QGraphicsScene problem/bug

[rubenvb]

Taken directly from the Qt 4.5.2 documentation, in the Detailed Description of QGraphicsGridLayout:

QGraphicsScene scene;
 QGraphicsWidget *textEdit = scene.addWidget(new QTextEdit);
 QGraphicsWidget *pushButton = scene.addWidget(new QPushButton);
 
 QGraphicsGridLayout *layout = new QGraphicsGridLayout;
 layout->addItem(textEdit, 0, 0);
 layout->addItem(pushButton, 0, 1);
 
 QGraphicsWidget *form = new QGraphicsWidget;
 form->setLayout(layout);
 scene.addItem(form);

QGraphicsScene scene;
 QGraphicsWidget *textEdit = scene.addWidget(new QTextEdit);
 QGraphicsWidget *pushButton = scene.addWidget(new QPushButton);

 QGraphicsGridLayout *layout = new QGraphicsGridLayout;
 layout->addItem(textEdit, 0, 0);
 layout->addItem(pushButton, 0, 1);

 QGraphicsWidget *form = new QGraphicsWidget;
 form->setLayout(layout);
 scene.addItem(form);

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First problem: I don't see anything if I wrap this in a simple QApplication:

int main()
{
QApplication app();
 
QWidget *widget;
 //the above code, with the first line:
 //QGraphicsScene scene(widget);
widget->show();
return app.exec();
}

int main()
{
QApplication app();

QWidget *widget;
 //the above code, with the first line:
 //QGraphicsScene scene(widget);
widget->show();
return app.exec();
}

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This structure is really important, but when I try to implement it in my class's constructor, it won't compile. What's wrong here? Thanks!