[Qt-interest] What is QDesktopWidget used for?

[Kermit Mei]

Dear all, for testing QDesktopWidget, I wrote the following codes:

#include <QApplication>
#include <QWidget>
#include <QDesktopWidget>


int main(int argc,char *argv[])
{
  QApplication app(argc,argv);
  QDesktopWidget *desktop = new QDesktopWidget();
                                               
  qDebug("winId = %d",int(desktop->winId()));
  desktop->show();
  qDebug("Is Hidden %s",desktop->isHidden() ? "true":"false");
  qDebug("x=%d, y=%d, w=%d, h=%d,",
         desktop->x(),desktop->y(),desktop->width(),desktop->height());
  return app.exec();
}

Compile and run it, the result is 

$ make
g++ -c -pipe -O2 -Wall -W -D_REENTRANT -DQT_NO_DEBUG -DQT_GUI_LIB
-DQT_CORE_LIB -DQT_SHARED
-I/usr/local/Trolltech/Qt-4.5.3/mkspecs/linux-g++ -I.
-I/usr/local/Trolltech/Qt-4.5.3/include/QtCore
-I/usr/local/Trolltech/Qt-4.5.3/include/QtGui
-I/usr/local/Trolltech/Qt-4.5.3/include -I. -I. -o main.o main.cpp
g++ -Wl,-O1 -Wl,-rpath,/usr/local/Trolltech/Qt-4.5.3/lib -o desktop
main.o    -L/usr/local/Trolltech/Qt-4.5.3/lib -lQtGui
-L/usr/local/Trolltech/Qt-4.5.3/lib -L/usr/X11R6/lib -lXext -lX11
-lQtCore -lm -lrt -ldl -lpthread

$ ./desktop 
winId = 256
Is Hidden false
x=0, y=0, w=1144, h=762,


But I can't see any new widget on my screen, why?
What is QDesktop used for?

Thanks
Kermit Mei