Basic Doubt in Virtual Classes

Code:

---

class Base
{
public :
int a;
};

class D1 : virtual public Base
{
public:
int b;
};

class D2 : virtual public Base
{
public:
int c;
void change_a()
{
a=5;
}
};

---

D2 makes a=5.
What effect does this have on the versions of "a" in Base and D1?
How is memory allocated actually in this program...
?

In this setup D1 is unrelated to D2, so changing a in an instance of D2 will have no effect on anything that is a D1. Did you mean to add a third class that inherits from both D1 and D2?

Yes! How did you know? Is it a typical example? or is there some other reason?
What will be the situation then?

Interesting read: http://en.wikipedia.org/wiki/Diamond_problem

>> How did you know?
Because a virtual base class doesn't make sense unless you are using multiple inheritance.