| <!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="Marks a function or static variable as a library/executable constructor. This uses OS-specific linker sections to call a specific function at load time."><meta name="keywords" content="rust, rustlang, rust-lang, ctor"><title>ctor in ctor - 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="sidebar-items.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 attr"><!--[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="../ctor/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="../ctor/index.html"><div class="logo-container"><img class="rust-logo" src="../rust-logo.svg" alt="logo"></div></a><div class="sidebar-elems"><h2><a href="index.html">In ctor</a></h2></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">Attribute Macro <a href="index.html">ctor</a>::<wbr><a class="attr" href="#">ctor</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/ctor/lib.rs.html#140-275">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><div class="item-decl"><pre class="rust attr"><code>#[ctor]</code></pre></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Marks a function or static variable as a library/executable constructor. |
| This uses OS-specific linker sections to call a specific function at |
| load time.</p> |
| <p>Multiple startup functions/statics are supported, but the invocation order is not |
| guaranteed.</p> |
| <h2 id="examples"><a href="#examples">Examples</a></h2> |
| <p>Print a startup message (using <code>libc_print</code> for safety):</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>libc_print::std_name::println; |
| |
| <span class="attribute">#[ctor] |
| </span><span class="kw">fn </span>foo() { |
| <span class="macro">println!</span>(<span class="string">"Hello, world!"</span>); |
| } |
| |
| <span class="macro">println!</span>(<span class="string">"main()"</span>);</code></pre></div> |
| <p>Make changes to <code>static</code> variables:</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">static </span>INITED: AtomicBool = AtomicBool::new(<span class="bool-val">false</span>); |
| |
| <span class="attribute">#[ctor] |
| </span><span class="kw">fn </span>foo() { |
| INITED.store(<span class="bool-val">true</span>, Ordering::SeqCst); |
| }</code></pre></div> |
| <p>Initialize a <code>HashMap</code> at startup time:</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attribute">#[ctor] |
| </span><span class="kw">static </span>STATIC_CTOR: HashMap<u32, String> = { |
| <span class="kw">let </span><span class="kw-2">mut </span>m = HashMap::new(); |
| <span class="kw">for </span>i <span class="kw">in </span><span class="number">0</span>..<span class="number">100 </span>{ |
| m.insert(i, <span class="macro">format!</span>(<span class="string">"x*100={}"</span>, i<span class="kw-2">*</span><span class="number">100</span>)); |
| } |
| m |
| }; |
| </code></pre></div> |
| <h2 id="details"><a href="#details">Details</a></h2> |
| <p>The <code>#[ctor]</code> macro makes use of linker sections to ensure that a |
| function is run at startup time.</p> |
| <p>The above example translates into the following Rust code (approximately):</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code> <span class="attribute">#[used] |
| #[cfg_attr(any(target_os = <span class="string">"linux"</span>, target_os = <span class="string">"android"</span>), link_section = <span class="string">".init_array"</span>)] |
| #[cfg_attr(target_os = <span class="string">"freebsd"</span>, link_section = <span class="string">".init_array"</span>)] |
| #[cfg_attr(target_os = <span class="string">"netbsd"</span>, link_section = <span class="string">".init_array"</span>)] |
| #[cfg_attr(target_os = <span class="string">"openbsd"</span>, link_section = <span class="string">".init_array"</span>)] |
| #[cfg_attr(target_os = <span class="string">"illumos"</span>, link_section = <span class="string">".init_array"</span>)] |
| #[cfg_attr(any(target_os = <span class="string">"macos"</span>, target_os = <span class="string">"ios"</span>), link_section = <span class="string">"__DATA,__mod_init_func"</span>)] |
| #[cfg_attr(target_os = <span class="string">"windows"</span>, link_section = <span class="string">".CRT$XCU"</span>)] |
| </span><span class="kw">static </span>FOO: <span class="kw">extern fn</span>() = { |
| <span class="attribute">#[cfg_attr(any(target_os = <span class="string">"linux"</span>, target_os = <span class="string">"android"</span>), link_section = <span class="string">".text.startup"</span>)] |
| </span><span class="kw">extern fn </span>foo() { <span class="comment">/* ... */ </span>}; |
| foo |
| };</code></pre></div> |
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