In Go, how can I convert a struct to a byte array?

I have an instance of a struct that I defined and I would like to convert it to an array of bytes. I tried []byte(my_struct), but that did not work. Also, I was pointed to the binary package, but I am not sure which function I should use and how I should use it. An example would be greatly appreciated.

Solution 1:

One possible solution is the "encoding/gob" standard package. The gob package creates an encoder/decoder that can encode any struct into an array of bytes and then decode that array back into a struct. There's a great post, here.

As others have pointed out, it's necessary to use a package like this because structs, by their nature, have unknown sizes and cannot be converted into arrays of bytes.

I've included some code and a play.

package main

import (
    "bytes"
    "encoding/gob"
    "fmt"
    "log"
)

type P struct {
    X, Y, Z int
    Name    string
}

type Q struct {
    X, Y *int32
    Name string
}

func main() {
    // Initialize the encoder and decoder.  Normally enc and dec would be
    // bound to network connections and the encoder and decoder would
    // run in different processes.
    var network bytes.Buffer        // Stand-in for a network connection
    enc := gob.NewEncoder(&network) // Will write to network.
    dec := gob.NewDecoder(&network) // Will read from network.
    // Encode (send) the value.
    err := enc.Encode(P{3, 4, 5, "Pythagoras"})
    if err != nil {
        log.Fatal("encode error:", err)
    }

    // HERE ARE YOUR BYTES!!!!
    fmt.Println(network.Bytes())

    // Decode (receive) the value.
    var q Q
    err = dec.Decode(&q)
    if err != nil {
        log.Fatal("decode error:", err)
    }
    fmt.Printf("%q: {%d,%d}\n", q.Name, *q.X, *q.Y)
}

Solution 2:

I assume you want something like the way C handles this. There is no built in way to do that. You will have to define your own serialization and deserialization to and from bytes for your struct. The binary package will help you encode the fields in your struct to bytes that you can add to the byte array but you will be responsible for specifying the lengths and offsets in the byte array that will hold the fields from your struct.

Your other options are to use one of the encoding packages: http://golang.org/pkg/encoding/ such as gob or json.

EDIT:

Since you want this for making a hash as you say in your comment the easisest thing to do is use []byte(fmt.Sprintf("%v", struct)) like so: http://play.golang.org/p/yY8mSdZ_kf