virtual diamonds are a programmers best enemy

pure_virtual.cpp

class Class1
{
public:
    Class1() { dummy2(); }
    virtual void dummy() = 0;
    void dummy2() {	dummy(); }
};

class Class2 : public Class1
{
public:
    virtual void dummy() { printf("Class2"); }
};

int _tmain(int argc, _TCHAR* argv[])
{
    Class2 *c2 = new Class2;
    delete c2;
}

virtual.cpp

class IBaseInterface

{
public:
    IBaseInterface() : counter(1) {}
    virtual ~IBaseInterface() {;}
    virtual int getCounter() {return(counter);}
    void grab() {++counter;}
private:
    mutable int counter;
};

class ISimpleInterface : public virtual IBaseInterface
{
    virtual void simple() {printf("simpleinterface");}
};

class ISimpleInterface2 : public virtual IBaseInterface
{
    void simple2() {printf("simpleinterface2");}
};

class BaseObject : public virtual ISimpleInterface
{
    virtual void work() {printf("baseobject");}
};

class BaseObject2 : public virtual ISimpleInterface2
{
    void work() {printf("baseobject2");}
};

int _tmain(int argc, _TCHAR* argv[])
{
    char buffer[256];
    BaseObject *obj = new BaseObject();
    BaseObject2 *obj2 = new BaseObject2();

    void *p;

    /* #1 */
    p = (void*)obj;
    printf("#1 Counter is %dn", ((IBaseInterface*)p)->getCounter());

    /* #2 */
    p = (void*)obj2;
    printf("#2 Counter is %dn", ((IBaseInterface*)p)->getCounter());

    /* #3 */
    p = (void*)obj;
    printf("#3 Counter is %dn", ((IBaseInterface*)(ISimpleInterface*)p)->getCounter());

    /* #4 */
    p = (void*)obj2;
    printf("#4 Counter is %dn", ((IBaseInterface*)(ISimpleInterface2*)p)->getCounter());

    gets(buffer);
    return 0;
}

// For extra credit
class Dummy : public virtual IBaseInterface
{
    virtual void dummy() = 0;
};

// [...]
int _tmain(int argc, _TCHAR* argv[])
{
     /* #5 */   
    p = (void*)obj;
    printf("#5 Counter is %dn", 
            ((IBaseInterface*)(Dummy*)p;
}