Retrieves pointers to the supported interfaces on an object.
This method calls IUnknown::AddRef on the pointer it returns.
HRESULT QueryInterface( Q **pp, );
This method returns S_OK if the interface is supported, and E_NOINTERFACE otherwise. If ppvObject is NULL, this method returns E_POINTER.
For any one object, a specific query for the IUnknown interface on any of the object's interfaces must always return the same pointer value. This enables a client to determine whether two pointers point to the same component by calling QueryInterface with IID_IUnknown and comparing the results. It is specifically not the case that queries for interfaces other than IUnknown (even the same interface through the same pointer) must return the same pointer value.
There are four requirements for implementations of QueryInterface (In these cases, "must succeed" means "must succeed barring catastrophic failure."):
- The set of interfaces accessible on an object through QueryInterface must be static, not dynamic. This means that if a call to QueryInterface for a pointer to a specified interface succeeds the first time, it must succeed again, and if it fails the first time, it must fail on all subsequent queries.
- It must be reflexive â€” if a client holds a pointer to an interface on an object, and queries for that interface, the call must succeed.
- It must be symmetric â€” if a client holding a pointer to one interface queries successfully for another, a query through the obtained pointer for the first interface must succeed.
- It must be transitive â€” if a client holding a pointer to one interface queries successfully for a second, and through that pointer queries successfully for a third interface, a query for the first interface through the pointer for the third interface must succeed.
|Windows version||Windows 2000 Professional [desktop apps only] Windows 2000 Server [desktop apps only]|