 Important: |
|---|
| This is retired content. This content is outdated and is no longer being maintained. It is provided as a courtesy for individuals who are still using these technologies. This content may contain URLs that were valid when originally published, but now link to sites or pages that no longer exist. |
This method returns a pointer to a specified interface on an object to which a client currently holds an interface pointer. This method must call IUnknown::AddRefon the pointer it returns.
HRESULT QueryInterface( REFIID iid , void ** ppvObject );
Parameters
- iid
- [in] Identifier of the interface being requested.
- ppvObject
- [out] Address of pointer variable that receives the interface
pointer requested in
riid. Upon successful return, *
ppvObjectcontains the requested interface pointer to the
object. If the object does not support the interface specified in
iid, *
ppvObjectis set to NULL.
Return Value
S_OK indicates that the interface is supported. E_NOINTERFACE indicates that the interface is not supported.
Remarks
The QueryInterfacemethod gives a client access to other interfaces on an object.
For any one object, a specific query for the IUnknowninterface 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 QueryInterfaceon 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 failure."):
- The set of interfaces accessible on an object through IUnknown::QueryInterfacemust be static, not dynamic. This means that if a call to QueryInterfacefor 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 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
succeed.
Requirements
Runs On Versions Defined in Include Link to Windows CE OS 1.0 and later Unknwn.h Note This API is part of the complete Windows CE OS package as provided by Microsoft. The functionality of a particular platform is determined by the original equipment manufacturer (OEM) and some devices may not support this API.
See Also