====== Quitting ======

There are a few ways to terminate a Qt app and so you might wonder what the BlessedHolyWay is. I'm not sure that I've figured that out, but for now I will document the different ways that are available of which I am aware.

===== QApplication::lastWindowClosed() =====
From the Qt help files:

<code cpp>void QApplication::lastWindowClosed () [signal]</code>
This signal is emitted from ''QApplication::exec()'' when the last visible primary window (i.e. window with no parent) with the ''Qt::WA_QuitOnClose'' attribute set is closed.

By default,
  * //This attribute is set for all widgets// except transient windows such as splash screens, tool windows, and popup menus.
  * //QApplication implicitly quits when this signal is emitted.// This feature can be turned off by setting ''quitOnLastWindowClosed'' to ''false''.((http://doc.trolltech.com/latest/qapplication.html#lastWindowClosed, emphasis added.))

So, one way to quit your app is to direct an event or action handler to the slot <code cpp>bool QWidget::close ()</code>
on your main window, e.g.:<code cpp>
void MainWindow::on_button_quit_event_clicked()
{
    this->close();
}</code> or (in ''MainWindow'''s constructor)<code cpp>
connect(widget.button_quit, SIGNAL(clicked()), this, SLOT(close()));</code>

===== QCoreApplication::exit ( returnCode ) =====

From the Qt help files:

<code cpp>void QCoreApplication::exit ( int returnCode = 0 ) [static]</code>
Tells the application to exit with a return code.

After this function has been called, the application leaves the main event loop and returns from the call to ''exec()''. The ''exec()'' function returns ''returnCode''. If the event loop is not running, this function does nothing.

By convention, a ''returnCode'' of ''0'' means success, and any non-zero value indicates an error.
Note that unlike the C library function of the same name, this function does return to the caller -- it is event processing that stops.((http://doc.trolltech.com/latest/qcoreapplication.html#exit))

So, you might,<code cpp>
void MainWindow::on_actionE_xit_triggered()
{
    qApp->exit();
}</code> or (in ''MainWindow'''s constructor)<code cpp>
connect(widget.button_exit_fail, SIGNAL(clicked()), &app, SLOT(exit(1)));</code>

===== QCoreApplication::quit () =====

From the Qt help files:

<code cpp>void QCoreApplication::quit () [static slot]</code>
Tells the application to exit with return code 0 (success). Equivalent to calling ''QCoreApplication::exit(0)''.

It's common to connect the ''QApplication::lastWindowClosed()'' signal to ''quit()'', and you also often connect e.g. ''QAbstractButton::clicked()'' or signals in ''QAction'', ''QMenu'', or ''QMenuBar'' to it.

Example:<code cpp>
QPushButton *quitButton = new QPushButton("Quit");
connect(quitButton, SIGNAL(clicked()), &app, SLOT(quit()));</code>((http://doc.trolltech.com/latest/qcoreapplication.html#quit))