ADA/C interfaces: type representations uncontrollable in C

[Anonymous Coward <bogus_addy@bogus_domain.net>]

In article <uk6fn758i.fsf@acm.org>, Stephen Leake wrote:
> 
> Hmm. You seem to be saying "convention (C) doesn't work for
> me". That seems like a bug. Can you post some code that doesn't
> work? Or have you submitted a bug report?

I should start by saying that I think the compiler I witnessed this on
is version 3.15p.  I'll have to check on that.

The pragma convention anomaly I've noticed relates to enums, not
records.  However, just because records have been represented in a
sequence of elements that matches the operational spec doesn't mean I
can count on it to work every time - it may have been chance.

I'm beginning to realize that it's impossible to write compiler
independant ADA code if it must interface with C code.  Even rep
spec'ing down to the bitwise rep specs makes no guarantess that the
chosen layout will match what all C compilers produce (since they can
potentially all be different).

What I don't understand is how GNAT can give the user representation
control over types, when C does not, considering that GNAT translates
ADA to C.  How does GNAT perform that intermediate C translation if
rep specs don't exist in C?