Re: access aliased obstacle

[guerby@gnat.com (Laurent Guerby)]

>>   I think of a C union as essentially a variant record with the
>> discriminant outside the record (in some other variable entirely).
>> C probably does think of this as a union, although it fits an Ada
>> discriminated record perfectly.  What is this 'Unchecked_Union'?
>> I don't see it in my LRM.

   A discriminated record isn't a C union type, because the
discriminant is stored in the record in Ada (accessible for reading),
and run-time checks are made on the discriminant when you access
variant parts. The pragma Unchecked_Union makes a simple Ada
discriminated record type match exactly a C union (discriminant not
stored, no checks). It is not in the RM, but all vendors agreed to
implement it. It is documented in the GNAT file "features" I think (or
gnatinfo.txt).

   I still assume you're interfacing a C array of union, but I'm not
sure, and cannot be more accurate without the code (C and what you
want in Ada).

-- 
Laurent Guerby <guerby@gnat.com>, Team Ada.
   "Use the Source, Luke. The Source will be with you, always (GPL)."