Correct way to quit a Qt program?

You can call qApp->exit();. I always use that and never had a problem with it.

If you application is a command line application, you might indeed want to return an exit code. It's completely up to you what the code is.

If you're using Qt Jambi, this should work:

QApplication.closeAllWindows();

QApplication is derived from QCoreApplication and thereby inherits quit() which is a public slot of QCoreApplication, so there is no difference between QApplication::quit() and QCoreApplication::quit().

As we can read in the documentation of QCoreApplication::quit() it "tells the application to exit with return code 0 (success).". If you want to exit because you discovered file corruption then you may not want to exit with return code zero which means success, so you should call QCoreApplication::exit() because you can provide a non-zero returnCode which, by convention, indicates an error.

It is important to note that "if the event loop is not running, this function (QCoreApplication::exit()) does nothing", so in that case you should call exit(EXIT_FAILURE).