<!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 `BufWriter` struct in crate `std`."><meta name="keywords" content="rust, rustlang, rust-lang, BufWriter"><title>std::io::BufWriter - 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 struct"><!--[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='../../std/index.html'><img src='https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png' alt='logo' width='100'></a><p class='location'>Struct BufWriter</p><div class="sidebar-elems"><div class="block items"><a class="sidebar-title" href="#methods">Methods</a><div class="sidebar-links"><a href="#method.new">new</a><a href="#method.with_capacity">with_capacity</a><a href="#method.get_ref">get_ref</a><a href="#method.get_mut">get_mut</a><a href="#method.into_inner">into_inner</a></div><a class="sidebar-title" href="#implementations">Trait Implementations</a><div class="sidebar-links"><a href="#impl-Write">Write</a><a href="#impl-Debug">Debug</a><a href="#impl-Seek">Seek</a><a href="#impl-Drop">Drop</a></div><a class="sidebar-title" href="#synthetic-implementations">Auto Trait Implementations</a><div class="sidebar-links"><a href="#impl-Send">Send</a><a href="#impl-Sync">Sync</a></div></div><p class='location'><a href='../index.html'>std</a>::<wbr><a href='index.html'>io</a></p><script>window.sidebarCurrent = {name: 'BufWriter', ty: 'struct', 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'>Struct <a href='../index.html'>std</a>::<wbr><a href='index.html'>io</a>::<wbr><a class="struct" href=''>BufWriter</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/std/io/buffered.rs.html#419-426' title='goto source code'>[src]</a></span></h1><div class="docblock type-decl"><pre class='rust struct'>pub struct BufWriter<W: <a class="trait" href="../../std/io/trait.Write.html" title="trait std::io::Write">Write</a>> { /* fields omitted */ }</pre></div><div class='docblock'><p>Wraps a writer and buffers its output.</p>
<p>It can be excessively inefficient to work directly with something that
implements <a href="../../std/io/trait.Write.html"><code>Write</code></a>. For example, every call to
<a href="../../std/net/struct.TcpStream.html#method.write"><code>write</code></a> on <a href="../../std/net/struct.TcpStream.html"><code>TcpStream</code></a> results in a system call. A
<code>BufWriter</code> keeps an in-memory buffer of data and writes it to an underlying
writer in large, infrequent batches.</p>
<p><code>BufWriter</code> can improve the speed of programs that make <em>small</em> and
<em>repeated</em> write calls to the same file or network socket. It does not
help when writing very large amounts at once, or writing just one or a few
times. It also provides no advantage when writing to a destination that is
in memory, like a <code>Vec<u8></code>.</p>
<p>When the <code>BufWriter</code> is dropped, the contents of its buffer will be written
out. However, any errors that happen in the process of flushing the buffer
when the writer is dropped will be ignored. Code that wishes to handle such
errors must manually call <a href="#method.flush"><code>flush</code></a> before the writer is dropped.</p>
<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
<p>Let's write the numbers one through ten to a <a href="../../std/net/struct.TcpStream.html"><code>TcpStream</code></a>:</p>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">io</span>::<span class="ident">prelude</span>::<span class="kw-2">*</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">net</span>::<span class="ident">TcpStream</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">stream</span> <span class="op">=</span> <span class="ident">TcpStream</span>::<span class="ident">connect</span>(<span class="string">"127.0.0.1:34254"</span>).<span class="ident">unwrap</span>();
<span class="kw">for</span> <span class="ident">i</span> <span class="kw">in</span> <span class="number">0</span>..<span class="number">10</span> {
<span class="ident">stream</span>.<span class="ident">write</span>(<span class="kw-2">&</span>[<span class="ident">i</span><span class="op">+</span><span class="number">1</span>]).<span class="ident">unwrap</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%3Aio%3A%3Aprelude%3A%3A*%3B%0Ause%20std%3A%3Anet%3A%3ATcpStream%3B%0A%0Alet%20mut%20stream%20%3D%20TcpStream%3A%3Aconnect(%22127.0.0.1%3A34254%22).unwrap()%3B%0A%0Afor%20i%20in%200..10%20%7B%0A%20%20%20%20stream.write(%26%5Bi%2B1%5D).unwrap()%3B%0A%7D%0A%7D">Run</a></pre>
<p>Because we're not buffering, we write each one in turn, incurring the
overhead of a system call per byte written. We can fix this with a
<code>BufWriter</code>:</p>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">io</span>::<span class="ident">prelude</span>::<span class="kw-2">*</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">io</span>::<span class="ident">BufWriter</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">net</span>::<span class="ident">TcpStream</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">stream</span> <span class="op">=</span> <span class="ident">BufWriter</span>::<span class="ident">new</span>(<span class="ident">TcpStream</span>::<span class="ident">connect</span>(<span class="string">"127.0.0.1:34254"</span>).<span class="ident">unwrap</span>());
<span class="kw">for</span> <span class="ident">i</span> <span class="kw">in</span> <span class="number">0</span>..<span class="number">10</span> {
<span class="ident">stream</span>.<span class="ident">write</span>(<span class="kw-2">&</span>[<span class="ident">i</span><span class="op">+</span><span class="number">1</span>]).<span class="ident">unwrap</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%3Aio%3A%3Aprelude%3A%3A*%3B%0Ause%20std%3A%3Aio%3A%3ABufWriter%3B%0Ause%20std%3A%3Anet%3A%3ATcpStream%3B%0A%0Alet%20mut%20stream%20%3D%20BufWriter%3A%3Anew(TcpStream%3A%3Aconnect(%22127.0.0.1%3A34254%22).unwrap())%3B%0A%0Afor%20i%20in%200..10%20%7B%0A%20%20%20%20stream.write(%26%5Bi%2B1%5D).unwrap()%3B%0A%7D%0A%7D">Run</a></pre>
<p>By wrapping the stream with a <code>BufWriter</code>, these ten writes are all grouped
together by the buffer, and will all be written out in one system call when
the <code>stream</code> is dropped.</p>
</div>
<h2 id='methods' class='small-section-header'>
Methods<a href='#methods' class='anchor'></a>
</h2>
<h3 id='impl' class='impl'><span class='in-band'><table class='table-display'><tbody><tr><td><code>impl<W: <a class="trait" href="../../std/io/trait.Write.html" title="trait std::io::Write">Write</a>> <a class="struct" href="../../std/io/struct.BufWriter.html" title="struct std::io::BufWriter">BufWriter</a><W></code><a href='#impl' class='anchor'></a></span></td><td><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../src/std/io/buffered.rs.html#456-581' title='goto source code'>[src]</a></span></td></tr></tbody></table></h3><div class='impl-items'><h4 id='method.new' class="method"><div class="important-traits"><div class='tooltip'>ⓘ<span class='tooltiptext'>Important traits for <a class="struct" href="../../std/io/struct.BufWriter.html" title="struct std::io::BufWriter">BufWriter</a><W></span></div><div class="content hidden"><h3 class="important">Important traits for <a class="struct" href="../../std/io/struct.BufWriter.html" title="struct std::io::BufWriter">BufWriter</a><W></h3><code class="content"><span class="where fmt-newline">impl<W: <a class="trait" href="../../std/io/trait.Write.html" title="trait std::io::Write">Write</a>> <a class="trait" href="../../std/io/trait.Write.html" title="trait std::io::Write">Write</a> for <a class="struct" href="../../std/io/struct.BufWriter.html" title="struct std::io::BufWriter">BufWriter</a><W></span></code></div></div><span id='new.v' class='invisible'><table class='table-display'><tbody><tr><td><code>pub fn <a href='#method.new' class='fnname'>new</a>(inner: W) -> <a class="struct" href="../../std/io/struct.BufWriter.html" title="struct std::io::BufWriter">BufWriter</a><W></code></span></td><td><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../src/std/io/buffered.rs.html#468-470' title='goto source code'>[src]</a></td></tr></tbody></table></span></h4><div class='docblock'><p>Creates a new <code>BufWriter</code> with a default buffer capacity.</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">io</span>::<span class="ident">BufWriter</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">net</span>::<span class="ident">TcpStream</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">buffer</span> <span class="op">=</span> <span class="ident">BufWriter</span>::<span class="ident">new</span>(<span class="ident">TcpStream</span>::<span class="ident">connect</span>(<span class="string">"127.0.0.1:34254"</span>).<span class="ident">unwrap</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%3Aio%3A%3ABufWriter%3B%0Ause%20std%3A%3Anet%3A%3ATcpStream%3B%0A%0Alet%20mut%20buffer%20%3D%20BufWriter%3A%3Anew(TcpStream%3A%3Aconnect(%22127.0.0.1%3A34254%22).unwrap())%3B%0A%7D">Run</a></pre>
</div><h4 id='method.with_capacity' class="method"><div class="important-traits"><div class='tooltip'>ⓘ<span class='tooltiptext'>Important traits for <a class="struct" href="../../std/io/struct.BufWriter.html" title="struct std::io::BufWriter">BufWriter</a><W></span></div><div class="content hidden"><h3 class="important">Important traits for <a class="struct" href="../../std/io/struct.BufWriter.html" title="struct std::io::BufWriter">BufWriter</a><W></h3><code class="content"><span class="where fmt-newline">impl<W: <a class="trait" href="../../std/io/trait.Write.html" title="trait std::io::Write">Write</a>> <a class="trait" href="../../std/io/trait.Write.html" title="trait std::io::Write">Write</a> for <a class="struct" href="../../std/io/struct.BufWriter.html" title="struct std::io::BufWriter">BufWriter</a><W></span></code></div></div><span id='with_capacity.v' class='invisible'><table class='table-display'><tbody><tr><td><code>pub fn <a href='#method.with_capacity' class='fnname'>with_capacity</a>(cap: <a class="primitive" href="../primitive.usize.html">usize</a>, inner: W) -> <a class="struct" href="../../std/io/struct.BufWriter.html" title="struct std::io::BufWriter">BufWriter</a><W></code></span></td><td><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../src/std/io/buffered.rs.html#486-492' title='goto source code'>[src]</a></td></tr></tbody></table></span></h4><div class='docblock'><p>Creates a new <code>BufWriter</code> with the specified buffer capacity.</p>
<h1 id="examples-2" class="section-header"><a href="#examples-2">Examples</a></h1>
<p>Creating a buffer with a buffer of a hundred bytes.</p>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">io</span>::<span class="ident">BufWriter</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">net</span>::<span class="ident">TcpStream</span>;
<span class="kw">let</span> <span class="ident">stream</span> <span class="op">=</span> <span class="ident">TcpStream</span>::<span class="ident">connect</span>(<span class="string">"127.0.0.1:34254"</span>).<span class="ident">unwrap</span>();
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">buffer</span> <span class="op">=</span> <span class="ident">BufWriter</span>::<span class="ident">with_capacity</span>(<span class="number">100</span>, <span class="ident">stream</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%3Aio%3A%3ABufWriter%3B%0Ause%20std%3A%3Anet%3A%3ATcpStream%3B%0A%0Alet%20stream%20%3D%20TcpStream%3A%3Aconnect(%22127.0.0.1%3A34254%22).unwrap()%3B%0Alet%20mut%20buffer%20%3D%20BufWriter%3A%3Awith_capacity(100%2C%20stream)%3B%0A%7D">Run</a></pre>
</div><h4 id='method.get_ref' class="method"><div class="important-traits"><div class='tooltip'>ⓘ<span class='tooltiptext'>Important traits for <a class="primitive" href="../primitive.reference.html">&'a mut </a>I</span></div><div class="content hidden"><h3 class="important">Important traits for <a class="primitive" href="../primitive.reference.html">&'a mut </a>I</h3><code class="content"><span class="where fmt-newline">impl<'a, I> <a class="trait" href="../../std/iter/trait.Iterator.html" title="trait std::iter::Iterator">Iterator</a> for <a class="primitive" href="../primitive.reference.html">&'a mut </a>I <span class="where fmt-newline">where<br> I: <a class="trait" href="../../std/iter/trait.Iterator.html" title="trait std::iter::Iterator">Iterator</a> + ?<a class="trait" href="../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>, </span></span><span class="where fmt-newline"> type <a href='../../std/iter/trait.Iterator.html#associatedtype.Item' class="type">Item</a> = <I as <a class="trait" href="../../std/iter/trait.Iterator.html" title="trait std::iter::Iterator">Iterator</a>>::<a class="type" href="../../std/iter/trait.Iterator.html#associatedtype.Item" title="type std::iter::Iterator::Item">Item</a>;</span><span class="where fmt-newline">impl<'a, R: <a class="trait" href="../../std/io/trait.Read.html" title="trait std::io::Read">Read</a> + ?<a class="trait" href="../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>> <a class="trait" href="../../std/io/trait.Read.html" title="trait std::io::Read">Read</a> for <a class="primitive" href="../primitive.reference.html">&'a mut </a>R</span><span class="where fmt-newline">impl<'a, W: <a class="trait" href="../../std/io/trait.Write.html" title="trait std::io::Write">Write</a> + ?<a class="trait" href="../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>> <a class="trait" href="../../std/io/trait.Write.html" title="trait std::io::Write">Write</a> for <a class="primitive" href="../primitive.reference.html">&'a mut </a>W</span></code></div></div><span id='get_ref.v' class='invisible'><table class='table-display'><tbody><tr><td><code>pub fn <a href='#method.get_ref' class='fnname'>get_ref</a>(&self) -> <a class="primitive" href="../primitive.reference.html">&</a>W</code></span></td><td><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../src/std/io/buffered.rs.html#535' title='goto source code'>[src]</a></td></tr></tbody></table></span></h4><div class='docblock'><p>Gets a reference to the underlying writer.</p>
<h1 id="examples-3" class="section-header"><a href="#examples-3">Examples</a></h1>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">io</span>::<span class="ident">BufWriter</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">net</span>::<span class="ident">TcpStream</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">buffer</span> <span class="op">=</span> <span class="ident">BufWriter</span>::<span class="ident">new</span>(<span class="ident">TcpStream</span>::<span class="ident">connect</span>(<span class="string">"127.0.0.1:34254"</span>).<span class="ident">unwrap</span>());
<span class="comment">// we can use reference just like buffer</span>
<span class="kw">let</span> <span class="ident">reference</span> <span class="op">=</span> <span class="ident">buffer</span>.<span class="ident">get_ref</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%3Aio%3A%3ABufWriter%3B%0Ause%20std%3A%3Anet%3A%3ATcpStream%3B%0A%0Alet%20mut%20buffer%20%3D%20BufWriter%3A%3Anew(TcpStream%3A%3Aconnect(%22127.0.0.1%3A34254%22).unwrap())%3B%0A%0A%2F%2F%20we%20can%20use%20reference%20just%20like%20buffer%0Alet%20reference%20%3D%20buffer.get_ref()%3B%0A%7D">Run</a></pre>
</div><h4 id='method.get_mut' class="method"><div class="important-traits"><div class='tooltip'>ⓘ<span class='tooltiptext'>Important traits for <a class="primitive" href="../primitive.reference.html">&'a mut </a>I</span></div><div class="content hidden"><h3 class="important">Important traits for <a class="primitive" href="../primitive.reference.html">&'a mut </a>I</h3><code class="content"><span class="where fmt-newline">impl<'a, I> <a class="trait" href="../../std/iter/trait.Iterator.html" title="trait std::iter::Iterator">Iterator</a> for <a class="primitive" href="../primitive.reference.html">&'a mut </a>I <span class="where fmt-newline">where<br> I: <a class="trait" href="../../std/iter/trait.Iterator.html" title="trait std::iter::Iterator">Iterator</a> + ?<a class="trait" href="../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>, </span></span><span class="where fmt-newline"> type <a href='../../std/iter/trait.Iterator.html#associatedtype.Item' class="type">Item</a> = <I as <a class="trait" href="../../std/iter/trait.Iterator.html" title="trait std::iter::Iterator">Iterator</a>>::<a class="type" href="../../std/iter/trait.Iterator.html#associatedtype.Item" title="type std::iter::Iterator::Item">Item</a>;</span><span class="where fmt-newline">impl<'a, R: <a class="trait" href="../../std/io/trait.Read.html" title="trait std::io::Read">Read</a> + ?<a class="trait" href="../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>> <a class="trait" href="../../std/io/trait.Read.html" title="trait std::io::Read">Read</a> for <a class="primitive" href="../primitive.reference.html">&'a mut </a>R</span><span class="where fmt-newline">impl<'a, W: <a class="trait" href="../../std/io/trait.Write.html" title="trait std::io::Write">Write</a> + ?<a class="trait" href="../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>> <a class="trait" href="../../std/io/trait.Write.html" title="trait std::io::Write">Write</a> for <a class="primitive" href="../primitive.reference.html">&'a mut </a>W</span></code></div></div><span id='get_mut.v' class='invisible'><table class='table-display'><tbody><tr><td><code>pub fn <a href='#method.get_mut' class='fnname'>get_mut</a>(&mut self) -> <a class="primitive" href="../primitive.reference.html">&mut </a>W</code></span></td><td><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../src/std/io/buffered.rs.html#553' title='goto source code'>[src]</a></td></tr></tbody></table></span></h4><div class='docblock'><p>Gets a mutable reference to the underlying writer.</p>
<p>It is inadvisable to directly write to the underlying writer.</p>
<h1 id="examples-4" class="section-header"><a href="#examples-4">Examples</a></h1>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">io</span>::<span class="ident">BufWriter</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">net</span>::<span class="ident">TcpStream</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">buffer</span> <span class="op">=</span> <span class="ident">BufWriter</span>::<span class="ident">new</span>(<span class="ident">TcpStream</span>::<span class="ident">connect</span>(<span class="string">"127.0.0.1:34254"</span>).<span class="ident">unwrap</span>());
<span class="comment">// we can use reference just like buffer</span>
<span class="kw">let</span> <span class="ident">reference</span> <span class="op">=</span> <span class="ident">buffer</span>.<span class="ident">get_mut</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%3Aio%3A%3ABufWriter%3B%0Ause%20std%3A%3Anet%3A%3ATcpStream%3B%0A%0Alet%20mut%20buffer%20%3D%20BufWriter%3A%3Anew(TcpStream%3A%3Aconnect(%22127.0.0.1%3A34254%22).unwrap())%3B%0A%0A%2F%2F%20we%20can%20use%20reference%20just%20like%20buffer%0Alet%20reference%20%3D%20buffer.get_mut()%3B%0A%7D">Run</a></pre>
</div><h4 id='method.into_inner' class="method"><span id='into_inner.v' class='invisible'><table class='table-display'><tbody><tr><td><code>pub fn <a href='#method.into_inner' class='fnname'>into_inner</a>(self) -> <a class="enum" href="../../std/result/enum.Result.html" title="enum std::result::Result">Result</a><W, <a class="struct" href="../../std/io/struct.IntoInnerError.html" title="struct std::io::IntoInnerError">IntoInnerError</a><<a class="struct" href="../../std/io/struct.BufWriter.html" title="struct std::io::BufWriter">BufWriter</a><W>>></code></span></td><td><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../src/std/io/buffered.rs.html#575-580' title='goto source code'>[src]</a></td></tr></tbody></table></span></h4><div class='docblock'><p>Unwraps this <code>BufWriter</code>, returning the underlying writer.</p>
<p>The buffer is written out before returning the writer.</p>
<h1 id="errors" class="section-header"><a href="#errors">Errors</a></h1>
<p>An <code>Err</code> will be returned if an error occurs while flushing the buffer.</p>
<h1 id="examples-5" class="section-header"><a href="#examples-5">Examples</a></h1>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">io</span>::<span class="ident">BufWriter</span>;
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">net</span>::<span class="ident">TcpStream</span>;
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">buffer</span> <span class="op">=</span> <span class="ident">BufWriter</span>::<span class="ident">new</span>(<span class="ident">TcpStream</span>::<span class="ident">connect</span>(<span class="string">"127.0.0.1:34254"</span>).<span class="ident">unwrap</span>());
<span class="comment">// unwrap the TcpStream and flush the buffer</span>
<span class="kw">let</span> <span class="ident">stream</span> <span class="op">=</span> <span class="ident">buffer</span>.<span class="ident">into_inner</span>().<span class="ident">unwrap</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%3Aio%3A%3ABufWriter%3B%0Ause%20std%3A%3Anet%3A%3ATcpStream%3B%0A%0Alet%20mut%20buffer%20%3D%20BufWriter%3A%3Anew(TcpStream%3A%3Aconnect(%22127.0.0.1%3A34254%22).unwrap())%3B%0A%0A%2F%2F%20unwrap%20the%20TcpStream%20and%20flush%20the%20buffer%0Alet%20stream%20%3D%20buffer.into_inner().unwrap()%3B%0A%7D">Run</a></pre>
</div></div>
<h2 id='implementations' class='small-section-header'>
Trait Implementations<a href='#implementations' class='anchor'></a>
</h2>
<div id='implementations-list'><h3 id='impl-Write' class='impl'><span class='in-band'><table class='table-display'><tbody><tr><td><code>impl<W: <a class="trait" href="../../std/io/trait.Write.html" title="trait std::io::Write">Write</a>> <a class="trait" href="../../std/io/trait.Write.html" title="trait std::io::Write">Write</a> for <a class="struct" href="../../std/io/struct.BufWriter.html" title="struct std::io::BufWriter">BufWriter</a><W></code><a href='#impl-Write' class='anchor'></a></span></td><td><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../src/std/io/buffered.rs.html#584-601' title='goto source code'>[src]</a></span></td></tr></tbody></table></h3><div class='impl-items'><h4 id='method.write' class="method"><span id='write.v' class='invisible'><table class='table-display'><tbody><tr><td><code>fn <a href='../../std/io/trait.Write.html#tymethod.write' class='fnname'>write</a>(&mut self, buf: <a class="primitive" href="../primitive.slice.html">&[</a><a class="primitive" href="../primitive.u8.html">u8</a><a class="primitive" href="../primitive.slice.html">]</a>) -> <a class="type" href="../../std/io/type.Result.html" title="type std::io::Result">Result</a><<a class="primitive" href="../primitive.usize.html">usize</a>></code></span></td><td><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../src/std/io/buffered.rs.html#585-597' title='goto source code'>[src]</a></td></tr></tbody></table></span></h4><div class='docblock'><p>Write a buffer into this object, returning how many bytes were written. <a href="../../std/io/trait.Write.html#tymethod.write">Read more</a></p>
</div><h4 id='method.flush' class="method"><span id='flush.v' class='invisible'><table class='table-display'><tbody><tr><td><code>fn <a href='../../std/io/trait.Write.html#tymethod.flush' class='fnname'>flush</a>(&mut self) -> <a class="type" href="../../std/io/type.Result.html" title="type std::io::Result">Result</a><<a class="primitive" href="../primitive.unit.html">()</a>></code></span></td><td><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../src/std/io/buffered.rs.html#598-600' title='goto source code'>[src]</a></td></tr></tbody></table></span></h4><div class='docblock'><p>Flush this output stream, ensuring that all intermediately buffered contents reach their destination. <a href="../../std/io/trait.Write.html#tymethod.flush">Read more</a></p>
</div><h4 id='method.write_all' class="method"><span id='write_all.v' class='invisible'><table class='table-display'><tbody><tr><td><code>fn <a href='../../std/io/trait.Write.html#method.write_all' class='fnname'>write_all</a>(&mut self, buf: <a class="primitive" href="../primitive.slice.html">&[</a><a class="primitive" href="../primitive.u8.html">u8</a><a class="primitive" href="../primitive.slice.html">]</a>) -> <a class="type" href="../../std/io/type.Result.html" title="type std::io::Result">Result</a><<a class="primitive" href="../primitive.unit.html">()</a>></code></span></td><td><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../src/std/io/mod.rs.html#1109-1120' title='goto source code'>[src]</a></td></tr></tbody></table></span></h4><div class='docblock'><p>Attempts to write an entire buffer into this write. <a href="../../std/io/trait.Write.html#method.write_all">Read more</a></p>
</div><h4 id='method.write_fmt' class="method"><span id='write_fmt.v' class='invisible'><table class='table-display'><tbody><tr><td><code>fn <a href='../../std/io/trait.Write.html#method.write_fmt' class='fnname'>write_fmt</a>(&mut self, fmt: <a class="struct" href="../../std/fmt/struct.Arguments.html" title="struct std::fmt::Arguments">Arguments</a>) -> <a class="type" href="../../std/io/type.Result.html" title="type std::io::Result">Result</a><<a class="primitive" href="../primitive.unit.html">()</a>></code></span></td><td><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../src/std/io/mod.rs.html#1161-1193' title='goto source code'>[src]</a></td></tr></tbody></table></span></h4><div class='docblock'><p>Writes a formatted string into this writer, returning any error encountered. <a href="../../std/io/trait.Write.html#method.write_fmt">Read more</a></p>
</div><h4 id='method.by_ref' class="method"><div class="important-traits"><div class='tooltip'>ⓘ<span class='tooltiptext'>Important traits for <a class="primitive" href="../primitive.reference.html">&'a mut </a>I</span></div><div class="content hidden"><h3 class="important">Important traits for <a class="primitive" href="../primitive.reference.html">&'a mut </a>I</h3><code class="content"><span class="where fmt-newline">impl<'a, I> <a class="trait" href="../../std/iter/trait.Iterator.html" title="trait std::iter::Iterator">Iterator</a> for <a class="primitive" href="../primitive.reference.html">&'a mut </a>I <span class="where fmt-newline">where<br> I: <a class="trait" href="../../std/iter/trait.Iterator.html" title="trait std::iter::Iterator">Iterator</a> + ?<a class="trait" href="../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>, </span></span><span class="where fmt-newline"> type <a href='../../std/iter/trait.Iterator.html#associatedtype.Item' class="type">Item</a> = <I as <a class="trait" href="../../std/iter/trait.Iterator.html" title="trait std::iter::Iterator">Iterator</a>>::<a class="type" href="../../std/iter/trait.Iterator.html#associatedtype.Item" title="type std::iter::Iterator::Item">Item</a>;</span><span class="where fmt-newline">impl<'a, R: <a class="trait" href="../../std/io/trait.Read.html" title="trait std::io::Read">Read</a> + ?<a class="trait" href="../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>> <a class="trait" href="../../std/io/trait.Read.html" title="trait std::io::Read">Read</a> for <a class="primitive" href="../primitive.reference.html">&'a mut </a>R</span><span class="where fmt-newline">impl<'a, W: <a class="trait" href="../../std/io/trait.Write.html" title="trait std::io::Write">Write</a> + ?<a class="trait" href="../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>> <a class="trait" href="../../std/io/trait.Write.html" title="trait std::io::Write">Write</a> for <a class="primitive" href="../primitive.reference.html">&'a mut </a>W</span></code></div></div><span id='by_ref.v' class='invisible'><table class='table-display'><tbody><tr><td><code>fn <a href='../../std/io/trait.Write.html#method.by_ref' class='fnname'>by_ref</a>(&mut self) -> <a class="primitive" href="../primitive.reference.html">&mut </a>Self <span class="where fmt-newline">where<br> Self: <a class="trait" href="../../std/marker/trait.Sized.html" title="trait std::marker::Sized">Sized</a>, </span></code></span></td><td><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../src/std/io/mod.rs.html#1217' title='goto source code'>[src]</a></td></tr></tbody></table></span></h4><div class='docblock'><p>Creates a "by reference" adaptor for this instance of <code>Write</code>. <a href="../../std/io/trait.Write.html#method.by_ref">Read more</a></p>
</div></div><h3 id='impl-Debug' class='impl'><span class='in-band'><table class='table-display'><tbody><tr><td><code>impl<W: <a class="trait" href="../../std/io/trait.Write.html" title="trait std::io::Write">Write</a>> <a class="trait" href="../../std/fmt/trait.Debug.html" title="trait std::fmt::Debug">Debug</a> for <a class="struct" href="../../std/io/struct.BufWriter.html" title="struct std::io::BufWriter">BufWriter</a><W> <span class="where fmt-newline">where<br> W: <a class="trait" href="../../std/fmt/trait.Debug.html" title="trait std::fmt::Debug">Debug</a>, </span></code><a href='#impl-Debug' class='anchor'></a></span></td><td><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../src/std/io/buffered.rs.html#604-611' title='goto source code'>[src]</a></span></td></tr></tbody></table></h3><div class='impl-items'><h4 id='method.fmt' class="method"><span id='fmt.v' class='invisible'><table class='table-display'><tbody><tr><td><code>fn <a href='../../std/fmt/trait.Debug.html#tymethod.fmt' class='fnname'>fmt</a>(&self, fmt: &mut <a class="struct" href="../../std/fmt/struct.Formatter.html" title="struct std::fmt::Formatter">Formatter</a>) -> <a class="type" href="../../std/fmt/type.Result.html" title="type std::fmt::Result">Result</a></code></span></td><td><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../src/std/io/buffered.rs.html#605-610' title='goto source code'>[src]</a></td></tr></tbody></table></span></h4><div class='docblock'><p>Formats the value using the given formatter. <a href="../../std/fmt/trait.Debug.html#tymethod.fmt">Read more</a></p>
</div></div><h3 id='impl-Seek' class='impl'><span class='in-band'><table class='table-display'><tbody><tr><td><code>impl<W: <a class="trait" href="../../std/io/trait.Write.html" title="trait std::io::Write">Write</a> + <a class="trait" href="../../std/io/trait.Seek.html" title="trait std::io::Seek">Seek</a>> <a class="trait" href="../../std/io/trait.Seek.html" title="trait std::io::Seek">Seek</a> for <a class="struct" href="../../std/io/struct.BufWriter.html" title="struct std::io::BufWriter">BufWriter</a><W></code><a href='#impl-Seek' class='anchor'></a></span></td><td><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../src/std/io/buffered.rs.html#614-621' title='goto source code'>[src]</a></span></td></tr></tbody></table></h3><div class='impl-items'><h4 id='method.seek' class="method"><span id='seek.v' class='invisible'><table class='table-display'><tbody><tr><td><code>fn <a href='../../std/io/trait.Seek.html#tymethod.seek' class='fnname'>seek</a>(&mut self, pos: <a class="enum" href="../../std/io/enum.SeekFrom.html" title="enum std::io::SeekFrom">SeekFrom</a>) -> <a class="type" href="../../std/io/type.Result.html" title="type std::io::Result">Result</a><<a class="primitive" href="../primitive.u64.html">u64</a>></code></span></td><td><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../src/std/io/buffered.rs.html#618-620' title='goto source code'>[src]</a></td></tr></tbody></table></span></h4><div class='docblock'><p>Seek to the offset, in bytes, in the underlying writer.</p>
<p>Seeking always writes out the internal buffer before seeking.</p>
</div></div><h3 id='impl-Drop' class='impl'><span class='in-band'><table class='table-display'><tbody><tr><td><code>impl<W: <a class="trait" href="../../std/io/trait.Write.html" title="trait std::io::Write">Write</a>> <a class="trait" href="../../std/ops/trait.Drop.html" title="trait std::ops::Drop">Drop</a> for <a class="struct" href="../../std/io/struct.BufWriter.html" title="struct std::io::BufWriter">BufWriter</a><W></code><a href='#impl-Drop' class='anchor'></a></span></td><td><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../src/std/io/buffered.rs.html#624-631' title='goto source code'>[src]</a></span></td></tr></tbody></table></h3><div class='impl-items'><h4 id='method.drop' class="method"><span id='drop.v' class='invisible'><table class='table-display'><tbody><tr><td><code>fn <a href='../../std/ops/trait.Drop.html#tymethod.drop' class='fnname'>drop</a>(&mut self)</code></span></td><td><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../src/std/io/buffered.rs.html#625-630' title='goto source code'>[src]</a></td></tr></tbody></table></span></h4><div class='docblock'><p>Executes the destructor for this type. <a href="../../std/ops/trait.Drop.html#tymethod.drop">Read more</a></p>
</div></div></div>
<h2 id='synthetic-implementations' class='small-section-header'>
Auto Trait Implementations<a href='#synthetic-implementations' class='anchor'></a>
</h2>
<div id='synthetic-implementations-list'>
<h3 id='impl-Send' class='impl'><span class='in-band'><table class='table-display'><tbody><tr><td><code>impl<W> <a class="trait" href="../../std/marker/trait.Send.html" title="trait std::marker::Send">Send</a> for <a class="struct" href="../../std/io/struct.BufWriter.html" title="struct std::io::BufWriter">BufWriter</a><W> <span class="where fmt-newline">where<br> W: <a class="trait" href="../../std/marker/trait.Send.html" title="trait std::marker::Send">Send</a>, </span></code><a href='#impl-Send' class='anchor'></a></span></td><td><span class='out-of-band'></span></td></tr></tbody></table></h3><div class='impl-items'></div><h3 id='impl-Sync' class='impl'><span class='in-band'><table class='table-display'><tbody><tr><td><code>impl<W> <a class="trait" href="../../std/marker/trait.Sync.html" title="trait std::marker::Sync">Sync</a> for <a class="struct" href="../../std/io/struct.BufWriter.html" title="struct std::io::BufWriter">BufWriter</a><W> <span class="where fmt-newline">where<br> W: <a class="trait" href="../../std/marker/trait.Sync.html" title="trait std::marker::Sync">Sync</a>, </span></code><a href='#impl-Sync' class='anchor'></a></span></td><td><span class='out-of-band'></span></td></tr></tbody></table></h3><div class='impl-items'></div></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><p>Search multiple things at once by splitting your query with comma (e.g. <code>str,u8</code> or <code>String,struct:Vec,test</code>)</p></div></div></aside><script>window.rootPath = "../../";window.currentCrate = "std";</script><script src="../../aliases.js"></script><script src="../../main.js"></script><script defer src="../../search-index.js"></script></body></html>
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