Panics on overflow

[Niklas Fiekas]

Hi, I just stumbled on a problem with overflows. I was expecting:

assert_eq!(None, atoi::<u8>(b"256"));

Instead it panics in debug mode and wraps around in release mode. I am not sure how to fix this, since there do not seem to be generic traits that provide checked addition/multiplication.

[Markus Klein]

Tough. Would switching to u32 and testing size afterwards do the trick for you?

[Markus Klein]

Can your use case be supported by choosing a larger type to read the value? Let's say you want to parse an u8:

if let Some(input) = atoi::<u32>(b"256"){
    if input > std::u8::Max as u32{
        // Deal with overflow
    }
}

If you are in doubt u32 might also not be large enough, to hold the ... wait a moment ...

[Markus Klein]

... I just realised that we would only need to check for the overflow after adding the third digit (for u8) or the say the tenth digit (for u32). Every number of digits smaller won't overflow and every number larger than that is guaranteed to do so. This just might be reasonable cheap.

[Markus Klein]

Closing this issue. Users can now opt into overflow checking using the checked crate. This also allows to distinguish between an overflow and not finding a number.

extern crate atoi;
extern crate checked;

fn main() {
    let number = atoi::atoi::<checked::Checked<u8>>(b"256");
    println!("Result: {:?}", number);
}

Prints: Result: Some("overflow").

[Niklas Fiekas]

Looks good. Thanks