IUnknown::Release

Decrements the reference count for the calling interface on a object. If the reference count on the object falls to 0, the object is freed from memory.

ULONG Release(void);

Return Value
Returns the resulting value of the reference count, which is used for diagnostic/testing purposes only. If you need to know that resources have been freed, use an interface with higher-level semantics.

Comments
If IUnknown::AddRef has been called on this object's interface n times and this is the n+1th call to IUnknown::Release, the implementation of IUnknown::AddRef must cause the interface pointer to free itself. When the released pointer is the only existing reference to an object (whether the object supports single or multiple interfaces), the implementation must free the object.

Note Aggregation of objects restricts the ability to recover interface pointers.

Notes to Callers
Call this function when you no longer need to use an interface pointer. If you are writing a function that takes an in-out parameter, call IUnknown::Release on the pointer you are passing in before copying the out-value on top of it.