<!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="API documentation for the Rust `format` macro in crate `alloc`."> <meta name="keywords" content="rust, rustlang, rust-lang, format"> <title>alloc::format - 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="../dark.css"> <link rel="stylesheet" type="text/css" href="../main.css" id="themeStyle"> <script src="../storage.js"></script> <link rel="shortcut icon" href="https://doc.rust-lang.org/favicon.ico"> </head> <body class="rustdoc macro"> <!--[if lte IE 8]> <div class="warning"> This old browser is unsupported and will most likely display funky things. </div> <![endif]--> <nav class="sidebar"> <div class="sidebar-menu">☰</div> <a href='../alloc/index.html'><img src='https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png' alt='logo' width='100'></a> <p class='location'><a href='index.html'>alloc</a></p><script>window.sidebarCurrent = {name: 'format', ty: 'macro', relpath: ''};</script><script defer src="sidebar-items.js"></script> </nav> <div class="theme-picker"> <button id="theme-picker" aria-label="Pick another theme!"> <img src="../brush.svg" width="18" alt="Pick another theme!"> </button> <div id="theme-choices"></div> </div> <script src="../theme.js"></script> <nav class="sub"> <form class="search-form js-only"> <div class="search-container"> <input class="search-input" name="search" autocomplete="off" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"> </div> </form> </nav> <section id='main' class="content"> <h1 class='fqn'><span class='in-band'>Macro <a href='index.html'>alloc</a>::<wbr><a class="macro" href=''>format</a></span><span class='out-of-band'><span class='since' title='Stable since Rust version 1.0.0'>1.0.0</span><span id='render-detail'> <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs"> [<span class='inner'>−</span>] </a> </span><a class='srclink' href='../src/alloc/macros.rs.html#105-107' title='goto source code'>[src]</a></span></h1> <pre class="rust macro"> <span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">format</span> { ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">arg</span>:<span class="ident">tt</span>)<span class="kw-2">*</span>) <span class="op">=></span> { ... }; }</pre> <div class='docblock'><p>Creates a <code>String</code> using interpolation of runtime expressions.</p> <p>The first argument <code>format!</code> receives is a format string. This must be a string literal. The power of the formatting string is in the <code>{}</code>s contained.</p> <p>Additional parameters passed to <code>format!</code> replace the <code>{}</code>s within the formatting string in the order given unless named or positional parameters are used, see <a href="../std/fmt/index.html"><code>std::fmt</code></a> for more information.</p> <p>A common use for <code>format!</code> is concatenation and interpolation of strings. The same convention is used with <a href="../std/macro.print.html"><code>print!</code></a> and <a href="../std/macro.write.html"><code>write!</code></a> macros, depending on the intended destination of the string.</p> <h1 id="panics" class="section-header"><a href="#panics">Panics</a></h1> <p><code>format!</code> panics if a formatting trait implementation returns an error. This indicates an incorrect implementation since <code>fmt::Write for String</code> never returns an error itself.</p> <h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1> <pre class="rust rust-example-rendered"> <span class="macro">format</span><span class="macro">!</span>(<span class="string">"test"</span>); <span class="macro">format</span><span class="macro">!</span>(<span class="string">"hello {}"</span>, <span class="string">"world!"</span>); <span class="macro">format</span><span class="macro">!</span>(<span class="string">"x = {}, y = {y}"</span>, <span class="number">10</span>, <span class="ident">y</span> <span class="op">=</span> <span class="number">30</span>);</pre> </div></section> <section id='search' class="content hidden"></section> <section class="footer"></section> <aside id="help" class="hidden"> <div> <h1 class="hidden">Help</h1> <div class="shortcuts"> <h2>Keyboard Shortcuts</h2> <dl> <dt><kbd>?</kbd></dt> <dd>Show this help dialog</dd> <dt><kbd>S</kbd></dt> <dd>Focus the search field</dd> <dt><kbd>↑</kbd></dt> <dd>Move up in search results</dd> <dt><kbd>↓</kbd></dt> <dd>Move down in search results</dd> <dt><kbd>↹</kbd></dt> <dd>Switch tab</dd> <dt><kbd>⏎</kbd></dt> <dd>Go to active search result</dd> <dt><kbd>+</kbd></dt> <dd>Expand all sections</dd> <dt><kbd>-</kbd></dt> <dd>Collapse all sections</dd> </dl> </div> <div class="infos"> <h2>Search Tricks</h2> <p> Prefix searches with a type followed by a colon (e.g. <code>fn:</code>) to restrict the search to a given type. </p> <p> Accepted types are: <code>fn</code>, <code>mod</code>, <code>struct</code>, <code>enum</code>, <code>trait</code>, <code>type</code>, <code>macro</code>, and <code>const</code>. </p> <p> Search functions by type signature (e.g. <code>vec -> usize</code> or <code>* -> vec</code>) </p> </div> </div> </aside> <script> window.rootPath = "../"; window.currentCrate = "alloc"; </script> <script src="../main.js"></script> <script defer src="../search-index.js"></script> </body> </html>