3.1.1.5.8 IUnknown Interface

The IUnknown interface enables clients to retrieve pointers to other interfaces on a given object through the QueryInterface method, and to 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 reserve opnums 0 through 2, inclusive, for every interface.

The IUnknown interface has the local IDL attribute (section 2.2.27).

The UUID for this interface is {00000000-0000-0000-C000-000000000046}.

Methods in RPC Opnum Order

Method	Description
Opnum0NotUsedOnWire	QueryInterface Reserved for local use. Opnum: 0
Opnum1NotUsedOnWire	AddRef Reserved for local use. Opnum: 1
Opnum2NotUsedOnWire	Release Reserved for local use. Opnum: 2

In the preceding table, the term "Reserved for local use" means that the client MUST NOT send the opnum, and the server behavior is undefined<50> since it does not affect interoperability.

All methods MUST NOT throw exceptions.