CComClassFactory Class


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This class implements the IClassFactory interface.

class CComClassFactory : 
    public IClassFactory, 
    public CComObjectRootEx<CComGlobalsThreadModel>

Public Methods

CComClassFactory::CreateInstanceCreates an object of the specified CLSID.
CComClassFactory::LockServerLocks the class factory in memory.

CComClassFactory implements the IClassFactory interface, which contains methods for creating an object of a particular CLSID, as well as locking the class factory in memory to allow new objects to be created more quickly. IClassFactory must be implemented for every class that you register in the system registry and to which you assign a CLSID.

ATL objects normally acquire a class factory by deriving from CComCoClass. This class includes the macro DECLARE_CLASSFACTORY, which declares CComClassFactory as the default class factory. To override this default, specify one of the DECLARE_CLASSFACTORYXXX macros in your class definition. For example, the DECLARE_CLASSFACTORY_EX macro uses the specified class for the class factory:

class ATL_NO_VTABLE CMyCustomClass :
   public CComObjectRootEx<CComSingleThreadModel>,
   public CComCoClass<CMyCustomClass, &CLSID_MyCustomClass>,
   public IDispatchImpl<IMyCustomClass, &IID_IMyCustomClass, &LIBID_NVC_ATL_COMLib, /*wMajor =*/ 1, /*wMinor =*/ 0>

   // Remainder of class declaration omitted.

The above class definition specifies that CMyClassFactory will be used as the object's default class factory. CMyClassFactory must derive from CComClassFactory and override CreateInstance.

ATL provides three other macros that declare a class factory:

Header: atlcom.h

Creates an object of the specified CLSID and retrieves an interface pointer to this object.

STDMETHOD(CreateInstance)(LPUNKNOWN pUnkOuter, REFIID riid, void** ppvObj);


[in] If the object is being created as part of an aggregate, then pUnkOuter must be the outer unknown. Otherwise, pUnkOuter must be NULL.

[in] The IID of the requested interface. If pUnkOuter is non- NULL, riid must be IID_IUnknown.

[out] A pointer to the interface pointer identified by riid. If the object does not support this interface, ppvObj is set to NULL.

Return Value

A standard HRESULT value.

Increments and decrements the module lock count by calling _Module::Lock and _Module::Unlock, respectively.

STDMETHOD(LockServer)(BOOL fLock);


[in] If TRUE, the lock count is incremented; otherwise, the lock count is decremented.

Return Value

A standard HRESULT value.


_Module refers to the global instance of CComModule or a class derived from it.

Calling LockServer allows a client to hold onto a class factory so that multiple objects can be created quickly.

CComObjectRootEx Class
Class Overview