mirror of
https://github.com/KaiserY/trpl-zh-cn
synced 2024-11-09 08:51:18 +08:00
188 lines
13 KiB
HTML
188 lines
13 KiB
HTML
<!DOCTYPE HTML>
|
||
<html lang="en">
|
||
<head>
|
||
<meta charset="UTF-8">
|
||
<title>读取文件 - Rust 程序设计语言 简体中文版</title>
|
||
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
|
||
<meta name="description" content="Rust 程序设计语言 简体中文版">
|
||
<meta name="viewport" content="width=device-width, initial-scale=1">
|
||
|
||
<base href="">
|
||
|
||
<link rel="stylesheet" href="book.css">
|
||
<link href='https://fonts.googleapis.com/css?family=Open+Sans:300italic,400italic,600italic,700italic,800italic,400,300,600,700,800' rel='stylesheet' type='text/css'>
|
||
|
||
<link rel="shortcut icon" href="favicon.png">
|
||
|
||
<!-- Font Awesome -->
|
||
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/font-awesome/4.3.0/css/font-awesome.min.css">
|
||
|
||
<link rel="stylesheet" href="highlight.css">
|
||
<link rel="stylesheet" href="tomorrow-night.css">
|
||
|
||
<!-- MathJax -->
|
||
<script type="text/javascript" src="https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML"></script>
|
||
|
||
<!-- Fetch JQuery from CDN but have a local fallback -->
|
||
<script src="https://code.jquery.com/jquery-2.1.4.min.js"></script>
|
||
<script>
|
||
if (typeof jQuery == 'undefined') {
|
||
document.write(unescape("%3Cscript src='jquery.js'%3E%3C/script%3E"));
|
||
}
|
||
</script>
|
||
</head>
|
||
<body class="light">
|
||
<!-- Set the theme before any content is loaded, prevents flash -->
|
||
<script type="text/javascript">
|
||
var theme = localStorage.getItem('theme');
|
||
if (theme == null) { theme = 'light'; }
|
||
$('body').removeClass().addClass(theme);
|
||
</script>
|
||
|
||
<!-- Hide / unhide sidebar before it is displayed -->
|
||
<script type="text/javascript">
|
||
var sidebar = localStorage.getItem('sidebar');
|
||
if (sidebar === "hidden") { $("html").addClass("sidebar-hidden") }
|
||
else if (sidebar === "visible") { $("html").addClass("sidebar-visible") }
|
||
</script>
|
||
|
||
<div id="sidebar" class="sidebar">
|
||
<ul class="chapter"><li><a href="ch01-00-introduction.html"><strong>1.</strong> 介绍</a></li><li><ul class="section"><li><a href="ch01-01-installation.html"><strong>1.1.</strong> 安装</a></li><li><a href="ch01-02-hello-world.html"><strong>1.2.</strong> Hello, World!</a></li></ul></li><li><a href="ch02-00-guessing-game-tutorial.html"><strong>2.</strong> 猜猜看教程</a></li><li><a href="ch03-00-common-programming-concepts.html"><strong>3.</strong> 通用编程概念</a></li><li><ul class="section"><li><a href="ch03-01-variables-and-mutability.html"><strong>3.1.</strong> 变量和可变性</a></li><li><a href="ch03-02-data-types.html"><strong>3.2.</strong> 数据类型</a></li><li><a href="ch03-03-how-functions-work.html"><strong>3.3.</strong> 函数如何工作</a></li><li><a href="ch03-04-comments.html"><strong>3.4.</strong> 注释</a></li><li><a href="ch03-05-control-flow.html"><strong>3.5.</strong> 控制流</a></li></ul></li><li><a href="ch04-00-understanding-ownership.html"><strong>4.</strong> 认识所有权</a></li><li><ul class="section"><li><a href="ch04-01-what-is-ownership.html"><strong>4.1.</strong> 什么是所有权</a></li><li><a href="ch04-02-references-and-borrowing.html"><strong>4.2.</strong> 引用 & 借用</a></li><li><a href="ch04-03-slices.html"><strong>4.3.</strong> Slices</a></li></ul></li><li><a href="ch05-00-structs.html"><strong>5.</strong> 结构体</a></li><li><ul class="section"><li><a href="ch05-01-method-syntax.html"><strong>5.1.</strong> 方法语法</a></li></ul></li><li><a href="ch06-00-enums.html"><strong>6.</strong> 枚举和模式匹配</a></li><li><ul class="section"><li><a href="ch06-01-defining-an-enum.html"><strong>6.1.</strong> 定义枚举</a></li><li><a href="ch06-02-match.html"><strong>6.2.</strong> <code>match</code>控制流运算符</a></li><li><a href="ch06-03-if-let.html"><strong>6.3.</strong> <code>if let</code>简单控制流</a></li></ul></li><li><a href="ch07-00-modules.html"><strong>7.</strong> 模块</a></li><li><ul class="section"><li><a href="ch07-01-mod-and-the-filesystem.html"><strong>7.1.</strong> <code>mod</code>和文件系统</a></li><li><a href="ch07-02-controlling-visibility-with-pub.html"><strong>7.2.</strong> 使用<code>pub</code>控制可见性</a></li><li><a href="ch07-03-importing-names-with-use.html"><strong>7.3.</strong> 使用<code>use</code>导入命名</a></li></ul></li><li><a href="ch08-00-common-collections.html"><strong>8.</strong> 通用集合类型</a></li><li><ul class="section"><li><a href="ch08-01-vectors.html"><strong>8.1.</strong> vector</a></li><li><a href="ch08-02-strings.html"><strong>8.2.</strong> 字符串</a></li><li><a href="ch08-03-hash-maps.html"><strong>8.3.</strong> 哈希 map</a></li></ul></li><li><a href="ch09-00-error-handling.html"><strong>9.</strong> 错误处理</a></li><li><ul class="section"><li><a href="ch09-01-unrecoverable-errors-with-panic.html"><strong>9.1.</strong> <code>panic!</code>与不可恢复的错误</a></li><li><a href="ch09-02-recoverable-errors-with-result.html"><strong>9.2.</strong> <code>Result</code>与可恢复的错误</a></li><li><a href="ch09-03-to-panic-or-not-to-panic.html"><strong>9.3.</strong> <code>panic!</code>还是不<code>panic!</code></a></li></ul></li><li><a href="ch10-00-generics.html"><strong>10.</strong> 泛型、trait 和生命周期</a></li><li><ul class="section"><li><a href="ch10-01-syntax.html"><strong>10.1.</strong> 泛型数据类型</a></li><li><a href="ch10-02-traits.html"><strong>10.2.</strong> trait：定义共享的行为</a></li><li><a href="ch10-03-lifetime-syntax.html"><strong>10.3.</strong> 生命周期与引用有效性</a></li></ul></li><li><a href="ch11-00-testing.html"><strong>11.</strong> 测试</a></li><li><ul class="section"><li><a href="ch11-01-writing-tests.html"><strong>11.1.</strong> 编写测试</a></li><li><a href="ch11-02-running-tests.html"><strong>11.2.</strong> 运行测试</a></li><li><a href="ch11-03-test-organization.html"><strong>11.3.</strong> 测试的组织结构</a></li></ul></li><li><a href="ch12-00-an-io-project.html"><strong>12.</strong> 一个 I/O 项目</a></li><li><ul class="section"><li><a href="ch12-01-accepting-command-line-arguments.html"><strong>12.1.</strong> 接受命令行参数</a></li><li><a href="ch12-02-reading-a-file.html" class="active"><strong>12.2.</strong> 读取文件</a></li><li><a href="ch12-03-improving-error-handling-and-modularity.html"><strong>12.3.</strong> 增强错误处理和模块化</a></li><li><a href="ch12-04-testing-the-librarys-functionality.html"><strong>12.4.</strong> 测试库的功能</a></li><li><a href="ch12-05-working-with-environment-variables.html"><strong>12.5.</strong> 处理环境变量</a></li><li><a href="ch12-06-writing-to-stderr-instead-of-stdout.html"><strong>12.6.</strong> 输出到<code>stderr</code>而不是<code>stdout</code></a></li></ul></li></ul>
|
||
</div>
|
||
|
||
<div id="page-wrapper" class="page-wrapper">
|
||
|
||
<div class="page">
|
||
<div id="menu-bar" class="menu-bar">
|
||
<div class="left-buttons">
|
||
<i id="sidebar-toggle" class="fa fa-bars"></i>
|
||
<i id="theme-toggle" class="fa fa-paint-brush"></i>
|
||
</div>
|
||
|
||
<h1 class="menu-title">Rust 程序设计语言 简体中文版</h1>
|
||
|
||
<div class="right-buttons">
|
||
<i id="print-button" class="fa fa-print" title="Print this book"></i>
|
||
</div>
|
||
</div>
|
||
|
||
<div id="content" class="content">
|
||
<a class="header" href="#读取文件" name="读取文件"><h2>读取文件</h2></a>
|
||
<blockquote>
|
||
<p><a href="https://github.com/rust-lang/book/blob/master/second-edition/src/ch12-02-reading-a-file.md">ch12-02-reading-a-file.md</a>
|
||
<br>
|
||
commit 4f2dc564851dc04b271a2260c834643dfd86c724</p>
|
||
</blockquote>
|
||
<p>现在有了一些包含我们需要的信息的变量了，让我们试着使用他们。下一步目标是打开需要搜索的文件。为此，我需要一个文件。在项目的根目录创建一个文件<code>poem.txt</code>，并写入一些艾米莉·狄金森（Emily Dickinson）的诗：</p>
|
||
<p><span class="filename">Filename: poem.txt</span></p>
|
||
<pre><code>I'm nobody! Who are you?
|
||
Are you nobody, too?
|
||
Then there's a pair of us — don't tell!
|
||
They'd banish us, you know.
|
||
|
||
How dreary to be somebody!
|
||
How public, like a frog
|
||
To tell your name the livelong day
|
||
To an admiring bog!
|
||
</code></pre>
|
||
<!-- Public domain Emily Dickinson poem. This will work best with something
|
||
short, but that has multiple lines and some repetition. We could search through
|
||
code; that gets a bit meta and possibly confusing... Changes to this are most
|
||
welcome. /Carol -->
|
||
<p>创建完这个文件后，让我们编辑 <em>src/main.rs</em> 并增加如列表 12-3 所示用来打开文件的代码：</p>
|
||
<figure>
|
||
<span class="filename">Filename: src/main.rs</span>
|
||
<pre><code class="language-rust">use std::env;
|
||
use std::fs::File;
|
||
use std::io::prelude::*;
|
||
|
||
fn main() {
|
||
let args: Vec<String> = env::args().collect();
|
||
|
||
let search = &args[1];
|
||
let filename = &args[2];
|
||
|
||
println!("Searching for {}", search);
|
||
println!("In file {}", filename);
|
||
|
||
let mut f = File::open(filename).expect("file not found");
|
||
|
||
let mut contents = String::new();
|
||
f.read_to_string(&mut contents).expect("something went wrong reading the file");
|
||
|
||
println!("With text:\n{}", contents);
|
||
}
|
||
</code></pre>
|
||
<figcaption>
|
||
<p>Listing 12-3: Read the contents of the file specified by the second argument</p>
|
||
</figcaption>
|
||
</figure>
|
||
<!-- Will add ghosting and wingdings in libreoffice /Carol -->
|
||
<p>这里增加了一些新内容。首先，需要更多的<code>use</code>语句来引入标准库中的相关部分：我们需要<code>std::fs::File</code>来处理文件，而<code>std::io::prelude::*</code>则包含许多对于 I/O 包括文件 I/O 有帮助的 trait。类似于 Rust 有一个通用的 prelude 来自动引入特定内容，<code>std::io</code>也有其自己的 prelude 来引入处理 I/O 时需要的内容。不同于默认的 prelude，必须显式<code>use</code>位于<code>std::io</code>中的 prelude。</p>
|
||
<p>在<code>main</code>中，我们增加了三点内容：第一，我们获取了文件的句柄并使用<code>File::open</code>函数与第二个参数中指定的文件名来打开这个文件。第二，我们在变量<code>contents</code>中创建了一个空的可变的<code>String</code>，接着对文件句柄调用<code>read_to_string</code>并以<code>contents</code>字符串作为参数，<code>contents</code>是<code>read_to_string</code>将会放置它读取到的数据地方。最后，我们打印出了整个文件的内容，这是一个确认目前为止的程序能够工作的方法。</p>
|
||
<p>尝试运行这些代码，随意指定第一个参数（因为还未实现搜索功能的部分）而将 <em>poem.txt</em> 文件将作为第二个参数：</p>
|
||
<pre><code>$ cargo run the poem.txt
|
||
Finished debug [unoptimized + debuginfo] target(s) in 0.0 secs
|
||
Running `target\debug\greprs.exe the poem.txt`
|
||
Searching for the
|
||
In file poem.txt
|
||
With text:
|
||
I'm nobody! Who are you?
|
||
Are you nobody, too?
|
||
Then there's a pair of us — don't tell!
|
||
They'd banish us, you know.
|
||
|
||
How dreary to be somebody!
|
||
How public, like a frog
|
||
To tell your name the livelong day
|
||
To an admiring bog!
|
||
</code></pre>
|
||
<p>好的！我们的代码可以工作了！然而，它还有一些瑕疵。因为程序还很小，这些瑕疵并不是什么大问题，不过随着程序功能的丰富，将会越来越难以用简单的方法修复他们。现在就让我们开始重构而不是等待之后处理。重构在只有少量代码时会显得容易得多。</p>
|
||
|
||
</div>
|
||
|
||
<!-- Mobile navigation buttons -->
|
||
|
||
<a href="ch12-01-accepting-command-line-arguments.html" class="mobile-nav-chapters previous">
|
||
<i class="fa fa-angle-left"></i>
|
||
</a>
|
||
|
||
|
||
|
||
<a href="ch12-03-improving-error-handling-and-modularity.html" class="mobile-nav-chapters next">
|
||
<i class="fa fa-angle-right"></i>
|
||
</a>
|
||
|
||
|
||
</div>
|
||
|
||
|
||
<a href="ch12-01-accepting-command-line-arguments.html" class="nav-chapters previous" title="You can navigate through the chapters using the arrow keys">
|
||
<i class="fa fa-angle-left"></i>
|
||
</a>
|
||
|
||
|
||
|
||
<a href="ch12-03-improving-error-handling-and-modularity.html" class="nav-chapters next" title="You can navigate through the chapters using the arrow keys">
|
||
<i class="fa fa-angle-right"></i>
|
||
</a>
|
||
|
||
|
||
</div>
|
||
|
||
|
||
<!-- Local fallback for Font Awesome -->
|
||
<script>
|
||
if ($(".fa").css("font-family") !== "FontAwesome") {
|
||
$('<link rel="stylesheet" type="text/css" href="_FontAwesome/css/font-awesome.css">').prependTo('head');
|
||
}
|
||
</script>
|
||
|
||
<!-- Livereload script (if served using the cli tool) -->
|
||
|
||
|
||
<script src="highlight.js"></script>
|
||
<script src="book.js"></script>
|
||
</body>
|
||
</html>
|