Rust string comparison failing

Question

This has me going crazy because it should be incredibly simple. I've just started learning Rust and was playing around with if statements. I'm failing to perform simple string comparisons, however.

I'm expecting my code to accept console input and if that input reads "Hello", then "Hi" should be printed. Unfortunately that isn't happening, and instead I get the else option: "I don't understand". <-- pretty apt.

use std::io;

fn main() {
    println!("Say a greeting!");
    loop {
        let mut input = String::new();
        match io::stdin().read_line(&mut input) {
            Ok(_) => {
                let res = say_hi_back(input);
                println!("{}", res);
            }
            Err(error) => println!("error: {}", error),
        }
    }
}

fn say_hi_back(greeting: String) -> String {
    let response = if greeting == "Hello" {
        "Hi".to_string()
    } else {
        "I don't understand".to_string()
    };
    return response;
}

Sorry this is such a noob question, but I'm wondering why greeting != "Hello" when given as input to the console? At first I thought it was some type error, but as far as I know you can freely compare &str types with String types.

How can I tell? I've tried using println to see it's value, but that doesn't show newlines — Luke, May 13 '21 at 12:51
Awesome, thank you. Looks like /r/n were appended! I'll write up the answer. Thanks again. — Luke, May 13 '21 at 13:14
You should probably have a look at str functions, for example `trim`. `\r\n` is platform-specific so you'd better avoid putting it in your code. — Denys Séguret, May 13 '21 at 13:17
Yep! In the end I solved it by just calling trim() on greeting. — Luke, May 13 '21 at 13:23

score 0 · Answer 1 · answered May 13 '21 at 13:17

0

Looks like read_line appends new line to string which means a comparison of "Hello" with "Hello\r\n" will of course fail. I actually found a relevant stack overflow answer: Weird behaviour when using read_line in a loop

answered May 13 '21 at 13:17

Luke

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Rust string comparison failing

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