Question

How should I quit a Qt Program, e.g when loading a data file, and discovered file corruption, and user need to quit this app or re-initiate data file?

Should I:

1. call exit(EXIT_FAILURE)
2. call QApplication::quit()
3. call QCoreApplication::quit()

And difference between (2) and (3)?

Answer 1

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).