<!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 `Write` trait in crate `core`."><meta name="keywords" content="rust, rustlang, rust-lang, Write"><title>core::fmt::Write - 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="../../light.css" id="themeStyle"><script src="../../storage.js"></script><link rel="shortcut icon" href="https://doc.rust-lang.org/favicon.ico"></head><body class="rustdoc trait"><!--[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='../../core/index.html'><img src='https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png' alt='logo' width='100'></a><p class='location'>Trait Write</p><div class="sidebar-elems"><div class="block items"><a class="sidebar-title" href="#required-methods">Required Methods</a><div class="sidebar-links"><a href="#tymethod.write_str">write_str</a></div><a class="sidebar-title" href="#provided-methods">Provided Methods</a><div class="sidebar-links"><a href="#method.write_char">write_char</a><a href="#method.write_fmt">write_fmt</a></div><a class="sidebar-title" href="#implementors">Implementors</a></div><p class='location'><a href='../index.html'>core</a>::<wbr><a href='index.html'>fmt</a></p><script>window.sidebarCurrent = {name: 'Write', ty: 'trait', relpath: ''};</script><script defer src="sidebar-items.js"></script></div></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"><a id="settings-menu" href="../../settings.html"><img src="../../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><span class='in-band'>Trait <a href='../index.html'>core</a>::<wbr><a href='index.html'>fmt</a>::<wbr><a class="trait" href=''>Write</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/core/fmt/mod.rs.html#121-229' title='goto source code'>[src]</a></span></h1><div class="docblock type-decl"><pre class='rust trait'>pub trait Write {
fn <a href='#tymethod.write_str' class='fnname'>write_str</a>(&mut self, s: &str) -> <a class="type" href="../../core/fmt/type.Result.html" title="type core::fmt::Result">Result</a>;
fn <a href='#method.write_char' class='fnname'>write_char</a>(&mut self, c: char) -> <a class="type" href="../../core/fmt/type.Result.html" title="type core::fmt::Result">Result</a> { ... }
<div class='item-spacer'></div> fn <a href='#method.write_fmt' class='fnname'>write_fmt</a>(&mut self, args: <a class="struct" href="../../core/fmt/struct.Arguments.html" title="struct core::fmt::Arguments">Arguments</a>) -> <a class="type" href="../../core/fmt/type.Result.html" title="type core::fmt::Result">Result</a> { ... }
}</pre></div><div class='docblock'><p>A collection of methods that are required to format a message into a stream.</p>
<p>This trait is the type which this modules requires when formatting
information. This is similar to the standard library's <a href="../../std/io/trait.Write.html"><code>io::Write</code></a> trait,
but it is only intended for use in libcore.</p>
<p>This trait should generally not be implemented by consumers of the standard
library. The <a href="../../std/macro.write.html"><code>write!</code></a> macro accepts an instance of <a href="../../std/io/trait.Write.html"><code>io::Write</code></a>, and the
<a href="../../std/io/trait.Write.html"><code>io::Write</code></a> trait is favored over implementing this trait.</p>
</div>
<h2 id='required-methods' class='small-section-header'>
Required Methods<a href='#required-methods' class='anchor'></a>
</h2>
<div class='methods'>
<h3 id='tymethod.write_str' class='method'><span id='write_str.v' class='invisible'><code>fn <a href='#tymethod.write_str' class='fnname'>write_str</a>(&mut self, s: &str) -> <a class="type" href="../../core/fmt/type.Result.html" title="type core::fmt::Result">Result</a></code></span></h3><div class='docblock'><p>Writes a slice of bytes into this writer, returning whether the write
succeeded.</p>
<p>This method can only succeed if the entire byte slice was successfully
written, and this method will not return until all data has been
written or an error occurs.</p>
<h1 id="errors" class="section-header"><a href="#errors">Errors</a></h1>
<p>This function will return an instance of <a href="struct.Error.html"><code>Error</code></a> on error.</p>
<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">fmt</span>::{<span class="ident">Error</span>, <span class="ident">Write</span>};
<span class="kw">fn</span> <span class="ident">writer</span><span class="op"><</span><span class="ident">W</span>: <span class="ident">Write</span><span class="op">></span>(<span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">W</span>, <span class="ident">s</span>: <span class="kw-2">&</span><span class="ident">str</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">Error</span><span class="op">></span> {
<span class="ident">f</span>.<span class="ident">write_str</span>(<span class="ident">s</span>)
}
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">buf</span> <span class="op">=</span> <span class="ident">String</span>::<span class="ident">new</span>();
<span class="ident">writer</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">buf</span>, <span class="string">"hola"</span>).<span class="ident">unwrap</span>();
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="kw-2">&</span><span class="ident">buf</span>, <span class="string">"hola"</span>);<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0Ause%20std%3A%3Afmt%3A%3A%7BError%2C%20Write%7D%3B%0A%0Afn%20writer%3CW%3A%20Write%3E(f%3A%20%26mut%20W%2C%20s%3A%20%26str)%20-%3E%20Result%3C()%2C%20Error%3E%20%7B%0A%20%20%20%20f.write_str(s)%0A%7D%0A%0Alet%20mut%20buf%20%3D%20String%3A%3Anew()%3B%0Awriter(%26mut%20buf%2C%20%22hola%22).unwrap()%3B%0Aassert_eq!(%26buf%2C%20%22hola%22)%3B%0A%7D">Run</a></pre>
</div></div>
<h2 id='provided-methods' class='small-section-header'>
Provided Methods<a href='#provided-methods' class='anchor'></a>
</h2>
<div class='methods'>
<h3 id='method.write_char' class='method'><span id='write_char.v' class='invisible'><code>fn <a href='#method.write_char' class='fnname'>write_char</a>(&mut self, c: char) -> <a class="type" href="../../core/fmt/type.Result.html" title="type core::fmt::Result">Result</a></code><div class='since' title='Stable since Rust version 1.1.0'>1.1.0</div></span></h3><div class='docblock'><p>Writes a <a href="../../std/primitive.char.html"><code>char</code></a> into this writer, returning whether the write succeeded.</p>
<p>A single <a href="../../std/primitive.char.html"><code>char</code></a> may be encoded as more than one byte.
This method can only succeed if the entire byte sequence was successfully
written, and this method will not return until all data has been
written or an error occurs.</p>
<h1 id="errors-1" class="section-header"><a href="#errors-1">Errors</a></h1>
<p>This function will return an instance of <a href="struct.Error.html"><code>Error</code></a> on error.</p>
<h1 id="examples-1" class="section-header"><a href="#examples-1">Examples</a></h1>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">fmt</span>::{<span class="ident">Error</span>, <span class="ident">Write</span>};
<span class="kw">fn</span> <span class="ident">writer</span><span class="op"><</span><span class="ident">W</span>: <span class="ident">Write</span><span class="op">></span>(<span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">W</span>, <span class="ident">c</span>: <span class="ident">char</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">Error</span><span class="op">></span> {
<span class="ident">f</span>.<span class="ident">write_char</span>(<span class="ident">c</span>)
}
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">buf</span> <span class="op">=</span> <span class="ident">String</span>::<span class="ident">new</span>();
<span class="ident">writer</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">buf</span>, <span class="string">'a'</span>).<span class="ident">unwrap</span>();
<span class="ident">writer</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">buf</span>, <span class="string">'b'</span>).<span class="ident">unwrap</span>();
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="kw-2">&</span><span class="ident">buf</span>, <span class="string">"ab"</span>);<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0Ause%20std%3A%3Afmt%3A%3A%7BError%2C%20Write%7D%3B%0A%0Afn%20writer%3CW%3A%20Write%3E(f%3A%20%26mut%20W%2C%20c%3A%20char)%20-%3E%20Result%3C()%2C%20Error%3E%20%7B%0A%20%20%20%20f.write_char(c)%0A%7D%0A%0Alet%20mut%20buf%20%3D%20String%3A%3Anew()%3B%0Awriter(%26mut%20buf%2C%20'a').unwrap()%3B%0Awriter(%26mut%20buf%2C%20'b').unwrap()%3B%0Aassert_eq!(%26buf%2C%20%22ab%22)%3B%0A%7D">Run</a></pre>
</div><h3 id='method.write_fmt' class='method'><span id='write_fmt.v' class='invisible'><code>fn <a href='#method.write_fmt' class='fnname'>write_fmt</a>(&mut self, args: <a class="struct" href="../../core/fmt/struct.Arguments.html" title="struct core::fmt::Arguments">Arguments</a>) -> <a class="type" href="../../core/fmt/type.Result.html" title="type core::fmt::Result">Result</a></code></span></h3><div class='docblock'><p>Glue for usage of the <a href="../../std/macro.write.html"><code>write!</code></a> macro with implementors of this trait.</p>
<p>This method should generally not be invoked manually, but rather through
the <a href="../../std/macro.write.html"><code>write!</code></a> macro itself.</p>
<h1 id="examples-2" class="section-header"><a href="#examples-2">Examples</a></h1>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">fmt</span>::{<span class="ident">Error</span>, <span class="ident">Write</span>};
<span class="kw">fn</span> <span class="ident">writer</span><span class="op"><</span><span class="ident">W</span>: <span class="ident">Write</span><span class="op">></span>(<span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">W</span>, <span class="ident">s</span>: <span class="kw-2">&</span><span class="ident">str</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">Error</span><span class="op">></span> {
<span class="ident">f</span>.<span class="ident">write_fmt</span>(<span class="macro">format_args</span><span class="macro">!</span>(<span class="string">"{}"</span>, <span class="ident">s</span>))
}
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">buf</span> <span class="op">=</span> <span class="ident">String</span>::<span class="ident">new</span>();
<span class="ident">writer</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">buf</span>, <span class="string">"world"</span>).<span class="ident">unwrap</span>();
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="kw-2">&</span><span class="ident">buf</span>, <span class="string">"world"</span>);<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0Ause%20std%3A%3Afmt%3A%3A%7BError%2C%20Write%7D%3B%0A%0Afn%20writer%3CW%3A%20Write%3E(f%3A%20%26mut%20W%2C%20s%3A%20%26str)%20-%3E%20Result%3C()%2C%20Error%3E%20%7B%0A%20%20%20%20f.write_fmt(format_args!(%22%7B%7D%22%2C%20s))%0A%7D%0A%0Alet%20mut%20buf%20%3D%20String%3A%3Anew()%3B%0Awriter(%26mut%20buf%2C%20%22world%22).unwrap()%3B%0Aassert_eq!(%26buf%2C%20%22world%22)%3B%0A%7D">Run</a></pre>
</div></div>
<h2 id='implementors' class='small-section-header'>
Implementors<a href='#implementors' class='anchor'></a>
</h2>
<ul class='item-list' id='implementors-list'>
<li><table class='table-display'><tbody><tr><td><code>impl<'a, W: <a class="trait" href="../../core/fmt/trait.Write.html" title="trait core::fmt::Write">Write</a> + ?<a class="trait" href="../../core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>> Write for &'a mut W</code><td><div class='out-of-band'><a class='srclink' href='../../src/core/fmt/mod.rs.html#232-244' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
<li><table class='table-display'><tbody><tr><td><code>impl<'a> Write for <a class="struct" href="../../core/fmt/struct.Formatter.html" title="struct core::fmt::Formatter">Formatter</a><'a></code><td><div class='out-of-band'><a class='srclink' href='../../src/core/fmt/mod.rs.html#1821-1833' title='goto source code'>[src]</a></div></td></tr></tbody></table></li>
</ul><script type="text/javascript">window.inlined_types=new Set([]);</script><script type="text/javascript" async
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