How to call different overridden methods on a vector

Question

i'm using vector for the first time in c++ and my problem is to call different overridden methods, let me explain: I got the CARD class subclassed by SPECIALCARD. In CARD there is a method printCard() and in SPECIALCARD the method is overridden. Then in the main i create a vector of Card. I put in the first position a card and in the second position a specialcard. When i try to call the printCard() method on the first and the second position it always run the method of the parent (but i want to call the parent method in first position and the son method in the second position). Here is the Card class:

CARD.H
using namespace std;

class Card
{
    public:
        Card(int number, string seed);
        virtual void printCard();

    protected:
        int number;
        string seed;
};

CARD.CPP
#include "Card.h"
#include <iostream>
#include <string>
using namespace std;

Card::Card(int number, string seed)
{
   this->number = number;
   this->seed = seed;
}

void Card::printCard()
{
    cout << "the card is " << number << " of " << seed << endl; 
}

And here is the SpecialCard class

SPECIALCARD.H
#include "Card.h"
#include <string>
using namespace std;

class Special_Card : public Card
{
    public:
        Special_Card(int number, string name, string seed);
        string getName();
        virtual void printCard();

    private:
        string name;
};

SPECIALCARD.CPP
#include <iostream>
#include "Special_Card.h"
#include "Card.h"
#include <string>
using namespace std;

Special_Card::Special_Card(int number, string name, string seed): Card(number, seed)
{
    this->number = number;
    this->name = name;
    this->seed = seed;
}

//overridden method
void Special_Card::printCard()
{
    cout << "the card is " << name << " of " << seed << endl;
}

finally we got the main where i create the vector

#include <iostream>
#include "Card.h"
#include "Special_Card.h"
#include <string>
#include <vector>
using namespace std;

int main()
{
    vector <Card> deck;
    deck.push_back(Card(1,"hearts"));
    deck.push_back(Special_Card(10,"J","hearts"));
    deck[0].printCard();
    deck[1].printCard();
}

The console output is the card is 1 of hearts /n the card is 10 of hearts (in the second i want to print "the card is a J of hearts")

`vector` means "vector of Card", not "vector of various different things that have Card as base class" — M.M, Jan 31 '17 at 12:20
http://stackoverflow.com/questions/17294909/storing-derived-object-into-container-of-base-type/17295075#17295075 — M.M, Jan 31 '17 at 12:22

score 4 · Answer 1 · answered Jan 31 '17 at 12:21

Your code in main will cause object slicing. To get proper polymorphic behavior you need to use pointers or references.

If you want your vector to own these objects, then I would make the vector contain std::unique_ptr which will allow the contained objects to act polymorphically.

#include <memory>
int main()
{
    std::vector<std::unique_ptr<Card>> deck;
    deck.push_back(std::make_unique<Card>(1,"hearts"));
    deck.push_back(std::make_unique<Special_Card>(10,"J","hearts"));
    deck[0]->printCard();
    deck[1]->printCard();
}

If i use this code the console give the error that "unique_ptr was not declared in this scope" and "make_unique" was not declared in this scope. Indeed i have use the #include and #include . Do you know where can I find this unique_ptr? — Alessandro Picardi, Jan 31 '17 at 16:35

score 0 · Answer 2 · answered Jan 31 '17 at 17:01

I finally solved this way: I use e vector of Card*

#include <iostream>
#include "Card.h"
#include "Special_Card.h"
#include <string>
#include <vector>

int main()
{
    vector <Card*> deck;
    deck.push_back(new Card(1,"hearts"));
    deck.push_back(new Special_Card(10,"J","hearts"));
}

How to call different overridden methods on a vector

2 Answers2