Basic COM Interfaces and Details

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.

Methods in Vtable Order

The IDispatch interface was initially designed to support Automation. It provides a late-binding mechanism to access and retrieve information about an object's methods and properties.

• GetTypeInfoCount —returns the number of type descriptions for the object. For objects that support IDispatch , the type information count is always one.
• GetTypeInfo —retrieves a description of the object's programmable interface.
• GetIDsOfNames —maps the name of a method or property to a DISPID, which is later used to invoke the method or property.
• Invoke —calls one of the object's methods, or gets or sets one of its properties.