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From: Robert Dewar <robert_dewar@my-deja.com>
Newsgroups: comp.lang.ada
Subject: Re: Does a null pointer always raise Constraint_Error?
Date: Wed, 13 Dec 2000 00:46:20 GMT
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Date: 2000-12-13T00:46:20+00:00
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In article <yec1yvdtmf1.fsf@king.cts.com>,
  Keith Thompson <kst@cts.com> wrote:
> Wayne Magor <none@nowhere.com> writes:
> [...]
> > I remember with one Ada compiler I wanted to make null to be
a
> > pointer to a zero-length segment so the null check would be
> > unnecessary (the hardware would do it for you).

No, that's not quite right, you can still miss things, consider

   subtype n is string (1 .. 0);
   type np is access n;
   a, b : np;

   if a.all = b.all then ...

it is a common compiler bug to translate this as

   for j in n'range loop
     if a.all (j) = b.all (j) ....

and the null loop causes no checks to be made :-)


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