--- Comment #10 from pinskia at gcc dot gnu dot org 2005-11-10 14:09
---
(In reply to comment #9)
> What you are saying is that:
> Pointer arithmetic is only valid on elements of the same array that are
> adjacent, and that any other uses of pointer arithmetic produces undefined
> behav
--- Comment #9 from j3p0uk at hotmail dot com 2005-11-10 14:02 ---
Sorry - I don't mean to pester you, I would just like to clarify your final
point.
What you are saying is that:
Pointer arithmetic is only valid on elements of the same array that are
adjacent, and that any other uses o
--- Comment #8 from pinskia at gcc dot gnu dot org 2005-11-10 13:58 ---
If pointer1 and pointer2 are not in the same array (+-1 element), the behavior
is undefined so what GCC is doing for your case is fine.
--
pinskia at gcc dot gnu dot org changed:
What|Removed
--- Comment #7 from j3p0uk at hotmail dot com 2005-11-10 13:54 ---
Created an attachment (id=10201)
--> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=10201&action=view)
More correct test program
Here is a test program designed to show the problem more clearly. When run the
pointer ar
--- Comment #6 from j3p0uk at hotmail dot com 2005-11-10 13:49 ---
I was not intending to show a correct fix for the problem, my simple test
program was merely intended to show that given sufficient distance between 2
pointers the result from ptr_a - ptr_b can be incorrect. I am not sur
--- Comment #5 from pinskia at gcc dot gnu dot org 2005-11-09 17:30 ---
This is invalid because otherwise you get the incorrect answer for &a[3]-&a[4]:
a = 0x8049668 b = 0x804966c
pointer ( a - b )
0x
non-pointer ( ( ((un
--- Comment #4 from j3p0uk at hotmail dot com 2005-11-09 17:25 ---
The test case was a simple test case where I tried to show the mathematical
behaviour in as simple a way as possible.
The reason I thought that this may be a bug is because the behaviour on a
64-bit system is different a
--- Comment #3 from rguenth at gcc dot gnu dot org 2005-11-09 15:53 ---
Note that obtaining the difference of pointers that don't point to the same
object is invoking undefined behavior, too.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24756
--- Comment #2 from pinskia at gcc dot gnu dot org 2005-11-09 15:19 ---
Why do you think this is a bug. The difference between &a[3]-&a[4] better be
-1. (where a is an array).
--
pinskia at gcc dot gnu dot org changed:
What|Removed |Added
---
--- Comment #1 from j3p0uk at hotmail dot com 2005-11-09 14:51 ---
Created an attachment (id=10186)
--> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=10186&action=view)
Test source (.i)
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24756
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