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From: Shark8 <onewingedshark@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: How do I write directly to a memory address?
Date: Fri, 4 Feb 2011 13:36:29 -0800 (PST)
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Date: 2011-02-04T13:36:29-08:00
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On Feb 4, 9:00=A0am, Hyman Rosen <hyro...@mail.com> wrote:
> You make two errors here. The first is to assume without
> any actual knowledge that it is possible for the argument
> to be a null pointer;

As presented it is not possible to determine IF it is not
possible to pass a null-pointer in; unlike Ada, C has no null
exclusion and so cannot guarantee from the contract-that-is-
the-parameter-list that to be the case -- He MUST reason it
from the code itself making the argument dependent on the
context in which it is used. {For example, it could be a part
contained in a header-file whose original using-program DID
have the impossibility of passing NULL, but if re-used then
it may be the case that there is no such guarantee.

> it is likely that the contract for
> this procedure requires that it not be. The second is that
> you test for the pointer being null each time through the
> loop rather than just once.

This is a deficiency, IMO, of C and somewhat even Pascal;
In Ada, even w/o null-exclusion, we would likely say:
Procedure Some_Procedure( Message : Access String ) is
begin
 if Message /=3D Null then
    Declare
       S : String Renames Message.All;
    Begin
       For Index in S'Range loop
          -- whatever processing and display
       End Loop;
    End;
 end if;
end Some_Procedure;

And within the procedure itself we capture the context which
would in the C-program and bind it directly to the procedure.
This becomes trivial with a not null access parameter.