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

Let the second interface be derived from the first interface, remove the declaration of virtual int common_func() = 0; from the second interface, & use the keyword virtual to guide the compiler to the implementation.

class Interface1 {
public:
    virtual int common_func() = 0;
    virtual ~Interface1() {};
};

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

class Interface2 : public virtual Interface1{
public:
    virtual int new_func() = 0;
    virtual ~Interface2() {};
};

class DerivedClass : public virtual BaseClass, public virtual Interface2 {
public:
    virtual int new_func() {
        return 20;
    }   
};