From: Jacob Repp <jacobrepp@...>
Date: 2006-02-22T04:19:07+09:00
Subject: Re: Question about String.unpack

I'm curious about binary protocol parsing in ruby and have scratched
around for some kind of BinaryReader-ish interface for strings. Seems
like you could solve this if you know that your struct is in a string
you could say:

str = fd.sysread(n)
name = str.read_str(30)
size = str.read_double
age = str.read_int
stuff = str.read_c

I was going to write a native extension to do this after I finish my
current Ruby/AIO extension project. Unless there is something that
does this already (maybe in a cleaner/more ruby-ish way?)

On 2/21/06, Logan Capaldo <logancapaldo@gmail.com> wrote:
>
> On Feb 21, 2006, at 9:28 AM, Eric Jacoboni wrote:
>
> > Hi,
> >
> > Say i've a C struct like that:
> >
> > typedef struct {
> >   char name[30];
> >   double size;
> >   int age;
> >   char stuff;
> > } enreg_t;
> >
> > This record is written in a file that i want to re-read with a Ruby
> > script (just a toy example... to understand).
> >
> > I've not found a "clean" way to unpack such a record...
> >
> > My C compiler gives me a total sizeof of 48, so i use a
> >   fd.sysread(48).unpack(A32dIC) to re-read. But that seems rather
> >   'tricky' (i suppose we don't have always such a
> >   information). Furthermore, the first element is completed with
> >   garbage if the name field have less than 30 "useful" chars ("Doe",
> >   for example).
> >
> > I'm sure i'm missing something but i've not managed to find the right
> > way to do that.
> >
> > Any clue?
> > --
> > Eric Jacoboni, ne il y a 1443970729 secondes
> >
>
> there isn't really a "clean" way to do this, since you are doing
> something inherently un-clean.
> However, to fix the string issue, a possible solution is:
>
> str.gsub!(/\000.*/, '')
>
> assuming of course that name is a c-string.
>
>
>