打开

可以使用 open 函数以只读模式打开文件。

File 拥有一个资源，即文件描述符，并在其被 drop 时负责关闭文件。

use std::fs::File;
use std::io::prelude::*;
use std::path::Path;

fn main() {
    // Create a path to the desired file
    let path = Path::new("hello.txt");
    let display = path.display();

    // Open the path in read-only mode, returns `io::Result<File>`
    let mut file = match File::open(&path) {
        Err(why) => panic!("couldn't open {}: {}", display, why),
        Ok(file) => file,
    };

    // Read the file contents into a string, returns `io::Result<usize>`
    let mut s = String::new();
    match file.read_to_string(&mut s) {
        Err(why) => panic!("couldn't read {}: {}", display, why),
        Ok(_) => print!("{} contains:\n{}", display, s),
    }

    // `file` goes out of scope, and the "hello.txt" file gets closed
}

以下是预期成功的输出

$ echo "Hello World!" > hello.txt
$ rustc open.rs && ./open
hello.txt contains:
Hello World!

（建议您在不同的失败条件下测试前面的示例：hello.txt 不存在，或者 hello.txt 不可读，等等。）