the pParent is a void pointer i.e. a pointer which can point to objects of any type.The void pointer does not know what type of object it is pointing to, so the void pointer must first be explicitly cast to another pointer type before it can be dereferenced.
And you want a pointer pTmp of type CPlaybackDlg which should point at the same object as pParent . So pParent is typecast to type CPlaybackDlg by placing (CPlaybackDlg*) in front of it and this typecast is used to initialize pTmp .
know more about void pointers here
some info on typecasting here
hope this helps .