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From: Michael Carman <mjcarman@home.com>
Subject: Re: Array access via pointer?
Date: 2000/08/02
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Date: 2000-08-02T00:00:00+00:00
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Ted Dennison wrote:
> 
> procedure Foo (Addr : in out Addr_Table;
>                I    : in     Integer) is
> begin
>    -- Do something with index I of the array at Addr
> end Foo;

Yes, that's much cleaner, thank you. Is it safe to assume that
internally Addr_Table is passed by reference? (It's a bit more data than
I want on the stack.)

> It may be much more constructive for you to tell us why you feel you
> need to use addresses and pointers. 
> [...]

Which pointers -- the ones to my arrays or the ones inside them? :) I
assure you that the latter are necessary; they tell me where to find
data from an external process. I'd happily get rid of the former ones,
though.

My example was simplified to illustrate the problem I was having.
Unfortunately, it oversimplified the situation a bit. I wasn't passing
in a pointer to an array just for fun. I determine which array to
process in a completely seperate part of the program. That is, I don't
actually call Foo() this way:

    Foo(Arr2'Address, 7);

I have some higher-up logic that's something like this:

if (<condition>) then
    Arr_Ptr := Arr1'Address;
else
    Arr_Ptr := Arr2'Address;
end if;

Deeper down, in a completely seperate part of things, I call

    Foo(Arr_Ptr, 7);

So the later code is fat, dumb and happy, knowing nothing about the
earlier logic. Your example passing Addr_Table instead of a pointer is
great, but I need to keep this functionality. Is there a way to alias
variables such that I can set "My_Array := Arr2" (without actually
creating a copy)? All I've been able to find is defining aliased
variables, and then using access types to get to them, which puts me
back in the pointer/dereference boat.

[To further complicate things, I can't use 'Access -- I'm trying to keep
my code Ada83 compatible -- I know how to work around it, it's just
messier.]

Of course, that's still better than what I'm currently doing.

-mjc