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<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" class="active"><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"><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<T> 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<T> 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<T> 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> 流（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> 宏</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>
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<main>
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<h2 id="hello-world"><a class="header" href="#hello-world">Hello, World!</a></h2>
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<blockquote>
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<p><a href="https://github.com/rust-lang/book/blob/main/src/ch01-02-hello-world.md">ch01-02-hello-world.md</a>
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<br>
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commit 1fb74c3f1d8aeba39373e9f4cdb9a4bdca95604f</p>
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</blockquote>
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<p>既然安装好了 Rust，是时候来编写第一个 Rust 程序了。当学习一门新语言的时候，使用该语言在屏幕上打印 <code>Hello, world!</code> 是一项传统，我们将沿用这一传统！</p>
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<blockquote>
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<p>注意：本书假设你熟悉基本的命令行操作。Rust 对于你的编辑器、工具，以及代码位于何处并没有特定的要求，如果你更倾向于使用集成开发环境（IDE），而不是命令行，请尽管使用你喜欢的 IDE。目前很多 IDE 都在一定程度上支持 Rust；查看 IDE 文档以了解更多细节。Rust 团队一直致力于借助 <code>rust-analyzer</code> 提供强大的 IDE 支持。详见<a href="appendix-04-useful-development-tools.html">附录 D</a><!-- ignore -->。</p>
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</blockquote>
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<h3 id="创建项目目录"><a class="header" href="#创建项目目录">创建项目目录</a></h3>
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<p>首先创建一个存放 Rust 代码的目录。Rust 并不关心代码的存放位置，不过对于本书的练习和项目来说，我们建议你在 home 目录中创建 <em>projects</em> 目录，并将你的所有项目存放在这里。</p>
|
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<p>打开终端并输入如下命令创建 <em>projects</em> 目录，并在 <em>projects</em> 目录中为 “Hello, world!” 项目创建一个目录。</p>
|
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<p>对于 Linux、macOS 和 Windows PowerShell，输入：</p>
|
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<pre><code class="language-console">$ mkdir ~/projects
|
|
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$ cd ~/projects
|
|
|
$ mkdir hello_world
|
|
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$ cd hello_world
|
|
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</code></pre>
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<p>对于 Windows CMD，输入：</p>
|
|
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<pre><code class="language-doscon">> mkdir "%USERPROFILE%\projects"
|
|
|
> cd /d "%USERPROFILE%\projects"
|
|
|
> mkdir hello_world
|
|
|
> cd hello_world
|
|
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</code></pre>
|
|
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<h3 id="编写并运行-rust-程序"><a class="header" href="#编写并运行-rust-程序">编写并运行 Rust 程序</a></h3>
|
|
|
<p>接下来，新建一个源文件，命名为 <em>main.rs</em>。Rust 源文件总是以 <em>.rs</em> 扩展名结尾。如果文件名包含多个单词，那么按照命名习惯，应当使用下划线来分隔单词。例如命名为 <em>hello_world.rs</em>，而不是 <em>helloworld.rs</em>。</p>
|
|
|
<p>现在打开刚创建的 <em>main.rs</em> 文件，输入示例 1-1 中的代码。</p>
|
|
|
<figure class="listing">
|
|
|
<p><span class="file-name">文件名：main.rs</span></p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
|
|
|
println!("Hello, world!");
|
|
|
}</code></pre></pre>
|
|
|
<figcaption>示例 1-1：一个打印 `Hello, world!` 的程序</figcaption>
|
|
|
</figure>
|
|
|
<p>保存文件，并回到当前目录为“~/projects/hello_world”的终端窗口。在 Linux 或 macOS 上，输入如下命令，编译并运行文件：</p>
|
|
|
<pre><code class="language-console">$ rustc main.rs
|
|
|
$ ./main
|
|
|
Hello, world!
|
|
|
</code></pre>
|
|
|
<p>在 Windows 上，输入命令 <code>.\main.exe</code>，而不是 <code>./main</code>：</p>
|
|
|
<pre><code class="language-powershell">> rustc main.rs
|
|
|
> .\main.exe
|
|
|
Hello, world!
|
|
|
</code></pre>
|
|
|
<p>不管使用何种操作系统，终端应该打印字符串 <code>Hello, world!</code>。如果没有看到这些输出，回到安装部分的 <a href="ch01-01-installation.html#%E6%95%85%E9%9A%9C%E6%8E%92%E9%99%A4troubleshooting">“故障排除”</a> 小节查找有帮助的方法。</p>
|
|
|
<p>如果 <code>Hello, world!</code> 出现了，恭喜你！你已经正式编写了一个 Rust 程序。现在你成为一名 Rust 程序员，欢迎！</p>
|
|
|
<h3 id="分析这个-rust-程序"><a class="header" href="#分析这个-rust-程序">分析这个 Rust 程序</a></h3>
|
|
|
<p>现在，让我们回过头来仔细看看这个 “Hello, world!” 程序。这是第一块拼图：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021">fn main() {
|
|
|
|
|
|
}</code></pre></pre>
|
|
|
<p>这几行定义了一个名叫 <code>main</code> 的函数。<code>main</code> 函数是一个特殊的函数：在可执行的 Rust 程序中，它总是最先运行的代码。第一行代码声明了一个叫做 <code>main</code> 的函数，它没有参数也没有返回值。如果有参数的话，它们的名称应该出现在小括号 <code>()</code> 中。</p>
|
|
|
<p>函数体被包裹在 <code>{}</code> 中。Rust 要求所有函数体都要用花括号包裹起来。一般来说，将左花括号与函数声明置于同一行并以空格分隔，是良好的代码风格。</p>
|
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|
<blockquote>
|
|
|
<p>注：如果你希望在 Rust 项目中保持一种标准风格，可以使用名为 <code>rustfmt</code> 的自动格式化工具将代码格式化为特定的风格（更多内容详见<a href="appendix-04-useful-development-tools.html">附录 D</a> 中的 <code>rustfmt</code><!-- ignore -->）。Rust 团队已经在标准的 Rust 发行版中包含了这个工具，就像 <code>rustc</code> 一样。所以它应该已经安装在你的电脑中了！</p>
|
|
|
</blockquote>
|
|
|
<p>在 <code>main</code> 函数中有如下代码：</p>
|
|
|
<pre><pre class="playground"><code class="language-rust edition2021"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span> println!("Hello, world!");
|
|
|
<span class="boring">}</span></code></pre></pre>
|
|
|
<p>这行代码完成这个简单程序的所有工作：在屏幕上打印文本。这里有四个重要的细节需要注意。首先 Rust 的缩进风格使用 4 个空格，而不是 1 个制表符（tab）。</p>
|
|
|
<p>第二，<code>println!</code> 调用了一个 Rust 宏（macro）。如果是调用函数，则应输入 <code>println</code>（没有<code>!</code>）。我们将在第二十章详细讨论宏。现在你只需记住，当看到符号 <code>!</code> 的时候，就意味着调用的是宏而不是普通函数，并且宏并不总是遵循与函数相同的规则。</p>
|
|
|
<p>第三，<code>"Hello, world!"</code> 是一个字符串。我们把这个字符串作为一个参数传递给 <code>println!</code>，字符串将被打印到屏幕上。</p>
|
|
|
<p>第四，该行以分号结尾（<code>;</code>），这代表一个表达式的结束和下一个表达式的开始。大部分 Rust 代码行以分号结尾。</p>
|
|
|
<h3 id="编译和运行是彼此独立的步骤"><a class="header" href="#编译和运行是彼此独立的步骤">编译和运行是彼此独立的步骤</a></h3>
|
|
|
<p>你刚刚运行了一个新创建的程序，那么让我们检查此过程中的每一个步骤。</p>
|
|
|
<p>在运行 Rust 程序之前，必须先使用 Rust 编译器编译它，即输入 <code>rustc</code> 命令并传入源文件名称，如下：</p>
|
|
|
<pre><code class="language-console">$ rustc main.rs
|
|
|
</code></pre>
|
|
|
<p>如果你有 C 或 C++ 背景，就会发现这与 <code>gcc</code> 和 <code>clang</code> 类似。编译成功后，Rust 会输出一个二进制的可执行文件。</p>
|
|
|
<p>在 Linux、macOS 或 Windows 的 PowerShell 上，在 shell 中输入 <code>ls</code> 命令可以看见这个可执行文件。</p>
|
|
|
<pre><code class="language-console">$ ls
|
|
|
main main.rs
|
|
|
</code></pre>
|
|
|
<p>在 Linux 和 macOS，你会看到两个文件。在 Windows PowerShell 中，你会看到同使用 CMD 相同的三个文件。在 Windows 的 CMD 上，则输入如下内容：</p>
|
|
|
<pre><code class="language-doscon">> dir /B %= the /B option says to only show the file names =%
|
|
|
main.exe
|
|
|
main.pdb
|
|
|
main.rs
|
|
|
</code></pre>
|
|
|
<p>这展示了扩展名为 <em>.rs</em> 的源文件、可执行文件（在 Windows 下是 <em>main.exe</em>，其它平台是 <em>main</em>），以及当使用 CMD 时会有一个包含调试信息、扩展名为 <em>.pdb</em> 的文件。从这里开始运行 <em>main</em> 或 <em>main.exe</em> 文件，如下：</p>
|
|
|
<pre><code class="language-console">$ ./main # Windows 是 .\main.exe
|
|
|
</code></pre>
|
|
|
<p>如果这里的 <em>main.rs</em> 是上文所述的 “Hello, world!” 程序，那么在终端上就会打印出 <code>Hello, world!</code>。</p>
|
|
|
<p>如果你更熟悉动态语言，如 Ruby、Python 或 JavaScript，则可能不习惯将编译和运行分为两个单独的步骤。Rust 是一种 <strong>预编译静态类型</strong>（<em>ahead-of-time compiled</em>）语言，这意味着你可以编译程序，并将可执行文件送给其他人，他们甚至不需要安装 Rust 就可以运行。如果你给他人一个 <em>.rb</em>、<em>.py</em> 或 <em>.js</em> 文件，他们需要先分别安装 Ruby，Python，JavaScript 实现（运行时环境，VM）。不过在这些语言中，只需要一句命令就可以编译和运行程序。这一切都是语言设计上的权衡取舍。</p>
|
|
|
<p>仅仅使用 <code>rustc</code> 编译简单程序是没问题的，不过随着项目的增长，你可能需要管理你项目的方方面面，并让代码易于分享。接下来，我们要介绍一个叫做 Cargo 的工具，它会帮助你编写真实世界中的 Rust 程序。</p>
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