Returns a pointer to a specified interface on a component to which a client
currently holds an interface pointer. This function must call IUnknown::AddRef
on the pointer it returns.
| REFIID iid,
||//Specifies the requested interface's IID
| void ** ppvObject
||//Receives an indirect pointer to the object
[in] Specifies the IID of the interface being requested.
[out] Receives a pointer to an interface pointer to the object on return. If
the interface specified in riid
is not supported by the object, ppvObj
is set to NULL
S_OK if the interface is supported, S_FALSE if not.
The QueryInterface method gives a client access to other interfaces on an
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 allows a client to determine whether two pointers point to the
same component by calling QueryInterface
on both and comparing the results. It is specifically not the case that
queries for interfaces (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
- The set of interfaces accessible on an object through IUnknown::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
- It must be symmetric if a client holds a pointer to an interface on an object, and queries for that
interface, the call must succeed.
- It must be reflexive 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 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
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