How to parse i64 from a string?

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)

score 37 · Accepted Answer · edited Dec 20 '20 at 11:47

37

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 '20 at 11:47

smbear

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answered Feb 01 '15 at 09:37

Dogbert

212,659
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4

Use `let i: i64 = "123".parse();` instead of ugly template syntax if possible. – Hauleth Feb 01 '15 at 11:46
3

@hauleth, `.parse()` returns `Option`, so that would have to be `let i: Option = "123".parse();`. – Dogbert Feb 01 '15 at 13:08
Yes. Of course. I've forgotten. – Hauleth Feb 01 '15 at 13:09
update: nowadays it returns `Result::Err>` so simple `.parse()` won't work, or am I wrong? – Keeper Hood Jul 04 '19 at 15:06
@KeeperHood A simple parse will still work; you just need to handle the error like you used to handle the `Option`. – Nic Sep 25 '19 at 02:52

How to parse i64 from a string?

1 Answers1