CODEWITHSUNDEEP
c++c++11vectorheader-files
t3rrh42d2
t3rrh42d2

Reputation: 134

Vector unknown size

I have a class Player which contains an instance variable: \

vector<Card> userCards;

In order to avoid any compilation errors I forward declared the class Card. However now when I try to Build Solution I get an error saying

Card *: Unknown size.

Basically I am trying to create a Player who contains a non-fixed number of cards, so I tried using a vector and now I cannot get it to work.

Player.h

#include <iostream>
#include <vector>

using std::string;
using std::vector;

#ifndef PLAYER_H_
#define PLAYER_H_

class Card;
class Player {
private:
    vector<Card> userCards;
};
#endif

Card.h

#include <iostream>

using std::string;

#ifndef CARD_H_
#define CARD_H_

class Card {
private:
    string name;
    string type;

public:
    Card(const string& name, const string& type);   
};
#endif

I have a bunch of different functions that are not related, so I did not include them.

Upvotes: 1

Views: 11635

Answers (4)

Ahmed Akhtar
Ahmed Akhtar

Reputation: 1463

I am assuming you included the Card.h header in the Player.h file using the #include "Card.h" directive

but, if you did not then be informed that std::vector<T> requires its parameter to be a complete type and you cannot pass a forward declared type as its template argument.

Here is a another question/answer that clarifies your problem: When can I use a forward declaration?

Upvotes: 3

LogicStuff
LogicStuff

Reputation: 19607

The type template argument of std::vector cannot be an incomplete type. It has to be defined (complete) before instantiation of std::vector<Card>. To do that, replace your forward declaration class Card; with #include "Card.h" directive.

You can see the further requirements on template arguments here.

Upvotes: 5

πάντα ῥεῖ
πάντα ῥεῖ

Reputation: 1

vector<Card> needs to see a complete declaration of Card. There are some certain functions that are needed for instantiation.

You can do something like a 

vector<unique_ptr<Card>> userCards;

though, which behaves as any pointer (reference) declaration, and accepts the forward declaration.

Upvotes: 2

Bo Persson
Bo Persson

Reputation: 92271

The vector doesn't have to know how many cards you want to store, but is has to know the size of a Card.

So don't forward declare, but #include the Card.h.

Upvotes: 2

Related Questions