You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
trpl-zh-cn/ch03-02-data-types.html

458 lines
49 KiB

This file contains ambiguous Unicode characters!

This file contains ambiguous Unicode characters that may be confused with others in your current locale. If your use case is intentional and legitimate, you can safely ignore this warning. Use the Escape button to highlight these characters.

<!DOCTYPE HTML>
<html lang="en" class="light" dir="ltr">
<head>
<!-- Book generated using mdBook -->
<meta charset="UTF-8">
<title>数据类型 - Rust 程序设计语言 简体中文版</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.svg">
<link rel="shortcut icon" href="favicon.png">
<link rel="stylesheet" href="css/variables.css">
<link rel="stylesheet" href="css/general.css">
<link rel="stylesheet" href="css/chrome.css">
<link rel="stylesheet" href="css/print.css" media="print">
<!-- Fonts -->
<link rel="stylesheet" href="FontAwesome/css/font-awesome.css">
<link rel="stylesheet" href="fonts/fonts.css">
<!-- Highlight.js Stylesheets -->
<link rel="stylesheet" href="highlight.css">
<link rel="stylesheet" href="tomorrow-night.css">
<link rel="stylesheet" href="ayu-highlight.css">
<!-- Custom theme stylesheets -->
<link rel="stylesheet" href="ferris.css">
<link rel="stylesheet" href="theme/2018-edition.css">
<link rel="stylesheet" href="theme/semantic-notes.css">
<link rel="stylesheet" href="theme/listing.css">
</head>
<body class="sidebar-visible no-js">
<div id="body-container">
<!-- Provide site root to javascript -->
<script>
var path_to_root = "";
var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "navy" : "light";
</script>
<!-- Work around some values being stored in localStorage wrapped in quotes -->
<script>
try {
var theme = localStorage.getItem('mdbook-theme');
var 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>
var theme;
try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
if (theme === null || theme === undefined) { theme = default_theme; }
var html = document.querySelector('html');
html.classList.remove('light')
html.classList.add(theme);
var body = document.querySelector('body');
body.classList.remove('no-js')
body.classList.add('js');
</script>
<input type="checkbox" id="sidebar-toggle-anchor" class="hidden">
<!-- Hide / unhide sidebar before it is displayed -->
<script>
var body = document.querySelector('body');
var sidebar = null;
var sidebar_toggle = document.getElementById("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 = sidebar === 'visible';
body.classList.remove('sidebar-visible');
body.classList.add("sidebar-" + sidebar);
</script>
<nav id="sidebar" class="sidebar" aria-label="Table of contents">
<div class="sidebar-scrollbox">
<ol class="chapter"><li class="chapter-item expanded affix "><a href="title-page.html">Rust 程序设计语言</a></li><li class="chapter-item expanded affix "><a href="foreword.html">前言</a></li><li class="chapter-item expanded affix "><a href="ch00-00-introduction.html">简介</a></li><li class="chapter-item expanded "><a href="ch01-00-getting-started.html"><strong aria-hidden="true">1.</strong> 入门指南</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch01-01-installation.html"><strong aria-hidden="true">1.1.</strong> 安装</a></li><li class="chapter-item expanded "><a href="ch01-02-hello-world.html"><strong aria-hidden="true">1.2.</strong> Hello, World!</a></li><li class="chapter-item expanded "><a href="ch01-03-hello-cargo.html"><strong aria-hidden="true">1.3.</strong> Hello, Cargo!</a></li></ol></li><li class="chapter-item expanded "><a href="ch02-00-guessing-game-tutorial.html"><strong aria-hidden="true">2.</strong> 写个猜数字游戏</a></li><li class="chapter-item expanded "><a href="ch03-00-common-programming-concepts.html"><strong aria-hidden="true">3.</strong> 常见编程概念</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch03-01-variables-and-mutability.html"><strong aria-hidden="true">3.1.</strong> 变量与可变性</a></li><li class="chapter-item expanded "><a href="ch03-02-data-types.html" class="active"><strong aria-hidden="true">3.2.</strong> 数据类型</a></li><li class="chapter-item expanded "><a href="ch03-03-how-functions-work.html"><strong aria-hidden="true">3.3.</strong> 函数</a></li><li class="chapter-item expanded "><a href="ch03-04-comments.html"><strong aria-hidden="true">3.4.</strong> 注释</a></li><li class="chapter-item expanded "><a href="ch03-05-control-flow.html"><strong aria-hidden="true">3.5.</strong> 控制流</a></li></ol></li><li class="chapter-item expanded "><a href="ch04-00-understanding-ownership.html"><strong aria-hidden="true">4.</strong> 认识所有权</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch04-01-what-is-ownership.html"><strong aria-hidden="true">4.1.</strong> 什么是所有权?</a></li><li class="chapter-item expanded "><a href="ch04-02-references-and-borrowing.html"><strong aria-hidden="true">4.2.</strong> 引用与借用</a></li><li class="chapter-item expanded "><a href="ch04-03-slices.html"><strong aria-hidden="true">4.3.</strong> Slice 类型</a></li></ol></li><li class="chapter-item expanded "><a href="ch05-00-structs.html"><strong aria-hidden="true">5.</strong> 使用结构体组织相关联的数据</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch05-01-defining-structs.html"><strong aria-hidden="true">5.1.</strong> 结构体的定义和实例化</a></li><li class="chapter-item expanded "><a href="ch05-02-example-structs.html"><strong aria-hidden="true">5.2.</strong> 结构体示例程序</a></li><li class="chapter-item expanded "><a href="ch05-03-method-syntax.html"><strong aria-hidden="true">5.3.</strong> 方法语法</a></li></ol></li><li class="chapter-item expanded "><a href="ch06-00-enums.html"><strong aria-hidden="true">6.</strong> 枚举和模式匹配</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch06-01-defining-an-enum.html"><strong aria-hidden="true">6.1.</strong> 枚举的定义</a></li><li class="chapter-item expanded "><a href="ch06-02-match.html"><strong aria-hidden="true">6.2.</strong> match 控制流结构</a></li><li class="chapter-item expanded "><a href="ch06-03-if-let.html"><strong aria-hidden="true">6.3.</strong> if let 简洁控制流</a></li></ol></li><li class="chapter-item expanded "><a href="ch07-00-managing-growing-projects-with-packages-crates-and-modules.html"><strong aria-hidden="true">7.</strong> 使用包、Crate 和模块管理不断增长的项目</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch07-01-packages-and-crates.html"><strong aria-hidden="true">7.1.</strong> 包和 Crate</a></li><li class="chapter-item expanded "><a href="ch07-02-defining-modules-to-control-scope-and-privacy.html"><strong aria-hidden="true">7.2.</strong> 定义模块来控制作用域与私有性</a></li><li class="chapter-item expanded "><a href="ch07-03-paths-for-referring-to-an-item-in-the-module-tree.html"><strong aria-hidden="true">7.3.</strong> 引用模块项目的路径</a></li><li class="chapter-item expanded "><a href="ch07-04-bringing-paths-into-scope-with-the-use-keyword.html"><strong aria-hidden="true">7.4.</strong> 使用 use 关键字将路径引入作用域</a></li><li class="chapter-item expanded "><a href="ch07-05-separating-modules-into-different-files.html"><strong aria-hidden="true">7.5.</strong> 将模块拆分成多个文件</a></li></ol></li><li class="chapter-item expanded "><a href="ch08-00-common-collections.html"><strong aria-hidden="true">8.</strong> 常见集合</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch08-01-vectors.html"><strong aria-hidden="true">8.1.</strong> 使用 Vector 储存列表</a></li><li class="chapter-item expanded "><a href="ch08-02-strings.html"><strong aria-hidden="true">8.2.</strong> 使用字符串储存 UTF-8 编码的文本</a></li><li class="chapter-item expanded "><a href="ch08-03-hash-maps.html"><strong aria-hidden="true">8.3.</strong> 使用 Hash Map 储存键值对</a></li></ol></li><li class="chapter-item expanded "><a href="ch09-00-error-handling.html"><strong aria-hidden="true">9.</strong> 错误处理</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch09-01-unrecoverable-errors-with-panic.html"><strong aria-hidden="true">9.1.</strong> 用 panic! 处理不可恢复的错误</a></li><li class="chapter-item expanded "><a href="ch09-02-recoverable-errors-with-result.html"><strong aria-hidden="true">9.2.</strong> 用 Result 处理可恢复的错误</a></li><li class="chapter-item expanded "><a href="ch09-03-to-panic-or-not-to-panic.html"><strong aria-hidden="true">9.3.</strong> 要不要 panic!</a></li></ol></li><li class="chapter-item expanded "><a href="ch10-00-generics.html"><strong aria-hidden="true">10.</strong> 泛型、Trait 和生命周期</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch10-01-syntax.html"><strong aria-hidden="true">10.1.</strong> 泛型数据类型</a></li><li class="chapter-item expanded "><a href="ch10-02-traits.html"><strong aria-hidden="true">10.2.</strong> Trait定义共同行为</a></li><li class="chapter-item expanded "><a href="ch10-03-lifetime-syntax.html"><strong aria-hidden="true">10.3.</strong> 生命周期确保引用有效</a></li></ol></li><li class="chapter-item expanded "><a href="ch11-00-testing.html"><strong aria-hidden="true">11.</strong> 编写自动化测试</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch11-01-writing-tests.html"><strong aria-hidden="true">11.1.</strong> 如何编写测试</a></li><li class="chapter-item expanded "><a href="ch11-02-running-tests.html"><strong aria-hidden="true">11.2.</strong> 控制测试如何运行</a></li><li class="chapter-item expanded "><a href="ch11-03-test-organization.html"><strong aria-hidden="true">11.3.</strong> 测试的组织结构</a></li></ol></li><li class="chapter-item expanded "><a href="ch12-00-an-io-project.html"><strong aria-hidden="true">12.</strong> 一个 I/O 项目:构建命令行程序</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch12-01-accepting-command-line-arguments.html"><strong aria-hidden="true">12.1.</strong> 接受命令行参数</a></li><li class="chapter-item expanded "><a href="ch12-02-reading-a-file.html"><strong aria-hidden="true">12.2.</strong> 读取文件</a></li><li class="chapter-item expanded "><a href="ch12-03-improving-error-handling-and-modularity.html"><strong aria-hidden="true">12.3.</strong> 重构以改进模块化与错误处理</a></li><li class="chapter-item expanded "><a href="ch12-04-testing-the-librarys-functionality.html"><strong aria-hidden="true">12.4.</strong> 采用测试驱动开发完善库的功能</a></li><li class="chapter-item expanded "><a href="ch12-05-working-with-environment-variables.html"><strong aria-hidden="true">12.5.</strong> 处理环境变量</a></li><li class="chapter-item expanded "><a href="ch12-06-writing-to-stderr-instead-of-stdout.html"><strong aria-hidden="true">12.6.</strong> 将错误信息输出到标准错误而不是标准输出</a></li></ol></li><li class="chapter-item expanded "><a href="ch13-00-functional-features.html"><strong aria-hidden="true">13.</strong> Rust 中的函数式语言功能:迭代器与闭包</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch13-01-closures.html"><strong aria-hidden="true">13.1.</strong> 闭包:可以捕获其环境的匿名函数</a></li><li class="chapter-item expanded "><a href="ch13-02-iterators.html"><strong aria-hidden="true">13.2.</strong> 使用迭代器处理元素序列</a></li><li class="chapter-item expanded "><a href="ch13-03-improving-our-io-project.html"><strong aria-hidden="true">13.3.</strong> 改进之前的 I/O 项目</a></li><li class="chapter-item expanded "><a href="ch13-04-performance.html"><strong aria-hidden="true">13.4.</strong> 性能比较:循环对迭代器</a></li></ol></li><li class="chapter-item expanded "><a href="ch14-00-more-about-cargo.html"><strong aria-hidden="true">14.</strong> 更多关于 Cargo 和 Crates.io 的内容</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch14-01-release-profiles.html"><strong aria-hidden="true">14.1.</strong> 采用发布配置自定义构建</a></li><li class="chapter-item expanded "><a href="ch14-02-publishing-to-crates-io.html"><strong aria-hidden="true">14.2.</strong> 将 crate 发布到 Crates.io</a></li><li class="chapter-item expanded "><a href="ch14-03-cargo-workspaces.html"><strong aria-hidden="true">14.3.</strong> Cargo 工作空间</a></li><li class="chapter-item expanded "><a href="ch14-04-installing-binaries.html"><strong aria-hidden="true">14.4.</strong> 使用 cargo install 安装二进制文件</a></li><li class="chapter-item expanded "><a href="ch14-05-extending-cargo.html"><strong aria-hidden="true">14.5.</strong> Cargo 自定义扩展命令</a></li></ol></li><li class="chapter-item expanded "><a href="ch15-00-smart-pointers.html"><strong aria-hidden="true">15.</strong> 智能指针</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch15-01-box.html"><strong aria-hidden="true">15.1.</strong> 使用 Box&lt;T&gt; 指向堆上数据</a></li><li class="chapter-item expanded "><a href="ch15-02-deref.html"><strong aria-hidden="true">15.2.</strong> 使用 Deref Trait 将智能指针当作常规引用处理</a></li><li class="chapter-item expanded "><a href="ch15-03-drop.html"><strong aria-hidden="true">15.3.</strong> 使用 Drop Trait 运行清理代码</a></li><li class="chapter-item expanded "><a href="ch15-04-rc.html"><strong aria-hidden="true">15.4.</strong> Rc&lt;T&gt; 引用计数智能指针</a></li><li class="chapter-item expanded "><a href="ch15-05-interior-mutability.html"><strong aria-hidden="true">15.5.</strong> RefCell&lt;T&gt; 与内部可变性模式</a></li><li class="chapter-item expanded "><a href="ch15-06-reference-cycles.html"><strong aria-hidden="true">15.6.</strong> 引用循环会导致内存泄漏</a></li></ol></li><li class="chapter-item expanded "><a href="ch16-00-concurrency.html"><strong aria-hidden="true">16.</strong> 无畏并发</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch16-01-threads.html"><strong aria-hidden="true">16.1.</strong> 使用线程同时地运行代码</a></li><li class="chapter-item expanded "><a href="ch16-02-message-passing.html"><strong aria-hidden="true">16.2.</strong> 使用消息传递在线程间通信</a></li><li class="chapter-item expanded "><a href="ch16-03-shared-state.html"><strong aria-hidden="true">16.3.</strong> 共享状态并发</a></li><li class="chapter-item expanded "><a href="ch16-04-extensible-concurrency-sync-and-send.html"><strong aria-hidden="true">16.4.</strong> 使用 Sync 与 Send Traits 的可扩展并发</a></li></ol></li><li class="chapter-item expanded "><a href="ch17-00-async-await.html"><strong aria-hidden="true">17.</strong> Async 和 await</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch17-01-futures-and-syntax.html"><strong aria-hidden="true">17.1.</strong> Futures 和 async 语法</a></li><li class="chapter-item expanded "><a href="ch17-02-concurrency-with-async.html"><strong aria-hidden="true">17.2.</strong> 并发与 async</a></li><li class="chapter-item expanded "><a href="ch17-03-more-futures.html"><strong aria-hidden="true">17.3.</strong> 使用任意数量的 futures</a></li><li class="chapter-item expanded "><a href="ch17-04-streams.html"><strong aria-hidden="true">17.4.</strong>Streams</a></li><li class="chapter-item expanded "><a href="ch17-05-traits-for-async.html"><strong aria-hidden="true">17.5.</strong> 深入理解 async 相关的 traits</a></li><li class="chapter-item expanded "><a href="ch17-06-futures-tasks-threads.html"><strong aria-hidden="true">17.6.</strong> Futures任务tasks和线程threads</a></li></ol></li><li class="chapter-item expanded "><a href="ch18-00-oop.html"><strong aria-hidden="true">18.</strong> Rust 的面向对象编程特性</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch18-01-what-is-oo.html"><strong aria-hidden="true">18.1.</strong> 面向对象语言的特点</a></li><li class="chapter-item expanded "><a href="ch18-02-trait-objects.html"><strong aria-hidden="true">18.2.</strong> 顾及不同类型值的 trait 对象</a></li><li class="chapter-item expanded "><a href="ch18-03-oo-design-patterns.html"><strong aria-hidden="true">18.3.</strong> 面向对象设计模式的实现</a></li></ol></li><li class="chapter-item expanded "><a href="ch19-00-patterns.html"><strong aria-hidden="true">19.</strong> 模式与模式匹配</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch19-01-all-the-places-for-patterns.html"><strong aria-hidden="true">19.1.</strong> 所有可能会用到模式的位置</a></li><li class="chapter-item expanded "><a href="ch19-02-refutability.html"><strong aria-hidden="true">19.2.</strong> Refutability可反驳性: 模式是否会匹配失效</a></li><li class="chapter-item expanded "><a href="ch19-03-pattern-syntax.html"><strong aria-hidden="true">19.3.</strong> 模式语法</a></li></ol></li><li class="chapter-item expanded "><a href="ch20-00-advanced-features.html"><strong aria-hidden="true">20.</strong> 高级特征</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch20-01-unsafe-rust.html"><strong aria-hidden="true">20.1.</strong> 不安全的 Rust</a></li><li class="chapter-item expanded "><a href="ch20-03-advanced-traits.html"><strong aria-hidden="true">20.2.</strong> 高级 trait</a></li><li class="chapter-item expanded "><a href="ch20-04-advanced-types.html"><strong aria-hidden="true">20.3.</strong> 高级类型</a></li><li class="chapter-item expanded "><a href="ch20-05-advanced-functions-and-closures.html"><strong aria-hidden="true">20.4.</strong> 高级函数与闭包</a></li><li class="chapter-item expanded "><a href="ch20-06-macros.html"><strong aria-hidden="true">20.5.</strong></a></li></ol></li><li class="chapter-item expanded "><a href="ch21-00-final-project-a-web-server.html"><strong aria-hidden="true">21.</strong> 最后的项目:构建多线程 web server</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch21-01-single-threaded.html"><strong aria-hidden="true">21.1.</strong> 建立单线程 web server</a></li><li class="chapter-item expanded "><a href="ch21-02-multithreaded.html"><strong aria-hidden="true">21.2.</strong> 将单线程 server 变为多线程 server</a></li><li class="chapter-item expanded "><a href="ch21-03-graceful-shutdown-and-cleanup.html"><strong aria-hidden="true">21.3.</strong> 优雅停机与清理</a></li></ol></li><li class="chapter-item expanded "><a href="appendix-00.html"><strong aria-hidden="true">22.</strong> 附录</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="appendix-01-keywords.html"><strong aria-hidden="true">22.1.</strong> A - 关键字</a></li><li class="chapter-item expanded "><a href="appendix-02-operators.html"><strong aria-hidden="true">22.2.</strong> B - 运算符与符号</a></li><li class="chapter-item expanded "><a href="appendix-03-derivable-traits.html"><strong aria-hidden="true">22.3.</strong> C - 可派生的 trait</a></li><li class="chapter-item expanded "><a href="appendix-04-useful-development-tools.html"><strong aria-hidden="true">22.4.</strong> D - 实用开发工具</a></li><li class="chapter-item expanded "><a href="appendix-05-editions.html"><strong aria-hidden="true">22.5.</strong> E - 版本</a></li><li class="chapter-item expanded "><a href="appendix-06-translation.html"><strong aria-hidden="true">22.6.</strong> F - 本书译本</a></li><li class="chapter-item expanded "><a href="appendix-07-nightly-rust.html"><strong aria-hidden="true">22.7.</strong> G - Rust 是如何开发的与 “Nightly Rust”</a></li></ol></li></ol>
</div>
<div id="sidebar-resize-handle" class="sidebar-resize-handle">
<div class="sidebar-resize-indicator"></div>
</div>
</nav>
<!-- Track and set sidebar scroll position -->
<script>
var sidebarScrollbox = document.querySelector('#sidebar .sidebar-scrollbox');
sidebarScrollbox.addEventListener('click', function(e) {
if (e.target.tagName === 'A') {
sessionStorage.setItem('sidebar-scroll', sidebarScrollbox.scrollTop);
}
}, { passive: true });
var sidebarScrollTop = sessionStorage.getItem('sidebar-scroll');
sessionStorage.removeItem('sidebar-scroll');
if (sidebarScrollTop) {
// preserve sidebar scroll position when navigating via links within sidebar
sidebarScrollbox.scrollTop = sidebarScrollTop;
} else {
// scroll sidebar to current active section when navigating via "next/previous chapter" buttons
var activeSection = document.querySelector('#sidebar .active');
if (activeSection) {
activeSection.scrollIntoView({ block: 'center' });
}
}
</script>
<div id="page-wrapper" class="page-wrapper">
<div class="page">
<div id="menu-bar-hover-placeholder"></div>
<div id="menu-bar" class="menu-bar sticky">
<div class="left-buttons">
<label id="sidebar-toggle" class="icon-button" for="sidebar-toggle-anchor" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar">
<i class="fa fa-bars"></i>
</label>
<button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list">
<i class="fa fa-paint-brush"></i>
</button>
<ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu">
<li role="none"><button role="menuitem" class="theme" id="light">Light</button></li>
<li role="none"><button role="menuitem" class="theme" id="rust">Rust</button></li>
<li role="none"><button role="menuitem" class="theme" id="coal">Coal</button></li>
<li role="none"><button role="menuitem" class="theme" id="navy">Navy</button></li>
<li role="none"><button role="menuitem" class="theme" id="ayu">Ayu</button></li>
</ul>
<button id="search-toggle" class="icon-button" type="button" title="Search. (Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar">
<i class="fa fa-search"></i>
</button>
</div>
<h1 class="menu-title">Rust 程序设计语言 简体中文版</h1>
<div class="right-buttons">
<a href="print.html" title="Print this book" aria-label="Print this book">
<i id="print-button" class="fa fa-print"></i>
</a>
<a href="https://github.com/KaiserY/trpl-zh-cn/tree/main" title="Git repository" aria-label="Git repository">
<i id="git-repository-button" class="fa fa-github"></i>
</a>
<a href="https://github.com/KaiserY/trpl-zh-cn/edit/main/src/ch03-02-data-types.md" title="Suggest an edit" aria-label="Suggest an edit">
<i id="git-edit-button" class="fa fa-edit"></i>
</a>
</div>
</div>
<div id="search-wrapper" class="hidden">
<form id="searchbar-outer" class="searchbar-outer">
<input type="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header">
</form>
<div id="searchresults-outer" class="searchresults-outer hidden">
<div id="searchresults-header" class="searchresults-header"></div>
<ul id="searchresults">
</ul>
</div>
</div>
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
<script>
document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) {
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
});
</script>
<div id="content" class="content">
<main>
<h2 id="数据类型"><a class="header" href="#数据类型">数据类型</a></h2>
<blockquote>
<p><a href="https://github.com/rust-lang/book/blob/main/src/ch03-02-data-types.md">ch03-02-data-types.md</a>
<br>
commit d0acb2595c891de97a133d06635c50ab449dd65c</p>
</blockquote>
<p>在 Rust 中,每一个值都属于某一个 <strong>数据类型</strong><em>data type</em>),这告诉 Rust 它被指定为何种数据以便明确数据处理方式。我们将看到两类数据类型子集标量scalar和复合compound</p>
<p>记住Rust 是 <strong>静态类型</strong><em>statically typed</em>)语言,也就是说在编译时就必须知道所有变量的类型。根据值及其使用方式,编译器通常可以推断出我们想要用的类型。当多种类型均有可能时,比如第二章的 <a href="ch02-00-guessing-game-tutorial.html#%E6%AF%94%E8%BE%83%E7%8C%9C%E6%B5%8B%E7%9A%84%E6%95%B0%E5%AD%97%E5%92%8C%E7%A7%98%E5%AF%86%E6%95%B0%E5%AD%97">“比较猜测的数字和秘密数字”</a> 使用 <code>parse</code><code>String</code> 转换为数字时,必须增加类型注解,像这样:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>let guess: u32 = "42".parse().expect("Not a number!");
<span class="boring">}</span></code></pre></pre>
<p>如果不像上面的代码这样添加类型注解 <code>: u32</code>Rust 会显示如下错误,这说明编译器需要我们提供更多信息,来了解我们想要的类型:</p>
<pre><code class="language-console">$ cargo build
Compiling no_type_annotations v0.1.0 (file:///projects/no_type_annotations)
error[E0284]: type annotations needed
--&gt; src/main.rs:2:9
|
2 | let guess = "42".parse().expect("Not a number!");
| ^^^^^ ----- type must be known at this point
|
= note: cannot satisfy `&lt;_ as FromStr&gt;::Err == _`
help: consider giving `guess` an explicit type
|
2 | let guess: /* Type */ = "42".parse().expect("Not a number!");
| ++++++++++++
For more information about this error, try `rustc --explain E0284`.
error: could not compile `no_type_annotations` (bin "no_type_annotations") due to 1 previous error
</code></pre>
<p>你会看到其它数据类型的各种类型注解。</p>
<h3 id="标量类型"><a class="header" href="#标量类型">标量类型</a></h3>
<p><strong>标量</strong><em>scalar</em>类型代表一个单独的值。Rust 有四种基本的标量类型:整型、浮点型、布尔类型和字符类型。你可能在其他语言中见过它们。让我们深入了解它们在 Rust 中是如何工作的。</p>
<h4 id="整型"><a class="header" href="#整型">整型</a></h4>
<p><strong>整数</strong> 是一个没有小数部分的数字。我们在第二章使用过 <code>u32</code> 整数类型。该类型声明表明,它关联的值应该是一个占据 32 比特位的无符号整数(有符号整数类型以 <code>i</code> 开头而不是 <code>u</code>)。表格 3-1 展示了 Rust 内建的整数类型。我们可以使用其中的任一个来声明一个整数值的类型。</p>
<p><span class="caption">表格 3-1: Rust 中的整型</span></p>
<div class="table-wrapper"><table><thead><tr><th>长度</th><th>有符号</th><th>无符号</th></tr></thead><tbody>
<tr><td>8-bit</td><td><code>i8</code></td><td><code>u8</code></td></tr>
<tr><td>16-bit</td><td><code>i16</code></td><td><code>u16</code></td></tr>
<tr><td>32-bit</td><td><code>i32</code></td><td><code>u32</code></td></tr>
<tr><td>64-bit</td><td><code>i64</code></td><td><code>u64</code></td></tr>
<tr><td>128-bit</td><td><code>i128</code></td><td><code>u128</code></td></tr>
<tr><td>arch</td><td><code>isize</code></td><td><code>usize</code></td></tr>
</tbody></table>
</div>
<p>每一个变体都可以是有符号或无符号的,并有一个明确的大小。<strong>有符号</strong><strong>无符号</strong> 代表数字能否为负值,换句话说,这个数字是否有可能是负数(有符号数),或者永远为正而不需要符号(无符号数)。这有点像在纸上书写数字:当需要考虑符号的时候,数字以加号或减号作为前缀;然而,可以安全地假设为正数时,加号前缀通常省略。有符号数以<a href="https://en.wikipedia.org/wiki/Two%27s_complement">补码形式twos complement representation</a> 存储。</p>
<p>每一个有符号的变体可以储存包含从 -(2<sup>n - 1</sup>) 到 2<sup>n - 1</sup> - 1 在内的数字,这里 <em>n</em> 是变体使用的位数。所以 <code>i8</code> 可以储存从 -(2<sup>7</sup>) 到 2<sup>7</sup> - 1 在内的数字,也就是从 -128 到 127。无符号的变体可以储存从 0 到 2<sup>n</sup> - 1 的数字,所以 <code>u8</code> 可以储存从 0 到 2<sup>8</sup> - 1 的数字,也就是从 0 到 255。</p>
<p>另外,<code>isize</code><code>usize</code> 类型依赖运行程序的计算机架构64 位架构上它们是 64 位的32 位架构上它们是 32 位的。</p>
<p>可以使用表格 3-2 中的任何一种形式编写数字字面值。请注意可以是多种数字类型的数字字面值允许使用类型后缀,例如 <code>57u8</code> 来指定类型,同时也允许使用 <code>_</code> 做为分隔符以方便读数,例如<code>1_000</code>,它的值与你指定的 <code>1000</code> 相同。</p>
<p><span class="caption">表格 3-2: Rust 中的整型字面值</span></p>
<div class="table-wrapper"><table><thead><tr><th>数字字面值</th><th>例子</th></tr></thead><tbody>
<tr><td>Decimal (十进制)</td><td><code>98_222</code></td></tr>
<tr><td>Hex (十六进制)</td><td><code>0xff</code></td></tr>
<tr><td>Octal (八进制)</td><td><code>0o77</code></td></tr>
<tr><td>Binary (二进制)</td><td><code>0b1111_0000</code></td></tr>
<tr><td>Byte (单字节字符)(仅限于<code>u8</code>)</td><td><code>b'A'</code></td></tr>
</tbody></table>
</div>
<p>那么该使用哪种类型的数字呢如果拿不定主意Rust 的默认类型通常是个不错的起点,数字类型默认是 <code>i32</code><code>isize</code><code>usize</code> 主要作为某些集合的索引。</p>
<blockquote>
<h5 id="整型溢出"><a class="header" href="#整型溢出">整型溢出</a></h5>
<p>比方说有一个 <code>u8</code> ,它可以存放从零到 <code>255</code> 的值。那么当你将其修改为 <code>256</code> 时会发生什么呢?这被称为 “整型溢出”“integer overflow” ),这会导致以下两种行为之一的发生。当在 debug 模式编译时Rust 检查这类问题并使程序 <em>panic</em>,这个术语被 Rust 用来表明程序因错误而退出。第九章 <a href="ch09-01-unrecoverable-errors-with-panic.html"><code>panic!</code> 与不可恢复的错误”</a> 部分会详细介绍 panic。</p>
<p>使用 <code>--release</code> flag 在 release 模式中构建时Rust <strong>不会</strong>检测会导致 panic 的整型溢出。相反发生整型溢出时Rust 会进行一种被称为二进制补码 wrapping<em>twos complement wrapping</em>)的操作。简而言之,比此类型能容纳最大值还大的值会回绕到最小值,值 <code>256</code> 变成 <code>0</code>,值 <code>257</code> 变成 <code>1</code>,依此类推。程序不会 panic不过变量可能也不会是你所期望的值。依赖整型溢出 wrapping 的行为被认为是一种错误。</p>
<p>为了显式地处理溢出的可能性,可以使用这几类标准库提供的原始数字类型方法:</p>
<ul>
<li>所有模式下都可以使用 <code>wrapping_*</code> 方法进行 wrapping<code>wrapping_add</code></li>
<li>如果 <code>checked_*</code> 方法出现溢出,则返回 <code>None</code></li>
<li><code>overflowing_*</code> 方法返回值和一个布尔值,表示是否出现溢出</li>
<li><code>saturating_*</code> 方法在值的最小值或最大值处进行饱和处理</li>
</ul>
</blockquote>
<h4 id="浮点型"><a class="header" href="#浮点型">浮点型</a></h4>
<p>Rust 也有两个原生的 <strong>浮点数</strong><em>floating-point numbers</em>类型它们是带小数点的数字。Rust 的浮点数类型是 <code>f32</code><code>f64</code>,分别占 32 位和 64 位。默认类型是 <code>f64</code>,因为在现代 CPU 中,它与 <code>f32</code> 速度几乎一样,不过精度更高。所有的浮点型都是有符号的。</p>
<p>这是一个展示浮点数的实例:</p>
<p><span class="filename">文件名src/main.rs</span></p>
<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
let x = 2.0; // f64
let y: f32 = 3.0; // f32
}</code></pre></pre>
<p>浮点数采用 IEEE-754 标准表示。<code>f32</code> 是单精度浮点数,<code>f64</code> 是双精度浮点数。</p>
<h4 id="数值运算"><a class="header" href="#数值运算">数值运算</a></h4>
<p>Rust 中的所有数字类型都支持基本数学运算:加法、减法、乘法、除法和取余。整数除法会向零舍入到最接近的整数。下面的代码展示了如何在 <code>let</code> 语句中使用它们:</p>
<p><span class="filename">文件名src/main.rs</span></p>
<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
// addition
let sum = 5 + 10;
// subtraction
let difference = 95.5 - 4.3;
// multiplication
let product = 4 * 30;
// division
let quotient = 56.7 / 32.2;
let truncated = -5 / 3; // 结果为 -1
// remainder
let remainder = 43 % 5;
}</code></pre></pre>
<p>这些语句中的每个表达式使用了一个数学运算符并计算出了一个值,然后绑定给一个变量。<a href="appendix-02-operators.html">附录 B</a><!-- ignore --> 包含 Rust 提供的所有运算符的列表。</p>
<h4 id="布尔型"><a class="header" href="#布尔型">布尔型</a></h4>
<p>正如其他大部分编程语言一样Rust 中的布尔类型有两个可能的值:<code>true</code><code>false</code>。Rust 中的布尔类型使用 <code>bool</code> 表示。例如:</p>
<p><span class="filename">文件名src/main.rs</span></p>
<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
let t = true;
let f: bool = false; // with explicit type annotation
}</code></pre></pre>
<p>使用布尔值的主要场景是条件表达式,例如 <code>if</code> 表达式。在 <a href="ch03-05-control-flow.html#%E6%8E%A7%E5%88%B6%E6%B5%81">“控制流”“Control Flow”</a> 部分将介绍 <code>if</code> 表达式在 Rust 中如何工作。</p>
<h4 id="字符类型"><a class="header" href="#字符类型">字符类型</a></h4>
<p>Rust 的 <code>char</code> 类型是语言中最原生的字母类型。下面是一些声明 <code>char</code> 值的例子:</p>
<p><span class="filename">文件名src/main.rs</span></p>
<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
let c = 'z';
let z: char = ''; // with explicit type annotation
let heart_eyed_cat = '😻';
}</code></pre></pre>
<p>注意,我们用单引号声明 <code>char</code> 字面量而与之相反的是使用双引号声明字符串字面量。Rust 的 <code>char</code> 类型的大小为四个字节 (four bytes),并代表了一个 Unicode 标量值Unicode Scalar Value这意味着它可以比 ASCII 表示更多内容。在 Rust 中带变音符号的字母Accented letters中文、日文、韩文等字符emoji绘文字以及零长度的空白字符都是有效的 <code>char</code> 值。Unicode 标量值包含从 <code>U+0000</code><code>U+D7FF</code><code>U+E000</code><code>U+10FFFF</code> 在内的值。不过,“字符” 并不是一个 Unicode 中的概念,所以人直觉上的 “字符” 可能与 Rust 中的 <code>char</code> 并不符合。第八章的 <a href="ch08-02-strings.html#%E4%BD%BF%E7%94%A8%E5%AD%97%E7%AC%A6%E4%B8%B2%E5%82%A8%E5%AD%98-utf-8-%E7%BC%96%E7%A0%81%E7%9A%84%E6%96%87%E6%9C%AC">“使用字符串储存 UTF-8 编码的文本”</a> 中将详细讨论这个主题。</p>
<h3 id="复合类型"><a class="header" href="#复合类型">复合类型</a></h3>
<p><strong>复合类型</strong><em>Compound types</em>可以将多个值组合成一个类型。Rust 有两个原生的复合类型元组tuple和数组array</p>
<h4 id="元组类型"><a class="header" href="#元组类型">元组类型</a></h4>
<p>元组是一个将多个其他类型的值组合进一个复合类型的主要方式。元组长度固定:一旦声明,其长度不会增大或缩小。</p>
<p>我们使用包含在圆括号中的逗号分隔的值列表来创建一个元组。元组中的每一个位置都有一个类型,而且这些不同值的类型也不必是相同的。这个例子中使用了可选的类型注解:</p>
<p><span class="filename">文件名src/main.rs</span></p>
<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
let tup: (i32, f64, u8) = (500, 6.4, 1);
}</code></pre></pre>
<p><code>tup</code> 变量绑定到整个元组上因为元组是一个单独的复合元素。为了从元组中获取单个值可以使用模式匹配pattern matching来解构destructure元组值像这样</p>
<p><span class="filename">文件名src/main.rs</span></p>
<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
let tup = (500, 6.4, 1);
let (x, y, z) = tup;
println!("The value of y is: {y}");
}</code></pre></pre>
<p>程序首先创建了一个元组并绑定到 <code>tup</code> 变量上。接着使用了 <code>let</code> 和一个模式将 <code>tup</code> 分成了三个不同的变量,<code>x</code><code>y</code><code>z</code>。这叫做 <strong>解构</strong><em>destructuring</em>),因为它将一个元组拆成了三个部分。最后,程序打印出了 <code>y</code> 的值,也就是 <code>6.4</code></p>
<p>我们也可以使用点号(<code>.</code>)后跟值的索引来直接访问它们。例如:</p>
<p><span class="filename">文件名src/main.rs</span></p>
<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
let x: (i32, f64, u8) = (500, 6.4, 1);
let five_hundred = x.0;
let six_point_four = x.1;
let one = x.2;
}</code></pre></pre>
<p>这个程序创建了一个元组,<code>x</code>,然后使用其各自的索引访问元组中的每个元素。跟大多数编程语言一样,元组的第一个索引值是 0。</p>
<p>不带任何值的元组有个特殊的名称,叫做 <strong>单元unit</strong> 元组。这种值以及对应的类型都写作 <code>()</code>,表示空值或空的返回类型。如果表达式不返回任何其他值,则会隐式返回单元值。</p>
<h4 id="数组类型"><a class="header" href="#数组类型">数组类型</a></h4>
<p>另一个包含多个值的方式是 <strong>数组</strong><em>array</em>。与元组不同数组中的每个元素的类型必须相同。Rust 中的数组与一些其他语言中的数组不同Rust 中的数组长度是固定的。</p>
<p>我们将数组的值写成在方括号内,用逗号分隔:</p>
<p><span class="filename">文件名src/main.rs</span></p>
<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
let a = [1, 2, 3, 4, 5];
}</code></pre></pre>
<p>当你想要在栈stack而不是在堆heap上为数据分配空间<a href="ch04-01-what-is-ownership.html#%E6%A0%88stack%E4%B8%8E%E5%A0%86heap">第四章</a>将讨论栈与堆的更多内容),或者是想要确保总是有固定数量的元素时,数组非常有用。但是数组并不如 vector 类型灵活。vector 类型是标准库提供的一个 <strong>允许</strong> 增长和缩小长度的类似数组的集合类型。当不确定是应该使用数组还是 vector 的时候,那么很可能应该使用 vector。<a href="ch08-01-vectors.html">第八章</a>会详细讨论 vector。</p>
<p>然而,当你确定元素个数不会改变时,数组会更有用。例如,当你在一个程序中使用月份名字时,你更应趋向于使用数组而不是 vector因为你确定只会有 12 个元素。</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>let months = ["January", "February", "March", "April", "May", "June", "July",
"August", "September", "October", "November", "December"];
<span class="boring">}</span></code></pre></pre>
<p>可以像这样编写数组的类型:在方括号中包含每个元素的类型,后跟分号,再后跟数组元素的数量。</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>let a: [i32; 5] = [1, 2, 3, 4, 5];
<span class="boring">}</span></code></pre></pre>
<p>这里,<code>i32</code> 是每个元素的类型。分号之后,数字 <code>5</code> 表明该数组包含五个元素。</p>
<p>你还可以通过在方括号中指定初始值加分号再加元素个数的方式来创建一个每个元素都为相同值的数组:</p>
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>let a = [3; 5];
<span class="boring">}</span></code></pre></pre>
<p>变量名为 <code>a</code> 的数组将包含 <code>5</code> 个元素,这些元素的值最初都将被设置为 <code>3</code>。这种写法与 <code>let a = [3, 3, 3, 3, 3];</code> 效果相同,但更简洁。</p>
<h5 id="访问数组元素"><a class="header" href="#访问数组元素">访问数组元素</a></h5>
<p>数组是可以在栈 (stack) 上分配的已知固定大小的单个内存块。可以使用索引来访问数组的元素,像这样:</p>
<p><span class="filename">文件名src/main.rs</span></p>
<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
let a = [1, 2, 3, 4, 5];
let first = a[0];
let second = a[1];
}</code></pre></pre>
<p>在这个例子中,叫做 <code>first</code> 的变量的值是 <code>1</code>,因为它是数组索引 <code>[0]</code> 的值。变量 <code>second</code> 将会是数组索引 <code>[1]</code> 的值 <code>2</code></p>
<h5 id="无效的数组元素访问"><a class="header" href="#无效的数组元素访问">无效的数组元素访问</a></h5>
<p>让我们看看如果我们访问数组结尾之后的元素会发生什么呢?比如你执行以下代码,它使用类似于第 2 章中的猜数字游戏的代码从用户那里获取数组索引:</p>
<p><span class="filename">文件名src/main.rs</span></p>
<pre><code class="language-rust ignore panics">use std::io;
fn main() {
let a = [1, 2, 3, 4, 5];
println!("Please enter an array index.");
let mut index = String::new();
io::stdin()
.read_line(&amp;mut index)
.expect("Failed to read line");
let index: usize = index
.trim()
.parse()
.expect("Index entered was not a number");
let element = a[index];
println!("The value of the element at index {index} is: {element}");
}</code></pre>
<p>此代码编译成功。如果您使用 <code>cargo run</code> 运行此代码并输入 <code>0</code><code>1</code><code>2</code><code>3</code><code>4</code>,程序将在数组中的索引处打印出相应的值。如果你输入一个超过数组末端的数字,如 10你会看到这样的输出</p>
<pre><code class="language-console">thread 'main' panicked at 'index out of bounds: the len is 5 but the index is 10', src/main.rs:19:19
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
</code></pre>
<p>程序在索引操作中使用一个无效的值时导致 <strong>运行时</strong> 错误。程序带着错误信息退出,并且没有执行最后的 <code>println!</code> 语句。当尝试用索引访问一个元素时Rust 会检查指定的索引是否小于数组的长度。如果索引超出了数组长度Rust 会 <em>panic</em>,这是 Rust 术语,它用于程序因为错误而退出的情况。这种检查必须在运行时进行,特别是在这种情况下,因为编译器不可能知道用户在以后运行代码时将输入什么值。</p>
<p>这是第一个在实战中遇到的 Rust 安全原则的例子。在很多底层语言中并没有进行这类检查这样当提供了一个不正确的索引时就会访问无效的内存。通过立即退出而不是允许内存访问并继续执行Rust 让你避开此类错误。第九章会更详细地讨论 Rust 的错误处理机制,以及如何编写可读性强而又安全的代码,使程序既不会 panic 也不会导致非法内存访问。</p>
</main>
<nav class="nav-wrapper" aria-label="Page navigation">
<!-- Mobile navigation buttons -->
<a rel="prev" href="ch03-01-variables-and-mutability.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
<i class="fa fa-angle-left"></i>
</a>
<a rel="next prefetch" href="ch03-03-how-functions-work.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
<i class="fa fa-angle-right"></i>
</a>
<div style="clear: both"></div>
</nav>
</div>
</div>
<nav class="nav-wide-wrapper" aria-label="Page navigation">
<a rel="prev" href="ch03-01-variables-and-mutability.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
<i class="fa fa-angle-left"></i>
</a>
<a rel="next prefetch" href="ch03-03-how-functions-work.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
<i class="fa fa-angle-right"></i>
</a>
</nav>
</div>
<script>
window.playground_copyable = true;
</script>
<script src="elasticlunr.min.js"></script>
<script src="mark.min.js"></script>
<script src="searcher.js"></script>
<script src="clipboard.min.js"></script>
<script src="highlight.js"></script>
<script src="book.js"></script>
<!-- Custom JS scripts -->
<script src="ferris.js"></script>
</div>
</body>
</html>