Creating a global object in QT GUI - c++

Question

I am trying to create an object called x from a class "Fan" inside the QT GUI mainwindow file, where I want it to be global. I want QT's button slot functions to be able to perform operations on the object. However, a compiler error "error: C4430: missing type specifier - int assumed" always occurs. Here is the header file:
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
private slots:
void on_btOn_clicked();
void on_btOff_clicked();
private:
Ui::MainWindow *ui;
Fan x; // This doesn't work
Fan * x; // This doesn't either
int x; // This does work
};
#endif // MAINWINDOW_H
And here is the cpp file:
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "fan.h"
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::on_btOn_clicked()
{
ui->lblState->setText("Fan is on");
}
void MainWindow::on_btOff_clicked()
{
x.turnOff(); // This does not work of course
x->turnOff(); // Or this
ui->lblState->setText("Fan is off");
}
I already told the cpp file to include the Fan class from the fan.h file. If I create the object within the window constructor, it initializes fine but is not global. Also, there is no circular inclusion of header files. Fan class does not include mainwindow.
Perhaps I don't know how to search for it, but I've already done some research into it to no avail. Any help is appreciated.
Edit:
Here is the fan.cpp file
#include "fan.h"
Fan::Fan(){
speed = 0;
isOn = false;
}
void Fan::setSpeed(int s){
speed = s;
}
int Fan::getSpeed(){
return speed;
}
void Fan::turnOn(){
isOn = true;
speed = 1;
}
void Fan::turnOff(){
isOn = false;
speed = 0;
}
bool Fan::getState(){
return isOn;
}
And the fan.h file:
#ifndef FAN_H
#define FAN_H
class Fan
{
private:
int speed;
bool isOn;
public:
Fan();
void setSpeed(int);
void turnOn();
void turnOff();
int getSpeed();
bool getState();
};
#endif // FAN_H

Answer 1

You forget to include or declare the class Fan in your Header File. If you use
Fan * x;
You could use
class Fan;
as a forward declaration at the beginning of your Header File. The Compiler only need to know that there is a class called Fan but inside the Header you only use a pointer. Butt don't forget to #include the real file in your CPP file.
If you use
Fan x;
you have to #include the Fan.h in your Header-File