void setUp(QCommandLineParser parser);

void ExecuteTask::setUp(QCommandLineParser parser){
    parser.setApplicationDescription("Learning console app in Qt");
    parser.addHelpOption();
}

...
    QCoreApplication app(argc, argv);
    ExecuteTask cmnd_line_func;
    QCommandLineParser parser;
    cmnd_line_func.setUp(parser);
    ...

parser.process(app)