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From: Adam Beneschan <adam@irvine.com>
Newsgroups: comp.lang.ada
Subject: Re: GNAT 4.4.5 order of conditional processing?
Date: Wed, 16 Nov 2011 16:00:52 -0800 (PST)
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Date: 2011-11-16T16:00:52-08:00
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On Nov 16, 2:40=A0pm, Adam Beneschan <a...@irvine.com> wrote:
>=A0For instance:
>
> =A0 subtype Index_Subtype is Integer range 1 .. 10;
> =A0 Arr : array (Index_Subtype) of Float;
> =A0 Curr_Index : Index_Subtype;
>
> =A0 if Curr_Index_Initialized and Arr(Curr_Index) < -1.0 then ...
>
> Suppose Curr_Index_Initialized is FALSE and Curr_Index has never been
> initialized to anything. =A0The result is that if the right side is
> evaluated, Curr_Index's uninitialized value may be a value outside the
> range 1..10, and then the code will read an element of Arr that is
> outside the bounds of Arr. =A0Big deal. =A0That's not likely to make a
> program fail. =A0(Unless the bit pattern it reads happens to be a
> Signaling NaN, maybe!!)

Clarification: Depending on how Curr_Index is represented (some
compilers would fit it into an 8-bit byte while others would make it
as big as an Integer), evaluating Arr(Curr_Index) could make the
program fail if Curr_Index is big enough to put the element's address
out of the program's memory space.  So it's more likely to fail than I
first claimed.  Keep in mind that this is just my example and I don't
know that the OP was doing any array indexing.

                           -- Adam