Ambiguity in multiple inheritance

Ambiguity in inheritance

Ambiguity arises when the compiler finds more than one possible meaning for a name and cannot choose. In multiple inheritance, if two base classes have a member (data or function) with the same name and the derived class does not define its own, a call such as obj.show() is ambiguous. A second case is the diamond problem, where the final class has two copies of a common grandparent.

It is resolved with the scope resolution operator (obj.A::show()), by redefining the member in the derived class, or by using a virtual base class for the diamond case.

Program showing ambiguity

#include <iostream>
using namespace std;

class Father {
public:
    void show() { cout << "Father's show()" << endl; }
};

class Mother {
public:
    void show() { cout << "Mother's show()" << endl; }
};

class Child : public Father, public Mother {
};

int main() {
    Child c;
    // c.show();       // ERROR: reference to 'show' is ambiguous
    c.Father::show();  // resolved using scope resolution operator
    c.Mother::show();
    return 0;
}

If the commented line c.show(); is enabled, the compiler gives an error like request for member 'show' is ambiguous, since both Father::show() and Mother::show() are equally valid.

Output (after resolution):

Father's show()
Mother's show()