将文件作为一个整体读取

use std::fs::File;
use std::io::Read;

fn main() {
    let filename = "src/main.rs";
    // Open the file in read-only mode.
    match File::open(filename) {
        // The file is open (no error).
        Ok(mut file) => {
            let mut content = String::new();

            // Read all the file content into a variable (ignoring the result of the operation).
            file.read_to_string(&mut content).unwrap();

            println!("{}", content);

            // The file is automatically closed when is goes out of scope.
        },
        // Error handling.
        Err(error) => {
            println!("Error opening file {}: {}", filename, error);
        },
    }
}