Loop Labels in Rust

Learn how to avoid confusion in complex loop structures with labels.

wonjoon

March 25, 2025 · 2 min read

#dev #rust #2025

Why Use Loop Labels in Rust? #

When you have nested loops, calling break or continue may only affect the nearest loop. If you want to target an outer loop, Rust lets you assign a label using the label_name: syntax.

Using loop with labels #

fn main() {
    let mut count = 0;

    'counting_up: loop {
        println!("count = {count}");
        let mut remaining = 10;

        loop {
            println!("remaining = {remaining}");
            
            if remaining == 9 {
                break; // exits this inner loop only
            }

            if count == 2 {
                break 'counting_up; // exits the labeled outer loop
            }
            
            remaining -= 1;
        }

        count += 1;
    }

    println!("End count = {count}");
}

break exits the inner loop
break 'counting_up exits the outer labeled loop
You can apply labels to any loop, not just loop blocks

Using while with labels #

fn main() {
    let mut i = 0;

    'outer: while i < 5 {
        let mut j = 0;
        while j < 5 {
            if i == 2 && j == 2 {
                break 'outer; // exits the outer while loop
            }
            j += 1;
        }
        i += 1;
    }

    println!("Done: i = {i}");
}

Using for with labels #

fn main() {
    'outer: for x in 0..5 {
        for y in 0..5 {
            if x == 2 && y == 2 {
                break 'outer; // exits the outer for loop
            }
            println!("x = {x}, y = {y}");
        }
    }
}

Using continue with labels #

'outer: for x in 0..3 {
    for y in 0..3 {
        if y == 1 {
            continue 'outer; // skips rest of inner loop and moves to next outer iteration
        }
        println!("x = {x}, y = {y}");
    }
}

Summary #

Concept	Description
break	Exits the nearest loop
break ’label	Exits the specific loop with the given label
continue ’label	Skips to the next iteration of the labeled loop
Label works on	`loop`, `while`, `for`, and `continue`