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<p class='location'><a href='../../index.html'>bitflags</a>::<wbr><a href='../index.html'>__core</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>
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<section id='main' class="content struct">
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<h1 class='fqn'><span class='in-band'>Struct <a href='../../index.html'>bitflags</a>::<wbr><a href='../index.html'>__core</a>::<wbr><a href='index.html'>io</a>::<wbr><a class='struct' href=''>BufWriter</a></span><span class='out-of-band'><span id='render-detail'>
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[<span class='inner'>−</span>]
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</span><a id='src-4000' class='srclink' href='https://doc.rust-lang.org/nightly/std/io/buffered/struct.BufWriter.html?gotosrc=4000' title='goto source code'>[src]</a></span></h1>
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<pre class='rust struct'>pub struct BufWriter<W> <span class='where'>where W: <a class='trait' href='../../../bitflags/__core/io/trait.Write.html' title='bitflags::__core::io::Write'>Write</a></span> {
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// some fields omitted
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}</pre><span class="since">1.0.0</span><div class='docblock'><p>Wraps a writer and buffers its output.</p>
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<p>It can be excessively inefficient to work directly with something that
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implements <code>Write</code>. For example, every call to <code>write</code> on <code>TcpStream</code>
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results in a system call. A <code>BufWriter</code> keeps an in-memory buffer of data
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and writes it to an underlying writer in large, infrequent batches.</p>
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<p>The buffer will be written out when the writer is dropped.</p>
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<h1 id='examples' class='section-header'><a href='#examples'>Examples</a></h1>
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<p>Let's write the numbers one through ten to a <code>TcpStream</code>:</p>
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<pre class='rust rust-example-rendered'>
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>io</span>::<span class='ident'>prelude</span>::<span class='op'>*</span>;
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>net</span>::<span class='ident'>TcpStream</span>;
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<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>();
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<span class='kw'>for</span> <span class='ident'>i</span> <span class='kw'>in</span> <span class='number'>1</span>..<span class='number'>10</span> {
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<span class='ident'>stream</span>.<span class='ident'>write</span>(<span class='kw-2'>&</span>[<span class='ident'>i</span>]).<span class='ident'>unwrap</span>();
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}</pre>
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<p>Because we're not buffering, we write each one in turn, incurring the
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overhead of a system call per byte written. We can fix this with a
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<code>BufWriter</code>:</p>
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<pre class='rust rust-example-rendered'>
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>io</span>::<span class='ident'>prelude</span>::<span class='op'>*</span>;
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>io</span>::<span class='ident'>BufWriter</span>;
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>net</span>::<span class='ident'>TcpStream</span>;
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<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>());
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<span class='kw'>for</span> <span class='ident'>i</span> <span class='kw'>in</span> <span class='number'>1</span>..<span class='number'>10</span> {
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<span class='ident'>stream</span>.<span class='ident'>write</span>(<span class='kw-2'>&</span>[<span class='ident'>i</span>]).<span class='ident'>unwrap</span>();
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}</pre>
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<p>By wrapping the stream with a <code>BufWriter</code>, these ten writes are all grouped
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together by the buffer, and will all be written out in one system call when
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the <code>stream</code> is dropped.</p>
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</div><h2 id='methods'>Methods</h2><h3 class='impl'><code>impl<W> <a class='struct' href='../../../bitflags/__core/io/struct.BufWriter.html' title='bitflags::__core::io::BufWriter'>BufWriter</a><W> <span class='where'>where W: <a class='trait' href='../../../bitflags/__core/io/trait.Write.html' title='bitflags::__core::io::Write'>Write</a></span></code></h3><div class='impl-items'><h4 id='method.new' class='method'><code>fn <a href='#method.new' class='fnname'>new</a>(inner: W) -> <a class='struct' href='../../../bitflags/__core/io/struct.BufWriter.html' title='bitflags::__core::io::BufWriter'>BufWriter</a><W></code></h4>
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<div class='docblock'><p>Creates a new <code>BufWriter</code> with a default buffer capacity.</p>
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<h1 id='examples-1' class='section-header'><a href='#examples-1'>Examples</a></h1>
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<pre class='rust rust-example-rendered'>
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>io</span>::<span class='ident'>BufWriter</span>;
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>net</span>::<span class='ident'>TcpStream</span>;
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<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>());</pre>
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</div><h4 id='method.with_capacity' class='method'><code>fn <a href='#method.with_capacity' class='fnname'>with_capacity</a>(cap: <a class='primitive' href='https://doc.rust-lang.org/nightly/bitflags/primitive.usize.html'>usize</a>, inner: W) -> <a class='struct' href='../../../bitflags/__core/io/struct.BufWriter.html' title='bitflags::__core::io::BufWriter'>BufWriter</a><W></code></h4>
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<div class='docblock'><p>Creates a new <code>BufWriter</code> with the specified buffer capacity.</p>
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<h1 id='examples-2' class='section-header'><a href='#examples-2'>Examples</a></h1>
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<p>Creating a buffer with a buffer of a hundred bytes.</p>
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<pre class='rust rust-example-rendered'>
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>io</span>::<span class='ident'>BufWriter</span>;
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>net</span>::<span class='ident'>TcpStream</span>;
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<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>();
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<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>);</pre>
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</div><h4 id='method.get_ref' class='method'><code>fn <a href='#method.get_ref' class='fnname'>get_ref</a>(&self) -> &W</code></h4>
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<div class='docblock'><p>Gets a reference to the underlying writer.</p>
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<h1 id='examples-3' class='section-header'><a href='#examples-3'>Examples</a></h1>
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<pre class='rust rust-example-rendered'>
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>io</span>::<span class='ident'>BufWriter</span>;
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>net</span>::<span class='ident'>TcpStream</span>;
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<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>());
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<span class='comment'>// we can use reference just like buffer</span>
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<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>();</pre>
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</div><h4 id='method.get_mut' class='method'><code>fn <a href='#method.get_mut' class='fnname'>get_mut</a>(&mut self) -> &mut W</code></h4>
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<div class='docblock'><p>Gets a mutable reference to the underlying writer.</p>
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<p>It is inadvisable to directly write to the underlying writer.</p>
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<h1 id='examples-4' class='section-header'><a href='#examples-4'>Examples</a></h1>
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<pre class='rust rust-example-rendered'>
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>io</span>::<span class='ident'>BufWriter</span>;
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>net</span>::<span class='ident'>TcpStream</span>;
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<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>());
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<span class='comment'>// we can use reference just like buffer</span>
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<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>();</pre>
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</div><h4 id='method.into_inner' class='method'><code>fn <a href='#method.into_inner' class='fnname'>into_inner</a>(self) -> <a class='enum' href='../../../bitflags/__core/result/enum.Result.html' title='bitflags::__core::result::Result'>Result</a><W, <a class='struct' href='../../../bitflags/__core/io/struct.IntoInnerError.html' title='bitflags::__core::io::IntoInnerError'>IntoInnerError</a><<a class='struct' href='../../../bitflags/__core/io/struct.BufWriter.html' title='bitflags::__core::io::BufWriter'>BufWriter</a><W>>></code></h4>
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<div class='docblock'><p>Unwraps this <code>BufWriter</code>, returning the underlying writer.</p>
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<p>The buffer is written out before returning the writer.</p>
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<h1 id='examples-5' class='section-header'><a href='#examples-5'>Examples</a></h1>
|
||
<pre class='rust rust-example-rendered'>
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||
<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>io</span>::<span class='ident'>BufWriter</span>;
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<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>());
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||
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<span class='comment'>// unwrap the TcpStream and flush the buffer</span>
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<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>();</pre>
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</div></div><h2 id='implementations'>Trait Implementations</h2><h3 class='impl'><code>impl<W> <a class='trait' href='../../../bitflags/__core/io/trait.Write.html' title='bitflags::__core::io::Write'>Write</a> for <a class='struct' href='../../../bitflags/__core/io/struct.BufWriter.html' title='bitflags::__core::io::BufWriter'>BufWriter</a><W> <span class='where'>where W: <a class='trait' href='../../../bitflags/__core/io/trait.Write.html' title='bitflags::__core::io::Write'>Write</a></span></code></h3><div class='impl-items'><h4 id='method.write' class='method'><code>fn <a href='../../../bitflags/__core/io/trait.Write.html#tymethod.write' class='fnname'>write</a>(&mut self, buf: <a class='primitive' href='https://doc.rust-lang.org/nightly/bitflags/primitive.slice.html'>&[</a><a class='primitive' href='https://doc.rust-lang.org/nightly/bitflags/primitive.u8.html'>u8</a><a class='primitive' href='https://doc.rust-lang.org/nightly/bitflags/primitive.slice.html'>]</a>) -> <a class='enum' href='../../../bitflags/__core/result/enum.Result.html' title='bitflags::__core::result::Result'>Result</a><<a class='primitive' href='https://doc.rust-lang.org/nightly/bitflags/primitive.usize.html'>usize</a>, <a class='struct' href='../../../bitflags/__core/io/struct.Error.html' title='bitflags::__core::io::Error'>Error</a>></code></h4>
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<h4 id='method.flush' class='method'><code>fn <a href='../../../bitflags/__core/io/trait.Write.html#tymethod.flush' class='fnname'>flush</a>(&mut self) -> <a class='enum' href='../../../bitflags/__core/result/enum.Result.html' title='bitflags::__core::result::Result'>Result</a><<a class='primitive' href='https://doc.rust-lang.org/nightly/bitflags/primitive.tuple.html'>()</a>, <a class='struct' href='../../../bitflags/__core/io/struct.Error.html' title='bitflags::__core::io::Error'>Error</a>></code></h4>
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<h4 id='method.write_all' class='method'><code>fn <a href='../../../bitflags/__core/io/trait.Write.html#method.write_all' class='fnname'>write_all</a>(&mut self, buf: <a class='primitive' href='https://doc.rust-lang.org/nightly/bitflags/primitive.slice.html'>&[</a><a class='primitive' href='https://doc.rust-lang.org/nightly/bitflags/primitive.u8.html'>u8</a><a class='primitive' href='https://doc.rust-lang.org/nightly/bitflags/primitive.slice.html'>]</a>) -> <a class='enum' href='../../../bitflags/__core/result/enum.Result.html' title='bitflags::__core::result::Result'>Result</a><<a class='primitive' href='https://doc.rust-lang.org/nightly/bitflags/primitive.tuple.html'>()</a>, <a class='struct' href='../../../bitflags/__core/io/struct.Error.html' title='bitflags::__core::io::Error'>Error</a>></code></h4>
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<h4 id='method.write_fmt' class='method'><code>fn <a href='../../../bitflags/__core/io/trait.Write.html#method.write_fmt' class='fnname'>write_fmt</a>(&mut self, fmt: <a class='struct' href='../../../bitflags/__core/fmt/struct.Arguments.html' title='bitflags::__core::fmt::Arguments'>Arguments</a>) -> <a class='enum' href='../../../bitflags/__core/result/enum.Result.html' title='bitflags::__core::result::Result'>Result</a><<a class='primitive' href='https://doc.rust-lang.org/nightly/bitflags/primitive.tuple.html'>()</a>, <a class='struct' href='../../../bitflags/__core/io/struct.Error.html' title='bitflags::__core::io::Error'>Error</a>></code></h4>
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<h4 id='method.by_ref' class='method'><code>fn <a href='../../../bitflags/__core/io/trait.Write.html#method.by_ref' class='fnname'>by_ref</a>(&mut self) -> &mut Self</code></h4>
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</div><h3 class='impl'><code>impl<W> <a class='trait' href='../../../bitflags/__core/fmt/trait.Debug.html' title='bitflags::__core::fmt::Debug'>Debug</a> for <a class='struct' href='../../../bitflags/__core/io/struct.BufWriter.html' title='bitflags::__core::io::BufWriter'>BufWriter</a><W> <span class='where'>where W: <a class='trait' href='../../../bitflags/__core/io/trait.Write.html' title='bitflags::__core::io::Write'>Write</a> + <a class='trait' href='../../../bitflags/__core/fmt/trait.Debug.html' title='bitflags::__core::fmt::Debug'>Debug</a></span></code></h3><div class='impl-items'><h4 id='method.fmt' class='method'><code>fn <a href='../../../bitflags/__core/fmt/trait.Debug.html#tymethod.fmt' class='fnname'>fmt</a>(&self, fmt: &mut <a class='struct' href='../../../bitflags/__core/fmt/struct.Formatter.html' title='bitflags::__core::fmt::Formatter'>Formatter</a>) -> <a class='enum' href='../../../bitflags/__core/result/enum.Result.html' title='bitflags::__core::result::Result'>Result</a><<a class='primitive' href='https://doc.rust-lang.org/nightly/bitflags/primitive.tuple.html'>()</a>, <a class='struct' href='../../../bitflags/__core/fmt/struct.Error.html' title='bitflags::__core::fmt::Error'>Error</a>></code></h4>
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</div><h3 class='impl'><code>impl<W> <a class='trait' href='../../../bitflags/__core/io/trait.Seek.html' title='bitflags::__core::io::Seek'>Seek</a> for <a class='struct' href='../../../bitflags/__core/io/struct.BufWriter.html' title='bitflags::__core::io::BufWriter'>BufWriter</a><W> <span class='where'>where W: <a class='trait' href='../../../bitflags/__core/io/trait.Write.html' title='bitflags::__core::io::Write'>Write</a> + <a class='trait' href='../../../bitflags/__core/io/trait.Seek.html' title='bitflags::__core::io::Seek'>Seek</a></span></code></h3><div class='impl-items'><h4 id='method.seek' class='method'><code>fn <a href='../../../bitflags/__core/io/trait.Seek.html#tymethod.seek' class='fnname'>seek</a>(&mut self, pos: <a class='enum' href='../../../bitflags/__core/io/enum.SeekFrom.html' title='bitflags::__core::io::SeekFrom'>SeekFrom</a>) -> <a class='enum' href='../../../bitflags/__core/result/enum.Result.html' title='bitflags::__core::result::Result'>Result</a><<a class='primitive' href='https://doc.rust-lang.org/nightly/bitflags/primitive.u64.html'>u64</a>, <a class='struct' href='../../../bitflags/__core/io/struct.Error.html' title='bitflags::__core::io::Error'>Error</a>></code></h4>
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<div class='docblock'><p>Seek to the offset, in bytes, in the underlying writer.</p>
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<p>Seeking always writes out the internal buffer before seeking.</p>
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</div></div><h3 class='impl'><code>impl<W> <a class='trait' href='../../../bitflags/__core/ops/trait.Drop.html' title='bitflags::__core::ops::Drop'>Drop</a> for <a class='struct' href='../../../bitflags/__core/io/struct.BufWriter.html' title='bitflags::__core::io::BufWriter'>BufWriter</a><W> <span class='where'>where W: <a class='trait' href='../../../bitflags/__core/io/trait.Write.html' title='bitflags::__core::io::Write'>Write</a></span></code></h3><div class='impl-items'><h4 id='method.drop' class='method'><code>fn <a href='../../../bitflags/__core/ops/trait.Drop.html#tymethod.drop' class='fnname'>drop</a>(&mut self)</code></h4>
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<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>
|
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