 `memoffset` crate."><meta name="keywords" content="rust, rustlang, rust-lang, memoffset"><title>memoffset - 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 mod"><!--[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><p class='location'>Crate memoffset</p><div class="sidebar-elems"><a id='all-types' href='all.html'><p>See all memoffset's items</p></a><div class="block items"><ul><li><a href="#macros">Macros</a></li></ul></div><p class='location'></p><script>window.sidebarCurrent = {name: 'memoffset', ty: 'mod', relpath: '../'};</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/lib.rs.html#21-70' title='goto source code'>[src]</a></span><span class='in-band'>Crate <a class="mod" href=''>memoffset</a></span></h1><div class='docblock'><p>A crate used for calculating offsets of struct members and their spans.</p>
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<p>Some of the funcationality of the crate makes no sense when used along with structs that
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are not <code>#[repr(C, packed)]</code>, but it is up to the user to make sure that they are.</p>
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<h2 id="examples" class="section-header"><a href="#examples">Examples</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">HelpMeIAmTrappedInAStructFactory</span> {
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<span class="ident">help_me_before_they_</span>: [<span class="ident">u8</span>; <span class="number">15</span>],
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<span class="ident">a</span>: <span class="ident">u32</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">HelpMeIAmTrappedInAStructFactory</span>, <span class="ident">a</span>), <span class="number">15</span>);
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="macro">span_of</span><span class="macro">!</span>(<span class="ident">HelpMeIAmTrappedInAStructFactory</span>, <span class="ident">a</span>), <span class="number">15</span>..<span class="number">19</span>);
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="macro">span_of</span><span class="macro">!</span>(<span class="ident">HelpMeIAmTrappedInAStructFactory</span>, <span class="ident">help_me_before_they_</span>[<span class="number">2</span>] .. <span class="ident">a</span>), <span class="number">2</span>..<span class="number">15</span>);
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}</pre></div>
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<p>This functionality can be useful, for example, for checksum calculations:</p>
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<div class='information'><div class='tooltip ignore'>ⓘ<span class='tooltiptext'>This example is not tested</span></div></div><div class="example-wrap"><pre class="rust rust-example-rendered ignore">
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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">Message</span> {
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<span class="ident">header</span>: <span class="ident">MessageHeader</span>,
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<span class="ident">fragment_index</span>: <span class="ident">u32</span>,
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<span class="ident">fragment_count</span>: <span class="ident">u32</span>,
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<span class="ident">payload</span>: [<span class="ident">u8</span>; <span class="number">1024</span>],
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<span class="ident">checksum</span>: <span class="ident">u16</span>
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}
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<span class="kw">let</span> <span class="ident">checksum_range</span> <span class="op">=</span> <span class="kw-2">&</span><span class="ident">raw</span>[<span class="macro">span_of</span><span class="macro">!</span>(<span class="ident">Message</span>, <span class="ident">header</span>..<span class="ident">checksum</span>)];
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<span class="kw">let</span> <span class="ident">checksum</span> <span class="op">=</span> <span class="ident">crc16</span>(<span class="ident">checksum_range</span>);</pre></div>
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</div><h2 id='macros' class='section-header'><a href="#macros">Macros</a></h2>
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<table><tr class='module-item'><td><a class="macro" href="macro.offset_of.html" title='memoffset::offset_of macro'>offset_of</a></td><td class='docblock-short'><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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</td></tr><tr class='module-item'><td><a class="macro" href="macro.span_of.html" title='memoffset::span_of macro'>span_of</a></td><td class='docblock-short'><p>Produces a range instance representing the sub-slice containing the specified member.</p>
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