# IClassFactory::CreateInstance

Creates an uninitialized object.

HRESULT CreateInstance(

IUnknown * pUnkOuter, | //Pointer to whether object is or isn’t part of an aggregate
REFIID riid, | //Reference to the identifier of the interface
void ** ppvObject | //Indirect pointer to the interface
); |

Parameters

pUnkOuter
  [in] If the object is being created as part of an aggregate, pointer to the controlling IUnknown interface of the aggregate. Otherwise, pUnkOuter must be NULL.
riid
  [in] Reference to the identifier of the interface to be used to communicate with the newly created object. If pUnkOuter is NULL, this parameter is frequently the IID of the initializing interface; if pUnkOuter is non-NULL, riid must be IID_IUnknown (defined in the header as the IID for IUnknown).
ppvObject
  [out] Indirect pointer to the requested interface. If the object does not support the interface specified in riid, ppvObject must be set to NULL.

Return Values

This method supports the standard return values E_UNEXPECTED, E_OUTOFMEMORY, and E_INVALIDARG, as well as the following:

S_OK
  The specified object was created.
CLASS_E_NOAGGREGATION
  The pUnkOuter parameter was non-NULL and the object does not support aggregation.
E_NOINTERFACE
  The object that ppvObject points to does not support the interface identified by riid.

Remarks

The IClassFactory interface is always on a class object. The CreateInstance method creates an uninitialized object of the class identified with the specified CLSID. When an object is created in this way, the CLSID must be registered in the system registry with CoRegisterClassObject.

The pUnkOuter parameter indicates whether the object is being created as part of an aggregate. Object definitions are not required to support aggregation &emdash; they must be specifically designed and implemented to support it.

The riid parameter specifies the IID (interface identifier) of the interface through which you will communicate with the new object. If pUnkOuter is non-NULL (indicating aggregation), the value of the riid parameter must be IID_IUnknown. If the object is not part of an aggregate, riid often specifies the interface though which the object will be initialized.

For OLE embeddings, the initialization interface is IPersistStorage, but in other situations, other interfaces are used. To initialize the object, there must be a subsequent call to an appropriate method in the initializing interface. Common initialization functions include IPersistStorage::InitNew (for new, blank embeddable components), IPersistStorage::Load (for reloaded embeddable components), IPersistStream::Load, (for objects stored in a stream object) or IPersistFile::Load (for objects stored in a file).

In general, if an application supports only one class of objects, and the class object is registered for single use, only one object can be created. The application must not create other objects, and a request to do so should return an error from IClassFactory::CreateInstance. The same is true for applications that support multiple classes, each with a class object registered for single use; a CreateInstance for one class followed by a CreateInstance for any of the classes should return an error.

To avoid returning an error, applications that support multiple classes with single-use class objects can revoke the registered class object of the first class by calling CoRevokeClassObject when a request for instantiating a second is received. For example, suppose there are two classes, A and B. When IClassFactory::CreateInstance is called for class A, revoke the class object for B. When B is created, revoke the class object for A. This solution complicates shutdown because one of the class objects might have already been revoked (and cannot be revoked twice).

See Also

CoRegisterClassObject, CoRevokeClassObject, CoCreateInstance, CoGetClassObject