From: Robert Klemme <bob.news@...>
Date: 2005-07-06T18:05:46+09:00
Subject: Re: Reading arbitrary data into a c-like structure

Michael Neumann wrote:
> Graham Nicholls wrote:
>> I mentioned before that I'm writing a tool to extract data from a
>> (dataease) database file according to a schema.   In 'C' I'd do
>> something like
>>
>> struct data
>> {
>>         char header 4;
>>         int recno;
>>         char name[30];
>>         char add_1[30];
>>         ...
>>         unsigned int cr_limit ;
>> } data;
>>
>> and if I set the compiler options right so the structure was closely
>> packed, I could simply read the file into this structure, and print
>> out the results using
>
> You need to read sizeof(data) bytes as a String, then unpack it.
>
> Simple example:
>
>    C:
>
>    struct data {
>      long a;
>      long b;
>    };
>
>    Ruby:
>
>    str = handle.read(8)
>    a, b = str.unpack('LL')
>
> Regards,
>
>    Michael

Plus, if you want to do further processing, you can use any of Hash,
Struct or OpenStruct for storage.  If you create a struct for your special
case you mighe even implement conversion methods:

# untested
Foo = Struct.new(:a, :b)

class Foo
  def to_binary()
    [a,b].pack('LL')
  end

  def self.from_io(io)
    new *io.read(8).unpack('LL')
  end
end

Kind regards

    robert