#include <QApplication>
#include <QPrinter>
#include <QPrintDialog>
#include <QPainter>

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

    QPrinter prn(QPrinter::HighResolution);
    prn.setPageMargins(20,20,20,20,QPrinter::Millimeter);
    prn.setPageSize(QPrinter::A4);
    QPrintDialog pd(&prn, 0);
    if(pd.exec()==QPrintDialog::Accepted){
        QPainter p(&prn);
        p.setPen(QPen(Qt::black, 2));
        p.drawRect(prn.pageRect());
        p.end();
    }

    return 0;
}