DllGetClassObject

Retrieves the class object from a DLL object handler or object application. DllGetClassObject 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 (COM) must implement DllGetClassObject in OLE object handlers or DLL applications.

STDAPI DllGetClassObject(

REFCLSID rclsid,

//CLSID for the class object

REFIID riid,

//Reference to the identifier of the interface that communicates with the class object

LPVOID * ppv

//Indirect pointer to the communicating interface

);

Parameters

rclsid: [in] CLSID that will associate the correct data and code.
riid: [in] Reference to the identifier of the interface that the caller is to use to communicate with the class object. Usually, this is IID_IClassFactory (defined in the OLE headers as the interface identifier for IClassFactory).
ppv: [out] Indirect pointer to the requested interface or, if an error occurs, to NULL.

Return Values

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

S_OK: The object was retrieved successfully.
CLASS_E_CLASSNOTAVAILABLE: The DLL does not support the class (object definition).

Remarks

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 Implementers

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 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

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