how to restart my own qt application ?

Restart my own qt appliactions:

#include <QApplication>
#include <QProcess>
 
...
 
// restart:
qApp->quit();
QProcess::startDetached(qApp->arguments()[0], qApp->arguments())

Here the solution is:

The qt applications are ; after the while statement of a do { … } while( … ); .

int main(int argc, char *argv[])
{
    const int RESTART_CODE = 1000;
   
    do
    {
        QApplication app(argc, argv);
        MainWindow main_window(app);
    } while( app.exec() == RESTART_CODE);
   
    return return_from_event_loop_code;
}

Alternative code is:

main.cxx
int main(int argc, char * argv[])
{
    int result = 0;
 
    do
    {
        QCoreApplication coreapp(argc, argv);
        MyClass myObj;
        result = coreapp.exec();
    } while( result == 1337 );
   
    return result;
}

Class.cxx

qApp->exit(1337);