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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="A macro for defining `#[cfg]` if-else statements."><title>cfg_if - 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-b0742ba02757f159.css"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="cfg_if" data-themes="" data-resource-suffix="" data-rustdoc-version="1.83.0 (90b35a623 2024-11-26)" data-channel="1.83.0" data-search-js="search-f0d225181b97f9a4.js" data-settings-js="settings-805db61a62df4bd2.js" ><script src="../static.files/storage-1d39b6787ed640ff.js"></script><script defer src="../crates.js"></script><script defer src="../static.files/main-f070b9041d14864c.js"></script><noscript><link rel="stylesheet" href="../static.files/noscript-0111fcff984fae8f.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 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" title="show sidebar"></button></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../cfg_if/index.html">cfg_if</a><span class="version">1.0.0</span></h2></div><div class="sidebar-elems"><ul class="block"><li><a id="all-types" href="all.html">All Items</a></li></ul><section id="rustdoc-toc"><h3><a href="#">Sections</a></h3><ul class="block top-toc"><li><a href="#example" title="Example">Example</a></li></ul><h3><a href="#macros">Crate Items</a></h3><ul class="block"><li><a href="#macros" title="Macros">Macros</a></li></ul></section><div id="rustdoc-modnav"></div></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>Crate <span>cfg_if</span><button id="copy-path" title="Copy item path to clipboard">Copy item path</button></h1><rustdoc-toolbar></rustdoc-toolbar><span class="sub-heading"><a class="src" href="../src/cfg_if/lib.rs.html#1-176">source</a> </span></div><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>A macro for defining <code>#[cfg]</code> if-else statements.</p>
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<p>The macro provided by this crate, <code>cfg_if</code>, is similar to the <code>if/elif</code> C
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preprocessor macro by allowing definition of a cascade of <code>#[cfg]</code> cases,
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emitting the implementation which matches first.</p>
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<p>This allows you to conveniently provide a long list <code>#[cfg]</code>’d blocks of code
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without having to rewrite each clause multiple times.</p>
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<h2 id="example"><a class="doc-anchor" href="#example">§</a>Example</h2>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="macro">cfg_if::cfg_if!</span> {
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<span class="kw">if </span><span class="attr">#[cfg(unix)] </span>{
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<span class="kw">fn </span>foo() { <span class="comment">/* unix specific functionality */ </span>}
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} <span class="kw">else if </span><span class="attr">#[cfg(target_pointer_width = <span class="string">"32"</span>)] </span>{
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<span class="kw">fn </span>foo() { <span class="comment">/* non-unix, 32-bit functionality */ </span>}
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} <span class="kw">else </span>{
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<span class="kw">fn </span>foo() { <span class="comment">/* fallback implementation */ </span>}
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}
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}
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</code></pre></div>
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</div></details><h2 id="macros" class="section-header">Macros<a href="#macros" class="anchor">§</a></h2><ul class="item-table"><li><div class="item-name"><a class="macro" href="macro.cfg_if.html" title="macro cfg_if::cfg_if">cfg_if</a></div><div class="desc docblock-short">The main macro provided by this crate. See crate documentation for more
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information.</div></li></ul></section></div></main></body></html>
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