Question

I need clarification in calling methodologies, i have a base class and from which i try to call derived class function using derived class object. is it possible

Pls tell me whats wrong in my code in this senario

#include "stdafx.h"
#include <malloc.h>

class derived;

class base
{
public:
    base()
    {

    }
    ~base()
    {
    }

    void setdptr(derived* dptr)
    {
        m_dptr = dptr;
        dptr->sayHello();
    }

    virtual void addfunc()
    {

        printf("base class add");
    }

    derived *m_dptr;

};

class derived : public base
{
public:
    derived()
    {
    }
    ~derived ()
    {
    }

    void addfunc()
    {
        printf("derived class add");
    }

    void sayHello()
    {
            printf("Say Hello");
    }

    void setDeriveToBase()
    {
       setdptr(this);
    }

};

int _tmain(int argc, _TCHAR* argv[])
{
    derived dp;
    dp.setDeriveToBase();
    return 0;
}

Answer 1

In the setdptr function in class base, you don’t have the derived class fulle defined yet so the compiler doesn’t yet know what members are in derived.

Move the actual definition of setdptr to after the declaration of derived and it should work.

Something like this:

class derived;

class base
{
    // ....

    void setdptr(derived* dptr);

    // ....
};

class derived : public base
{
    // ....
};

void base::setdptr(derived* dptr)
{
    m_dptr = dptr;
    dptr->sayHello();
}