Question

I am implementing a card game. I want the window ui to be an object of class Rule, so that Rule can modify the GUI directly.

So Rule has an object Window * ui initialized in the constructor.

But during compilation, the compiler tells me that in rule.h, “Window has not been declared”, “Window is not a type”. I included <window.h>, everything has the same type, everything is initialized, so I run out of ideas of why it does not work.

EDIT: I edited the code following alexisdm’s notes. In addition, in rule.h, I had to change the definition of ui from Window * ui to Ui::Window *ui, because in window.h, ui is defined as Ui::Window * ui, and this is the object I want Rule::rule to control.

But now, in rule.cpp, ui->do_stuff() does not compile, because Ui::Window does not have the do_stuff() function, but Window does…

Arg! What to do?!! ui->do_stuff() works fine in window.cpp. Inheritance problem?

window.cpp:

    Window::Window(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Window)
{
    ui->setupUi(this);

    player = new Game_state();                  /* Game state                   */
    rule = new Rule(player, ui);                /* Implement the action of cards*/
}
void Window::do_stuff(){
//Do stuff
}

window.h

#include <QDialog>
#include "game_state.h"
#include "rule.h"

class Rule;
namespace Ui {
    class Window;
}

class Window : public QDialog
{
    Q_OBJECT

public:
    explicit Window(QWidget *parent = 0);
    ~Window();
    Game_state      * player;
    Rule            * rule;
    void do_stuff();

private:
    Ui::Window *ui;
};

rule.h

#ifndef RULE_H
#define RULE_H
#include "window.h"
#include <game_state.h>

class Window;

class Rule{
public:
    Rule(Game_state *, Ui::Window *);
    void action(Card *);

private:
    Game_state * player;
    Ui::Window     * ui;
};


#endif // RULE_H

rule.cpp

    #include <rule.h>

    Rule::Rule(Game_state * game, Ui::Window * window){
        player = game;
        ui = window;
    }
    void Rule::stuff(){
        ui->do_stuff();
    }

Answer 1

There is a circular dependency in your headers: window.h and rule.h are referencing each other.

You should replace both #include by forward declarations to avoid it.

class Window;  // instead of #include "window.h"
class Rule;  // instead of #include "rule.h"

You’ll still need to add #include "window.h" in rule.cpp, and #include "rule.h" in window.cpp.