<!DOCTYPE HTML>
< html lang = "zh-CN" class = "light sidebar-visible" dir = "ltr" >
< head >
<!-- Book generated using mdBook -->
< meta charset = "UTF-8" >
< title > 字符串与切片 - Rust语言圣经(Rust Course)< / title >
<!-- Custom HTML head -->
< meta name = "description" content = "" >
< meta name = "viewport" content = "width=device-width, initial-scale=1" >
< meta name = "theme-color" content = "#ffffff" >
< link rel = "icon" href = "../../favicon-de23e50b.svg" >
< link rel = "shortcut icon" href = "../../favicon-8114d1fc.png" >
< link rel = "stylesheet" href = "../../css/variables-8adf115d.css" >
< link rel = "stylesheet" href = "../../css/general-2459343d.css" >
< link rel = "stylesheet" href = "../../css/chrome-ae938929.css" >
< link rel = "stylesheet" href = "../../css/print-9e4910d8.css" media = "print" >
<!-- Fonts -->
< link rel = "stylesheet" href = "../../fonts/fonts-9644e21d.css" >
<!-- Highlight.js Stylesheets -->
< link rel = "stylesheet" id = "mdbook-highlight-css" href = "../../highlight-493f70e1.css" >
< link rel = "stylesheet" id = "mdbook-tomorrow-night-css" href = "../../tomorrow-night-4c0ae647.css" >
< link rel = "stylesheet" id = "mdbook-ayu-highlight-css" href = "../../ayu-highlight-3fdfc3ac.css" >
<!-- Custom theme stylesheets -->
< link rel = "stylesheet" href = "../../theme/style-78591068.css" >
<!-- Provide site root and default themes to javascript -->
< script >
const path_to_root = "../../";
const default_light_theme = "light";
const default_dark_theme = "navy";
window.path_to_searchindex_js = "../../searchindex-848c21ce.js";
< / script >
<!-- Start loading toc.js asap -->
< script src = "../../toc-42887675.js" > < / script >
< / head >
< body >
< div id = "mdbook-help-container" >
< div id = "mdbook-help-popup" >
< h2 class = "mdbook-help-title" > Keyboard shortcuts< / h2 >
< div >
< p > Press < kbd > ←< / kbd > or < kbd > →< / kbd > to navigate between chapters< / p >
< p > Press < kbd > S< / kbd > or < kbd > /< / kbd > to search in the book< / p >
< p > Press < kbd > ?< / kbd > to show this help< / p >
< p > Press < kbd > Esc< / kbd > to hide this help< / p >
< / div >
< / div >
< / div >
< div id = "mdbook-body-container" >
<!-- Work around some values being stored in localStorage wrapped in quotes -->
< script >
try {
let theme = localStorage.getItem('mdbook-theme');
let sidebar = localStorage.getItem('mdbook-sidebar');
if (theme.startsWith('"') & & theme.endsWith('"')) {
localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1));
}
if (sidebar.startsWith('"') & & sidebar.endsWith('"')) {
localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1));
}
} catch (e) { }
< / script >
<!-- Set the theme before any content is loaded, prevents flash -->
< script >
const default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? default_dark_theme : default_light_theme;
let theme;
try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
if (theme === null || theme === undefined) { theme = default_theme; }
const html = document.documentElement;
html.classList.remove('light')
html.classList.add(theme);
html.classList.add("js");
< / script >
< input type = "checkbox" id = "mdbook-sidebar-toggle-anchor" class = "hidden" >
<!-- Hide / unhide sidebar before it is displayed -->
< script >
let sidebar = null;
const sidebar_toggle = document.getElementById("mdbook-sidebar-toggle-anchor");
if (document.body.clientWidth >= 1080) {
try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
sidebar = sidebar || 'visible';
} else {
sidebar = 'hidden';
sidebar_toggle.checked = false;
}
if (sidebar === 'visible') {
sidebar_toggle.checked = true;
} else {
html.classList.remove('sidebar-visible');
}
< / script >
< nav id = "mdbook-sidebar" class = "sidebar" aria-label = "Table of contents" >
<!-- populated by js -->
< mdbook-sidebar-scrollbox class = "sidebar-scrollbox" > < / mdbook-sidebar-scrollbox >
< noscript >
< iframe class = "sidebar-iframe-outer" src = "../../toc.html" > < / iframe >
< / noscript >
< div id = "mdbook-sidebar-resize-handle" class = "sidebar-resize-handle" >
< div class = "sidebar-resize-indicator" > < / div >
< / div >
< / nav >
< div id = "mdbook-page-wrapper" class = "page-wrapper" >
< div class = "page" >
< div id = "mdbook-menu-bar-hover-placeholder" > < / div >
< div id = "mdbook-menu-bar" class = "menu-bar sticky" >
< div class = "left-buttons" >
< label id = "mdbook-sidebar-toggle" class = "icon-button" for = "mdbook-sidebar-toggle-anchor" title = "Toggle Table of Contents" aria-label = "Toggle Table of Contents" aria-controls = "mdbook-sidebar" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 448 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M0 96C0 78.3 14.3 64 32 64H416c17.7 0 32 14.3 32 32s-14.3 32-32 32H32C14.3 128 0 113.7 0 96zM0 256c0-17.7 14.3-32 32-32H416c17.7 0 32 14.3 32 32s-14.3 32-32 32H32c-17.7 0-32-14.3-32-32zM448 416c0 17.7-14.3 32-32 32H32c-17.7 0-32-14.3-32-32s14.3-32 32-32H416c17.7 0 32 14.3 32 32z" / > < / svg > < / span >
< / label >
< button id = "mdbook-theme-toggle" class = "icon-button" type = "button" title = "Change theme" aria-label = "Change theme" aria-haspopup = "true" aria-expanded = "false" aria-controls = "mdbook-theme-list" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 576 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M371.3 367.1c27.3-3.9 51.9-19.4 67.2-42.9L600.2 74.1c12.6-19.5 9.4-45.3-7.6-61.2S549.7-4.4 531.1 9.6L294.4 187.2c-24 18-38.2 46.1-38.4 76.1L371.3 367.1zm-19.6 25.4l-116-104.4C175.9 290.3 128 339.6 128 400c0 3.9 .2 7.8 .6 11.6c1.8 17.5-10.2 36.4-27.8 36.4H96c-17.7 0-32 14.3-32 32s14.3 32 32 32H240c61.9 0 112-50.1 112-112c0-2.5-.1-5-.2-7.5z" / > < / svg > < / span >
< / button >
< ul id = "mdbook-theme-list" class = "theme-popup" aria-label = "Themes" role = "menu" >
< li role = "none" > < button role = "menuitem" class = "theme" id = "mdbook-theme-default_theme" > Auto< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "mdbook-theme-light" > Light< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "mdbook-theme-rust" > Rust< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "mdbook-theme-coal" > Coal< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "mdbook-theme-navy" > Navy< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "mdbook-theme-ayu" > Ayu< / button > < / li >
< / ul >
< button id = "mdbook-search-toggle" class = "icon-button" type = "button" title = "Search (`/`)" aria-label = "Toggle Searchbar" aria-expanded = "false" aria-keyshortcuts = "/ s" aria-controls = "mdbook-searchbar" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 512 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M416 208c0 45.9-14.9 88.3-40 122.7L502.6 457.4c12.5 12.5 12.5 32.8 0 45.3s-32.8 12.5-45.3 0L330.7 376c-34.4 25.2-76.8 40-122.7 40C93.1 416 0 322.9 0 208S93.1 0 208 0S416 93.1 416 208zM208 352c79.5 0 144-64.5 144-144s-64.5-144-144-144S64 128.5 64 208s64.5 144 144 144z" / > < / svg > < / span >
< / button >
< / div >
< h1 class = "menu-title" > Rust语言圣经(Rust Course)< / h1 >
< div class = "right-buttons" >
< a href = "../../print.html" title = "Print this book" aria-label = "Print this book" >
< span class = fa-svg id = "print-button" > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 512 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M128 0C92.7 0 64 28.7 64 64v96h64V64H354.7L384 93.3V160h64V93.3c0-17-6.7-33.3-18.7-45.3L400 18.7C388 6.7 371.7 0 354.7 0H128zM384 352v32 64H128V384 368 352H384zm64 32h32c17.7 0 32-14.3 32-32V256c0-35.3-28.7-64-64-64H64c-35.3 0-64 28.7-64 64v96c0 17.7 14.3 32 32 32H64v64c0 35.3 28.7 64 64 64H384c35.3 0 64-28.7 64-64V384zm-16-88c-13.3 0-24-10.7-24-24s10.7-24 24-24s24 10.7 24 24s-10.7 24-24 24z" / > < / svg > < / span >
< / a >
< a href = "https://github.com/sunface/rust-course" title = "Git repository" aria-label = "Git repository" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 496 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M165.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6zm-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3zm44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9zM244.8 8C106.1 8 0 113.3 0 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C428.2 457.8 496 362.9 496 252 496 113.3 383.5 8 244.8 8zM97.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1zm-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7zm32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1zm-11.4-14.7c-1.6 1-1.6 3.6 0 5.9 1.6 2.3 4.3 3.3 5.6 2.3 1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2z" / > < / svg > < / span >
< / a >
< a href = "https://github.com/sunface/rust-course/edit/main/src/basic/compound-type/string-slice.md" title = "Suggest an edit" aria-label = "Suggest an edit" rel = "edit" >
< span class = fa-svg id = "git-edit-button" > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 512 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M421.7 220.3l-11.3 11.3-22.6 22.6-205 205c-6.6 6.6-14.8 11.5-23.8 14.1L30.8 511c-8.4 2.5-17.5 .2-23.7-6.1S-1.5 489.7 1 481.2L38.7 353.1c2.6-9 7.5-17.2 14.1-23.8l205-205 22.6-22.6 11.3-11.3 33.9 33.9 62.1 62.1 33.9 33.9zM96 353.9l-9.3 9.3c-.9 .9-1.6 2.1-2 3.4l-25.3 86 86-25.3c1.3-.4 2.5-1.1 3.4-2l9.3-9.3H112c-8.8 0-16-7.2-16-16V353.9zM453.3 19.3l39.4 39.4c25 25 25 65.5 0 90.5l-14.5 14.5-22.6 22.6-11.3 11.3-33.9-33.9-62.1-62.1L314.3 67.7l11.3-11.3 22.6-22.6 14.5-14.5c25-25 65.5-25 90.5 0z" / > < / svg > < / span >
< / a >
< / div >
< / div >
< div id = "mdbook-search-wrapper" class = "hidden" >
< form id = "mdbook-searchbar-outer" class = "searchbar-outer" >
< div class = "search-wrapper" >
< input type = "search" id = "mdbook-searchbar" name = "searchbar" placeholder = "Search this book ..." aria-controls = "mdbook-searchresults-outer" aria-describedby = "searchresults-header" >
< div class = "spinner-wrapper" >
< span class = fa-svg id = "fa-spin" > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 512 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M304 48c0-26.5-21.5-48-48-48s-48 21.5-48 48s21.5 48 48 48s48-21.5 48-48zm0 416c0-26.5-21.5-48-48-48s-48 21.5-48 48s21.5 48 48 48s48-21.5 48-48zM48 304c26.5 0 48-21.5 48-48s-21.5-48-48-48s-48 21.5-48 48s21.5 48 48 48zm464-48c0-26.5-21.5-48-48-48s-48 21.5-48 48s21.5 48 48 48s48-21.5 48-48zM142.9 437c18.7-18.7 18.7-49.1 0-67.9s-49.1-18.7-67.9 0s-18.7 49.1 0 67.9s49.1 18.7 67.9 0zm0-294.2c18.7-18.7 18.7-49.1 0-67.9S93.7 56.2 75 75s-18.7 49.1 0 67.9s49.1 18.7 67.9 0zM369.1 437c18.7 18.7 49.1 18.7 67.9 0s18.7-49.1 0-67.9s-49.1-18.7-67.9 0s-18.7 49.1 0 67.9z" / > < / svg > < / span >
< / div >
< / div >
< / form >
< div id = "mdbook-searchresults-outer" class = "searchresults-outer hidden" >
< div id = "mdbook-searchresults-header" class = "searchresults-header" > < / div >
< ul id = "mdbook-searchresults" >
< / ul >
< / div >
< / div >
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
< script >
document.getElementById('mdbook-sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
document.getElementById('mdbook-sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
Array.from(document.querySelectorAll('#mdbook-sidebar a')).forEach(function(link) {
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
});
< / script >
< div id = "mdbook-content" class = "content" >
< main >
< h1 id = "字符串" > < a class = "header" href = "#字符串" > 字符串< / a > < / h1 >
< p > 在其他语言中，字符串往往是送分题，因为实在是太简单了，例如 < code > "hello, world"< / code > 就是字符串章节的几乎全部内容了，但是如果你带着同样的想法来学 Rust， ， ， < strong > 因此这一章大家一定要重视，仔细阅读，这里有很多其它 Rust 书籍中没有的内容< / strong > 。< / p >
< p > 首先来看段很简单的代码：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
let my_name = "Pascal";
greet(my_name);
}
fn greet(name: String) {
println!("Hello, {}!", name);
}< / code > < / pre >
< p > < code > greet< / code > 函数接受字符串类型的 < code > name< / code > 参数，打印到终端控制台中，非常好理解。但大家猜猜，这段代码能否通过编译？< / p >
< pre > < code class = "language-console" > error[E0308]: mismatched types
--> src/main.rs:3:11
|
3 | greet(my_name);
| ^^^^^^^
| |
| expected struct `std::string::String`, found `& str`
| help: try using a conversion method: `my_name.to_string()`
error: aborting due to previous error
< / code > < / pre >
< p > Bingo， ， < code > greet< / code > 函数需要一个 < code > String< / code > 类型的字符串，却传入了一个 < code > & str< / code > 类型的字符串，相信读者心中现在一定有几头草泥马呼啸而过，怎么字符串也能整出这么多花活？< / p >
< p > 在讲解字符串之前，先来看看什么是切片?< / p >
< h2 id = "切片slice" > < a class = "header" href = "#切片slice" > 切片(slice)< / a > < / h2 >
< p > 切片并不是 Rust 独有的概念，在 Go 语言中就非常流行，它允许你引用集合中部分连续的元素序列，而不是引用整个集合。< / p >
< p > 对于字符串而言，切片就是对 < code > String< / code > 类型中某一部分的引用，它看起来像这样：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > let s = String::from("hello world");
let hello = & s[0..5];
let world = & s[6..11];
< span class = "boring" > }< / span > < / code > < / pre >
< p > < code > hello< / code > 没有引用整个 < code > String s< / code > ，而是引用了 < code > s< / code > 的一部分内容，通过 < code > [0..5]< / code > 的方式来指定。< / p >
< p > 这就是创建切片的语法，使用方括号包括的一个序列：< strong > [开始索引..终止索引]< / strong > ，其中开始索引是切片中第一个元素的索引位置，而终止索引是最后一个元素后面的索引位置。换句话说，这是一个 < code > 右半开区间< / code > （或称为左闭右开区间）——指的是在区间的左端点是包含在内的，而右端点是不包含在内的。在切片数据结构内部会保存开始的位置和切片的长度，其中长度是通过 < code > 终止索引< / code > - < code > 开始索引< / code > 的方式计算得来的。< / p >
< p > 对于 < code > let world = & s[6..11];< / code > 来说，< code > world< / code > 是一个切片，该切片的指针指向 < code > s< / code > 的第 7 个字节(索引从 0 开始, 6 是第 7 个字节)，且该切片的长度是 < code > 5< / code > 个字节。< / p >
< img alt = "" src = "https://pic1.zhimg.com/80/v2-69da917741b2c610732d8526a9cc86f5_1440w.jpg" class = "center" style = "width: 50%;" / >
< p > 在使用 Rust 的 < code > ..< / code > < a href = "https://course.rs/basic/base-type/numbers.html#序列range" > range 序列< / a > 语法时，如果你想从索引 0 开始，可以使用如下的方式，这两个是等效的：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > let s = String::from("hello");
let slice = & s[0..2];
let slice = & s[..2];
< span class = "boring" > }< / span > < / code > < / pre >
< p > 同样的，如果你的切片想要包含 < code > String< / code > 的最后一个字节，则可以这样使用：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > let s = String::from("hello");
let len = s.len();
let slice = & s[4..len];
let slice = & s[4..];
< span class = "boring" > }< / span > < / code > < / pre >
< p > 你也可以截取完整的 < code > String< / code > 切片：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > let s = String::from("hello");
let len = s.len();
let slice = & s[0..len];
let slice = & s[..];
< span class = "boring" > }< / span > < / code > < / pre >
< blockquote >
< p > 在对字符串使用切片语法时需要格外小心，切片的索引必须落在字符之间的边界位置，也就是 UTF-8 字符的边界，例如中文在 UTF-8 中占用三个字节，下面的代码就会崩溃：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > let s = "中国人";
let a = & s[0..2];
println!("{}",a);
< span class = "boring" > }< / span > < / code > < / pre >
< p > 因为我们只取 < code > s< / code > 字符串的前两个字节，但是本例中每个汉字占用三个字节，因此没有落在边界处，也就是连 < code > 中< / code > 字都取不完整，此时程序会直接崩溃退出，如果改成 < code > & s[0..3]< / code > ，则可以正常通过编译。
因此，当你需要对字符串做切片索引操作时，需要格外小心这一点，关于该如何操作 UTF-8 字符串，参见< a href = "#操作-utf-8-字符串" > 这里< / a > 。< / p >
< / blockquote >
< p > 字符串切片的类型标识是 < code > & str< / code > ，因此我们可以这样声明一个函数，输入 < code > String< / code > 类型，返回它的切片：< code > fn first_word(s: & String) -> & str < / code > 。< / p >
< p > 有了切片就可以写出这样的代码：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
let mut s = String::from("hello world");
let word = first_word(& s);
s.clear(); // error!
println!("the first word is: {}", word);
}
fn first_word(s: & String) -> & str {
& s[..1]
}< / code > < / pre >
< p > 编译器报错如下：< / p >
< pre > < code class = "language-console" > error[E0502]: cannot borrow `s` as mutable because it is also borrowed as immutable
--> src/main.rs:18:5
|
16 | let word = first_word(& s);
| -- immutable borrow occurs here
17 |
18 | s.clear(); // error!
| ^^^^^^^^^ mutable borrow occurs here
19 |
20 | println!("the first word is: {}", word);
| ---- immutable borrow later used here
< / code > < / pre >
< p > 回忆一下借用的规则：当我们已经有了可变借用时，就无法再拥有不可变的借用。因为 < code > clear< / code > 需要清空改变 < code > String< / code > ，因此它需要一个可变借用（利用 VSCode 可以看到该方法的声明是 < code > pub fn clear(& mut self)< / code > ，参数是对自身的可变借用 ）；而之后的 < code > println!< / code > 又使用了不可变借用，也就是在 < code > s.clear()< / code > 处可变借用与不可变借用试图同时生效，因此编译无法通过。< / p >
< p > 从上述代码可以看出， < code > API< / code > 更加容易使用，而且也在编译期就消除了大量错误！< / p >
< h4 id = "其它切片" > < a class = "header" href = "#其它切片" > 其它切片< / a > < / h4 >
< p > 因为切片是对集合的部分引用，因此不仅仅字符串有切片，其它集合类型也有，例如数组：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > let a = [1, 2, 3, 4, 5];
let slice = & a[1..3];
assert_eq!(slice, & [2, 3]);
< span class = "boring" > }< / span > < / code > < / pre >
< p > 该数组切片的类型是 < code > & [i32]< / code > ，数组切片和字符串切片的工作方式是一样的，例如持有一个引用指向原始数组的某个元素和长度。< / p >
< h2 id = "字符串字面量是切片" > < a class = "header" href = "#字符串字面量是切片" > 字符串字面量是切片< / a > < / h2 >
< p > 之前提到过字符串字面量，但是没有提到它的类型：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > let s = "Hello, world!";
< span class = "boring" > }< / span > < / code > < / pre >
< p > 实际上，< code > s< / code > 的类型是 < code > & str< / code > ，因此你也可以这样声明：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > let s: & str = "Hello, world!";
< span class = "boring" > }< / span > < / code > < / pre >
< p > 该切片指向了程序可执行文件中的某个点，这也是为什么字符串字面量是不可变的，因为 < code > & str< / code > 是一个不可变引用。< / p >
< p > 了解完切片，可以进入本节的正题了。< / p >
< h2 id = "什么是字符串" > < a class = "header" href = "#什么是字符串" > 什么是字符串?< / a > < / h2 >
< p > 顾名思义，字符串是由字符组成的连续集合，但是在上一节中我们提到过，< strong > Rust 中的字符是 Unicode 类型，因此每个字符占据 4 个字节内存空间，但是在字符串中不一样，字符串是 UTF-8 编码，也就是字符串中的字符所占的字节数是变化的(1 - 4)< / strong > ，这样有助于大幅降低字符串所占用的内存空间。< / p >
< p > Rust 在语言级别，只有一种字符串类型： < code > str< / code > ，它通常是以引用类型出现 < code > & str< / code > ，也就是上文提到的字符串切片。虽然语言级别只有上述的 < code > str< / code > 类型，但是在标准库里，还有多种不同用途的字符串类型，其中使用最广的即是 < code > String< / code > 类型。< / p >
< p > < code > str< / code > 类型是硬编码进可执行文件，也无法被修改，但是 < code > String< / code > 则是一个可增长、可改变且具有所有权的 UTF-8 编码字符串，< strong > 当 Rust 用户提到字符串时，往往指的就是 < code > String< / code > 类型和 < code > & str< / code > 字符串切片类型，这两个类型都是 UTF-8 编码< / strong > 。< / p >
< p > 除了 < code > String< / code > 类型的字符串， < code > OsString< / code > ， < code > OsStr< / code > ， < code > CString< / code > 和 < code > CStr< / code > 等，注意到这些名字都以 < code > String< / code > 或者 < code > Str< / code > 结尾了吗？它们分别对应的是具有所有权和被借用的变量。< / p >
< h2 id = "string-与-str-的转换" > < a class = "header" href = "#string-与-str-的转换" > String 与 & str 的转换< / a > < / h2 >
< p > 在之前的代码中，已经见到好几种从 < code > & str< / code > 类型生成 < code > String< / code > 类型的操作：< / p >
< ul >
< li > < code > String::from("hello,world")< / code > < / li >
< li > < code > "hello,world".to_string()< / code > < / li >
< / ul >
< p > 那么如何将 < code > String< / code > 类型转为 < code > & str< / code > 类型呢？答案很简单，取引用即可：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
let s = String::from("hello,world!");
say_hello(& s);
say_hello(& s[..]);
say_hello(s.as_str());
}
fn say_hello(s: & str) {
println!("{}",s);
}< / code > < / pre >
< p > 实际上这种灵活用法是因为 < code > deref< / code > 隐式强制转换，具体我们会在 < a href = "https://course.rs/advance/smart-pointer/deref.html" > < code > Deref< / code > 特征< / a > 进行详细讲解。< / p >
< h2 id = "字符串索引" > < a class = "header" href = "#字符串索引" > 字符串索引< / a > < / h2 >
< p > 在其它语言中，使用索引的方式访问字符串的某个字符或者子串是很正常的行为，但是在 Rust 中就会报错：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > let s1 = String::from("hello");
let h = s1[0];
< span class = "boring" > }< / span > < / code > < / pre >
< p > 该代码会产生如下错误：< / p >
< pre > < code class = "language-console" > 3 | let h = s1[0];
| ^^^^^ `String` cannot be indexed by `{integer}`
|
= help: the trait `Index< {integer}> ` is not implemented for `String`
< / code > < / pre >
< h4 id = "深入字符串内部" > < a class = "header" href = "#深入字符串内部" > 深入字符串内部< / a > < / h4 >
< p > 字符串的底层的数据存储格式实际上是[ < code > u8< / code > ]，一个字节数组。对于 < code > let hello = String::from("Hola");< / code > 这行代码来说，< code > Hola< / code > 的长度是 < code > 4< / code > 个字节，因为 < code > "Hola"< / code > 中的每个字母在 UTF-8 编码中仅占用 1 个字节，但是对于下面的代码呢？< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > let hello = String::from("中国人");
< span class = "boring" > }< / span > < / code > < / pre >
< p > 如果问你该字符串多长，你可能会说 < code > 3< / code > ，但是实际上是 < code > 9< / code > 个字节的长度，因为大部分常用汉字在 UTF-8 中的长度是 < code > 3< / code > 个字节，因此这种情况下对 < code > hello< / code > 进行索引，访问 < code > & hello[0]< / code > 没有任何意义，因为你取不到 < code > 中< / code > 这个字符，而是取到了这个字符三个字节中的第一个字节，这是一个非常奇怪而且难以理解的返回值。< / p >
< h4 id = "字符串的不同表现形式" > < a class = "header" href = "#字符串的不同表现形式" > 字符串的不同表现形式< / a > < / h4 >
< p > 现在看一下用梵文写的字符串 < code > “नमस्ते”< / code > , 它底层的字节数组如下形式：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > [224, 164, 168, 224, 164, 174, 224, 164, 184, 224, 165, 141, 224, 164, 164,
224, 165, 135]
< span class = "boring" > }< / span > < / code > < / pre >
< p > 长度是 18 个字节，这也是计算机最终存储该字符串的形式。如果从字符的形式去看，则是：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > ['न', 'म', 'स', '्', 'त', 'े']
< span class = "boring" > }< / span > < / code > < / pre >
< p > 但是这种形式下，第四和六两个字母根本就不存在，没有任何意义，接着再从字母串的形式去看：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > ["न", "म", "स्", "ते"]
< span class = "boring" > }< / span > < / code > < / pre >
< p > 所以，可以看出来 Rust 提供了不同的字符串展现方式，这样程序可以挑选自己想要的方式去使用，而无需去管字符串从人类语言角度看长什么样。< / p >
< p > 还有一个原因导致了 Rust 不允许去索引字符串：因为索引操作，我们总是期望它的性能表现是 O(1)，然而对于 < code > String< / code > 类型来说，无法保证这一点，因为 Rust 可能需要从 0 开始去遍历字符串来定位合法的字符。< / p >
< h2 id = "字符串切片" > < a class = "header" href = "#字符串切片" > 字符串切片< / a > < / h2 >
< p > 前文提到过，字符串切片是非常危险的操作，因为切片的索引是通过字节来进行，但是字符串又是 UTF-8 编码，因此你无法保证索引的字节刚好落在字符的边界上，例如：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > let hello = "中国人";
let s = & hello[0..2];
< span class = "boring" > }< / span > < / code > < / pre >
< p > 运行上面的程序，会直接造成崩溃：< / p >
< pre > < code class = "language-console" > thread 'main' panicked at 'byte index 2 is not a char boundary; it is inside '中' (bytes 0..3) of `中国人`', src/main.rs:4:14
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
< / code > < / pre >
< p > 这里提示的很清楚，我们索引的字节落在了 < code > 中< / code > 字符的内部，这种返回没有任何意义。< / p >
< p > 因此在通过索引区间来访问字符串时，< strong > 需要格外的小心< / strong > ，一不注意，就会导致你程序的崩溃！< / p >
< h2 id = "操作字符串" > < a class = "header" href = "#操作字符串" > 操作字符串< / a > < / h2 >
< p > 由于 < code > String< / code > 是可变字符串，下面介绍 Rust 字符串的修改，添加，删除等常用方法：< / p >
< h4 id = "追加-push" > < a class = "header" href = "#追加-push" > 追加 (Push)< / a > < / h4 >
< p > 在字符串尾部可以使用 < code > push()< / code > 方法追加字符 < code > char< / code > ，也可以使用 < code > push_str()< / code > 方法追加字符串字面量。这两个方法都是< strong > 在原有的字符串上追加，并不会返回新的字符串< / strong > 。由于字符串追加操作要修改原来的字符串，则该字符串必须是可变的，即< strong > 字符串变量必须由 < code > mut< / code > 关键字修饰< / strong > 。< / p >
< p > 示例代码如下：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
let mut s = String::from("Hello ");
s.push_str("rust");
println!("追加字符串 push_str() -> {}", s);
s.push('!');
println!("追加字符 push() -> {}", s);
}< / code > < / pre >
< p > 代码运行结果：< / p >
< pre > < code class = "language-console" > 追加字符串 push_str() -> Hello rust
追加字符 push() -> Hello rust!
< / code > < / pre >
< h4 id = "插入-insert" > < a class = "header" href = "#插入-insert" > 插入 (Insert)< / a > < / h4 >
< p > 可以使用 < code > insert()< / code > 方法插入单个字符 < code > char< / code > ，也可以使用 < code > insert_str()< / code > 方法插入字符串字面量，与 < code > push()< / code > 方法不同，这俩方法需要传入两个参数，第一个参数是字符（串）插入位置的索引，第二个参数是要插入的字符（串），索引从 0 开始计数，如果越界则会发生错误。由于字符串插入操作要< strong > 修改原来的字符串< / strong > ，则该字符串必须是可变的，即< strong > 字符串变量必须由 < code > mut< / code > 关键字修饰< / strong > 。< / p >
< p > 示例代码如下：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
let mut s = String::from("Hello rust!");
s.insert(5, ',');
println!("插入字符 insert() -> {}", s);
s.insert_str(6, " I like");
println!("插入字符串 insert_str() -> {}", s);
}< / code > < / pre >
< p > 代码运行结果：< / p >
< pre > < code class = "language-console" > 插入字符 insert() -> Hello, rust!
插入字符串 insert_str() -> Hello, I like rust!
< / code > < / pre >
< h4 id = "替换-replace" > < a class = "header" href = "#替换-replace" > 替换 (Replace)< / a > < / h4 >
< p > 如果想要把字符串中的某个字符串替换成其它的字符串，那可以使用 < code > replace()< / code > 方法。与替换有关的方法有三个。< / p >
< p > 1、< code > replace< / code > < / p >
< p > 该方法可适用于 < code > String< / code > 和 < code > & str< / code > 类型。< code > replace()< / code > 方法接收两个参数，第一个参数是要被替换的字符串，第二个参数是新的字符串。该方法会替换所有匹配到的字符串。< strong > 该方法是返回一个新的字符串，而不是操作原来的字符串< / strong > 。< / p >
< p > 示例代码如下：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
let string_replace = String::from("I like rust. Learning rust is my favorite!");
let new_string_replace = string_replace.replace("rust", "RUST");
dbg!(new_string_replace);
}< / code > < / pre >
< p > 代码运行结果：< / p >
< pre > < code class = "language-console" > new_string_replace = "I like RUST. Learning RUST is my favorite!"
< / code > < / pre >
< p > 2、< code > replacen< / code > < / p >
< p > 该方法可适用于 < code > String< / code > 和 < code > & str< / code > 类型。< code > replacen()< / code > 方法接收三个参数，前两个参数与 < code > replace()< / code > 方法一样，第三个参数则表示替换的个数。< strong > 该方法是返回一个新的字符串，而不是操作原来的字符串< / strong > 。< / p >
< p > 示例代码如下：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
let string_replace = "I like rust. Learning rust is my favorite!";
let new_string_replacen = string_replace.replacen("rust", "RUST", 1);
dbg!(new_string_replacen);
}< / code > < / pre >
< p > 代码运行结果：< / p >
< pre > < code class = "language-console" > new_string_replacen = "I like RUST. Learning rust is my favorite!"
< / code > < / pre >
< p > 3、< code > replace_range< / code > < / p >
< p > 该方法仅适用于 < code > String< / code > 类型。< code > replace_range< / code > 接收两个参数， （ ） ， < strong > 该方法是直接操作原来的字符串，不会返回新的字符串。该方法需要使用 < code > mut< / code > 关键字修饰< / strong > 。< / p >
< p > 示例代码如下：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
let mut string_replace_range = String::from("I like rust!");
string_replace_range.replace_range(7..8, "R");
dbg!(string_replace_range);
}< / code > < / pre >
< p > 代码运行结果：< / p >
< pre > < code class = "language-console" > string_replace_range = "I like Rust!"
< / code > < / pre >
< h4 id = "删除-delete" > < a class = "header" href = "#删除-delete" > 删除 (Delete)< / a > < / h4 >
< p > 与字符串删除相关的方法有 4 个，它们分别是 < code > pop()< / code > ， < code > remove()< / code > ， < code > truncate()< / code > ， < code > clear()< / code > 。这四个方法仅适用于 < code > String< / code > 类型。< / p >
< p > 1、 < code > pop< / code > —— 删除并返回字符串的最后一个字符< / p >
< p > < strong > 该方法是直接操作原来的字符串< / strong > 。但是存在返回值，其返回值是一个 < code > Option< / code > 类型，如果字符串为空，则返回 < code > None< / code > 。< / p >
< p > 示例代码如下：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
let mut string_pop = String::from("rust pop 中文!");
let p1 = string_pop.pop();
let p2 = string_pop.pop();
dbg!(p1);
dbg!(p2);
dbg!(string_pop);
}< / code > < / pre >
< p > 代码运行结果：< / p >
< pre > < code class = "language-console" > p1 = Some(
'!',
)
p2 = Some(
'文',
)
string_pop = "rust pop 中"
< / code > < / pre >
< p > 2、 < code > remove< / code > —— 删除并返回字符串中指定位置的字符< / p >
< p > < strong > 该方法是直接操作原来的字符串< / strong > 。但是存在返回值，其返回值是删除位置的字符串，只接收一个参数，表示该字符起始索引位置。< code > remove()< / code > 方法是按照字节来处理字符串的，如果参数所给的位置不是合法的字符边界，则会发生错误。< / p >
< p > 示例代码如下：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
let mut string_remove = String::from("测试remove方法");
println!(
"string_remove 占 {} 个字节",
std::mem::size_of_val(string_remove.as_str())
);
// 删除第一个汉字
string_remove.remove(0);
// 下面代码会发生错误
// string_remove.remove(1);
// 直接删除第二个汉字
// string_remove.remove(3);
dbg!(string_remove);
}< / code > < / pre >
< p > 代码运行结果：< / p >
< pre > < code class = "language-console" > string_remove 占 18 个字节
string_remove = "试remove方法"
< / code > < / pre >
< p > 3、< code > truncate< / code > —— 删除字符串中从指定位置开始到结尾的全部字符< / p >
< p > < strong > 该方法是直接操作原来的字符串< / strong > 。无返回值。该方法 < code > truncate()< / code > 方法是按照字节来处理字符串的，如果参数所给的位置不是合法的字符边界，则会发生错误。< / p >
< p > 示例代码如下：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
let mut string_truncate = String::from("测试truncate");
string_truncate.truncate(3);
dbg!(string_truncate);
}< / code > < / pre >
< p > 代码运行结果：< / p >
< pre > < code class = "language-console" > string_truncate = "测"
< / code > < / pre >
< p > 4、< code > clear< / code > —— 清空字符串< / p >
< p > < strong > 该方法是直接操作原来的字符串< / strong > 。调用后，删除字符串中的所有字符，相当于 < code > truncate()< / code > 方法参数为 0 的时候。< / p >
< p > 示例代码如下：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
let mut string_clear = String::from("string clear");
string_clear.clear();
dbg!(string_clear);
}< / code > < / pre >
< p > 代码运行结果：< / p >
< pre > < code class = "language-console" > string_clear = ""
< / code > < / pre >
< h4 id = "连接-concatenate" > < a class = "header" href = "#连接-concatenate" > 连接 (Concatenate)< / a > < / h4 >
< p > 1、使用 < code > +< / code > 或者 < code > +=< / code > 连接字符串< / p >
< p > 使用 < code > +< / code > 或者 < code > +=< / code > 连接字符串， （ ） < code > +< / code > 的操作符时，相当于调用了 < code > std::string< / code > 标准库中的 < a href = "https://doc.rust-lang.org/std/string/struct.String.html#method.add" > < code > add()< / code > < / a > 方法，这里 < code > add()< / code > 方法的第二个参数是一个引用的类型。因此我们在使用 < code > +< / code > 时， 必须传递切片引用类型。不能直接传递 < code > String< / code > 类型。< strong > < code > +< / code > 是返回一个新的字符串，所以变量声明可以不需要 < code > mut< / code > 关键字修饰< / strong > 。< / p >
< p > 示例代码如下：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
let string_append = String::from("hello ");
let string_rust = String::from("rust");
// & string_rust会自动解引用为& str
let result = string_append + & string_rust;
let mut result = result + "!"; // `result + "!"` 中的 `result` 是不可变的
result += "!!!";
println!("连接字符串 + -> {}", result);
}< / code > < / pre >
< p > 代码运行结果：< / p >
< pre > < code class = "language-console" > 连接字符串 + -> hello rust!!!!
< / code > < / pre >
< p > < code > add()< / code > 方法的定义：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > fn add(self, s: & str) -> String
< span class = "boring" > }< / span > < / code > < / pre >
< p > 因为该方法涉及到更复杂的特征功能，因此我们这里简单说明下：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
let s1 = String::from("hello,");
let s2 = String::from("world!");
// 在下句中， ，
let s3 = s1 + & s2;
assert_eq!(s3,"hello,world!");
// 下面的语句如果去掉注释，就会报错
// println!("{}",s1);
}< / code > < / pre >
< p > < code > self< / code > 是 < code > String< / code > 类型的字符串 < code > s1< / code > ，该函数说明，只能将 < code > & str< / code > 类型的字符串切片添加到 < code > String< / code > 类型的 < code > s1< / code > 上，然后返回一个新的 < code > String< / code > 类型，所以 < code > let s3 = s1 + & s2;< / code > 就很好解释了，将 < code > String< / code > 类型的 < code > s1< / code > 与 < code > & str< / code > 类型的 < code > s2< / code > 进行相加，最终得到 < code > String< / code > 类型的 < code > s3< / code > 。< / p >
< p > 由此可推，以下代码也是合法的：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > let s1 = String::from("tic");
let s2 = String::from("tac");
let s3 = String::from("toe");
// String = String + & str + & str + & str + & str
let s = s1 + "-" + & s2 + "-" + & s3;
< span class = "boring" > }< / span > < / code > < / pre >
< p > < code > String + & str< / code > 返回一个 < code > String< / code > ，然后再继续跟一个 < code > & str< / code > 进行 < code > +< / code > 操作，返回一个 < code > String< / code > 类型，不断循环，最终生成一个 < code > s< / code > ，也是 < code > String< / code > 类型。< / p >
< p > < code > s1< / code > 这个变量通过调用 < code > add()< / code > 方法后，所有权被转移到 < code > add()< / code > 方法里面， < code > add()< / code > 方法调用后就被释放了，同时 < code > s1< / code > 也被释放了。再使用 < code > s1< / code > 就会发生错误。这里涉及到< a href = "https://course.rs/basic/ownership/ownership.html#转移所有权" > 所有权转移（ ） < / a > 的相关知识。< / p >
< p > 2、使用 < code > format!< / code > 连接字符串< / p >
< p > < code > format!< / code > 这种方式适用于 < code > String< / code > 和 < code > & str< / code > 。< code > format!< / code > 的用法与 < code > print!< / code > 的用法类似，详见< a href = "https://course.rs/basic/formatted-output.html#printprintlnformat" > 格式化输出< / a > 。< / p >
< p > 示例代码如下：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
let s1 = "hello";
let s2 = String::from("rust");
let s = format!("{} {}!", s1, s2);
println!("{}", s);
}
< / code > < / pre >
< p > 代码运行结果：< / p >
< pre > < code class = "language-console" > hello rust!
< / code > < / pre >
< h2 id = "字符串转义" > < a class = "header" href = "#字符串转义" > 字符串转义< / a > < / h2 >
< p > 我们可以通过转义的方式 < code > \< / code > 输出 ASCII 和 Unicode 字符。< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
// 通过 \ + 字符的十六进制表示，转义输出一个字符
let byte_escape = "I'm writing \x52\x75\x73\x74!";
println!("What are you doing\x3F (\\x3F means ?) {}", byte_escape);
// \u 可以输出一个 unicode 字符
let unicode_codepoint = "\u{211D}";
let character_name = "\"DOUBLE-STRUCK CAPITAL R\"";
println!(
"Unicode character {} (U+211D) is called {}",
unicode_codepoint, character_name
);
// 换行了也会保持之前的字符串格式
// 使用\忽略换行符
let long_string = "String literals
can span multiple lines.
The linebreak and indentation here -> \
< - can be escaped too!";
println!("{}", long_string);
}< / code > < / pre >
< p > 当然，在某些情况下，可能你会希望保持字符串的原样，不要转义：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > fn main() {
println!("{}", "hello \\x52\\x75\\x73\\x74");
let raw_str = r"Escapes don't work here: \x3F \u{211D}";
println!("{}", raw_str);
// 如果字符串包含双引号，可以在开头和结尾加 #
let quotes = r#"And then I said: "There is no escape!""#;
println!("{}", quotes);
// 如果字符串中包含 # 号，可以在开头和结尾加多个 # 号， ，
let longer_delimiter = r###"A string with "# in it. And even "##!"###;
println!("{}", longer_delimiter);
}< / code > < / pre >
< h2 id = "操作-utf-8-字符串" > < a class = "header" href = "#操作-utf-8-字符串" > 操作 UTF-8 字符串< / a > < / h2 >
< p > 前文提到了几种使用 UTF-8 字符串的方式，下面来一一说明。< / p >
< h4 id = "字符" > < a class = "header" href = "#字符" > 字符< / a > < / h4 >
< p > 如果你想要以 Unicode 字符的方式遍历字符串，最好的办法是使用 < code > chars< / code > 方法，例如：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > for c in "中国人".chars() {
println!("{}", c);
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 输出如下< / p >
< pre > < code class = "language-console" > 中
国
人
< / code > < / pre >
< h4 id = "字节" > < a class = "header" href = "#字节" > 字节< / a > < / h4 >
< p > 这种方式是返回字符串的底层字节数组表现形式：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > for b in "中国人".bytes() {
println!("{}", b);
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 输出如下：< / p >
< pre > < code class = "language-console" > 228
184
173
229
155
189
228
186
186
< / code > < / pre >
< h4 id = "获取子串" > < a class = "header" href = "#获取子串" > 获取子串< / a > < / h4 >
< p > 想要准确的从 UTF-8 字符串中获取子串是较为复杂的事情，例如想要从 < code > holla中国人नमस्ते< / code > 这种变长的字符串中取出某一个子串，使用标准库你是做不到的。
你需要在 < code > crates.io< / code > 上搜索 < code > utf8< / code > 来寻找想要的功能。< / p >
< p > 可以考虑尝试下这个库：< a href = "https://crates.io/crates/utf8_slice" > utf8_slice< / a > 。< / p >
< h2 id = "字符串深度剖析" > < a class = "header" href = "#字符串深度剖析" > 字符串深度剖析< / a > < / h2 >
< p > 那么问题来了，为啥 < code > String< / code > 可变，而字符串字面值 < code > str< / code > 却不可以？< / p >
< p > 就字符串字面值来说，我们在编译时就知道其内容，最终字面值文本被直接硬编码进可执行文件中，这使得字符串字面值快速且高效，这主要得益于字符串字面值的不可变性。不幸的是，我们不能为了获得这种性能，而把每一个在编译时大小未知的文本都放进内存中（你也做不到！），因为有的字符串是在程序运行的过程中动态生成的。< / p >
< p > 对于 < code > String< / code > 类型，为了支持一个可变、可增长的文本片段，需要在堆上分配一块在编译时未知大小的内存来存放内容，这些都是在程序运行时完成的：< / p >
< ul >
< li > 首先向操作系统请求内存来存放 < code > String< / code > 对象< / li >
< li > 在使用完成后，将内存释放，归还给操作系统< / li >
< / ul >
< p > 其中第一部分由 < code > String::from< / code > 完成，它创建了一个全新的 < code > String< / code > 。< / p >
< p > 重点来了，到了第二部分，就是百家齐放的环节，在有< strong > 垃圾回收 GC< / strong > 的语言中， < / p >
< p > 对于 Rust 而言，安全和性能是写到骨子里的核心特性，如果使用 GC， ； ， ， ？ ， < / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > {
let s = String::from("hello"); // 从此处起，
// 使用 s
} // 此作用域已结束，
// s 不再有效，内存被释放
< span class = "boring" > }< / span > < / code > < / pre >
< p > 与其它系统编程语言的 < code > free< / code > 函数相同， < code > drop< / code > ，但是不同的是，其它语言要手动调用 < code > free< / code > 来释放每一个变量占用的内存，而 Rust 则在变量离开作用域时，自动调用 < code > drop< / code > 函数： ， < code > }< / code > 处自动调用 < code > drop< / code > 。< / p >
< blockquote >
< p > 其实，在 C++ 中，也有这种概念：< em > Resource Acquisition Is Initialization (RAII)< / em > 。如果你使用过 RAII 模式的话应该对 Rust 的 < code > drop< / code > 函数并不陌生。< / p >
< / blockquote >
< p > 这个模式对编写 Rust 代码的方式有着深远的影响，在后面章节我们会进行更深入的介绍。< / p >
< h2 id = "课后练习" > < a class = "header" href = "#课后练习" > 课后练习< / a > < / h2 >
< blockquote >
< p > Rust By Practice， ， < / p >
< ul >
< li > < a href = "https://practice-zh.course.rs/compound-types/string.html" > 字符串< / a >
< ul >
< li > < a href = "https://github.com/sunface/rust-by-practice/blob/master/solutions/compound-types/string.md" > 习题解答< / a > < / li >
< / ul >
< / li >
< li > < a href = "https://practice-zh.course.rs/compound-types/slice.html" > 切片< / a >
< ul >
< li > < a href = "https://github.com/sunface/rust-by-practice/blob/master/solutions/compound-types/slice.md" > 习题解答< / a > < / li >
< / ul >
< / li >
< li > < a href = "https://practice-zh.course.rs/collections/string.html" > String< / a >
< ul >
< li > < a href = "https://github.com/sunface/rust-by-practice/blob/master/solutions/collections/String.md" > 习题解答< / a > < / li >
< / ul >
< / li >
< / ul >
< / blockquote >
< hr / >
< h2 id = "引用资料" > < a class = "header" href = "#引用资料" > 引用资料< / a > < / h2 >
< ol >
< li > https://blog.csdn.net/a1595901624/article/details/119294443< / li >
< / ol >
< / main >
< nav class = "nav-wrapper" aria-label = "Page navigation" >
<!-- Mobile navigation buttons -->
< a rel = "prev" href = "../../basic/compound-type/intro.html" class = "mobile-nav-chapters previous" title = "Previous chapter" aria-label = "Previous chapter" aria-keyshortcuts = "Left" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 320 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M41.4 233.4c-12.5 12.5-12.5 32.8 0 45.3l160 160c12.5 12.5 32.8 12.5 45.3 0s12.5-32.8 0-45.3L109.3 256 246.6 118.6c12.5-12.5 12.5-32.8 0-45.3s-32.8-12.5-45.3 0l-160 160z" / > < / svg > < / span >
< / a >
< a rel = "next prefetch" href = "../../basic/compound-type/tuple.html" class = "mobile-nav-chapters next" title = "Next chapter" aria-label = "Next chapter" aria-keyshortcuts = "Right" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 320 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M278.6 233.4c12.5 12.5 12.5 32.8 0 45.3l-160 160c-12.5 12.5-32.8 12.5-45.3 0s-12.5-32.8 0-45.3L210.7 256 73.4 118.6c-12.5-12.5-12.5-32.8 0-45.3s32.8-12.5 45.3 0l160 160z" / > < / svg > < / span >
< / a >
< div style = "clear: both" > < / div >
< / nav >
< / div >
< / div >
< nav class = "nav-wide-wrapper" aria-label = "Page navigation" >
< a rel = "prev" href = "../../basic/compound-type/intro.html" class = "nav-chapters previous" title = "Previous chapter" aria-label = "Previous chapter" aria-keyshortcuts = "Left" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 320 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M41.4 233.4c-12.5 12.5-12.5 32.8 0 45.3l160 160c12.5 12.5 32.8 12.5 45.3 0s12.5-32.8 0-45.3L109.3 256 246.6 118.6c12.5-12.5 12.5-32.8 0-45.3s-32.8-12.5-45.3 0l-160 160z" / > < / svg > < / span >
< / a >
< a rel = "next prefetch" href = "../../basic/compound-type/tuple.html" class = "nav-chapters next" title = "Next chapter" aria-label = "Next chapter" aria-keyshortcuts = "Right" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 320 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M278.6 233.4c12.5 12.5 12.5 32.8 0 45.3l-160 160c-12.5 12.5-32.8 12.5-45.3 0s-12.5-32.8 0-45.3L210.7 256 73.4 118.6c-12.5-12.5-12.5-32.8 0-45.3s32.8-12.5 45.3 0l160 160z" / > < / svg > < / span >
< / a >
< / nav >
< / div >
< template id = fa-eye > < span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 576 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M288 32c-80.8 0-145.5 36.8-192.6 80.6C48.6 156 17.3 208 2.5 243.7c-3.3 7.9-3.3 16.7 0 24.6C17.3 304 48.6 356 95.4 399.4C142.5 443.2 207.2 480 288 480s145.5-36.8 192.6-80.6c46.8-43.5 78.1-95.4 93-131.1c3.3-7.9 3.3-16.7 0-24.6c-14.9-35.7-46.2-87.7-93-131.1C433.5 68.8 368.8 32 288 32zM432 256c0 79.5-64.5 144-144 144s-144-64.5-144-144s64.5-144 144-144s144 64.5 144 144zM288 192c0 35.3-28.7 64-64 64c-11.5 0-22.3-3-31.6-8.4c-.2 2.8-.4 5.5-.4 8.4c0 53 43 96 96 96s96-43 96-96s-43-96-96-96c-2.8 0-5.6 .1-8.4 .4c5.3 9.3 8.4 20.1 8.4 31.6z" / > < / svg > < / span > < / template >
< template id = fa-eye-slash > < span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 640 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M38.8 5.1C28.4-3.1 13.3-1.2 5.1 9.2S-1.2 34.7 9.2 42.9l592 464c10.4 8.2 25.5 6.3 33.7-4.1s6.3-25.5-4.1-33.7L525.6 386.7c39.6-40.6 66.4-86.1 79.9-118.4c3.3-7.9 3.3-16.7 0-24.6c-14.9-35.7-46.2-87.7-93-131.1C465.5 68.8 400.8 32 320 32c-68.2 0-125 26.3-169.3 60.8L38.8 5.1zM223.1 149.5C248.6 126.2 282.7 112 320 112c79.5 0 144 64.5 144 144c0 24.9-6.3 48.3-17.4 68.7L408 294.5c5.2-11.8 8-24.8 8-38.5c0-53-43-96-96-96c-2.8 0-5.6 .1-8.4 .4c5.3 9.3 8.4 20.1 8.4 31.6c0 10.2-2.4 19.8-6.6 28.3l-90.3-70.8zm223.1 298L373 389.9c-16.4 6.5-34.3 10.1-53 10.1c-79.5 0-144-64.5-144-144c0-6.9 .5-13.6 1.4-20.2L83.1 161.5C60.3 191.2 44 220.8 34.5 243.7c-3.3 7.9-3.3 16.7 0 24.6c14.9 35.7 46.2 87.7 93 131.1C174.5 443.2 239.2 480 320 480c47.8 0 89.9-12.9 126.2-32.5z" / > < / svg > < / span > < / template >
< template id = fa-copy > < span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 512 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M502.6 70.63l-61.25-61.25C435.4 3.371 427.2 0 418.7 0H255.1c-35.35 0-64 28.66-64 64l.0195 256C192 355.4 220.7 384 256 384h192c35.2 0 64-28.8 64-64V93.25C512 84.77 508.6 76.63 502.6 70.63zM464 320c0 8.836-7.164 16-16 16H255.1c-8.838 0-16-7.164-16-16L239.1 64.13c0-8.836 7.164-16 16-16h128L384 96c0 17.67 14.33 32 32 32h47.1V320zM272 448c0 8.836-7.164 16-16 16H63.1c-8.838 0-16-7.164-16-16L47.98 192.1c0-8.836 7.164-16 16-16H160V128H63.99c-35.35 0-64 28.65-64 64l.0098 256C.002 483.3 28.66 512 64 512h192c35.2 0 64-28.8 64-64v-32h-47.1L272 448z" / > < / svg > < / span > < / template >
< template id = fa-play > < span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 384 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M73 39c-14.8-9.1-33.4-9.4-48.5-.9S0 62.6 0 80V432c0 17.4 9.4 33.4 24.5 41.9s33.7 8.1 48.5-.9L361 297c14.3-8.7 23-24.2 23-41s-8.7-32.2-23-41L73 39z" / > < / svg > < / span > < / template >
< template id = fa-clock-rotate-left > < span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 512 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M75 75L41 41C25.9 25.9 0 36.6 0 57.9V168c0 13.3 10.7 24 24 24H134.1c21.4 0 32.1-25.9 17-41l-30.8-30.8C155 85.5 203 64 256 64c106 0 192 86 192 192s-86 192-192 192c-40.8 0-78.6-12.7-109.7-34.4c-14.5-10.1-34.4-6.6-44.6 7.9s-6.6 34.4 7.9 44.6C151.2 495 201.7 512 256 512c141.4 0 256-114.6 256-256S397.4 0 256 0C185.3 0 121.3 28.7 75 75zm181 53c-13.3 0-24 10.7-24 24V256c0 6.4 2.5 12.5 7 17l72 72c9.4 9.4 24.6 9.4 33.9 0s9.4-24.6 0-33.9l-65-65V152c0-13.3-10.7-24-24-24z" / > < / svg > < / span > < / template >
< script >
window.playground_copyable = true;
< / script >
< script src = "../../ace-2a3cd908.js" > < / script >
< script src = "../../mode-rust-2c9d5c9a.js" > < / script >
< script src = "../../editor-16ca416c.js" > < / script >
< script src = "../../theme-dawn-4493f9c8.js" > < / script >
< script src = "../../theme-tomorrow_night-9dbe62a9.js" > < / script >
< script src = "../../elasticlunr-ef4e11c1.min.js" > < / script >
< script src = "../../mark-09e88c2c.min.js" > < / script >
< script src = "../../searcher-c2a407aa.js" > < / script >
< script src = "../../clipboard-1626706a.min.js" > < / script >
< script src = "../../highlight-abc7f01d.js" > < / script >
< script src = "../../book-a0b12cfe.js" > < / script >
<!-- Custom JS scripts -->
< script src = "../../assets/custom-7d8ae1df.js" > < / script >
< script src = "../../assets/bigPicture-be03f9c8.js" > < / script >
< / div >
< / body >
< / html >
