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<!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="Prints to `stdout`, with a newline."><title>println in anstream - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-46f98efaafac5295.ttf.woff2,FiraSans-Regular-018c141bf0843ffd.woff2,FiraSans-Medium-8f9a781e4970d388.woff2,SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2,SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../static.files/rustdoc-dd39b87e5fcfba68.css"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="anstream" data-themes="" data-resource-suffix="" data-rustdoc-version="1.80.0 (051478957 2024-07-21)" data-channel="1.80.0" data-search-js="search-d52510db62a78183.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../static.files/storage-118b08c4c78b968e.js"></script><script defer src="sidebar-items.js"></script><script defer src="../static.files/main-20a3ad099b048cf2.js"></script><noscript><link rel="stylesheet" href="../static.files/noscript-df360f571f6edeae.css"></noscript><link rel="alternate icon" type="image/png" href="../static.files/favicon-32x32-422f7d1d52889060.png"><link rel="icon" type="image/svg+xml" href="../static.files/favicon-2c020d218678b618.svg"></head><body class="rustdoc macro"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle" title="show sidebar"></button></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../anstream/index.html">anstream</a><span class="version">0.6.15</span></h2></div><div class="sidebar-elems"></div></nav><div class="sidebar-resizer"></div><main><div class="width-limiter"><rustdoc-search></rustdoc-search><section id="main-content" class="content"><div class="main-heading"><h1>Macro <a href="index.html">anstream</a>::<wbr><a class="macro" href="#">println</a><button id="copy-path" title="Copy item path to clipboard">Copy item path</button></h1><span class="out-of-band"><a class="src" href="../src/anstream/macros.rs.html#139-169">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>−</span>]</button></span></div><pre class="rust item-decl"><span class="macro">macro_rules!</span> println {
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() => { ... };
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($(<span class="macro-nonterminal">$arg</span>:tt)<span class="kw-2">*</span>) => { ... };
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}</pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Prints to <a href="fn.stdout.html" title="fn anstream::stdout"><code>stdout</code></a>, with a newline.</p>
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<p>On all platforms, the newline is the LINE FEED character (<code>\n</code>/<code>U+000A</code>) alone
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(no additional CARRIAGE RETURN (<code>\r</code>/<code>U+000D</code>)).</p>
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<p>This macro uses the same syntax as <a href="https://doc.rust-lang.org/1.80.0/alloc/macro.format.html" title="macro alloc::format"><code>format!</code></a>, but writes to the standard output instead.
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See <a href="https://doc.rust-lang.org/1.80.0/alloc/fmt/index.html" title="mod alloc::fmt"><code>std::fmt</code></a> for more information.</p>
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<p><strong>NOTE:</strong> The <code>println!</code> macro will lock the standard output on each call. If you call
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<code>println!</code> within a hot loop, this behavior may be the bottleneck of the loop.
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To avoid this, lock stdout with <a href="struct.AutoStream.html#method.lock" title="method anstream::AutoStream::lock"><code>AutoStream::lock</code></a>:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>std::io::Write <span class="kw">as _</span>;
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<span class="kw">let </span><span class="kw-2">mut </span>lock = anstream::stdout().lock();
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<span class="macro">writeln!</span>(lock, <span class="string">"hello world"</span>).unwrap();</code></pre></div>
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<p>Use <code>println!</code> only for the primary output of your program. Use
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<a href="https://doc.rust-lang.org/1.80.0/std/macro.eprintln.html" title="macro std::eprintln"><code>eprintln!</code></a> instead to print error and progress messages.</p>
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<p><strong>NOTE:</strong> Not all <code>println!</code> calls will be captured in tests like <a href="https://doc.rust-lang.org/1.80.0/std/macro.println.html" title="macro std::println"><code>std::println!</code></a></p>
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<ul>
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<li>Capturing will automatically be activated in test binaries</li>
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<li>Otherwise, only when the <code>test</code> feature is enabled</li>
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</ul>
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<h2 id="panics"><a class="doc-anchor" href="#panics">§</a>Panics</h2>
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<p>Panics if writing to <code>stdout</code> fails for any reason <strong>except</strong> broken pipe.</p>
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<p>Writing to non-blocking stdout can cause an error, which will lead
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this macro to panic.</p>
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<h2 id="examples"><a class="doc-anchor" href="#examples">§</a>Examples</h2>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>anstream::println;
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<span class="macro">println!</span>(); <span class="comment">// prints just a newline
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</span><span class="macro">println!</span>(<span class="string">"hello there!"</span>);
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<span class="macro">println!</span>(<span class="string">"format {} arguments"</span>, <span class="string">"some"</span>);
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<span class="kw">let </span>local_variable = <span class="string">"some"</span>;
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<span class="macro">println!</span>(<span class="string">"format {local_variable} arguments"</span>);</code></pre></div>
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</div></details></section></div></main></body></html> |