how to Read and Write a Structure to a File in Binary Mode

[Jian Zhou]

Anyone can help me about how to read and write a structure in binary mode like c/c++?

I tried but failed.

[minux]

golang.org/pkg/encoding/binary, but beware the alignment issues.

[Stephen Weinberg]

You need to somehow marshal/encode the structure. A good, easy, no
work solution is to use http://golang.org/pkg/encoding/gob/. You can
also use encoding/binary to turn ints into bytes and marshal manually.

-- Stephen

[Jian Zhou]

Thanks!

This code works.

package main

import (
        "fmt"
        "bytes"
        "encoding/binary"
)

func main() {
    buf := new(bytes.Buffer)
    var data = []interface{}{
        uint16(61374),
        int8(-54),
        uint8(254),
    }
    for _, v := range data {
        err := binary.Write(buf, binary.LittleEndian, v)
        if err != nil {
            fmt.Println("binary.Write failed:", err)
        }
    }
    fmt.Printf("%x", buf.Bytes())

[Jian Zhou]

Thanks!

Does go support pointer types conversion? That would be more easy. I've tried many times..

Maybe I'm still think in c...

[minux]

On Fri, Mar 30, 2012 at 2:06 AM, Jian Zhou <zhou...@tiaozhanshu.net> wrote:

Does go support pointer types conversion? That would be more easy. I've tried many times..

It does support it, but use this feature isn't portable and quite dangerous (don't use it!).

like this (cast *uint to *byte):

package main

import ("unsafe"; "fmt")

func main() {

var a uint = 0xbeefcafe

fmt.Println(*(*byte)(unsafe.Pointer(&a)))

}

[steve wang]

Could you elaborate on "alignment issues"? 

[John Beisley]

encoding/binary writes Go structs packed - that is: without any padding to align members to word boundaries (which don't make sense for a serialised format). In contrast, if someone were to write the raw in-memory bytes of a struct to a serialised format, then they would find padding bytes are present.

(I think that's what was meant by 'alignment issues')

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[steve wang]

Thanks. I mistook what he meant.

I thought he meant that alignment should be made explicitly when using encoding/binary.