#include <QApplication>

#include <QWidget>
#include <QPushButton>
#include <QDebug>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QWidget w1;
    w1.setGeometry(0,0, 400, 300);

    QPushButton pb1(&w1);
    pb1.setGeometry(100,50, 100, 50);

    w1.show();

    QWidget *target = 0;
    QPoint pt;
    pt.setX(110);
    pt.setY(60);
    if (QWidget *topLevel = qApp->topLevelAt(pt)) {
        QWidget *child = topLevel->childAt(topLevel->mapFromGlobal(pt));
        target = child ? child : topLevel;
    }

    qDebug() << target;

    return a.exec();
}