2017-03-02 23:36:03 +08:00
<!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" >
2017-03-13 23:27:01 +08:00
< 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： < / 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.h
2017-03-02 23:36:03 +08:00
< / 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" >
2017-03-05 00:41:41 +08:00
< 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 > ， （ ） ： < / 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， < 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 >
2017-03-02 23:36:03 +08:00
< / 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 >
