[fpc-devel] possible 'dynlibs' unit issue
Michael Van Canneyt
michael at freepascal.org
Tue Jan 19 13:53:11 CET 2010
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:
> while p<q do
> 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.
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