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From: Ken Garlington <GarlingtonKE@lmtas.lmco.com>
Subject: Re: Sequential IO on OpenVMS (was: CRC in Ada?)
Date: 1997/03/24
Message-ID: <3336DC57.25DB@lmtas.lmco.com>#1/1
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References: <1997Mar2.220652@nova.wright.edu>
 <331bf6ce.2832564@news.logica.co.uk> <dewar.857509168@merv>
 <332B5EBD.3D9E@worldnet.att.net> <dewar.858525008@merv>
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 <33320957.B@worldnet.att.net> <dewar.859022250@merv>
Organization: Lockheed Martin Tactical Aircraft Systems
Newsgroups: comp.lang.ada
Date: 1997-03-24T00:00:00+00:00
List-Id: <comp.lang.ada>


Robert Dewar wrote:
> 
> i<<I totally disagree with your use of the term "misuse" here. The only other
> Ada 83 I/O package that can possibly be used to read a binary file is Direct I/O
> >>
> 
> Nope, Direct_IO is also unsuitable for simulating stream_io in Ada 83 in a
> portable manner.
> 
> As for writing waivers, no one ever rqeuired a waiver for using pragma
> Interface to interface to existing libraries, especially ANSI C libraries,
> the idea is absurd. 

Actually, yes they do, if the library becomes delivered as part of the
total
system. (And to answer the obvious follow-up question, yes I have
processed
waivers for assembly routines contained within the Ada run-time!)

The real question is: "So you have to write a waiver. So what?"

> Yes, I know, some procurement people do absurd
> things.
> 
> Your "use" of sequential_io was still inappropriate, because you were
> writing highly non-portable code, which might even have broken using
> the next version of the sam e compiler, let alone a different compiler.

By the way, on a related topic: On VAX/OpenVMS systems, the end-of-file
marker
is embedded within the file header. Even for sequential, fixed-length
record files, the EOF can be placed in the middle of a record
(effectively
truncating it). I have recently come to discover that doing Sequential
IO
on such files has what I consider to be a strange outcome: the truncated
record is read normally, and so "garbage" values past the end of the
file
are processed. On the next record read, END_ERROR is raised. Does the
GNAT implementation for Alpha/OpenVMS mimic this philosophy, as opposed
to
(for example) raising DATA_ERROR on the truncated record? Because of
this problem, we have had to switch to "C" I/O for these files... 

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