Tips on memory management with C++ and Qt

[Jeff Mitchell]

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Maximilian Kossick wrote:
>> 3)
>> Never, ever, use private d-pointer classes in QObject derived subclasses:
>>
>> What can happen is that you do a "delete d;" in your destructor, and
>> then Qt goes ahead and auto-deletes other QObject pointers contained
>> in the private class again, through means of its automatic deleting of
>> QObjects with a parent Object. -> <BOOOOM>
>>
>> Read more about this topic in Michael Pyne's interesting blog article:
>>
>> http://www.purinchu.net/wp/2009/02/04/another-programming-tidbit/
> 
> This is not correct. Using d-pointers in QObjects is perfectly fine as
> long as the destructors are written correctly. The referenced article
> only says that one has to be careful about deleting a private
> d-pointer when other classes keep pointers to members of the private
> class around.

Right.  There are two keys to doing this safely:

1) Always write your own destructor.  NEVER use QObject's default
destructor in this case (you *can* do it safely, but you have to be very
careful, keeping #2 in mind...).

2) Control access to members of the private d-pointer class as much as
possible.

- --Jeff
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