ex15.23.cpp

/***************************************************************************
 *  @file       main.cpp
 *  @author     Alan.W
 *  @date       24  Jan 2014
 *  @remark     This code is for the exercises from C++ Primer 5th Edition
 *  @note
 ***************************************************************************/
//
// Exercise 15.23:
// Assuming class D1 on page 620 had intended to override its inherited fcn
// function, how would you fix that class? Assuming you fixed the class so
// that fcn matched the definition in Base, how would the calls in that section
// be resolved?
//  remove the parameter int.
//  Disscussion on SO :
//  http://stackoverflow.com/questions/21320779/trying-to-understand-dynamic-binding-and-virtual-functions

#include <iostream>
#include <string>

class Base
{
public:
    virtual int fcn(){ std::cout << "Base::fcn()\n"; return 0; }
};

class D1 : public Base
{
public:
    int fcn() override  { std::cout << "D1::fcn()\n";return 0; }
    // ^^^--fixed to override the inherited version
    virtual void f2() { std::cout << "D1::f2()\n"; }
};

class D2 : public D1
{
public:
    int fcn(int);
    int fcn() override { std::cout << "D2::fcn()\n";return 0; }
    void f2() override { std::cout << "D2::f2()\n"; }
};

int main()
{
    Base bobj;
    D1 d1obj;
    D2 d2obj;

    Base *bp1 = &bobj, *bp2 = &d1obj, *bp3 = &d2obj;
    //bp1->fcn(); // virtual call, will call Base::fcn at run time
    //bp2->fcn(); // virtual call, will call D1::fcn   at run time
    //bp3->fcn(); // virtual call, will call D2::fcn   at run time

    D1 *d1p = &d1obj; D2 *d2p = &d2obj;

    //bp2->f2();
 //^^^^^^^^^^^^
    // @note   You are calling virtual member functions via a pointer
    // to Base. That means that you can only call methods that exist
    // in the Base class. You cannot simply add methods to a type
    // dynamically.
    //d1p->f2();    // virtual call, will call D1::f2() at run time
    //d2p->f2();    // virtual call, will call D2::f2() at run time

    return 0;
}