Qt example notepad program not displaying any controls - c++

Question

I am following the Qt example listed in the QtSDK titled: "Getting Started Programming with Qt". My problem is that the program doesn't display any of the objects.
My main.cpp looks like so:
#include <QtGui>
#include <notepad.h>
int main(int argv, char **args) {
QApplication app(argv, args);
QVBoxLayout layout;
Notepad notepad();
QWidget window;
window.setLayout(&layout);
window.show();
return app.exec();
}
The 'notepad.h' file:
#ifndef NOTEPAD_H
#define NOTEPAD_H
#include <QtGui>
class Notepad : public QMainWindow {
Q_OBJECT
public:
Notepad();
private slots:
void open();
void save();
void quit();
private:
QTextEdit *text_edit;
QAction *open_action;
QAction *save_action;
QAction *exit_action;
QMenu *file_menu;
};
#endif // NOTEPAD_H
The 'notepad.cpp' file:
#include "notepad.h"
Notepad::Notepad() {
open_action = new QAction(tr("&Open"), this);
save_action = new QAction(tr("&Save"), this);
exit_action = new QAction(tr("&Exit"), this);
connect(open_action, SIGNAL(triggered()), this, SLOT(open()));
connect(save_action, SIGNAL(triggered()), this, SLOT(save()));
connect(exit_action, SIGNAL(triggered()), qApp, SLOT(quit()));
file_menu = menuBar()->addMenu(tr("&File"));
file_menu->addAction(open_action);
file_menu->addAction(save_action);
file_menu->addSeparator();
file_menu->addAction(exit_action);
text_edit = new QTextEdit;
setCentralWidget(text_edit);
setWindowTitle(tr("Notepad"));
}
void Notepad::open() {
...
}
void Notepad::save() {
...
}
void Notepad::quit() {
}
Any help in resolving the matter would be much appreciated.
Edit
My original question asked why I was I was getting a compile time error for not implementing the "quit" function incase you are wondering :).

Answer 1

You have to implement quit() method defined as private slot in notepad.h . Unresolved errors are linking errors and tells you that linker hasn't found any implementation for the function declaration. Add this to notepad.cpp :
void Notepad::quit() {
...
}
For new question :
Try notepad.show(). Your MainWindow can be notepad object because it is a QMainWindow.
int main(int argv, char **args) {
QApplication app(argv, args);
Notepad notepad();
notepad.show();
return app.exec();
}