force error when parsing "01" from string to number in rust

Question

I've have a string like this

"32" or "28", "01", "001"

and I want to parse them to a number. However it should not parse a string that starts with 0.

Currently, I'm doing this

let num = str.parse().unwrap_or(-1);

With this implementation it converts "01" to 1 but I want to force -1 when the string stars with 0.

harmic · Accepted Answer · 2022-11-10 22:22:26Z

1

As mentioned in the comments - you could use this:

let num = if s.len() > 1 && s.starts_with('0') {
    -1
} else {
    s.parse().unwrap_or(-1)
};

answered Nov 10, 2022 at 6:48

harmic

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4 Comments

"0" is ok, I only want to return -1 when it's something like this "00" or "01"

just add s != "0" && to the condition

@cafce25 yeah it works but I wish there was a more elegant solution

If you're willing to add a dependency you cold use regex crate Regex::new(r"^0\d+").unwrap().is_match(s)