How to convert an array of bytes to an array of strings in Go?

Question

I'm trying to complete this exercise in the Tour of Go, https://tour.golang.org/methods/18, to implement a String() method for an IPAddr type consisting of an array of four bytes. So far I've tried:

package main

import (
    "fmt"
    "strings"
)

type IPAddr [4]byte

func (ipaddr IPAddr) String() string {
    ipaddrStrings := make([]string, 4)
    for i, b := range ipaddr {
        ipaddrStrings[i] = string(b)
    }
    return strings.Join(ipaddrStrings, ".")
}

func main() {
    hosts := map[string]IPAddr{
        "loopback":  {127, 0, 0, 1},
        "googleDNS": {8, 8, 8, 8},
    }
    for name, ip := range hosts {
        fmt.Printf("%v: %v\n", name, ip)
    }
}

However, this prints

loopback: ...
googleDNS:.

I've also tried, following https://programming.guide/go/convert-byte-slice-to-string.html, to do string(ipaddr), but this results in a

cannot convert ipaddr (type IPAddr) to type string

How can I complete this exercise?

Answer 1

Add this method:

func (a IPAddr) String() string {
    return fmt.Sprintf("%d.%d.%d.%d", a[0], a[1], a[2], a[3])
}

Answer 2

Instead of string(b), try strconv.Itoa(int(b)) to convert the numeric value to a string.

Answer 3

Independently, I came up with the same solution as outlined by bserdar:

package main

import (
    "fmt"
    "strconv"
    "strings"
)

type IPAddr [4]byte

func (ipaddr IPAddr) String() string {
    ipaddrStrings := make([]string, 4)
    for i, b := range ipaddr {
        ipaddrStrings[i] = strconv.Itoa(int(b))
    }
    return strings.Join(ipaddrStrings, ".")
}

func main() {
    hosts := map[string]IPAddr{
        "loopback":  {127, 0, 0, 1},
        "googleDNS": {8, 8, 8, 8},
    }
    for name, ip := range hosts {
        fmt.Printf("%v: %v\n", name, ip)
    }

}

This prints:

loopback: 127.0.0.1
googleDNS: 8.8.8.8