rustLogic errorMedium

UTF-8 byte index is not a char boundary panic

Time: 0:00

BugFind the bug and fix the code

What it should do

Extract first 2 characters from header string safely. Example: extract_header_prefix("🦀 Rust") -> "🦀 "

What happens instead

panicked at 'byte index 2 is not a char boundary; it is inside '🦀' (bytes 0..4)'

fn extract_header_prefix(s: &str) -> String {
    // Slicing &s[0..2] cuts through a 4-byte UTF-8 emoji
    if s.len() < 2 {
        s.to_string()
    } else {
        s[0..2].to_string()
    }
}

fn main() {
    println!("{}", extract_header_prefix("🦀 Rust"));
}

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

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Hint 3

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This bug belongs to the logic errors pattern

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

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fn extract_header_prefix(s: &str) -> String { // Slicing &s[0..2] cuts through a 4-byte UTF-8 emoji if s.len() < 2 { s.to_string() } else { s[0..2].to_string() } } fn main() { println!("{}", extract_header_prefix("🦀 Rust")); }

UTF-8 byte index is not a char boundary panic

What it should do

What happens instead

More logic errors to practise

UTF-8 byte index is not a char boundary panic

What it should do

What happens instead

More logic errors to practise