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#include "iostream"

typedef void (*pfunc)(void*);

class D
{
    D(): a(5),f1(**(pfunc**)this)
    {
        std::cout << "object of class D has created." << std::endl;
    }
    virtual void func()
    {
        std::cout << "a: " << a << " from D." << std::endl;
    }
    friend class F;
    pfunc f1;
    int a;
};

class F: public D
{
  public:
    F()
    {
        std::cout << "object of class F has created." << std::endl;
        f1(this); // func from D
        func(); // func from F
    }
    void func()
    {
        std::cout << "a: " << a << " from F." << std::endl;
    }
};

int main()
{
    F g;
    return 0;
}