IUnknown

AddRef() and Release()

  1. Functions that return an interface pointer should call AddRef()
  2. Functions that use an interface pointer provided by another function are responsible for calling Release()
  3. If you copy an interface pointer, the best practice is to call AddRef() and Release()

QueryInterface()

Microsoft defines a bunch of goofy and pseudo-mathematical rules which state in essence that, if you have a pointer to any interface on an object, you can always get a pointer to any other interface on that object, including IUnknown.

References