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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."><meta name="keywords" content="rust, rustlang, rust-lang, cfg_if"><title>cfg_if - 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="../light.css" id="themeStyle"><link rel="stylesheet" type="text/css" href="../dark.css" disabled ><link rel="stylesheet" type="text/css" href="../ayu.css" disabled ><script id="default-settings"></script><script src="../storage.js"></script><script src="../crates.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="icon" type="image/svg+xml" href="../favicon.svg">
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<p>The macro provided by this crate, <code>cfg_if</code>, is similar to the <code>if/elif</code> C
preprocessor macro by allowing definition of a cascade of <code>#[cfg]</code> cases,
emitting the implementation which matches first.</p>
<p>This allows you to conveniently provide a long list <code>#[cfg]</code>’d blocks of code
without having to rewrite each clause multiple times.</p>
<h1 id="example" class="section-header"><a href="#example">Example</a></h1>
<div class="example-wrap"><pre class="rust rust-example-rendered">
<span class="macro">cfg_if::cfg_if!</span> {
<span class="kw">if</span> <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">unix</span>)]</span> {
<span class="kw">fn</span> <span class="ident">foo</span>() { <span class="comment">/* unix specific functionality */</span> }
} <span class="kw">else</span> <span class="kw">if</span> <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">target_pointer_width</span> <span class="op">=</span> <span class="string">&quot;32&quot;</span>)]</span> {
<span class="kw">fn</span> <span class="ident">foo</span>() { <span class="comment">/* non-unix, 32-bit functionality */</span> }
} <span class="kw">else</span> {
<span class="kw">fn</span> <span class="ident">foo</span>() { <span class="comment">/* fallback implementation */</span> }
}
}
</pre></div>
</div></details><h2 id="macros" class="section-header"><a href="#macros">Macros</a></h2>
<table><tr class="module-item"><td><a class="macro" href="macro.cfg_if.html" title="cfg_if::cfg_if macro">cfg_if</a></td><td class="docblock-short"><p>The main macro provided by this crate. See crate documentation for more
information.</p>
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