CODEWITHSUNDEEP
c++oopscopeclass-design
Nezo
Nezo

Reputation: 597

How do I share variables with another class in c++

I have two classes, Player and Controller. The Controller has the main game loop, and contains a Player. It also stores the world map. The Controller class passes user input to the player by calling various methods of the Player class, such as moveForward(). I am now implementing collision detection, and to do so, I need a way for the Player class to see the world map, but this is in the Controller class in which the Player class is.

In other words:

struct Controller {
    int worldMap[16][16][16];
    Player p;
    ...
}

struct Player {
    movePlayer() {
        #How do I check world map here?
    }
}

Upvotes: 0

Views: 85

Answers (3)

Emil Laine
Emil Laine

Reputation: 42828

Pass the data that movePlayer() needs as a reference parameter:

void movePlayer(const int (&map)[16][16][16]) { ... }

Passing the whole Controller object would be bad if movePlayer() only needs access to worldMap.

Alternatively, you could store a pointer to the current map in the Player object itself:

struct Player {
    // ...

private:
    int* Location;
};

Upvotes: 0

Ruijter
Ruijter

Reputation: 85

Since you are propably accessing the controller a lot, you can pass in a pointer to the Player and there you assign it to a member.

struct Controller {
    int worldMap[16][16][16];
    Player p;
    ...

    Controller() {
        p.setController( this );
    }
};

struct Player {
    Controller* mController;
    movePlayer() {

        mController->...

    }
    setController( Controller* controller ) {
        mController = controller;
    }
};

If you need access to it at a low interval, you can pass a reference into the function.

    Player::movePlayer( Controller* controller ) {

        mController->...

    }

Upvotes: 1

danielschemmel
danielschemmel

Reputation: 11116

For simplicity let us assume that all you want to do is call a simple function (checking the other member works the same way but leads to more complicated examples):

void move(Player&);

You can only access non-static members if you have an object at hand. If you do, it is as simple as:

struct Player {
    void movePlayer(Controller& controller) {
        move(controller.p);
    }
};

Note the ; following the struct declaration, it is required.

If you have static members on the other hand they are valid for the whole class and thus don't even need an object:

struct Player {
    void movePlayer();
};

struct Controller {
    static Player p;
};

void Player::movePlayer() {
    move(Controller::p);
}

Note the order in which the declarations appear: To declare a variable of type Player, you need to first declare the struct Player.

Upvotes: 1

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