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<meta name="description" content="API documentation for the Rust `LineWriter` struct in crate `bitflags`.">
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<title>bitflags::__core::io::LineWriter - Rust</title>
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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: 'LineWriter', 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=''>LineWriter</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-4135' class='srclink' href='https://doc.rust-lang.org/nightly/std/io/buffered/struct.LineWriter.html?gotosrc=4135' title='goto source code'>[src]</a></span></h1>
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<pre class='rust struct'>pub struct LineWriter<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 output to it, flushing whenever a newline
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(<code>0x0a</code>, <code>'\n'</code>) is detected.</p>
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<p>The <a href="struct.BufWriter.html"><code>BufWriter</code></a> struct wraps a writer and buffers its output.
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But it only does this batched write when it goes out of scope, or when the
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internal buffer is full. Sometimes, you'd prefer to write each line as it's
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completed, rather than the entire buffer at once. Enter <code>LineWriter</code>. It
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does exactly that.</p>
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<p>If there's still a partial line in the buffer when the <code>LineWriter</code> is
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dropped, it will flush those contents.</p>
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<h1 id='examples' class='section-header'><a href='#examples'>Examples</a></h1>
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<p>We can use <code>LineWriter</code> to write one line at a time, significantly
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reducing the number of actual writes to the file.</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'>fs</span>::<span class='ident'>File</span>;
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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'>LineWriter</span>;
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<span class='kw'>let</span> <span class='ident'>road_not_taken</span> <span class='op'>=</span> <span class='string'>b"I shall be telling this with a sigh
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Somewhere ages and ages hence:
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Two roads diverged in a wood, and I -
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I took the one less traveled by,
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And that has made all the difference."</span>;
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<span class='kw'>let</span> <span class='ident'>file</span> <span class='op'>=</span> <span class='macro'>try</span><span class='macro'>!</span>(<span class='ident'>File</span>::<span class='ident'>create</span>(<span class='string'>"poem.txt"</span>));
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<span class='kw'>let</span> <span class='kw-2'>mut</span> <span class='ident'>file</span> <span class='op'>=</span> <span class='ident'>LineWriter</span>::<span class='ident'>new</span>(<span class='ident'>file</span>);
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<span class='kw'>for</span> <span class='kw-2'>&</span><span class='ident'>byte</span> <span class='kw'>in</span> <span class='ident'>road_not_taken</span>.<span class='ident'>iter</span>() {
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<span class='ident'>file</span>.<span class='ident'>write</span>(<span class='kw-2'>&</span>[<span class='ident'>byte</span>]).<span class='ident'>unwrap</span>();
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}
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<span class='comment'>// let's check we did the right thing.</span>
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<span class='kw'>let</span> <span class='kw-2'>mut</span> <span class='ident'>file</span> <span class='op'>=</span> <span class='macro'>try</span><span class='macro'>!</span>(<span class='ident'>File</span>::<span class='ident'>open</span>(<span class='string'>"poem.txt"</span>));
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<span class='kw'>let</span> <span class='kw-2'>mut</span> <span class='ident'>contents</span> <span class='op'>=</span> <span class='ident'>String</span>::<span class='ident'>new</span>();
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<span class='macro'>try</span><span class='macro'>!</span>(<span class='ident'>file</span>.<span class='ident'>read_to_string</span>(<span class='kw-2'>&</span><span class='kw-2'>mut</span> <span class='ident'>contents</span>));
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<span class='macro'>assert_eq</span><span class='macro'>!</span>(<span class='ident'>contents</span>.<span class='ident'>as_bytes</span>(), <span class='kw-2'>&</span><span class='ident'>road_not_taken</span>[..]);</pre>
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