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From: Matthew Heaney <matthew_heaney@acm.org>
Subject: Re: help with pointerproblem.
Date: 1998/09/17
Message-ID: <m34su75zgm.fsf@mheaney.ni.net>#1/1
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NNTP-Posting-Date: Thu, 17 Sep 1998 00:50:36 PDT
Newsgroups: comp.lang.ada
Date: 1998-09-17T00:00:00+00:00
List-Id: <comp.lang.ada>

dewarr@my-dejanews.com writes:

> It is actually quite rare to point to a descriptor (I think
> that the RR compiler may have done this at least at one
> point).

Access objects designating unconstrained arrays in the VMS Ada compiler
(circa 1990) pointed to the descriptor, which pointed to the array
itself.

To get around this, bindings would be written to point to a large
constrained array, as in:

type Character_Array is 
  array (Natural range 0 .. 1_000_000) of Character;

type String is access Character_Array;
for String'Storage_Size use 0;

Obviously, you don't ever designate an actual array of that size, but
the representation of the access type matches that of the C code on the
other side.  It's up to the programmer to find the real end of the array
(usually by searching for the null character, or for whatever value
designates the end-of-array).

The SUN compiler I'm using now implements unconstrained array access
types using the thin pointer technique.