How to check if string contains substring in Rust

Using String contains Function

The easiest way to check if a Rust string contains a substring is to use String::contains method.

The contains method Returns true if the given pattern matches a sub-slice of this string slice.

fn main() {
  let s = "Apple,世界";

  // pub fn contains<'a, P>(&'a self, pat: P) -> bool
  println!("{}", s.contains("e"));
  println!("{}", s.contains("世"));
}

true
true

The pattern can be a &str, char, a slice of chars, or a function or closure that determines if a character matches.

Using String find Method

Returns the byte index of the first character of this string slice that matches the pattern.

Returns None if the pattern doesn’t match.

fn main() {
  let s = "Löwe";

  if s.find('ö') != None {
    // Found
    println!("Found")
  }
  println!("{:?}", s.find('ö'));
  println!("{:?}", s.find('o'));
}

Found
Some(1)
None

Using String chars Method

You can use chars method to check if the string contains at least one lowercase alphabet character.

fn main() {
  let s = "Löwe";

  let b = s.chars().any(|c| c.eq(&'ö'));
  println!("{}", b);
}

true