IUnknown

In programming, the IUnknown interface is the fundamental interface in the Component Object Model (COM). The published [http://www.microsoft.com/com/resources/comdocs.asp COM specification] mandates that COM objects must minimally implement this interface. Furthermore, every other COM interface must be derived from IUnknown.

Methods

The IUnknown interface exposes three methods (sometimes called functions): QueryInterface, AddRef, and Release: [http://msdn2.microsoft.com/en-us/library/ms680509.aspx IUnknown definition] at [http://microsoft microsoft.com] ; accessed 18-Jan-2008]

* QueryInterface is used to obtain a pointer to another interface, given a GUID that uniquely identifies that interface (commonly known as an interface ID, or IID). If the COM object does not implement that interface, an E_NOINTERFACE error is returned instead.
* AddRef is used by clients to indicate that a COM object is being referenced. This is necessary to ensure that a COM object is not disposed prematurely.
* Release is used by clients to indicate that they have finished using the COM object. An unreferenced COM object may be safely disposed.interface IUnknown{ virtual HRESULT QueryInterface(REFIID riid, void **ppvObject) = 0; virtual ULONG AddRef(void) = 0; virtual ULONG Release(void) = 0;};The IUnknown interface ID is defined as a GUID with the value of {00000000-0000-0000-C000-000000000046}.

Miscellaneous

*Components designed under the ActiveX standard must, at minimal, implement the IUnknown interface. [http://msdn2.microsoft.com/en-us/library/aa751968.aspx ActiveX Controls] at [http://microsoft.com microsoft.com] ; accessed 18-Jan-2008]
*IUnknown serves as the base for Mac OS X's Core Foundation CFPlugIn framework.Fact|date=June 2008

Notes

ee also

* IDispatch