CODEWITHSUNDEEP
error-handlingrustmatch
Norbert
Norbert

Reputation: 765

How can I match against a std::io::Error with a Windows error code?

In my tiny little Rust program, I'm calling a Windows API and want to make sure that everything went OK. In order to do so, I'm using the functionality provided by std::io::Error::last_os_error(). I also want to deliberately ignore some of the errors that may occur.

I could not find any information on how to do that, other than just printing out the Error returned by that function. What I actually need is a kind of a match statement in which I can handle the various known errors.

I understand that the function returns an std::io::Error struct but I could not find any information on error IDs or similar concepts.

Currently, my code reads like

use std::io::Error;

fn main() {
    // do some stuff that may lead to an error

    match Error::last_os_error() {
        163 => // Do nothing. This error is to be expected
        // _ =>  Err("Something went wrong "),
    }
}

The actual problem is that last_os_error() returns an error struct but I want to match on the ID of the error that is listed in WinError.h (this program only runs under Windows).

Can anybody help me on how to distinguish the various errors behind the error structs in such a match statement?

Upvotes: 2

Views: 1571

Answers (1)

Shepmaster
Shepmaster

Reputation: 432239

You can use io::Error::raw_os_error to get the original error code and then match against that:

match Error::last_os_error().raw_os_error() {
    Some(163) => {} // Do nothing. This error is to be expected
    Some(e) => panic!("Unknown OS error {}", e),
    None => panic!("Not an OS error!"),
}

It's a different question of whether this is a good idea or not. You can also match against known error types. I'd recommend using that where possible. You may also want to create (or find) an enum that maps the various error codes to human-readable values, as it's a lot easier to tell that you meant NotEnoughMemory instead of SecurityDescriptorInvalid than it is to tell the difference of 123 and 132.

Upvotes: 2

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