From: "Simon Kröger" <SimonKroeger@...>
Date: 2006-07-18T05:37:43+09:00
Subject: Re: How can I parse binary files?

ara.t.howard@noaa.gov wrote:
> On Tue, 18 Jul 2006, Fabio Vitale wrote:
> 
>> Daniel Martin wrote:
>>> Fabio Vitale <fabio@sferaconsulting.it> writes:
>>>
>>>> I've the need to parse a binary file with the following structure:
>>>> How can I accomplish this in Ruby?
>>>
>> require 'bit-struct'
>>
>>  class MRK < BitStruct
>>    unsigned    :version,             4,     "Version"
>>    unsigned    :uid_Validity,        4,     "UIDValidity"
>>    unsigned    :uid_next,            4,     "UIDNext"
>>    unsigned    :last_write_counter,  4,     "LastWriteCounter"
>>    rest        :unused,                     "Unused"
>>  end
>>
>>  mrk = MRK.new
>>
>> And now: how to populate the mrk instance just created from the imap.mrk
>> binary file?
> 
> without even looking at the docs i'd guess you could do
> 
>   data = IO.read 'your.data'
> 
>   mrk = MRK.new data
> 
> 
> and, indeed, this seems to work:
> 
> [snip]

This looks like a nice way.
I just wanted to show that in such a simple case unpack isn't that ugly, too.

open('file.bin', 'rb').do |f|
  version, uidValid, uidNext, lwCounter = f.read(36).unpack('IIII')
  name, flags, uid, size, date = f.read(36).unpack('Z23CIII')

  #do something
end

This is of course untested because i don't have such a file, but i hope
the idea is clear.

cheers

Simon