COM - Implementing DllGetClassObject - c++

Question

I am attempting to understand creating/using COM components without the help of MFC/ATL to know its inner workings.
I am using this codeguru article for reference.Following are the steps followed by me.
Created a Wind32 Dll,
Added a MIDL file and declared the interface IAdd and library name DemoMath; compiled the code using MIDL compiler.
Created CAddObj class deriving IAdd interface,provided implementation for IAdd and IUnknown interfaces.
Created class CAddFactory deriving from IClassFactory interface;provided implementation for IClassFactory methods.
Now creating DllGetClassObject to give client an option to invoke this function to get an instance of the class factory.
Following is the code:
#include "stdafx.h"
#include <objbase.h>
#include "AddObjFactory.h"
#include "IAdd_i.c"
STDAPI DllGetClassObject(const CLSID& clsid,
const IID& iid,
void** ppv)
{
//
//Check if the requested COM object is implemented in this DLL
//There can be more than 1 COM object implemented in a DLL
//
if (clsid == CLSID_AddObject)
{
//
//iid specifies the requested interface for the factory object
//The client can request for IUnknown, IClassFactory,
//IClassFactory2
//
CAddFactory *pAddFact = new CAddFactory;
if (pAddFact == NULL)
return E_OUTOFMEMORY;
else
{
return pAddFact->QueryInterface(iid , ppv);
}
}
//
//if control reaches here then that implies that the object
//specified by the user is not implemented in this DLL
//
return CLASS_E_CLASSNOTAVAILABLE;
}
Now where is CLSID_AddObject constant suppose to be defined
or Is it generated while compiling MIDL file(I didn't find it though)?

Answer 1

coclass IDL item will typically get you CLSID:
library Foo
{
//...
[
//...
]
coclass AddObject
{
//...
};
then on your "IAdd_i.c" you are already including:
MIDL_DEFINE_GUID(CLSID, CLSID_AddObject, ...);
this is what defines CLSID_AddObject.