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DllGetClassObject

Retrieves the class object from a DLL object handler or object application. It is called from within the CoGetClassObject function when the class context is a DLL.

Note OLE does not provide this function. DLLs that support the OLE Component Object Model must implement DllGetClassObject in OLE object handlers or DLL applications.

HRESULT DllGetClassObject(

REFCLSID rclsid,
//CLSID for the class object
REFIID riid,
//Identifier that identifies the interface that communicates with the class object
LPVOID * ppv
//Points to the pointer of the communicating interface
);

Parameters

rclsid

Specifies the CLSID that will associate the correct data and code.

riid

Specifies the interface that the caller is to use to communicate with the class object. Usually, this is IID_IClassFactory.

ppv

Points either to the pointer of the requested interface or, if an error occurs, to NULL.

Return Values

S_OK

Indicates that the object was retrieved successfully.

CLASS_E_CLASSNOTAVAILABLE

Indicates that the DLL does not support the class (object definition).

E_OUTOFMEMORY

Out of memory.

E_INVALIDARG

Indicates that one or more arguments are invalid.

E_UNEXPECTED

Indicates that an unexpected error occurred.

Comments

If a call to the CoGetClassObject function finds the class object that is to be loaded in a DLL, CoGetClassObject uses the DLL's exported DllGetClassObject function.

Notes to Callers

You should not call DllGetClassObject directly. When an object is defined in a DLL, CoGetClassObject calls the CoLoadLibrary function to load the DLL, which, in turn, calls DllGetClassObject.

Notes to Implementors

You need to implement DllGetClassObject in (and export it from) DLLs that support the OLE Component Object Model.

Example

Following is an example (in C++) of an implementation of DllGetClassObject. In this example, DllGetClassObject creates a class factory object and calls its QueryInterface method to retrieve a pointer to the interface requested in riid. The implementation safely releases the reference it holds to the IClassFactory interface because it returns a reference-counted pointer to IClassFactory to the caller.

HRESULT_export PASCAL DllGetClassObject

(REFCLSID rclsid, REFIID riid, LPVOID * ppvObj)

{

HRESULT hres = E_OUTOFMEMORY;

  • ppvObj = NULL;

CClassFactory *pClassFactory = new CClassFactory(rclsid);

if (pClassFactory != NULL) {

hRes = pClassFactory->QueryInterface(riid, ppvObj);

pClassFactory->Release();

}

return hRes;

}

See Also

CoGetClassObject, DllCanUnloadNow


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