goLogic errorMedium

Truncating multi-byte string by raw byte slice

Time: 0:00

BugFind the bug and fix the code

What it should do

Truncate string to at most n characters. Example: safeTruncateString("Hello 世界", 7) -> "Hello 世"

What happens instead

Raw byte truncation cuts unicode rune in half, producing replacement char

package main

import "fmt"

func safeTruncateString(s string, maxChars int) string {
	// Slices raw bytes, corrupting multibyte UTF-8 characters
	if len(s) <= maxChars {
		return s
	}
	return s[:maxChars]
}

func main() {
	fmt.Println(safeTruncateString("Hello 世界", 7))
}

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

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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.

Learn the logic errors pattern Step through your own code

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package main import "fmt" func safeTruncateString(s string, maxChars int) string { // Slices raw bytes, corrupting multibyte UTF-8 characters if len(s) <= maxChars { return s } return s[:maxChars] } func main() { fmt.Println(safeTruncateString("Hello 世界", 7)) }

Truncating multi-byte string by raw byte slice

What it should do

What happens instead

More logic errors to practise

Truncating multi-byte string by raw byte slice

What it should do

What happens instead

More logic errors to practise