#include <QLabel>
    #include <QApplication>

    int main(int argc, char** argv)
    {
      QApplication app{argc, argv};
      QLabel label{"hello world!"};
      label.show();
      return app.exec();
    }

    $ g++ -O2 -g0 -fPIC hello.cpp -I/usr/include/qt -I/usr/include/qt/QtWidgets -lQt5Widgets -lQt5Core
    $ du -csh a.out
    16K	a.out