In golang string is a sequence of bytes. A string literal actually represents a UTF-8 sequence of bytes. In UTF-8, ASCII characters are single-byte corresponding to the first 128 Unicode characters.All other characters are between 1 -4 bytes. That is why it is not possible to get the exact length of the string using the built-in len function of go. It might work if the string only contains ASCII characters. But if the string contains Non-ASCII characters then it will give the correct output.
For example, see below the program and its output. £ in the string below is a Non-ASCII character.
package main
import "fmt"
func main() {
sample := "ab£c"
for i := 0; i < 4; i++ {
fmt.Printf("%c\n", sample[i])
}
fmt.Printf("Length is %d\n", len(sample))
}Output:
a
b
Â
£
Length is 5As you might have noticed , it prints different characters than expected and length is also 5 instead of 4. Why is that? To answer please remember we said that a string is essentially a slice of bytes. Let's print that slice of bytes using
sample := "ab£c"
fmt.Println([]byte(sample))Output will be
[97 98 194 163 99]This is the mapping of each of character to its byte sequence. As you can notice a, b, c take each 1 byte but £ takes two bytes. That is why the length of the string is 5 and not 4
| a | 97 |
| b | 98 |
| £ | 194, 163 |
| c | 99 |
There are two alternatives to get the correct length of a string
- Using rune data type . rune data type represents a Unicode point. Once a string is converted to an array of rune then it is possible to get the correct length of a string.
- Using range operator over the string and calculating the length. range operator iterates over the UTF-8 characters in a string.
The below code illustrates the above two points.
package main
import "fmt"
func main() {
sample := "ab£c"
//Using rune
s := []rune(sample)
fmt.Println(len(s))
//Using range
len := 0
for range sample {
len++
}
fmt.Println(len)
}Output:
4
4