C++ Sample Code - 01

C++ Sample Code - 01
Skill Level: Intermediate

This sample explains the need of the virtual functions. Scroll down for the download links.

//============================================================================
// Name        : Sample-01.cpp
// Author      : Raghavendra Nayak
// Version     :
// Date        : 07-June-2008
// Copyright   : (c) 2008, Raghavendra Nayak. All rights reserved.
// Description : Sample C++ program. This sample explains the need of
//                 virtual functions.
//============================================================================

/*
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/*
 * Case: 01
 * Please note that, in this program by default we don't use virtual functions,
 * due to which always base class functions are called!
 *
 * To change this behavior define the value of the macro USE_VIRTUAL_FUNC as 1.
 * This will add "virtual" to the base class function prototype.
 *
 * ie; virtual void setData(int inData);
 *
 * After this, you will notice that, proper functions are called..
 *
 * Case: 02
 * Also, note that, virtual functions are hierarchical, ie, if the very first base
 * class is virtual, all the subsequent derived classes will automatically get that
 * property.
 *
 * ie, In this example, myClassC inherits from myClassB and if you
 * define USE_VIRTUAL_FUNC as 1 . This will add virtual keyword to the functions
 * of myClassA (Base class).
 *
 * After this, when you call setData/getData functions, you will see that proper
 * functions are called!
 */

/*
 * Conclusions:
 *
 * 01. If you don' use virtual functions, always base call functions are called.
 * (When called through base class pointer/reference).
 *
 * 02. virtual functions are hierarchical, if the base class has virtual property,
 * all the derived classes automatically get that property..
 */

#include <iostream>

/*
 * Define the value of this macro to 1 to use virtual functions
 */
#define USE_VIRTUAL_FUNC        0

class myClassA {
protected:

        int myData;
public:
#if USE_VIRTUAL_FUNC
        virtual
#endif //USE_VIRTUAL_FUNC
        void setData(int inData)
        {

                std::cout<<"\nWe are in myClassA setData";
                myData = inData;
        }
#if USE_VIRTUAL_FUNC
        virtual
#endif //USE_VIRTUAL_FUNC
        int getData()
        {
                std::cout<<"\nWe are in myClassA getData";

                return myData;
        }
};

class myClassB : public myClassA {

public:
        void setData(int inData)
        {
                std::cout<<"\nWe are in myClassB setData";

                myData = inData;
        }
        
        int getData()
        {
                std::cout<<"\nWe are in myClassB getData";

                return myData;
        }
};

class myClassC : public myClassA {

public:
        void setData(int inData)
        {
                std::cout<<"\nWe are in myClassC setData";

                myData = inData;
        }
        
        int getData()
        {
                std::cout<<"\nWe are in myClassC getData";

                return myData;
        }
};

int main (int argc, char * const argv[])
{

        int option = 1;
        
        std::cout<<"\nWhich case you want to run ? [1/2] : ";

        std::cin>>option;
        
        myClassA *myObjPointer;
        
        if (option == 1)

                myObjPointer = new myClassB; // Case: 01
        else
                myObjPointer = new myClassC; // Case: 02

        
        myObjPointer->setData(10);
        myObjPointer->getData();
        
        return 0;
}

Downloads Links:

1. XCode project
   
2. Eclipse project
   
3. Source file