DllGetClassObject

Article
06/30/2006

This function 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.

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,
  REFIID riid,
  LPVOID* ppv 
);

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] Address of pointer variable that receives the interface pointer requested in riid. Upon successful return, *ppv contains the requested interface pointer. If an error occurs, the interface pointer is 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.

To determine whether the platform supports this function, see Determining Supported COM APIs.

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;

Requirements

OS Versions: Windows CE 3.0 and later.
Header: Objbase.h.
Link Library: Ole32.lib.

Share via