C++ Allocation of incomplete type

Question

I'm tring to create Card and Deck classes but I'm getting an error message that says

Allocation of incomplete type 'Card'

The problem is happening in Deck::Deck() of Deck.cpp

//
//Deck.h

#ifndef JS_DECK_H
#define JS_DECK_H

#include <iostream>
using std::cout;

#include <vector>
using std::vector;

//forward declaration
class Card;

namespace JS {
    class Deck {

    public:
        Deck();
    private:
        vector<Card *>cards;
    };

}

#endif

//
//Deck.cpp

#include "Deck.h"

using namespace JS;

Deck::Deck(){

    for(int suit = 0; suit < 4; suit++){
        for(int rank = 1; rank < 14; rank++){

            cards.push_back(new Card(rank, suit));//allocation of incomplete type 'Card'
        }
    }
}

//
//Card.h

#ifndef JS_CARD_H
#define JS_CARD_H

#include <ostream>
using std::ostream;

#include <string>
using std::string;

#include <vector>
using std::vector;

namespace JS {
    class Card {

    friend ostream &operator<<(ostream &out, const Card &rhs);

    public:
        enum Suit { DIAMONDS, HEARTS, SPADES, CLUBS };
        enum Rank { ACE = 1, JACK = 11, QUEEN = 12, KING = 13 };

        Card(int rank, int suit) : rank(rank), suit(suit){}

        string getRank() const;
        string getSuit() const;
        int getRankValue() const;

        int operator+(const Card& rhs);
        void displayCard(const Card &rhs);

    private:
        int rank;
        int suit;
    };

}

#endif

Answer 1

In the implementation of Deck (i.e. the Deck.cpp file) you need the full definition of Card to be able to allocate objects of that type. So the solution is simply to include Card.h in Deck.cpp.