Why does my string not match when reading user inp

问题:

I'm trying to get user input and check if the user put in "y" or "n". Surprisingly, in the below code, neither the if nor the if else case executes! Apparently, correct_name is neither "y" nor "n". How can that be? Am I doing my string conversion wrong or something?

use std::io;

fn main() {
    let mut correct_name = String::new();
    io::stdin().read_line(&mut correct_name).expect("Failed to read line");
    if correct_name == "y" {
        println!("matched y!");
    } else if correct_name == "n" {
        println!("matched n!");
    }
}

回答1:

read_line includes the terminating newline in the returned string. Add .trim_right_matches("\r\n") to your definition of correct_name to remove the terminating newline.

回答2:

Instead of trim_right_matches, I'd recommend using trim_right or even better, just trim:

use std::io;

fn main() {
    let mut correct_name = String::new();
    io::stdin().read_line(&mut correct_name).expect("Failed to read line");

    let correct_name = correct_name.trim();

    if correct_name == "y" {
        println!("matched y!");
    } else if correct_name.trim() == "n" {
        println!("matched n!");
    }
}

This last case handles lots of types of whitespace:

Returns a string slice with leading and trailing whitespace removed.

'Whitespace' is defined according to the terms of the Unicode Derived Core Property White_Space.

So Windows / Linux / macOS shouldn't matter.

---

You could also use the trimmed result's length to truncate the original String, but in this case you should only use trim_right!

let trimmed_len = correct_name.trim_right().len();
correct_name.truncate(trimmed_len);

回答3:

You can use the chomp-nl crate which provides a chomp function which returns a string slice without the newline characters.

There is also a trait ChompInPlace if you prefer to do this in-place.

Disclaimer: I am the author of this library.