Cookbooks
Rust
Chapter 2. Strings
Finding the length of a string

Rust:
Finding the length of a string

How to:

Rust gives you len() for straight-up length:

fn main() {
    let greeting = "Hello, world!";
    println!("Length: {}", greeting.len());
}

Output: Length: 13

But beware, len() counts bytes, not characters. For character count, use .chars().count():

fn main() {
    let greeting = "¡Hola, mundo!";
    println!("Character count: {}", greeting.chars().count());
}

Output: Character count: 12

Deep Dive

len() counts bytes because Rust strings are UTF-8 encoded. Historically, early computers used ASCII, representing each character with a single byte. UTF-8, however, supports a vast array of characters, using 1 to 4 bytes each.

When you call len(), Rust counts the bytes in a string, which is fast but won’t always match the character count. For instance, emojis or certain accented characters take more than one byte. That’s why .chars().count() matters—it iterates over the characters and gives the Unicode scalar value count, which is the actual character count most people expect.

As for alternatives, .chars().count() is accurate but slow for long strings because it has to iterate through each character. If performance is critical, and you’re sure about dealing with ASCII or fixed-width Unicode characters, len() is more efficient.

Lastly, remember Rust’s string indexing doesn’t allow direct access by character position because of how UTF-8 encoding works. Rust prevents operations that could accidentally break or slice strings at invalid points, which might not represent full characters.

See Also

Extracting substringsInterpolating a string