文件:: open（）的恐慌，當文件不存在

Question

我運行此：

use std::error::Error; 
use std::fs::File; 

fn main() { 
    try_main().unwrap(); 
} 

fn try_main() -> Result<(), Box<Error>> { 
    try!(check_file("andre")); 
    Ok(()) 
} 

fn check_file(user: &str) -> Result<(), Box<Error>>{ 
    let suspend_file_name = format!("{}{}", "/var/cpanel/suspended/", user); 
    let suspend_file = try!(File::open(suspend_file_name)); 

    Ok(()) 
} 

而且收到此錯誤：

Running `target/debug/test` 
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:731 
An unknown error occurred 

我想這應該返回一個錯誤？我正在使用Rust 1.3，不知道我做錯了什麼。

Answer 1

您的程序正在按照您所說的完成。檢查此版本：

use std::error::Error; 
use std::fs::File; 

fn main() { 
    let x = try_main(); 
    println!("{}", x.is_ok()); 
} 

fn try_main() -> Result<(), Box<Error>> { 
    try!(check_file("andre")); 
    Ok(()) 
} 

fn check_file(user: &str) -> Result<(), Box<Error>>{ 
    let suspend_file_name = format!("{}{}", "/var/cpanel/suspended/", user); 
    let _suspend_file = try!(File::open(suspend_file_name)); 

    Ok(()) 
} 

輸出爲false，這表明的try_main結果是一個Err。如果您unwrap說：

Panics if the value is an Err, with a panic message provided by the Err's value.

所以，File::open不慌，但方法明確表示，將恐慌上Err值上Err值確實恐慌。