CODEWITHSUNDEEP
c++inheritancederivedvirtual-functions
Striding Dragon
Striding Dragon

Reputation: 243

Calling function of one derived class in second derived class

I have a bit of a problem with multiple inheritances. I have a class C that has two base classes, A and B. A is the main base class and B provides a specialization. However, B needs to be able to call a method that is part of A.

My question is, how can I expose A.foo() to B so that it can be called? I've been googling and reading up like crazy but I can't find anything that works for my scenario. I tried template classes, but that opened up another can of worms. I tried all sorts of virtual functions but they all caused Linker errors at best.

This here is essentially what I want to be able to do…

    class A
    {
    public:
        void foo() { std::cout << "Hello there!"; }
    };

    class B
    {
    public:
        void bar() { foo(); }    // Call A::foo() here somehow
    };

    class C : public A, public B
    {
    };

    int main( void )
    {
        C _test;
        _test.bar();
    }

Does anyone have any pointers for me how I would go about this? I also tried using another class that A and B both derive from and then using virtual inheritance and sister classes, but I could not get that to work either.

    class Z
    {
    public:
        virtual void foo()=0;
    };

    class A : public Z
    {
    public:
        void foo() { std::cout << "Hello there!"; }
    };

    class B : public Z
    {
    public:
        void bar() { foo(); }
    };

    class C : public A, public B
    {
    public:
    //  virtual void foo();
    };

    int main( void )
    {
        C _test;

        _test.bar();
    }

Any suggestions would be really appreciated because this is a major feature I need to implement… somehow. :)

Upvotes: 0

Views: 1274

Answers (2)

Striding Dragon
Striding Dragon

Reputation: 243

Here is the implementation, as suggested by Sam Varshavchik. It is doesn't require an additional base class, so it is a bit leaner and works perfectly fine.

    class A
    {
    public:
        void foo() { std::cout << "Hello there!"; }
    };

    class B
    {
    public:
        virtual void foo() = 0;
        void bar() { foo(); }
    };

    class C : public A, public B
    {
    public:
        void foo() { A::foo(); }
    };

    int main(int argc, const char * argv[])
    {
        C _test;
        _test.bar();
    }

Upvotes: 1

Ari0nhh
Ari0nhh

Reputation: 5920

A::foo() is a class member function. To call it you either must have a class instance pointer, or make it static. If B must call A methods, perhaps it should be derived from A. Other solution is reworking your entire class hierarchy, to move function call to the class, derived from A and B. Also you could pass A pointer to the B constructor to call it from there.

Upvotes: 0

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