Qt Application – Command Line Arguments

Up to now, the source code has been modified to use Qt support classes, but the program is not yet a Qt application.  A Qt application has a GUI (usually though it is possible to have a command line Qt application).  A GUI application has an event processing loop, which basically means that instead of processing sequentially from start to end, it processes events when they occur such as a keyboard press or a mouse click and calling the appropriate function to carry out the selected action.

A Qt application starts by creating an instance of a QApplication (or a QCoreApplication for a command line application).  Since this project will have a GUI, a QApplication instance will be created, but no GUI will be started if either the version or a test mode options are selected on the command line.

The command line arguments, via the argc and argv arguments of main(), are passed to the QApplication constructor because there are some Qt options that can be specified on the command line.  The arguments() member function of QApplication is used to obtain a QStringList of the remaining options (with the Qt options removed).  The first string in this list is still the name of the program.  The argc and argv arguments to the various functions were changed to QStringList &args, which is set to the arguments.