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From: dale@cs.rmit.edu.au (Dale Stanbrough)
Subject: Re: Alternate to Unchecked_Conversion - Portable?
Date: 1999/02/26
Message-ID: <dale-2602991000050001@dale.bu.cs.rmit.edu.au>#1/1
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Organization: Department of Computer Science, RMIT
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Newsgroups: comp.lang.ada
Date: 1999-02-25T22:56:45+00:00
List-Id: <comp.lang.ada>


> The only meaningful way to do that is to follow the
> prescription I gave. Trying to convert constrained to
> unconstrained pointers is always meaningless (and indeed
> will typically not even come close to "working" in many
> compilers)
> 
> > It can often be made to work ...
> 
> Famous last words. What this means is that by tweaking
> and fiddling, you can write something that appears to
> work at least in the limited cases in which you try it
> out on the particular version of the particular compiler
> you are using.



Why can't we have a routine (it would no doubt have been best
in  System.Address_To_Access_Conversions) that allows
for the creation of unconstrained pointers...

e.g.

   pointer := to_unconstrained_pointer (some_address, low_bound, upper_bound);

This way we could recover some of the Ada semantics back into our
arrays when interfacing with other langauges (esp. as we often know
the dimensions of the arrays we are dealing with).

Perhaps...

   System.Address_To_Access_Conversions.Array_Access

or
   System.Address_To_Array_Access_Conversions

?

For example if you have a pointer to a C string, you could use
the above as...


   X : String_Access := To_Unconstrained_Pointer (
                              C_String'address, 1, strlen (C_String));



Certainly this could only be reliably provided by the compiler vendors,
for the reasons already stated.

Dale