i defined game class globally in main.cpp like this:
Qt Code: 
  1. #include "game.h"
  2.  
  3. #include <QApplication>
  4. #include <QTextCodec>
  5.  
  6. Game *game;
  7.  
  8. int main(int argc, char *argv[])
  9. {
  10.     QApplication a(argc, argv);
  11.  
  12.     srand(time(0));
  13.     game = new Game;
  14.     game->show();
  15.     return a.exec();
  16. }
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And in the Bars.cpp its initialized like this:
Qt Code: 
  1. #include "game.h"
  2.  
  3. extern Game *game;
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And if it helps here is the game.h file
Qt Code: 
  1. #ifndef GAME_H
  2. #define GAME_H
  3. #include "player.h"
  4. #include "button.h"
  5. #include "sea.h"
  6. #include "land.h"
  7. #include "hotbarslots.h"
  8. #include "soundeffects.h"
  9. #include "story.h"
  10. #include "rabbithole.h"
  11. #include "tree.h"
  12. #include "rock.h"
  13. #include "bars.h"
  14.  
  15. #include <QGraphicsView>
  16. #include <QGraphicsScene>
  17. #include <QObject>
  18. #include <QMouseEvent>
  19. #include <QGraphicsSceneMouseEvent>
  20. #include <QGraphicsScene>
  21. #include <QWidget>
  22. #include <QKeyEvent>
  23.  
  24. class Game: public QGraphicsView{
  25.     Q_OBJECT
  26. public:
  27.  // this class stuff
  28.     static QString in_room;
  29.     static QString day_or_night;
  30.     static int language; // 0~ENG, 1~SLO,
  31.     Game(QWidget *parent=NULL);
  33.     void languageMenu();
  34.     void menu();
  35.     void createMap();
  36.     void createPlayer();
  37.     void createHotbarSlots();
  38.     void spawnAnimals();
  39.     void spawnTrees();
  40.     void spawnRocks();
  41.     void drawBars();
  42.     void setStopRectCreated(bool t);
  43.     bool getStopRectCreated();
  44.     int getDesktopHeight();
  45.     int getDesktopWidth();
  46.     int getViewHeight();
  47.     int getViewWidth();
  48.     void setViewWidthToDesktop();
  49.     void setViewHeightToDesktop();
  50.     void setViewWidthToNormal();
  51.     void setViewHeightToNormal();
  52.     void changeColorOfButton();
  53.     QGraphicsRectItem *stopRect;
  54.     void wheelEvent(QWheelEvent *event);
  55. // dark screen stuff
  56.     QGraphicsRectItem *darkScreen;
  57.     QTimer *darkScreenTimer;
  58.     void deleteDarkScreen();
  59.  // other class stuff
  60.     RabbitHole *rabbitHole;
  61.     Story *story;
  62.     Player *player;
  63.     Land *land;
  64.     Sea *sea;
  65.     HotbarSlots *hotbarSlots;
  66.     SoundEffects *soundEffects;
  67.     Tree *tree[3];
  68.     Rock *rock[3];
  69.     Bars *bars;
  70.  // static stuff
  71. private:
  72.  // dark screen stuff
  73.     double darking_opacity;
  74.     bool dark_screen_on;
  75.  // this class stuff
  76.     int curr_pos_in_menu;
  77.     bool stop_rect_created;
  78.     int desktop_height;
  79.     int desktop_width;
  80.     int current_height;
  81.     int current_width;
  82.     int starting_width;
  83.     int starting_height;
  84. public slots:
  85.     void setLanguageToSlovenian();
  86.     void setLanguageToEnglish();
  87.     void startStory();
  88.     void start();
  89.  // dark screen stuff
  90.     void screenGoesDark();
  91.     void screenComesFromDark();
  92. };
  93.  
  94. #endif // GAME_H
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