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4/8/2010

This function retrieves the class object from a DLL object handler or object application. DllGetClassObjectis called from within the CoGetClassObjectfunction when the class context is a DLL.

OLE does not provide this function. DLLs that support the OLE Component Object Model (COM) must implement DllGetClassObjectin OLE object handlers or DLL applications.

Syntax

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, * ppvcontains the requested interface pointer. If an error occurs, the interface pointer is NULL.

Return Value

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 CoGetClassObjectfunction finds the class object that is to be loaded in a DLL, CoGetClassObjectuses the DLL's exported DllGetClassObjectfunction.

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

Notes to Callers

The application should not call DllGetClassObjectdirectly. When an object is defined in a DLL, CoGetClassObjectcalls the CoLoadLibraryfunction to load the DLL, which, in turn, calls DllGetClassObject.

Notes to Implementers

You need to implement DllGetClassObjectin (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, DllGetClassObjectcreates a class object and calls its QueryInterfacemethod to retrieve a pointer to the interface requested in riid.

The implementation safely releases the reference it holds to the IClassFactoryinterface because it returns a reference-counted pointer to IClassFactoryto the caller.

Copy Code
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

Header objbase.h
Library ole32.lib
Windows Embedded CE Windows CE 3.0 and later
Windows Mobile Windows Mobile Version 5.0 and later

See Also