Qt : Show Window In Center Screen

I want to create a program in Qt when running show window in center screen. We must include header QStyle and QDesktopWidget to show window in center screen. This is a simple method how to create a program in Qt when running show window in center of screen :

#include <QtGui/QApplication>
#include "runonlyone.h"  //change with your include window application
#include <QStyle>
#include <QDesktopWidget>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    runOnlyOne w;  //change with your window application

    w.setGeometry(QStyle::alignedRect(Qt::LeftToRight,
         Qt::AlignCenter, w.size(), qApp->desktop()->availableGeometry()));
    w.show();
    return a.exec();
}

You can change runOnlyOne with your window application. I am success to compile this  Qt: Show Window In Center Screen program in Ubuntu with Qt 4.6.2.