Re: Sequential_IO Data Portability

[Tony Matthews <tony.matthews@SpamJam.gecm.com>]

Nick Roberts wrote:
> 
> A question was asked in GNAT chat recently as to (I hope I paraphrase
> closely enough) whether, in general, the data written, via Sequential_IO, by
> a brand of Ada compiler for one machine/OS target can be expected to be read
> by a program, using the same type and Sequential_IO, compiled by the same
> brand of compiler, but for a different target.
> 

The question raiser was me, so I think a little explananation might be
useful
to anyone out there who might be interested.

The project I work on comprises several sub-systems, one of which is an
air
traffic control simulator, and another is the exercise preparation
system for the simulator.

The ex-prep sub-system comprises several workstations and a server
running an Oracle RDBMS,
all running on SCO OpenServer Unix.

The simulator comprises a large number of workstations and servers, all
running LynxOs Unix.

We use Alsys Ada '83 and Oracle's ProAda precompiler tool to extract the
exercise data from
the ex-prep database and write out a large number (100's) of
sequential_io data files which can
then be transferred via LAN over to the simulator, where they are read
when the supervisor chooses
to load and run the respective exercise.

Sequential_io files are used because they minimise the data file sizes,
they enable fastest loading
times on the simulator (once transferred!), and provide independent
operation of the sub-systems.

We get away with this because we use the same version Alsys Ada compiler
on both sub-systems, and we
don't even need to use rep specs!

However - Alsys Ada '83 (AdaWorld) is now getting a bit long in the
tooth, and some of the other Oracle
based tools we use on the ex-prep system are also approaching the end of
their useful lives.

So - whilst considering how we might move the project onward to Ada '95,
and possibly to alternative
PC based operating systems (Linux and Windows NT spring to mind here) we
are constrained by our
dependence on Oracle and sequential_io portability.

Being able to use another compiler (ie GNAT95) in the same manner
without having to expend vast amounts
of effort on translating or rep spec'ing file formats (which would be
tedious and error prone) means we
could concentrate our resources on system improvements.

So that's the background. If anyone has any practical experience
(positive or negative) of sharing binary
files between Linux, LynxOs, SCO and/or Windows NT using GNAT95 I would
be delighted to hear from you.

In his GNAT Chat mailing list response, David C Hoos kindly pointed me
at the GLADE source code
(as in Ada95 RM Annex E - Distributed Systems, not the Glade GUI Builder
that is associated with the
GTKAda graphical toolkit), which uses Ada.Streams. Thanks David - I will
try and follow up your lead
as soon as I can.

Thanks to all respondents.