IUnknown
The
IUnknown interface lets clients get pointers to other interfaces on a given object
through the
QueryInterface method, and manage the existence of the object through the
IUnknown::AddRef and
IUnknown::Release methods. All other COM interfaces are inherited, directly or indirectly, from
IUnknown. Therefore, the three methods in
IUnknown are the first entries in the VTable for every interface.
When to Implement
You must implement
IUnknown as part of every interface. If you are using C++ multiple inheritance to
implement multiple interfaces, the various interfaces can share one implementation
of
IUnknown. If you are using nested classes to implement multiple interfaces, you must
implement
IUnknown once for each interface you implement.
When to Use
Use
IUnknown methods to switch between interfaces on an object, add references, and
release objects.
Methods in Vtable Order
IUnknown Methods
| Description
|
QueryInterface
| Returns pointers to supported interfaces.
|
AddRef
| Increments reference count.
|
Release
| Decrements reference count.
|
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