Learn Rust Coding · Lesson

UTF-8 and Chars

Unicode handling.

UTF-8 and Chars is a free Learn Rust Coding lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Learn Rust Coding learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Rust Strings Are UTF-8

Every Rust String and &str is encoded as UTF-8. This means text can include any Unicode character, not just ASCII.

fn main() {
    let s = String::from("caf\u{e9}");
    println!("{}", s);
}

What Is UTF-8?

UTF-8 encodes each Unicode character using one to four bytes. ASCII characters use a single byte; accented letters and emoji use more.

fn main() {
    let ascii = "A";          // 1 byte
    let accent = "\u{e9}";    // 2 bytes (e-acute)
    println!("{} bytes vs {} bytes", ascii.len(), accent.len());
}

Bytes vs Characters

Because of multi-byte encoding, len() returns bytes, while the number of characters may be smaller.

fn main() {
    let s = "caf\u{e9}";
    println!("bytes {}", s.len());
    println!("chars {}", s.chars().count());
}

The char Type Is Unicode

A Rust char is a 4-byte value that can hold any Unicode scalar value, far beyond a single byte.

fn main() {
    let letter = 'Z';
    let accented = '\u{f1}'; // n with tilde
    println!("{} {}", letter, accented);
}

Iterating Characters

Use chars() to walk through text by character. This correctly handles multi-byte characters.

fn main() {
    let s = "a\u{e9}z";
    for c in s.chars() {
        println!("{}", c);
    }
}

Why You Cannot Index by Number

Rust does not allow s[0] on a string. Because characters vary in byte size, indexing by a single number would be ambiguous and unsafe.

fn main() {
    let s = "hello";
    // let c = s[0]; // error: cannot index a str
    let first = s.chars().next().unwrap();
    println!("{}", first);
}

Getting the nth Character

Use the iterator method nth to fetch a character by position. It returns an Option.

fn main() {
    let s = "abcdef";
    let third = s.chars().nth(2);
    println!("{:?}", third);
}

Iterating Bytes

When you truly need raw bytes, use bytes() which yields u8 values.

fn main() {
    let s = "AB";
    for b in s.bytes() {
        println!("{}", b);
    }
}

Slicing on Byte Boundaries

String slices use byte indices. Slicing must land on a valid character boundary, or the program panics.

fn main() {
    let s = "hello";
    let part = &s[0..3]; // valid ASCII boundary
    println!("{}", part);
}

char Methods

The char type has handy methods like is_alphabetic, is_numeric, and to_uppercase.

fn main() {
    let c = 'k';
    println!("alpha {} numeric {}", c.is_alphabetic(), c.is_numeric());
    println!("upper {}", c.to_uppercase());
}

Counting Specific Characters

Combine chars with filter to count characters matching a condition.

fn main() {
    let s = "banana";
    let a_count = s.chars().filter(|&c| c == 'a').count();
    println!("a appears {} times", a_count);
}

Quick Check

Recall why string length can surprise you.

Recap

UTF-8 and chars in Rust:

Strings are UTF-8; characters use 1 to 4 bytes.
len() gives bytes; chars().count() gives characters.
You cannot index a string by number; use chars() or nth.
Slices must fall on character boundaries.

fn main() {
    let s = "sm\u{ee}le";
    println!("bytes {} chars {}", s.len(), s.chars().count());
    for c in s.chars() {
        print!("{} ", c);
    }
    println!();
}

Frequently asked questions

Is the “UTF-8 and Chars” lesson free?

Yes — the full text of “UTF-8 and Chars” is free to read here on the web, and the Learn Rust Coding course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Learn Rust Coding course, upgrade to CoddyKit PRO.

What will I learn in “UTF-8 and Chars”?

Unicode handling. You practise Learn Rust Coding with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Learn Rust Coding?

No prior experience is required. Learn Rust Coding on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “UTF-8 and Chars” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Learn Rust Coding lesson?

Yes. Every Learn Rust Coding lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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