How to parse i64 from a string? [duplicate]

Question

Apparently, something has changed and thus I can't parse i64 from string:

use std::from_str::FromStr;

let tree1: BTreeMap<String, String> = //....
let my_i64: i64 = from_str(tree1.get("key1").unwrap().as_slice()).unwrap();

Error:

16:27 error: unresolved import `std::from_str::FromStr`. Could not find `from_str` in `std`

$ rustc -V
rustc 1.0.0-nightly (4be79d6ac 2015-01-23 16:08:14 +0000)

smbear · Accepted Answer · 2020-12-20 11:47:15Z

45

Your import fails because the FromStr trait is now std::str::FromStr. Also, from_str is no longer in the prelude. The preferred way to convert strings to integers is str::parse

fn main() {
    let i = "123".parse::<i64>();
    println!("{:?}", i);
}

prints

Ok(123)

Demo

edited Dec 20, 2020 at 11:47

smbear

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answered Feb 1, 2015 at 9:37

Dogbert

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5 Comments

Hauleth Over a year ago

Use let i: i64 = "123".parse(); instead of ugly template syntax if possible.

Dogbert Over a year ago

@hauleth, .parse() returns Option<T>, so that would have to be let i: Option<i64> = "123".parse();.

Hauleth Over a year ago

Yes. Of course. I've forgotten.

Keeper Hood Over a year ago

update: nowadays it returns Result<F, <F as FromStr>::Err> so simple .parse() won't work, or am I wrong?

anon Over a year ago

@KeeperHood A simple parse will still work; you just need to handle the error like you used to handle the Option.

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