How do I match on a string read from standard input? [duplicate]

Question

In an exercise to learn Rust, I'm trying a simple program that will accept your name, then print your name if it's Valid.

Only "Alice" and "Bob" are valid names.

use std::io;

fn main() {
    println!("What's your name?");
    let mut name = String::new();

    io::stdin().read_line(&mut name)
    .ok()
    .expect("Failed to read line");

    greet(&name);
}

fn greet(name: &str) {
    match name {
        "Alice" => println!("Your name is Alice"),
        "Bob"   => println!("Your name is Bob"),
        _ => println!("Invalid name: {}", name),
    }
}

When I cargo run this main.rs file, I get:

What's your name?
Alice
Invalid name: Alice

Now, my guess is, because "Alice" is of type &'static str and name is of type &str, maybe it's not matching correctly...

Try match name.trim() { ... }. I can't test it at the moment but I bet there's a newline character in the input. — A.B.
– A.B., Commented Jul 21, 2015 at 14:14
that was it... i always forget about that, thanks! If you post an answer, i'll upvote and accept. — ddavison
– ddavison, Commented Jul 21, 2015 at 14:15
If there had been type mismatch it would not have compiled. You can see precisely what’s in a string by formatting it with Debug ({:?}) instead of Display ({}), too. — Chris Morgan
– Chris Morgan, Commented Jul 22, 2015 at 1:01

Hauleth · Accepted Answer · 2015-07-21 14:17:18Z

9

I bet that it isn't caused by type mismatch. I place my bet on that there are some invisible characters (new line in this case). To achieve your goal you should trim your input string:

match name.trim() {
    "Alice" => println!("Your name is Alice"),
    "Bob"   => println!("Your name is Bob"),
    _ => println!("Invalid name: {}", name),
}

answered Jul 21, 2015 at 14:17

Hauleth

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1 Comment

ddavison Over a year ago

A.B. hasn't submitted an answer yet, so i'll just accept yours.

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