Why Doesn't String Indexing in Go Always Return the Expected Character?

Indexing Characters in Golang Strings

To retrieve characters from a string, you use indexing operations. However, you may encounter cases where the indexed value doesn't match the expected character. For instance, in the code below:

package main

import "fmt"

func main() {
    fmt.Print("HELLO"[1])
}

The output is 69 instead of the letter "E."

Understanding Golang String Encoding

Golang uses UTF-8 encoding for string literals. ASCII characters, including the letter "E," occupy a single byte. However, larger Unicode characters may be represented by multiple bytes.

Using Runes for Character Indexing

To index characters correctly, use runes: integers representing Unicode code points. A rune is the underlying type for characters in UTF-8. You can convert a byte to a rune using the rune() function.

Converting Bytes to Characters

To convert a byte to its corresponding character, you can use the string() function:

fmt.Println(string("Hello"[1])) // ASCII only

This approach works well for ASCII characters.

Converting Runes to Characters

For Unicode characters, you can convert a rune to a character using the []rune() slice:

fmt.Println(string([]rune("Hello, 世界")[1])) // UTF-8

Example with Unicode Characters

Consider the following example:

fmt.Println(string([]rune("Hello, 世界")[8])) // UTF-8

This will print "界," which is the Unicode code point for the Chinese character "world."

Additional Resources

• [Go Programming Language Specification section on Conversions](https://golang.org/ref/spec#Conversions)
• [The Go Blog: Strings, bytes, runes and characters in Go](https://blog.golang.org/strings-bytes-runes-and-characters-in-go)

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