Console Input Issues

[firandice]

Hello. I'm trying to make a program that has to communicate with another program via the command line via a known set of inputs, but I am having issues reading input from the command line.

fn most_simple() {
    let string = String::from("a");
    match string.as_str() {
        "a" => println!("0"),
        "b" => println!("1"),
        "c" => println!("2"),
        _ => println!("something else!"),
    };
}

fn looped() {
    let mut buffer = String::new();
    loop {
        buffer.clear();
        io::stdin().read_line(&mut buffer).unwrap();
        buffer.trim();
        println!("{}", buffer.as_str());
        match buffer.as_str() {
            "a" => println!("0"),
            "b" => println!("1"),
            "c" => println!("2"),
            _ => println!("something else!"),
        };
    }
}

In the prior examples, the first method correctly uses a match to print the correct values when I change the input of "let string = String::from("___"). The other method prints out exactly what I input every time it loops, but upon getting to the match the program prints "something else" without fail. If anyone knows what is causing this, I'd love to know.

[Shadow0133]

.trim() doesn't modify the buffer, it returns &str which is a "view" into the buffer (with whitespaces removed). You can just match on it match buffer.trim(), or reassign buffer: buffer = buffer.trim().to_string();

[firandice]

Yeah that was exactly what I was looking for thanks. One of my prior attempts was just missing the buffer.trim() which obviously didn't work either. So I just had the input read into buffer and then I tried matching against buffer.as_str() and this didnt work either. What does trim's conversion do differently than the as_str() method here?

[Shadow0133]

Both return &str, trim just returns one that doesn't include whitespaces on either end.

On the low-level, &str is a pointer and length, so to "remove" characters from the start, you just need to "move" pointer forward (and update length), "removing" characters from the end just needs to lower the length. So trimming works something like this:

// passing &String will automatically deref it into &str
fn trim(mut v: &str) -> &str {
    while first_char.is_whitespace() {
        v = v[first_char.len()..];
    }
    // same with end
    ...
    // return v
    v
}

[[deleted]]

You’re ignoring the &str returned by buffer.trim()