59.cpp

// This program uses virtual base classes.
#include <iostream>
using namespace std;
class base {
    public:
        int i;
};

// derived1 inherits base as virtual.
class derived1 : virtual public base {
    public:
        int j;
};

// derived2 inherits base as virtual.
class derived2 : virtual public base {
    public:
        int k;
};

/* derived3 inherits both derived1 and derived2.
This time, there is only one copy of base class. */
class derived3 : public derived1, public derived2 {
    public:
        int sum;
};
int main()
{
    derived3 ob;
    ob.i = 10; // now unambiguous
    ob.j = 20;
    ob.k = 30;
    // unambiguous
    ob.sum = ob.i + ob.j + ob.k;
    // unambiguous
    cout << ob.i << " ";
    cout << ob.j << " " << ob.k << " ";
    cout << ob.sum;
    return 0;
}