Golang : Count number of runes in string

This just a note for myself and perhaps it can be useful to you as well.

To count a length(size) of a string, typically a programmer will just settle for the the builtin.Len() function. However, when dealing with strings with utf8 characters. Please use the utf8.RuneCountInString() function. See the code below to know why :

 package main

 import (

 func main() {
 str := "abc"

 fmt.Printf("Length %s with len() is %d\n", str, len(str)) // correct

 unicodeStr := "fuß"

 fmt.Printf("Length %s with len() is %d\n", unicodeStr, len(unicodeStr)) // incorrect

 fmt.Printf("Length %s with utf8.RuneCountInString() is %d\n", unicodeStr, utf8.RuneCountInString(unicodeStr)) // correct

 unicodeStr2 := "你好"

 fmt.Printf("Length %s with len() is %d\n", unicodeStr2, len(unicodeStr2)) // incorrect

 fmt.Printf("Length %s with utf8.RuneCountInString() is %d\n", unicodeStr2, utf8.RuneCountInString(unicodeStr2)) // correct


Output :

Length abc with len() is 3

Length fuß with len() is 4

Length fuß with utf8.RuneCountInString() is 3

Length 你好 with len() is 6

Length 你好 with utf8.RuneCountInString() is 2

  See also : Golang : convert rune to integer value

By Adam Ng

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