What is the difference between the quit and Exit methods of qApp?

Question

I’m testing the example Getting Started Programming with Qt Widgets and found a call for a method to exit the application:

void Notepad::on_quitButton_clicked()
{
    qApp->quit();
}

I took a look at the other methods and found one that apparently does the same thing:

qApp->exit();

What is the difference between these two methods and when I should use one or the other?

Answer 1

The variable qApp is a global pointer that refers to the single object application. It is equivalent to the pointer returned by the function QCoreApplication::instance(), except that, in GUI applications, it is a pointer to an instance of QApplication. http://doc.qt.io/qt-4.8/qapplication.html#qApp

Being qApp an instance of QCoreApplication, one of the differences is that the method quit is a SLOT, that is, it can be used in response to a Qt signal.

Signals & Slots

Another difference between the methods is that the quit always returns 0 (zero), while the method exit can receive an integer number to return a different code.

void Qcoreapplication::quit()

void Qcoreapplication::Exit(int returnCode = 0)

That is, both methods should be used when the application should be closed, but the quit, which does not allow error code assignment, can be used directly in connection with a signal, and the exit, which allows error code assignment, can only be used in the conventional way.