[fpc-devel] possible 'dynlibs' unit issue

[Daniël Mantione]

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?

Daniël