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?

string(ipaddr[:]) seems to just return an empty string. Also, according to en.wikipedia.org/wiki/IP_address#IPv4_addresses, an IPv4 address consists of 32 bits or 4 bytes, so I believe the problem is stated realistically. — Kurt Peek
– Kurt Peek, Commented Sep 15, 2019 at 18:28

Everton · Accepted Answer · 2019-09-15 18:26:02Z

5

Add this method:

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

answered Sep 15, 2019 at 18:26

Everton

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Comments

Burak Serdar · Accepted Answer · 2019-09-15 18:26:17Z

3

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

answered Sep 15, 2019 at 18:26

Burak Serdar

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Comments

Kurt Peek · Accepted Answer · 2019-09-15 18:36:02Z

2

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

answered Sep 15, 2019 at 18:36

Kurt Peek

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