rust - 将结果的错误代码转换为字符串

Question

我想打开一个文件，但是在我的程序无法打开它的情况下，我想向用户打印一条错误消息并提早退出。

use std::fs::File;

fn main() {
    let file = "something.txt";
    let file = match File::open(file) {
        Ok(val) => val,
        Err(e) => {
            //err_string is not a real function, what would you use?
            println!("failed to open file: {}", e.err_string());
            return;
        }
    };
}

Answer 1

向用户显示错误消息并提早退出:
1.您可以使用File::open("something.txt")?，尝试以下示例(无需 panic ，仅显示错误消息):

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

fn main() -> std::io::Result<()> {
    let mut file = File::open("something.txt")?;
    let mut contents = String::new();
    file.read_to_string(&mut contents)?;
    assert_eq!(contents, "Hello, world!");
    Ok(())
}

输出(错误时):

Error: Os { code: 2, kind: NotFound, message: "No such file or directory" }

使用.expect("msg"): panic (如果值是Err)，并带有包括所传递消息的 panic 消息和Err的内容(开发人员友好的，因为显示了文件名和行号):

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

fn main() {
    let mut file = File::open("something.txt").expect("failed to open file");
    let mut contents = String::new();
    file.read_to_string(&mut contents)
        .expect("failed to read file");
    assert_eq!(contents, "Hello, world!");
}

输出(错误时):

thread 'main' panicked at 'failed to open file: 
Os { code: 2, kind: NotFound, message: "No such file or directory" }', 
src/main.rs:17:20
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

无需 panic ，只显示一条错误消息:

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

fn main() {
    let mut file = match File::open("something.txt") {
        Ok(val) => val,
        Err(e) => {
            println!("failed to open file: {}", e);
            return;
        }
    };

    let mut contents = String::new();
    file.read_to_string(&mut contents)
        .expect("failed to read file");
    assert_eq!(contents, "Hello, world!");
}

输出(错误时):

failed to open file: No such file or directory (os error 2)