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<ol class="chapter"><li class="chapter-item expanded "><a href="Chapter_0.html"><strong aria-hidden="true">1.</strong> Updates</a></li><li class="chapter-item expanded "><a href="Chapter_1.html"><strong aria-hidden="true">2.</strong> Introduction</a></li><li class="chapter-item expanded "><a href="Chapter_2.html"><strong aria-hidden="true">3.</strong> Who am I?</a></li><li class="chapter-item expanded "><a href="Chapter_3.html"><strong aria-hidden="true">4.</strong> Writing Rust in Easy English</a></li><li class="chapter-item expanded "><a href="Chapter_4.html"><strong aria-hidden="true">5.</strong> Rust Playground</a></li><li class="chapter-item expanded "><a href="Chapter_5.html"><strong aria-hidden="true">6.</strong> 🚧 and ⚠️</a></li><li class="chapter-item expanded "><a href="Chapter_6.html"><strong aria-hidden="true">7.</strong> Comments</a></li><li class="chapter-item expanded "><a href="Chapter_7.html"><strong aria-hidden="true">8.</strong> Types</a></li><li class="chapter-item expanded "><a href="Chapter_8.html"><strong aria-hidden="true">9.</strong> Type inference</a></li><li class="chapter-item expanded "><a href="Chapter_9.html"><strong aria-hidden="true">10.</strong> Printing 'hello, world!'</a></li><li class="chapter-item expanded "><a href="Chapter_10.html"><strong aria-hidden="true">11.</strong> Display and debug</a></li><li class="chapter-item expanded "><a href="Chapter_11.html"><strong aria-hidden="true">12.</strong> Mutability (changing)</a></li><li class="chapter-item expanded "><a href="Chapter_12.html"><strong aria-hidden="true">13.</strong> The stack, the heap, and pointers</a></li><li class="chapter-item expanded "><a href="Chapter_13.html" class="active"><strong aria-hidden="true">14.</strong> More about printing</a></li><li class="chapter-item expanded "><a href="Chapter_14.html"><strong aria-hidden="true">15.</strong> Strings</a></li><li class="chapter-item expanded "><a href="Chapter_15.html"><strong aria-hidden="true">16.</strong> const and static</a></li><li class="chapter-item expanded "><a href="Chapter_16.html"><strong aria-hidden="true">17.</strong> More on references</a></li><li class="chapter-item expanded "><a href="Chapter_17.html"><strong aria-hidden="true">18.</strong> Mutable references</a></li><li class="chapter-item expanded "><a href="Chapter_18.html"><strong aria-hidden="true">19.</strong> Giving references to functions</a></li><li class="chapter-item expanded "><a href="Chapter_19.html"><strong aria-hidden="true">20.</strong> Copy types</a></li><li class="chapter-item expanded "><a href="Chapter_20.html"><strong aria-hidden="true">21.</strong> Collection types</a></li><li class="chapter-item expanded "><a href="Chapter_21.html"><strong aria-hidden="true">22.</strong> Vectors</a></li><li class="chapter-item expanded "><a href="Chapter_22.html"><strong aria-hidden="true">23.</strong> Tuples</a></li><li class="chapter-item expanded "><a href="Chapter_23.html"><strong aria-hidden="true">24.</strong> Control flow</a></li><li class="chapter-item expanded "><a href="Chapter_24.html"><strong aria-hidden="true">25.</strong> Structs</a></li><li class="chapter-item expanded "><a href="Chapter_25.html"><strong aria-hidden="true">26.</strong> Enums</a></li><li class="chapter-item expanded "><a href="Chapter_26.html"><strong aria-hidden="true">27.</strong> Loops</a></li><li class="chapter-item expanded "><a href="Chapter_27.html"><strong aria-hidden="true">28.</strong> Implementing structs and enums</a></li><li class="chapter-item expanded "><a href="Chapter_28.html"><strong aria-hidden="true">29.</strong> Destructuring</a></li><li class="chapter-item expanded "><a href="Chapter_29.html"><strong aria-hidden="true">30.</strong> References and the dot operator</a></li><li class="chapter-item expanded "><a href="Chapter_30.html"><strong aria-hidden="true">31.</strong> Generics</a></li><li class="chapter-item expanded "><a href="Chapter_31.html"><strong aria-hidden="true">32.</strong> Option and Result</a></li><li class="chapter-item expanded "><a href="Chapter_32.html"><strong aria-hidden="true">33.</strong> Other collections</a></li><li class="chapter-item expanded "><a href="Chapter_33.html"><strong aria-hidden="true">34.</strong> The ? operator</a></li><li class="chapter-item expanded "><a href="Chapter_34.html"><strong aria-hidden="true">35.</strong> Traits</a></li><li class="chapter-item expanded "><a href="Chapter_35.html"><strong aria-hidden="true">36.</strong> Chaining methods</a></li><li class="chapter-item expanded "><a href="Chapter_36.html"><strong aria-hidden="true">37.</strong> Iterators</a></li><li class="chapter-item expanded "><a href="Chapter_37.html"><strong aria-hidden="true">38.</strong> Closures</a></li><li class="chapter-item expanded "><a href="Chapter_38.html"><strong aria-hidden="true">39.</strong> The dbg! macro and .inspect</a></li><li class="chapter-item expanded "><a href="Chapter_39.html"><strong aria-hidden="true">40.</strong> Types of &str</a></li><li class="chapter-item expanded "><a href="Chapter_40.html"><strong aria-hidden="true">41.</strong> Lifetimes</a></li><li class="chapter-item expanded "><a href="Chapter_41.html"><strong aria-hidden="true">42.</strong> Interior mutability</a></li><li class="chapter-item expanded "><a href="Chapter_42.html"><strong aria-hidden="true">43.</strong> Cow</a></li><li class="chapter-item expanded "><a href="Chapter_43.html"><strong aria-hidden="true">44.</strong> Type aliases</a></li><li class="chapter-item expanded "><a href="Chapter_44.html"><strong aria-hidden="true">45.</strong> The todo! macro</a></li><li class="chapter-item expanded "><a href="Chapter_45.html"><strong aria-hidden="true">46.</strong> Rc</a></li><li class="chapter-item expanded "><a href="Chapter_46.html"><strong aria-hidden="true">47.</strong> Multiple threads</a></li><li class="chapter-item expanded "><a href="Chapter_47.html"><strong aria-hidden="true">48.</strong> Closures in functions</a></li><li class="chapter-item expanded "><a href="Chapter_48.html"><strong aria-hidden="true">49.</strong> impl Trait</a></li><li class="chapter-item expanded "><a href="Chapter_49.html"><strong aria-hidden="true">50.</strong> Arc</a></li><li class="chapter-item expanded "><a href="Chapter_50.html"><strong aria-hidden="true">51.</strong> Channels</a></li><li class="chapter-item expanded "><a href="Chapter_51.html"><strong aria-hidden="true">52.</strong> Reading Rust documentation</a></li><li class="chapter-item expanded "><a href="Chapter_52.html"><strong aria-hidden="true">53.</strong> Attributes</a></li><li class="chapter-item expanded "><a href="Chapter_53.html"><strong aria-hidden="true">54.</strong> Box</a></li><li class="chapter-item expanded "><a href="Chapter_54.html"><strong aria-hidden="true">55.</strong> Box around traits</a></li><li class="chapter-item expanded "><a href="Chapter_55.html"><strong aria-hidden="true">56.</strong> Default and the builder pattern</a></li><li class="chapter-item expanded "><a href="Chapter_56.html"><strong aria-hidden="true">57.</strong> Deref and DerefMut</a></li><li class="chapter-item expanded "><a href="Chapter_57.html"><strong aria-hidden="true">58.</strong> Crates and modules</a></li><li class="chapter-item expanded "><a href="Chapter_58.html"><strong aria-hidden="true">59.</strong> Testing</a></li><li class="chapter-item expanded "><a href="Chapter_59.html"><strong aria-hidden="true">60.</strong> External crates</a></li><li class="chapter-item expanded "><a href="Chapter_60.html"><strong aria-hidden="true">61.</strong> A tour of the standard library</a></li><li class="chapter-item expanded "><a href="Chapter_61.html"><strong aria-hidden="true">62.</strong> Writing macros</a></li><li class="chapter-item expanded "><a href="Chapter_62.html"><strong aria-hidden="true">63.</strong> cargo</a></li><li class="chapter-item expanded "><a href="Chapter_63.html"><strong aria-hidden="true">64.</strong> Taking user input</a></li><li class="chapter-item expanded "><a href="Chapter_64.html"><strong aria-hidden="true">65.</strong> Using files</a></li><li class="chapter-item expanded "><a href="Chapter_65.html"><strong aria-hidden="true">66.</strong> cargo doc</a></li><li class="chapter-item expanded "><a href="Chapter_66.html"><strong aria-hidden="true">67.</strong> The end?</a></li></ol>
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<main>
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<h2 id="more-about-printing"><a class="header" href="#more-about-printing">More about printing</a></h2>
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<p>In Rust you can print things in almost any way you want. Here are some more things to know about printing.</p>
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<p>Adding <code>\n</code> will make a new line, and <code>\t</code> will make a tab:</p>
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<pre><pre class="playground"><code class="language-rust">fn main() {
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// Note: this is print!, not println!
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print!("\t Start with a tab\nand move to a new line");
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}
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</code></pre></pre>
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<p>This prints:</p>
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<pre><code class="language-text"> Start with a tab
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and move to a new line
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</code></pre>
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<p>Inside <code>""</code> you can write over many lines with no problem, but be careful with the spacing:</p>
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<pre><pre class="playground"><code class="language-rust">fn main() {
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// Note: After the first line you have to start on the far left.
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// If you write directly under println!, it will add the spaces
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println!("Inside quotes
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you can write over
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many lines
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and it will print just fine.");
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println!("If you forget to write
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on the left side, the spaces
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will be added when you print.");
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}
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</code></pre></pre>
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<p>This prints:</p>
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<pre><code class="language-text">Inside quotes
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you can write over
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many lines
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and it will print just fine.
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If you forget to write
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on the left side, the spaces
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will be added when you print.
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</code></pre>
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<p>If you want to print characters like <code>\n</code> (called "escape characters"), you can add an extra <code>\</code>:</p>
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<pre><pre class="playground"><code class="language-rust">fn main() {
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println!("Here are two escape characters: \\n and \\t");
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}
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</code></pre></pre>
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<p>This prints:</p>
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<pre><code class="language-text">Here are two escape characters: \n and \t
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</code></pre>
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<p>Sometimes you have too many <code>"</code> and escape characters, and want Rust to ignore everything. To do this, you can add <code>r#</code> to the beginning and <code>#</code> to the end.</p>
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<pre><pre class="playground"><code class="language-rust">fn main() {
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println!("He said, \"You can find the file at c:\\files\\my_documents\\file.txt.\" Then I found the file."); // We used \ five times here
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println!(r#"He said, "You can find the file at c:\files\my_documents\file.txt." Then I found the file."#)
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}
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</code></pre></pre>
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<p>This prints the same thing, but using <code>r#</code> makes it easier for humans to read.</p>
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<pre><code class="language-text">He said, "You can find the file at c:\files\my_documents\file.txt." Then I found the file.
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He said, "You can find the file at c:\files\my_documents\file.txt." Then I found the file.
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</code></pre>
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<p>If you need to print with a <code>#</code> inside, then you can start with <code>r##</code> and end with <code>##</code>. And if you need more than one, you can add one more # on each side.</p>
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<p>Here are four examples:</p>
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<pre><pre class="playground"><code class="language-rust">fn main() {
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let my_string = "'Ice to see you,' he said."; // single quotes
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let quote_string = r#""Ice to see you," he said."#; // double quotes
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let hashtag_string = r##"The hashtag #IceToSeeYou had become very popular."##; // Has one # so we need at least ##
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let many_hashtags = r####""You don't have to type ### to use a hashtag. You can just use #.""####; // Has three ### so we need at least ####
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println!("{}\n{}\n{}\n{}\n", my_string, quote_string, hashtag_string, many_hashtags);
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}
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</code></pre></pre>
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<p>This will print:</p>
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<pre><code class="language-text">'Ice to see you,' he said.
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"Ice to see you," he said.
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The hashtag #IceToSeeYou had become very popular.
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"You don't have to type ### to use a hashtag. You can just use #."
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</code></pre>
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<p><code>r#</code> has another use: with it you can use a keyword (words like <code>let</code>, <code>fn</code>, etc.) as a variable name.</p>
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<pre><pre class="playground"><code class="language-rust">fn main() {
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let r#let = 6; // The variable's name is let
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let mut r#mut = 10; // This variable's name is mut
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}
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</code></pre></pre>
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<p><code>r#</code> has this function because older versions of Rust had fewer keywords than Rust now. So with <code>r#</code> you can avoid mistakes with variable names that were not keywords before.</p>
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<p>Or maybe for some reason you <em>really</em> need a function to have a name like <code>return</code>. Then you can write this:</p>
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<pre><pre class="playground"><code class="language-rust">fn r#return() -> u8 {
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println!("Here is your number.");
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8
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}
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fn main() {
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let my_number = r#return();
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println!("{}", my_number);
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}
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</code></pre></pre>
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<p>This prints:</p>
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<pre><code class="language-text">Here is your number.
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8
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</code></pre>
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<p>So you probably won't need it, but if you really need to use a keyword for a variable then you can use <code>r#</code>.</p>
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<p>If you want to print the bytes of a <code>&str</code> or a <code>char</code>, you can just write <code>b</code> before the string. This works for all ASCII characters. These are all the ASCII characters:</p>
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<pre><code class="language-text">☺☻♥♦♣♠♫☼►◄↕‼¶§▬↨↑↓→∟↔▲▼123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~
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</code></pre>
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<p>So when you print this:</p>
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<pre><pre class="playground"><code class="language-rust">fn main() {
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println!("{:?}", b"This will look like numbers");
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}
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</code></pre></pre>
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<p>Here is the result:</p>
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<pre><code class="language-text">[84, 104, 105, 115, 32, 119, 105, 108, 108, 32, 108, 111, 111, 107, 32, 108, 105, 107, 101, 32, 110, 117, 109, 98, 101, 114, 115]
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</code></pre>
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<p>For a <code>char</code> this is called a <em>byte</em>, and for a <code>&str</code> it's called a <em>byte string</em>.</p>
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<p>You can also put <code>b</code> and <code>r</code> together if you need to:</p>
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<pre><pre class="playground"><code class="language-rust">fn main() {
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println!("{:?}", br##"I like to write "#"."##);
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}
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</code></pre></pre>
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<p>That will print <code>[73, 32, 108, 105, 107, 101, 32, 116, 111, 32, 119, 114, 105, 116, 101, 32, 34, 35, 34, 46]</code>.</p>
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<p>There is also a Unicode escape that lets you print any Unicode character inside a string: <code>\u{}</code>. A hexadecimal number goes inside the <code>{}</code> to print it. Here is a short example of how to get the Unicode number, and how to print it again.</p>
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<pre><pre class="playground"><code class="language-rust">fn main() {
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println!("{:X}", '행' as u32); // Cast char as u32 to get the hexadecimal value
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println!("{:X}", 'H' as u32);
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println!("{:X}", '居' as u32);
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println!("{:X}", 'い' as u32);
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println!("\u{D589}, \u{48}, \u{5C45}, \u{3044}"); // Try printing them with unicode escape \u
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}
|
|
</code></pre></pre>
|
|
<p>We know that <code>println!</code> can print with <code>{}</code> (for Display) and <code>{:?}</code> (for Debug), plus <code>{:#?}</code> for pretty printing. But there are many other ways to print.</p>
|
|
<p>For example, if you have a reference, you can use <code>{:p}</code> to print the <em>pointer address</em>. Pointer address means the location in your computer's memory.</p>
|
|
<pre><pre class="playground"><code class="language-rust">fn main() {
|
|
let number = 9;
|
|
let number_ref = &number;
|
|
println!("{:p}", number_ref);
|
|
}
|
|
</code></pre></pre>
|
|
<p>This prints <code>0xe2bc0ffcfc</code> or some other address. It might be different every time, depending on where your computer stores it.</p>
|
|
<p>Or you can print binary, hexadecimal and octal:</p>
|
|
<pre><pre class="playground"><code class="language-rust">fn main() {
|
|
let number = 555;
|
|
println!("Binary: {:b}, hexadecimal: {:x}, octal: {:o}", number, number, number);
|
|
}
|
|
</code></pre></pre>
|
|
<p>This prints <code>Binary: 1000101011, hexadecimal: 22b, octal: 1053</code>.</p>
|
|
<p>Or you can add numbers to change the order. The first variable will be in index 0, the next in index 1, and so on.</p>
|
|
<pre><pre class="playground"><code class="language-rust">fn main() {
|
|
let father_name = "Vlad";
|
|
let son_name = "Adrian Fahrenheit";
|
|
let family_name = "Țepeș";
|
|
println!("This is {1} {2}, son of {0} {2}.", father_name, son_name, family_name);
|
|
}
|
|
</code></pre></pre>
|
|
<p><code>father_name</code> is in position 0, <code>son_name</code> is in position 1, and <code>family_name</code> is in position 2. So it prints <code>This is Adrian Fahrenheit Țepeș, son of Vlad Țepeș</code>.</p>
|
|
<p>Maybe you have a very complex string to print with too many variables inside the <code>{}</code> curly brackets. Or maybe you need to print a variable more than one time. Then it can help to add names to the <code>{}</code>:</p>
|
|
<pre><pre class="playground"><code class="language-rust">fn main() {
|
|
println!(
|
|
"{city1} is in {country} and {city2} is also in {country},
|
|
but {city3} is not in {country}.",
|
|
city1 = "Seoul",
|
|
city2 = "Busan",
|
|
city3 = "Tokyo",
|
|
country = "Korea"
|
|
);
|
|
}
|
|
</code></pre></pre>
|
|
<p>That will print:</p>
|
|
<pre><code class="language-text">Seoul is in Korea and Busan is also in Korea,
|
|
but Tokyo is not in Korea.
|
|
</code></pre>
|
|
<p>Very complex printing is also possible in Rust if you want to use it. Here is how to do it:</p>
|
|
<p>{variable:padding alignment minimum.maximum}</p>
|
|
<p>To understand this, look at the</p>
|
|
<ol>
|
|
<li>Do you want a variable name? Write that first, like when we wrote {country} above.
|
|
(Then add a <code>:</code> after it if you want to do more things)</li>
|
|
<li>Do you want a padding character? For example, 55 with three "padding zeros" looks like 00055.</li>
|
|
<li>What alignment (left / middle / right) for the padding?</li>
|
|
<li>Do you want a minimum length? (just write a number)</li>
|
|
<li>Do you want a maximum length? (write a number with a <code>.</code> in front)</li>
|
|
</ol>
|
|
<p>For example, if I want to write "a" with five ㅎ characters on the left and five ㅎ characters on the right:</p>
|
|
<pre><pre class="playground"><code class="language-rust">fn main() {
|
|
let letter = "a";
|
|
println!("{:ㅎ^11}", letter);
|
|
}
|
|
</code></pre></pre>
|
|
<p>This prints <code>ㅎㅎㅎㅎㅎaㅎㅎㅎㅎㅎ</code>. Let's look at 1) to 5) for this to understand how the compiler reads it.</p>
|
|
<ul>
|
|
<li>Do you want a variable name? <code>{:ㅎ^11}</code> There is no variable name. There is nothing before <code>:</code>.</li>
|
|
<li>Do you want a padding character? <code>{:ㅎ^11}</code> Yes. ㅎ comes after the <code>:</code> and has a <code>^</code>. <code><</code> means padding with the character on the left, <code>></code> means on the right, and <code>^</code> means in the middle.</li>
|
|
<li>Do you want a minimum length? <code>{:ㅎ^11}</code> Yes: there is an 11 after.</li>
|
|
<li>Do you want a maximum length? <code>{:ㅎ^11}</code> No: there is no number with a <code>.</code> before.</li>
|
|
</ul>
|
|
<p>Here is an example of many types of formatting.</p>
|
|
<pre><pre class="playground"><code class="language-rust">fn main() {
|
|
let title = "TODAY'S NEWS";
|
|
println!("{:-^30}", title); // no variable name, pad with -, put in centre, 30 characters long
|
|
let bar = "|";
|
|
println!("{: <15}{: >15}", bar, bar); // no variable name, pad with space, 15 characters each, one to the left, one to the right
|
|
let a = "SEOUL";
|
|
let b = "TOKYO";
|
|
println!("{city1:-<15}{city2:->15}", city1 = a, city2 = b); // variable names city1 and city2, pad with -, one to the left, one to the right
|
|
}
|
|
</code></pre></pre>
|
|
<p>It prints:</p>
|
|
<pre><code class="language-text">---------TODAY'S NEWS---------
|
|
| |
|
|
SEOUL--------------------TOKYO
|
|
</code></pre>
|
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