Strings and Runes

A Go string is a read-only slice of bytes. The language and the standard library treat strings as containers of text encoded in UTF-8. In other languages strings are made of characters; in Go, a character is called a rune, an integer that represents a Unicode code point.

package main

import (
	"fmt"
	"unicode/utf8"
)

func main() {

s is a string holding the word "hello" in Thai. String literals are UTF-8 encoded text.

	const s = "สวัสดี"

Since strings are bytes, len gives the number of raw bytes.

	fmt.Println("Len:", len(s))

Indexing a string gives the byte at each index.

	for i := 0; i < len(s); i++ {
		fmt.Printf("%x ", s[i])
	}
	fmt.Println()

To count runes, use the utf8 package. Some Thai characters are made of several code points, so the count may surprise you.

	fmt.Println("Rune count:", utf8.RuneCountInString(s))

range decodes each rune and its byte offset.

	for idx, runeValue := range s {
		fmt.Printf("%#U starts at %d\n", runeValue, idx)
	}

The same iteration with utf8.DecodeRuneInString.

	fmt.Println("\nUsing DecodeRuneInString")
	for i, w := 0, 0; i < len(s); i += w {
		runeValue, width := utf8.DecodeRuneInString(s[i:])
		fmt.Printf("%#U starts at %d\n", runeValue, i)
		w = width

A rune can be passed to a function and compared to a rune literal.

		examineRune(runeValue)
	}

Strings cannot be changed in place. Convert to []rune or []byte, change that, and convert back.

	r := []rune("hello")
	r[0] = 'j'
	fmt.Println(string(r))

Raw string literals use backquotes: no escapes, and they can span lines.

	fmt.Println(`C:\no\escapes`)
}

func examineRune(r rune) {

Values in single quotes are rune literals.

	if r == 't' {
		fmt.Println("found tee")
	} else if r == 'ส' {
		fmt.Println("found so sua")
	}
}

$ go run ./18_strings_and_runes
Len: 18
e0 b8 aa e0 b8 a7 e0 b8 b1 e0 b8 aa e0 b8 94 e0 b8 b5 
Rune count: 6
U+0E2A 'ส' starts at 0
U+0E27 'ว' starts at 3
U+0E31 'ั' starts at 6
U+0E2A 'ส' starts at 9
U+0E14 'ด' starts at 12
U+0E35 'ี' starts at 15

Using DecodeRuneInString
U+0E2A 'ส' starts at 0
found so sua
U+0E27 'ว' starts at 3
U+0E31 'ั' starts at 6
U+0E2A 'ส' starts at 9
found so sua
U+0E14 'ด' starts at 12
U+0E35 'ี' starts at 15
jello
C:\no\escapes

View on GitHub