| <!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="This library provides heavily optimized routines for string search primitives."><meta name="keywords" content="rust, rustlang, rust-lang, memchr"><title>memchr - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../normalize.css"><link rel="stylesheet" href="../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../ayu.css" disabled><link rel="stylesheet" href="../dark.css" disabled><link rel="stylesheet" href="../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../storage.js"></script><script defer src="../crates.js"></script><script defer src="../main.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../favicon.svg"></head><body class="rustdoc mod crate"><!--[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">☰</button><a class="sidebar-logo" href="../memchr/index.html"><div class="logo-container"><img class="rust-logo" src="../rust-logo.svg" alt="logo"></div></a><h2></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../memchr/index.html"><div class="logo-container"><img class="rust-logo" src="../rust-logo.svg" alt="logo"></div></a><h2 class="location"><a href="#">Crate memchr</a></h2><div class="sidebar-elems"><ul class="block"><li class="version">Version 2.5.0</li><li><a id="all-types" href="all.html">All Items</a></li></ul><section><ul class="block"><li><a href="#modules">Modules</a></li><li><a href="#structs">Structs</a></li><li><a href="#functions">Functions</a></li></ul></section></div></nav><main><div class="width-limiter"><nav class="sub"><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1 class="fqn">Crate <a class="mod" href="#">memchr</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../clipboard.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="srclink" href="../src/memchr/lib.rs.html#1-181">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>This library provides heavily optimized routines for string search primitives.</p> |
| <h2 id="overview"><a href="#overview">Overview</a></h2> |
| <p>This section gives a brief high level overview of what this crate offers.</p> |
| <ul> |
| <li>The top-level module provides routines for searching for 1, 2 or 3 bytes |
| in the forward or reverse direction. When searching for more than one byte, |
| positions are considered a match if the byte at that position matches any |
| of the bytes.</li> |
| <li>The <a href="memmem/index.html" title="memmem"><code>memmem</code></a> sub-module provides forward and reverse substring search |
| routines.</li> |
| </ul> |
| <p>In all such cases, routines operate on <code>&[u8]</code> without regard to encoding. This |
| is exactly what you want when searching either UTF-8 or arbitrary bytes.</p> |
| <h2 id="example-using-memchr"><a href="#example-using-memchr">Example: using <code>memchr</code></a></h2> |
| <p>This example shows how to use <code>memchr</code> to find the first occurrence of <code>z</code> in |
| a haystack:</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"foo bar baz quuz"</span>; |
| <span class="macro">assert_eq!</span>(<span class="prelude-val">Some</span>(<span class="number">10</span>), memchr(<span class="string">b'z'</span>, haystack));</code></pre></div> |
| <h2 id="example-matching-one-of-three-possible-bytes"><a href="#example-matching-one-of-three-possible-bytes">Example: matching one of three possible bytes</a></h2> |
| <p>This examples shows how to use <code>memrchr3</code> to find occurrences of <code>a</code>, <code>b</code> or |
| <code>c</code>, starting at the end of the haystack.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>memchr::memchr3_iter; |
| |
| <span class="kw">let </span>haystack = <span class="string">b"xyzaxyzbxyzc"</span>; |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>it = memchr3_iter(<span class="string">b'a'</span>, <span class="string">b'b'</span>, <span class="string">b'c'</span>, haystack).rev(); |
| <span class="macro">assert_eq!</span>(<span class="prelude-val">Some</span>(<span class="number">11</span>), it.next()); |
| <span class="macro">assert_eq!</span>(<span class="prelude-val">Some</span>(<span class="number">7</span>), it.next()); |
| <span class="macro">assert_eq!</span>(<span class="prelude-val">Some</span>(<span class="number">3</span>), it.next()); |
| <span class="macro">assert_eq!</span>(<span class="prelude-val">None</span>, it.next());</code></pre></div> |
| <h2 id="example-iterating-over-substring-matches"><a href="#example-iterating-over-substring-matches">Example: iterating over substring matches</a></h2> |
| <p>This example shows how to use the <a href="memmem/index.html" title="memmem"><code>memmem</code></a> sub-module to find occurrences of |
| a substring in a haystack.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>memchr::memmem; |
| |
| <span class="kw">let </span>haystack = <span class="string">b"foo bar foo baz foo"</span>; |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>it = memmem::find_iter(haystack, <span class="string">"foo"</span>); |
| <span class="macro">assert_eq!</span>(<span class="prelude-val">Some</span>(<span class="number">0</span>), it.next()); |
| <span class="macro">assert_eq!</span>(<span class="prelude-val">Some</span>(<span class="number">8</span>), it.next()); |
| <span class="macro">assert_eq!</span>(<span class="prelude-val">Some</span>(<span class="number">16</span>), it.next()); |
| <span class="macro">assert_eq!</span>(<span class="prelude-val">None</span>, it.next());</code></pre></div> |
| <h2 id="example-repeating-a-search-for-the-same-needle"><a href="#example-repeating-a-search-for-the-same-needle">Example: repeating a search for the same needle</a></h2> |
| <p>It may be possible for the overhead of constructing a substring searcher to be |
| measurable in some workloads. In cases where the same needle is used to search |
| many haystacks, it is possible to do construction once and thus to avoid it for |
| subsequent searches. This can be done with a <a href="memmem/struct.Finder.html" title="memmem::Finder"><code>memmem::Finder</code></a>:</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>memchr::memmem; |
| |
| <span class="kw">let </span>finder = memmem::Finder::new(<span class="string">"foo"</span>); |
| |
| <span class="macro">assert_eq!</span>(<span class="prelude-val">Some</span>(<span class="number">4</span>), finder.find(<span class="string">b"baz foo quux"</span>)); |
| <span class="macro">assert_eq!</span>(<span class="prelude-val">None</span>, finder.find(<span class="string">b"quux baz bar"</span>));</code></pre></div> |
| <h2 id="why-use-this-crate"><a href="#why-use-this-crate">Why use this crate?</a></h2> |
| <p>At first glance, the APIs provided by this crate might seem weird. Why provide |
| a dedicated routine like <code>memchr</code> for something that could be implemented |
| clearly and trivially in one line:</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">fn </span>memchr(needle: u8, haystack: <span class="kw-2">&</span>[u8]) -> <span class="prelude-ty">Option</span><usize> { |
| haystack.iter().position(|<span class="kw-2">&</span>b| b == needle) |
| }</code></pre></div> |
| <p>Or similarly, why does this crate provide substring search routines when Rust’s |
| core library already provides them?</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">fn </span>search(haystack: <span class="kw-2">&</span>str, needle: <span class="kw-2">&</span>str) -> <span class="prelude-ty">Option</span><usize> { |
| haystack.find(needle) |
| }</code></pre></div> |
| <p>The primary reason for both of them to exist is performance. When it comes to |
| performance, at a high level at least, there are two primary ways to look at |
| it:</p> |
| <ul> |
| <li><strong>Throughput</strong>: For this, think about it as, “given some very large haystack |
| and a byte that never occurs in that haystack, how long does it take to |
| search through it and determine that it, in fact, does not occur?”</li> |
| <li><strong>Latency</strong>: For this, think about it as, “given a tiny haystack—just a |
| few bytes—how long does it take to determine if a byte is in it?”</li> |
| </ul> |
| <p>The <code>memchr</code> routine in this crate has <em>slightly</em> worse latency than the |
| solution presented above, however, its throughput can easily be over an |
| order of magnitude faster. This is a good general purpose trade off to make. |
| You rarely lose, but often gain big.</p> |
| <p><strong>NOTE:</strong> The name <code>memchr</code> comes from the corresponding routine in libc. A key |
| advantage of using this library is that its performance is not tied to its |
| quality of implementation in the libc you happen to be using, which can vary |
| greatly from platform to platform.</p> |
| <p>But what about substring search? This one is a bit more complicated. The |
| primary reason for its existence is still indeed performance, but it’s also |
| useful because Rust’s core library doesn’t actually expose any substring |
| search routine on arbitrary bytes. The only substring search routine that |
| exists works exclusively on valid UTF-8.</p> |
| <p>So if you have valid UTF-8, is there a reason to use this over the standard |
| library substring search routine? Yes. This routine is faster on almost every |
| metric, including latency. The natural question then, is why isn’t this |
| implementation in the standard library, even if only for searching on UTF-8? |
| The reason is that the implementation details for using SIMD in the standard |
| library haven’t quite been worked out yet.</p> |
| <p><strong>NOTE:</strong> Currently, only <code>x86_64</code> targets have highly accelerated |
| implementations of substring search. For <code>memchr</code>, all targets have |
| somewhat-accelerated implementations, while only <code>x86_64</code> targets have highly |
| accelerated implementations. This limitation is expected to be lifted once the |
| standard library exposes a platform independent SIMD API.</p> |
| <h2 id="crate-features"><a href="#crate-features">Crate features</a></h2> |
| <ul> |
| <li><strong>std</strong> - When enabled (the default), this will permit this crate to use |
| features specific to the standard library. Currently, the only thing used |
| from the standard library is runtime SIMD CPU feature detection. This means |
| that this feature must be enabled to get AVX accelerated routines. When |
| <code>std</code> is not enabled, this crate will still attempt to use SSE2 accelerated |
| routines on <code>x86_64</code>.</li> |
| <li><strong>libc</strong> - When enabled (<strong>not</strong> the default), this library will use your |
| platform’s libc implementation of <code>memchr</code> (and <code>memrchr</code> on Linux). This |
| can be useful on non-<code>x86_64</code> targets where the fallback implementation in |
| this crate is not as good as the one found in your libc. All other routines |
| (e.g., <code>memchr[23]</code> and substring search) unconditionally use the |
| implementation in this crate.</li> |
| </ul> |
| </div></details><h2 id="modules" class="small-section-header"><a href="#modules">Modules</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="mod" href="memmem/index.html" title="memchr::memmem mod">memmem</a></div><div class="item-right docblock-short">This module provides forward and reverse substring search routines.</div></div></div><h2 id="structs" class="small-section-header"><a href="#structs">Structs</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Memchr.html" title="memchr::Memchr struct">Memchr</a></div><div class="item-right docblock-short">An iterator for <code>memchr</code>.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Memchr2.html" title="memchr::Memchr2 struct">Memchr2</a></div><div class="item-right docblock-short">An iterator for <code>memchr2</code>.</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Memchr3.html" title="memchr::Memchr3 struct">Memchr3</a></div><div class="item-right docblock-short">An iterator for <code>memchr3</code>.</div></div></div><h2 id="functions" class="small-section-header"><a href="#functions">Functions</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.memchr.html" title="memchr::memchr fn">memchr</a></div><div class="item-right docblock-short">Search for the first occurrence of a byte in a slice.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.memchr2.html" title="memchr::memchr2 fn">memchr2</a></div><div class="item-right docblock-short">Like <code>memchr</code>, but searches for either of two bytes instead of just one.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.memchr2_iter.html" title="memchr::memchr2_iter fn">memchr2_iter</a></div><div class="item-right docblock-short">An iterator over all occurrences of the needles in a haystack.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.memchr3.html" title="memchr::memchr3 fn">memchr3</a></div><div class="item-right docblock-short">Like <code>memchr</code>, but searches for any of three bytes instead of just one.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.memchr3_iter.html" title="memchr::memchr3_iter fn">memchr3_iter</a></div><div class="item-right docblock-short">An iterator over all occurrences of the needles in a haystack.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.memchr_iter.html" title="memchr::memchr_iter fn">memchr_iter</a></div><div class="item-right docblock-short">An iterator over all occurrences of the needle in a haystack.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.memrchr.html" title="memchr::memrchr fn">memrchr</a></div><div class="item-right docblock-short">Search for the last occurrence of a byte in a slice.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.memrchr2.html" title="memchr::memrchr2 fn">memrchr2</a></div><div class="item-right docblock-short">Like <code>memrchr</code>, but searches for either of two bytes instead of just one.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.memrchr2_iter.html" title="memchr::memrchr2_iter fn">memrchr2_iter</a></div><div class="item-right docblock-short">An iterator over all occurrences of the needles in a haystack, in reverse.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.memrchr3.html" title="memchr::memrchr3 fn">memrchr3</a></div><div class="item-right docblock-short">Like <code>memrchr</code>, but searches for any of three bytes instead of just one.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.memrchr3_iter.html" title="memchr::memrchr3_iter fn">memrchr3_iter</a></div><div class="item-right docblock-short">An iterator over all occurrences of the needles in a haystack, in reverse.</div></div><div class="item-row"><div class="item-left module-item"><a class="fn" href="fn.memrchr_iter.html" title="memchr::memrchr_iter fn">memrchr_iter</a></div><div class="item-right docblock-short">An iterator over all occurrences of the needle in a haystack, in reverse.</div></div></div></section></div></main><div id="rustdoc-vars" data-root-path="../" data-current-crate="memchr" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
