From: jason@... (Jason Voegele)
Date: 2001-10-05T23:00:50+09:00
Subject: [ruby-talk:22129] Re: Help with Array#pack

Paul Brannan <pbrannan@atdesk.com> wrote in message news:<Pine.LNX.4.40.0110041212580.27796-100000@zaphod.atdesk.com>...
> On Fri, 5 Oct 2001, Jason Voegele wrote:
> 
> > command = [1, 0, 1|2, 0x1000, 99, 0]
> >
> > These six entries in the array should correspond to the six fields in
> > the message header above.  So the above array should be converted to
> > the binary string:
> >
> > BYTE 1 | BYTE 2 | BYTES 3&4 | BYTES 5-8 | BYTES 9-12 | BYTES 13-16
> > ------ | ------ | --------- | --------- | ---------- | -----------
> >    1   |   0    |    3      |    4096   |     99     |     0
> 
> Try this:
> 
>   def pack(arr)
>     arr.pack("CCnnnn")
>   end
> 
>   def display(x)
>     x.each_byte do |b|
>       puts b
>     end
>   end
> 
>   x = pack([1, 0, 1|2, 0x1000, 99, 0])
>   display x
> 
> The 'C' means unsigned char, and the 'n' means 16-bit short (in
> network-byte-order, which is very important).

Thanks for the information, Paul, and thanks for pointing out that
it's big-endian order.  I forgot to mention that.

But doesn't pack("CCnnnn") lead to a 10 byte string rather than a 16
byte string?  Note that field 3 is two bytes, while fields 4, 5, and 6
are four bytes.  With this guidance, though, I think I've figured it
out.  The pack string should be "CCnNNN".  That leads to a 16 byte
string in the format I need.

Again, thanks for your help.

Jason Voegele