String Indexing Returns Bytes Not Runes

Why This Happens

Go strings are byte sequences, not character sequences. Indexing a string returns a byte, which may be only part of a multi-byte Unicode character. For range loops over strings yield runes (full Unicode code points), which is usually what you want for text processing.

The Problem

func main() {
    s := "Hello, \u4e16\u754c"
    fmt.Println(len(s))    // 13 (bytes, not characters)
    fmt.Println(s[7])      // 228 (first byte of a 3-byte rune)
}

The Fix

func main() {
    s := "Hello, \u4e16\u754c"
    runes := []rune(s)
    fmt.Println(len(runes)) // 9 (characters)
    fmt.Println(string(runes[7])) // prints correct character
}

Step-by-Step Fix

1. 1

   Identify byte vs rune access

   Check if your code indexes strings directly when it should handle Unicode characters.

2. 2

   Use range for iteration

   for i, r := range s gives you the rune and its byte offset.

3. 3

   Convert to []rune for indexing

   If you need random access to characters, convert the string to []rune first.