Rust: fail to parse integer to string, ParseIntError [duplicate]

Question

I just started to experiment with Rust, so I've implemented modified version from Book's "Guessing game". Every first time I'm trying to enter the number, program fails to parse integer from string:

Guess the number!
Input your guess:
50
You guessed 50
 (4 bytes)!
thread 'main' panicked at 'Wrong number format!: ParseIntError { kind: InvalidDigit }', src\libcore\result.rs:997:5
note: Run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
error: process didn't exit successfully: `target\release\experiment.exe` (exit code: 101)

Code applied below.

I already tried other integer types.

use std::io;
use rand::Rng;

fn main() {
    println!("Guess the number!\nInput your guess:");

    let mut guess = String::new();

    let secnum = rand::thread_rng().gen_range(1,101);

    'br: loop { 
        match io::stdin().read_line(&mut guess) {
            Ok(okay) => {
                println!("You guessed {} ({} bytes)!", guess, okay);

                let intguess = guess.parse::<u8>()
                    .expect("Wrong number format!");

                match secnum.cmp(&intguess) {
                    std::cmp::Ordering::Less => {
                        println!("Your guess is smaller!");
                    }
                    std::cmp::Ordering::Greater => {
                        println!("Your guess is bigger!");
                    }
                    std::cmp::Ordering::Equal => {
                        println!("You guessed right!");
                        break 'br;
                    } 
                }
            }
            Err(erro) => {
                println!("Failed to read the line: {}!", erro);
            }
        }
    }
}

The result of read_line includes the '\n' character, which is causing the parse error. — Peter Hall
– Peter Hall, Commented Mar 31, 2019 at 6:59
You can just call string.clear() to reuse the same string. In this kind of IO code, there is really very little impact to allocating a new String each time though. — Peter Hall
– Peter Hall, Commented Mar 31, 2019 at 10:47
Does fs:: read_string also do the same, like includes the \n character ? I was reading from this file adventofcode.com/2020/day/1/input — Aritro Shome
– Aritro Shome, Commented Jun 12, 2021 at 6:20

Peter Hall · Accepted Answer · 2020-07-31 10:39:14Z

7

The string output from read_line includes a trailing newline character, so you will need to strip that out in order to parse the number. You can do that with trim_end (or just trim to handle leading whitespace too):

let guess: u8 = guess
    .trim_end()
    .parse()
    .expect("Wrong number format!");

edited Jul 31, 2020 at 10:39

answered Mar 31, 2019 at 7:03

Peter Hall

59.7k17 gold badges168 silver badges229 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Rust: fail to parse integer to string, ParseIntError [duplicate]

1 Answer 1

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Linked

Related