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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="Search for the first occurrence of a byte in a slice."><title>memchr in memchr - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-46f98efaafac5295.ttf.woff2,FiraSans-Regular-018c141bf0843ffd.woff2,FiraSans-Medium-8f9a781e4970d388.woff2,SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2,SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../static.files/rustdoc-dd39b87e5fcfba68.css"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="memchr" data-themes="" data-resource-suffix="" data-rustdoc-version="1.80.0 (051478957 2024-07-21)" data-channel="1.80.0" data-search-js="search-d52510db62a78183.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../static.files/storage-118b08c4c78b968e.js"></script><script defer src="sidebar-items.js"></script><script defer src="../static.files/main-20a3ad099b048cf2.js"></script><noscript><link rel="stylesheet" href="../static.files/noscript-df360f571f6edeae.css"></noscript><link rel="alternate icon" type="image/png" href="../static.files/favicon-32x32-422f7d1d52889060.png"><link rel="icon" type="image/svg+xml" href="../static.files/favicon-2c020d218678b618.svg"></head><body class="rustdoc fn"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle" title="show sidebar"></button></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../memchr/index.html">memchr</a><span class="version">2.7.4</span></h2></div><div class="sidebar-elems"></div></nav><div class="sidebar-resizer"></div><main><div class="width-limiter"><rustdoc-search></rustdoc-search><section id="main-content" class="content"><div class="main-heading"><h1>Function <a href="index.html">memchr</a>::<wbr><a class="fn" href="#">memchr</a><button id="copy-path" title="Copy item path to clipboard">Copy item path</button></h1><span class="out-of-band"><a class="src" href="../src/memchr/memchr.rs.html#27-35">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>&#x2212;</span>]</button></span></div><pre class="rust item-decl"><code>pub fn memchr(needle: <a class="primitive" href="https://doc.rust-lang.org/1.80.0/std/primitive.u8.html">u8</a>, haystack: &amp;[<a class="primitive" href="https://doc.rust-lang.org/1.80.0/std/primitive.u8.html">u8</a>]) -&gt; <a class="enum" href="https://doc.rust-lang.org/1.80.0/core/option/enum.Option.html" title="enum core::option::Option">Option</a>&lt;<a class="primitive" href="https://doc.rust-lang.org/1.80.0/std/primitive.usize.html">usize</a>&gt;</code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Search for the first occurrence of a byte in a slice.</p>
<p>This returns the index corresponding to the first occurrence of <code>needle</code> in
<code>haystack</code>, or <code>None</code> if one is not found. If an index is returned, it is
guaranteed to be less than <code>haystack.len()</code>.</p>
<p>While this is semantically the same as something like
<code>haystack.iter().position(|&amp;b| b == needle)</code>, this routine will attempt to
use highly optimized vector operations that can be an order of magnitude
faster (or more).</p>
<h2 id="example"><a class="doc-anchor" href="#example">§</a>Example</h2>
<p>This shows how to find the first position of a byte in a byte string.</p>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>memchr::memchr;
<span class="kw">let </span>haystack = <span class="string">b"the quick brown fox"</span>;
<span class="macro">assert_eq!</span>(memchr(<span class="string">b'k'</span>, haystack), <span class="prelude-val">Some</span>(<span class="number">8</span>));</code></pre></div>
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