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From: Adam Beneschan <adam@irvine.com>
Newsgroups: comp.lang.ada
Subject: Re: Memory Access
Date: Mon, 7 Nov 2011 14:42:53 -0800 (PST)
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Date: 2011-11-07T14:42:53-08:00
List-Id: <comp.lang.ada>

On Nov 7, 2:21=A0pm, Adam Beneschan <a...@irvine.com> wrote:
>
> If you known the address of the array data, then something like this
> will work even if you don't know the address until runtime:
>
> =A0 =A0 Data_Address : System.Address;
> =A0 =A0 ...
> begin
> =A0 =A0 -- do some stuff that sets Data_Address to the address. =A0Or you
>     -- could make
> =A0 =A0 -- Data_Address be a parameter to a subroutine, or something
> =A0 =A0 -- Then:
>
> =A0 =A0 declare
> =A0 =A0 =A0 =A0Dev_Table : Dev_Table_Type (1 .. Num_Devs_Cnst);
> =A0 =A0 =A0 =A0for Dev_Table'Address use Data_Address;
> =A0 =A0 begin
> =A0 =A0 =A0 =A0-- and you can use Dev_Table in here
> =A0 =A0 end;
>
> This will work whether Num_Devs_Cnst is known at compile time or not.
> (The _Cnst makes it look like it's a constant that's known at compile
> time. =A0But it doesn't need to be.)

An alternative, if you don't want to use an Address clause:

with System.Address_To_Access_Conversions;

...
   Data_Address : System.Address;
begin
   -- set Data_Address to something as above
   declare
      subtype Constrained_Dev_Table is Dev_Table_Type (1 ..
Num_Devs_Cnst);
      package Dev_Table_Pointer is new
         System.Address_To_Access_Conversions (Constrained_Dev_Table);
      Dev_Table : Dev_Table_Pointer.Object_Pointer :=3D
         Dev_Table_Pointer.To_Pointer (Data_Address);
   begin
      ...
   end;

Dev_Table is now declared as an access (pointer) to a constrained
array subtype, rather than an array, but you should still be able to
use it in the same way.  This method still won't let you create a
Dev_Table_Ptr_Type that points to the array, though.

                       -- Adam