Converting several bytes in an array to another type in Go

Question

I just started yesterday with Go so I apologise in advance for the silly question.

Imagine that I have a byte array such as:

func main(){
    arrayOfBytes := [10]byte{1,2,3,4,5,6,7,8,9,10}
}

Now what if I felt like taking the first four bytes of that array and using it as an integer? Or perhaps I have a struct that looks like this:

type eightByteType struct {
    a uint32
    b uint32
}

Can I easily take the first 8 bytes of my array and turn it into an object of type eightByteType?

I realise these are two different questions but I think they may have similar answers. I've looked through the documentation and haven't seen a good example to achieve this.

Being able to cast a block of bytes to anything is one of the things I really like about C. Hopefully I can still do it in Go.

Does this stackoverflow.com/a/53429894/12817546 and this play.golang.org/p/IYpv3YJsZO5 answer your question in part? — user12817546
– user12817546, Commented Sep 19, 2020 at 9:46

cthom06 · Accepted Answer · 2010-11-30 02:25:23Z

3

Look at encoding/binary, as well as bytes.Buffer

TL;DR version:

import (
    "encoding/binary"
    "bytes"
)

func main() {
    var s eightByteType
    binary.Read(bytes.NewBuffer(array[:]), binary.LittleEndian, &s)
}

A few things to note here: we pass array[:], alternatively you could declare your array as a slice instead ([]byte{1, 2, 3, 4, 5}) and let the compiler worry about sizes, etc, and eightByteType won't work as is (IIRC) because binary.Read won't touch private fields. This would work:

type eightByteType struct {
    A, B uint32
}

edited Nov 30, 2010 at 2:25

answered Nov 29, 2010 at 22:11

cthom06

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4 Comments

mkm Over a year ago

Does this code actually copy data from the array to the struct?

cthom06 Over a year ago

@ithkuil what do you mean? Actually copy as opposed to what?

mkm Over a year ago

as opposed to what you can do in C, cast a bytearray to a struct, so that the struct uses the same memory region occupied by the bytearray without copying. This was my interpretation of the last part of the question: "Being able to cast a block of bytes to anything is one of the things I really like about C. Hopefully I can still do it in Go."

cthom06 Over a year ago

@ithkuil in that case you need to use package unsafe

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