错误时打印当前预期路径

Question

这里生锈新手.我正在尝试打开一个文件:

let file = File::open("file.txt").unwrap();

由于我的构建设置,它看起来像我的二进制和txt不是我期望它或我做错了所以我得到一个:

thread '<main>' panicked at 'called `Result::unwrap()` on an `Err` value: Error { repr: Os { code: 2, message: "No such file or directory" } }', ../src/libcore/result.rs:736

错误消息没有说明txt必须存在的预期路径应该是什么,以便我的程序和测试看到它.如何打印此预期路径？我想打印一条消息,如:

The file "/expected/folder/file.txt" does not exist

Answer 1

只是匹配Result显式返回所需的错误,如下所示:

use std::fs::File;
use std::io::ErrorKind;

fn main() {
    match File::open("file.txt") {
        Ok(file) => 
            println!("The file is of {} bytes", file.metadata().unwrap().len()),
        Err(ref e) if e.kind() == ErrorKind::NotFound =>
            println!("The file {}/file.txt does not exist", std::env::current_dir().unwrap().display()),
        Err(e) => 
            panic!("unexpected error: {:?}", e),
    }
}

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