Derived class implementing multiple interfaces with a common function signature

Question

I\'m getting a compile error when I try to compile my code. The error is this:

multi.cc: In function ‘int main()’:
multi.cc:35: error: cannot declare variabl         


        

Answer 1

You need to define a common_func() anyway in MostDerivedClass to satisfy your inheritance from Interface2

you can try something like

virtual int common_func() {
    return InterimClass::common_func();
}

This is most useful if you cannot change the first Interface1

If you want a real inheritance relationship between your classes you need to follow Lol4t0 advice. Extract a superclass from Interface1, and make Interface2 subclass of this newly created class. Example :

class RootInterface{
public :
    virtual int common_func() = 0;
    virtual ~RootInterface(){}
};

class Interface1 : public virtual RootInterface{
public:
    virtual ~Interface1() {};
};

class Interface2 : public virtual RootInterface{
    public:
    virtual int new_func() = 0;
    virtual ~Interface2() {};
};

class InterimClass : public Interface1 {
    public:
    virtual int common_func() {
        return 10;
    }
};

class MostDerivedClass : public InterimClass, public Interface2 {
public:
    virtual int new_func() {
        return 20;
    }
};