これってどうよ？

#include <iostream>
using namespace std;
class CBase
{
int m_id1;
public:
CBase(int id1 = 1):m_id1(id1){}
int GetID1() const { return m_id1; }
};
class CDerived : public CBase
{
int m_id2;
public:
CDerived(int id2 = 1):m_id2(id2),CBase(id2*10){}
int GetID2() const { return m_id2; }
};
class CFactory
{
protected:
CFactory(){}
public:
static CBase* GetInstance(){ return new CBase(111); }
};
int main()
{
CBase* p = CFactory::GetInstance();
cout << ((CDerived*)p)->GetID2() << endl;
}