IUnknown for MAPI

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The IUnknown interface for the Windows Mobile Messaging Application Programming Interface (MAPI) manages the existence of a MAPI object through the AddRef and Release methods.

Note   To conserve memory on Windows Mobile–based devices, the QueryInterface method is not implemented on many Windows Mobile-based MAPI interfaces for Pocket PC and Smartphone 2002 and Windows Mobile 2003.

Methods in Vtable Order

IUnknown methods Description
QueryInterface Returns a pointer to a specified interface.
AddRef Increments the reference count for an interface on an object.
Release Decrements the reference count for the calling interface on an object.


All Windows Mobile-based MAPI interfaces use COM and therefore inherit IUnknown. However, to conserve memory on Windows Mobile-based devices, the QueryInterface method of many Windows Mobile-based MAPI interfaces returns an error indicating that the method is not implemented (E_NOTIMPL). However, the AddRef and Release methods are always implemented on Windows Mobile-based MAPI interfaces.


Pocket PC: Pocket PC 2002 and later
Smartphone: Smartphone 2002 and later
OS Versions: Windows CE 3.0 and later
Header: unknwn.h

See Also

MAPI Interfaces | Messaging

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