Multiple (diamond) inheritance compiles without “virtual”, but doesn't with

Question

Given the following code (without virtual inheritance) :

class A
{
public:
    virtual void f() = 0;
};

class B : public A
{
 public:
    virtual void f()          


        

Answer 1

With the virtual inheritance a D object has a single base-class A sub-object. This single sub-object can’t have two different implementations of a virtual function. In contrast, without virtual inheritance a D object has two distinct base-class A sub-objects, each with its own implementation of the function (which is OK until you try to call it on a D object, at which point you need to indicate which one you want).

Cheers & hth.