On Tue, 19 Jan 2010, Daniël Mantione wrote:
Op Tue, 19 Jan 2010, schreef Graeme Geldenhuys:
Michael Van Canneyt wrote:
Why should it be better ? It doesn't really matter anyway.
PtrUInt has a larger range than PtrInt (allowing full access to memory
address range). Plus, I don't think pointers can be negative values.
The problem occurs when doing pointer arithmetic "ptrint+integer" is a bug,
because it will overflow if the original pointer<$8000000 and the result
pointer>=$8000000. It is especially dangerous in loops like:
q:=p+distance;
while p<q do
begin
{...}
inc(p);
end;
I don't want to think how many bugs have been coded this way :)
However, when using pointers as handles it is another matter... Handles are
not to be used in any calculation, so they cannot overflow. Who cares if you
get a negative handle?
That is what I meant. The TLibhandle type is opaque. You're not supposed to
know that it is a pointer, integer or whatnot. And definitely you should not
do math on them.
Michael.
_______________________________________________
fpc-devel maillist - fpc-devel@lists.freepascal.org
http://lists.freepascal.org/mailman/listinfo/fpc-devel
