Eddie Ringle

I do some things sometimes
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Parsing Strings to Integers in Rust

Starting off my first real post to this new blog with something useful, I figured I'd share a solution to an annoying problem I ran into while learning Rust. The other day, as an exercise, I was porting a prime number benchmark to get a feel for how Rust handles things like program arguments and precise timers.

One of the first issues I encountered was in trying to convert arguments passed to the program as a String to an integer type. In C, this is easily handled using the atoi() function, so I was dismayed that an equivalently simple solution was immediately available (or at least, my attempts to peruse the Rust documentation made it seem that way).

Most of my Google searches led me to the FromStr trait and its from_str function. Results from early in Rust's history suggested it was as simple as C's atoi(), in that it existed as a standalone function I could call at any time, with a call to unwrap() chained onto the end:

let two: i32 = from_str("2").unwrap();

No importing modules or anything special needed. Alas, further Googling began turning up less and less helpful material. I finally managed to get it working by importing the FromStr trait and calling the function through it:

use std::str::FromStr;


let two: i32 = FromStr::from_str("2").unwrap();

This seemed rather clunky to me, but it worked and I was tired of searching for any further solution so I stuck to it.

Fast-forward to today, and I stumbled across this thread on the /r/rust subreddit. There, what I presume to be two Rust team members stated that from_str() had been removed in December, and it was replaced by str.parse(). I was a little annoyed since the from_str() function is still documented in Rust's standard library reference, with no mention whatsoever that it had been replaced.

Anyways, I present to you what I can only hope is the cutting edge in parsing strings to integers in Rust:

let two: i32 = "2".parse().unwrap();

How nifty is that? Much better than the mess above, and you also don't have to bother with importing any additional modules or traits.

Hopefully this helps someone out while they learn Rust as the language itself arrives at 1.0 (which I trust means we'll see less of the above insanity soon).