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From: mab@dst17.wdl.loral.com (Mark A Biggar)
Subject: Re: C++'s pointer vs Ada's Access type
Date: 1996/08/01
Message-ID: <4tqkns$o2u@wdl1.wdl.lmco.com>#1/1
X-Deja-AN: 171423305
references: <31FFD4A6.41C6@afit.af.mil> <DvFu6E.Atz.0.-s@inmet.camb.inmet.com>
organization: Loral Western Development Labs
newsgroups: comp.lang.ada
Date: 1996-08-01T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <DvFu6E.Atz.0.-s@inmet.camb.inmet.com> stt@henning.camb.inmet.com (johndoe) writes:
>Ding-yuan Sheu (dsheu@afit.af.mil) wrote:
>: 	I think C++'s pointer type is basically similar to Ada's access
>: type. Therefore, for the following C++ declaraction:
>: 	int*	ip;  
>: I convert it into Ada:
>: 	type Integer_Ptr is access all Integer;
>: 	ip : Integer_Ptr;
>: However, there comes a problem.
>: In C++, ip can be a pointer that points to a integer array.
>: Therefore, C++ programmers can do the following initialization:
>: 	int	Array[100];
>: 	ip = &Array;
>: 	for (i:=0;i++,99) { (*ip+i)   = 0; }
>: My question is how I can do the same thing in Ada by using ip 
>: to initialize Array instead to directly initialize Array. 
>This is somewhat odd looking C/C++ code.  I would have expected:
>    for (ip = Array; ip < &Array[100]; ) *ip++ = 0;
>In any case, the corresponding Ada would generally not use
>pointers at all:
>    An_Array : array (1..100) of Integer;
>
>    for I in An_Array'Range loop
>        An_Array[I] := 0;
>    end loop;

Or even more likely:

     An_Array : array (1..100) of Integer := (1..100 => 0);

--
Mark Biggar
mab@wdl.lmco.com

>
>If you are intent on using a pointer, the following would work, though
>I can't imagine a case where it would be preferable to the above.
>
>    type Int_Array is array(1..100) of Integer;
>
>    type Array_Ptr is access all Int_Array;
>    An_Array : aliased Int_Array;
>    IP : Array_Ptr := An_Array'Access;
>
>    for I in IP.all'Range loop
>        IP.all[I] := 0;
>    end loop;
>
> (both of the "IP.all" above could be shortened to simply "IP")
>
>: I know my question might be stupid for you Ada experts.
>: Your comments are preciou to me. Any Help will be appreciated.
>
>Generally pointers to arrays are not used very much in Ada.  
>Pointers to records are used, when you are allocating objects on the heap.
>C/C++ programmers sometimes use pointers to perform manual "strength
>reduction" when manipulating arrays, but in Ada one generally
>just uses normal array indexing, while relying on the compiler to 
>use pointer arithmetic at the machine level as appropriate.
>
>: 	Steven
>
>-Tucker Taft   stt@inmet.com   http://www.inmet.com/~stt/
>Intermetrics, Inc.  Cambridge, MA  USA