rustLogic errorMedium

Truncate string on non-char boundary panics

Time: 0:00

BugFind the bug and fix the code

What it should do

Truncate string to n characters safely. Example: safe_truncate_string("Hello 🌍", 7) -> "Hello 🌍"

What happens instead

panicked at 'byte index 7 is not a char boundary'

fn safe_truncate_string(mut s: String, max_chars: usize) -> String {
    // String::truncate takes a byte index, not a character count!
    if s.len() > max_chars {
        s.truncate(max_chars);
    }
    s
}

fn main() {
    println!("{}", safe_truncate_string("Hello 🌍".to_string(), 7));
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

⏱️0:00

Hints

🏆 0 hints = Flawless Solve

Think & Test Cooldown

2:00 remaining

Take a moment to read the bug symptom and trace the code with Run & Check before unlocking Hint 1.

Hint 2

Unlocks after Hint 1

Hint 3

Unlocks after Hint 2

This bug belongs to the logic errors pattern

The wrong operator, an inverted condition, a formula the right way round but backwards.

Learn the logic errors pattern Step through your own code

<iframe src="https://trybughunt.com/embed/c99e6f71-826a-46e9-bcf8-170862cca5b8" title="Debugging challenge: Truncate string on non-char boundary panics" width="100%" height="580" loading="lazy" style="border:1px solid #d4d4d8;border-radius:12px;max-width:760px"></iframe> <p style="font-size:14px">Debugging challenge from <a href="https://trybughunt.com/challenges/c99e6f71-826a-46e9-bcf8-170862cca5b8">TryBugHunt</a></p>

fn safe_truncate_string(mut s: String, max_chars: usize) -> String { // String::truncate takes a byte index, not a character count! if s.len() > max_chars { s.truncate(max_chars); } s } fn main() { println!("{}", safe_truncate_string("Hello 🌍".to_string(), 7)); }

Truncate string on non-char boundary panics

What it should do

What happens instead

More logic errors to practise

Truncate string on non-char boundary panics

What it should do

What happens instead

More logic errors to practise