Remove single trailing newline from String without cloning

Question

I have written a function to prompt for input and return the result. In this version the returned string includes a trailing newline from the user. I would like to return th

Answer 1

You can use String::pop or String::truncate:

fn main() {
    let mut s = "hello\n".to_string();
    s.pop();
    assert_eq!("hello", &s);

    let mut s = "hello\n".to_string();
    let len = s.len();
    s.truncate(len - 1);
    assert_eq!("hello", &s);
}

Answer 2

A cross-platform way of stripping a single trailing newline without reallocating the string is this:

fn trim_newline(s: &mut String) {
    if s.ends_with('\n') {
        s.pop();
        if s.ends_with('\r') {
            s.pop();
        }
    }
}

This will strip either "\n" or "\r\n" from the end of the string, but no additional whitespace.

Answer 3

A more generic solution than the accepted one, that works with any kind of line ending:

fn main() {
    let mut s = "hello\r\n".to_string();
    let len_withoutcrlf = s.trim_right().len();
    s.truncate(len_withoutcrlf);
    assert_eq!("hello", &s);
}