Re: packed structures usefulness

[Marco Maggi]

"address@hidden" wrote:
> "Marco Maggi" writes:
>> Remembering that, IMHO, there is no way to
>> mimic the C structure fields alignment from a
>> Scheme level inteface, I wonder if such a module
>> would be useful or not.
>
>I'm not convinced.  :-)
>
>Most  "modern"  C   libraries  use  opaque  types,
>typically pointers  to structs, so  you rarely get
>to access the fields directly.


"Thien-Thi Nguyen" wrote:
>> I wonder if such a module would be useful or not.
>
>i  think so,  if it  can handle  char,  short, and
>bitfields.  presuming it has length and signedness
>checks,   it   would  be   nice   to  have   those
>configurable,  as  well  (ie.,  error vs  warn  vs
>auto-normalize).


"Neil Jerram" wrote:
>I   implemented  something   like   this  for   an
>application  whose   basic  control  mechanism  is
>message passing using flat C structures ("flat" =>
>no pointers), because I wanted to be able to build
>and manipulate the structures from Scheme.
>[...]
>So to  answer your  actual question: yes,  I think
>this is useful, but only in a rather specific kind
>of application context.


(Thanks (expt 10 3)). I have decided to enqueue it
in  my  to  do  list.   I  will  write  it  as  an
independent module, but  with the specific purpose
of  having a tool  to write  an interface  to Ralf
Engelschall's OSSP MM: a library for shared memory
usage [1].

It is a small project  that I started one year ago
and then  put aside, because  I had no  clear idea
about  how  to  define  a "mask"  of  data  fields
through  which  "look"  at  the  allocated  shared
memory.

I will use (sub)SMOBs and define the struct format
from the Scheme level only,  I do not want to make
it  a way  to "see"  a foreign  C struct  from the
Scheme  level.  There  should  be  no  problem  to
register   an  assertion   function   and  set/get
conversion functions.

But...  ahem...  bitfields?  These are *boring* to
code... ;-)


[1] <http://www.ossp.org/pkg/lib/mm/>

--
Marco Maggi

"Now feel the funk blast!"
Rage Against the Machine - "Calm like a bomb"