Qt Application – Event Loop

The Qt event loop is started with a call to the exec() member function of QApplication.  Normally when the users requests the program to exit from the GUI, the exec() function returns.  This occurs when the quit() function is called from one of the GUI elements (for example, the close on the application windows of Exit from the File menu).

Since no GUI elements have been implemented yet including any window, somehow the quit() function needs to be called.  This is accomplished with a single shot timer initiated with the call:

QTimer::singleShot(0, &app, SLOT(quit()));

This timer times out immediately and calls the quit() slot of the QApplication instance, but fortunately this does not occur until the exec() function is called.  Once exec() is called, it immediately returns, exiting the application.