Thread: inheritance and virtual methods

I'm having some problems with these 2 concepts. Any Advice?

Thanks

My errors:

Code:

eclared in class ‘expandedKey128’
expandedKey.cpp:10: error: no ‘void expandedKey192::printKey()’ member function declared in class ‘expandedKey192’
expandedKey.cpp:14: error: no ‘void expandedKey256::printKey()’ member function declared in class ‘expandedKey256’

Header:

Code:

#ifndef _EXPANDED_KEY_H_
#define _EXPANDED_KEY_H_

class expandedKey {
        public:
                virtual void printKey();
};

class expandedKey128: public expandedKey {
        public:
                char expandedKey[4][4];
};

class expandedKey192: public expandedKey {
        public:
                char expandedKey[4][4];
};

class expandedKey256: public expandedKey {
        public:
                char expandedKey[4][4];
};

#endif

Source:

Code:

#include <iostream>
using namespace std;

#include "expandedKey.h"

void expandedKey128::printKey() {
        cout << "print key" << endl;
}

void expandedKey192::printKey() {
        cout << "print key" << endl;
}

void expandedKey256::printKey() {
        cout << "print key" << endl;
}

You have to include this:

Code:

class expandedKey128: public expandedKey {
        public:
                char expandedKey[4][4];
                void printKey();
};

So this printKey will override the virtual printKey().

The idea is that there will be also a expandedKey:rintKey() declared, otherwise you don't need a virtual function simple a normal printKey() function.

If you want to make sure that every class will have a version of the function you should declare a pure virtual method like:

Code:

class expandedKey {
        public:
                virtual void printKey() = 0;
};

so that every subclass has to have a printKey() class


If you just want every class to have the printKey() function then virtual is not what you want. Just declare a normal function printKey(). Every inherited class will have it.