String to Byte conversion

[Stéphane phenetas]

Hello,

I am trying to convert from String to Byte, here is my code :

ip0:=byte(sliceIPDestination[0])

And the error message :

./main.go:325: cannot convert sliceIPDestination[0] (type string) to type byte

Probably something obvious I have missed ?

Thank you.

[Jonathan]

Use []byte, not byte

[Stéphane phenetas]

Thank you, but I need it to be byte, not []byte.

Or maybe I could convert to []byte and then make an other conversion to byte ?

[Dan Kortschak]

Do you want the first byte of the string, then s[0]? If you want more
than that can you more clearly explain what you are trying to do?

Maybe you are trying to parse a string representation of a number to a
byte? Then strconv.Atoi or strconv.ParseInt and type convert the
int/int64 to a byte.

[Stéphane phenetas]

Yes I will try to explain more precisely.

I have an IP address stored in a string variable. The IP is like "X.X.X.X" where X are numbers.

I use strings.Split to split the IP and it returns me a []string with 4 elements inside corresponding to the 4 numericals of the IP.

Then I need to send these numericals in an other function who takes byte in entry.

Example :

at the beginning I have variable := "1.2.3.4" which is a string, and at the end I need to send 1 and 2 and 3 and 4 in a function like this myFunction(a byte, b byte, c byte, d byte)

[Dan Kortschak]

Use http://golang.org/pkg/net/#ParseIP?

On Thu, 2015-08-06 at 16:48 -0700, Stéphane phenetas wrote:
> Yes I will try to explain more precisely.
>
> I have an IP address stored in a string variable. The IP is like "X.X.X.X"
> where X are numbers.
> I use strings.Split to split the IP and it returns me a []string with 4
> elements inside corresponding to the 4 numericals of the IP.
>
> Then I need to send these numericals in an other function who takes byte in
> entry.
>
> Example :
>

> at the beginning I have *variable := "1.2.3.4"* which is a string, and at

[Stéphane phenetas]

Thank you for the link, , but are you sure this will output me with a []byte ?

The program compiles now, but the logic does not work, I am not sure the output is what is expected.

For example I do this :

IPDestination := "10.11.204.205"

    IPAddress:=net.ParseIP(IPDestination)

    fmt.Printf("%s\n",IPAddress[3])

    fmt.Printf("%s\n",IPAddress)

The output is :

%!s(uint8=0)
10.11.204.205


I am not sure the output has been sliced.

[Dave Cheney]

What you're seeing is the net.IP type has a String method, so it implements fmt.Stringer. Because of this fmt's %s formatter knows how to print this value as a string. 

net.IP is defined as a slice of bytes, so IPAddress[0] evaluates to a type of byte, which is not compatible for the %s verb. byte is also an alias for uint8, so that is why fmt complains.

You could try using the %v verb which knows how to print just about everything.

Thanks

Dave

[Sam Mortimer]

You have to To4() it before you can access it that way.

[Stéphane phenetas]

I am afraid that it does not print the correct thing, even if I use %v, or %s. It prints "0", instead of what the IP really is.

[Dan Kortschak]

On Thu, 2015-08-06 at 17:24 -0700, Stéphane phenetas wrote:
> Thank you for the link, , but are you sure this will output me with a

> []byte ? '

net.IP is defined as `type IP []byte` (http://golang.org/pkg/net/#IP) so
it is directly convertible, but if you really want to `myFunction(a, b,
c, d byte)` (which seems a little odd to me, but it's your code - I'd
just have the function take a net.IP) you can just call
`myFunction(ip[0], ip[1], ip[2], ip[3])` without any conversion.

[Stéphane phenetas]

I tried to do so, simplest possible :

func main() {

    IPDestination := "10.11.204.205"

    conn, err := net.ListenUDP("udp", &net.UDPAddr{IP: net.IPv4zero, Port: 0})

       IPAddress:=net.ParseIP(IPDestination)

    _, err = conn.WriteToUDP([]byte("wake"), &net.UDPAddr{IP: net.IP{IPAddress[0], IPAddress[1], IPAddress[2], IPAddress[3]}, Port: 7})

    if err!=nil{

    }


fmt.Printf("%v",IPAddress[0])

    fmt.Printf("%v",IPAddress[1])

    fmt.Printf("%v",IPAddress[2])

    fmt.Printf("%v",IPAddress[3])

}

All outputs are "0", I guess I don't use "ParseIP" correctly.

[Stéphane phenetas]

Of course, I am just trying to print the variables to "see" if it works or not. The all line "

_, err = conn.WriteToUDP([]byte("wake"), &net.UDPAddr{IP: net.IP{IPAddress[0], IPAddress[1], IPAddress[2], IPAddress[3]}, Port: 7})" is supposed to send a UDP message. It does not work after the conversion we are talking about.

[Nigel Tao]

Try calling To4.

http://play.golang.org/p/9XA7ycUZTL

[Dan Kortschak]

http://play.golang.org/p/gs6DPmP3oD