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From: Richard Riehle <richard@adaworks.com>
Newsgroups: comp.lang.ada
Subject: Re: Commercial C To Ada 95 compiler
Date: Sun, 09 Jun 2002 10:49:17 -0700
Organization: AdaWorks Software Engineering
Message-ID: <3D03951D.B0A476ED@adaworks.com>
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Date: 2002-06-09T17:46:43+00:00
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Jim Rogers wrote:

> Richard Riehle wrote:
>
> > Jim Rogers wrote:
> >
> >
> >>One simple example is indexing past the end of an array.
> >>C compilers simply will not catch this problem. Ada compilers will.
> >>
> >
> > Actually, note that the following program that indexes off the end
> > of an array will compile in Ada.
> >
> >      procedure Index_Past_The_End is
> >              type Vector is array(Positive range <>) of Integer;
> >              The_Vector : Vector (1..100) := (others => 0);
> >     begin
> >           for I in The_Vector'First .. The_Vector'Last + 1
> >               loop
> >                    null;
> >               end loop;
> >     end Index_Past_The_End;
>
> Ah, but you are not indexing the array. You are merely creating
> a range based upon the array index range. You can iterate through
> any range you want. You will get a compiler error when you
> attempt to access (index) an array "element" beyond either end of
> the array.
>
>     The_Vector(The_Vector'Last + 1) := 10;
>
> Jim Rogers

You are correct about this example Jim.   It is also true that in my
original example,  the null statement does not cause a run-time error.
I used the null because I was being lazy.

However, in my other post where I suggested adding,
               The_Vector(I) := 10;
the code is doing an indexed operation and will, at execution,
attempt to index past the end of the array.   This will raise
a constraint_error at run-time that is not detected by the compiler.

Richard Riehle