Qt4 application crash, segmentaton fault when click connected button - c++

Question

I've created a simple application with QGraphicsView and I have a problem with connected button.
There is a simple window with QGraphicsScene and one QPushButton and a function which should add a rectangle to my scene. Compilation is ok, it works and after I click this button application crash.
.h file:
class Canvas : public QWidget{
Q_OBJECT
public:
Canvas(QWidget *parent = 0);
private slots:
void addPoint();
private:
QGraphicsScene *scene;
QPushButton *btn;
};
.cpp file:
Canvas::Canvas(QWidget *parent)
: QWidget(parent)
{
QVBoxLayout *vbox = new QVBoxLayout(this);
vbox->setSpacing(1);
QPushButton *btn = new QPushButton("test", this);
QGraphicsView *view = new QGraphicsView(this);
QGraphicsScene *scene = new QGraphicsScene(this);
view->setScene(scene);
vbox->addWidget(view);
vbox->addWidget(btn);
setLayout(vbox);
connect(btn, SIGNAL(clicked()), this, SLOT(addPoint()));
}
void Canvas::addPoint()
{
scene->addRect(100,0,80,100);
}
Also debuger said:
The inferior stopped because it received a signal from the Operating System.
Signal name : SIGSEGV
Signal meaning : Segmentation fault
And points this line:
{ return addRect(QRectF(x, y, w, h), pen, brush); }
What am I doing wrong? Thanks in advance.

Answer 1

The following statement in your constructor is a local variable definition and initialization:
QGraphicsScene *scene = new QGraphicsScene(this);
The actual scene member variable is never initialized and anything that tries to use this->scene will crash the application.
As you want to initialize the existing scene variable, you should omit the type in front of the variable:
scene = new QGraphicsScene(this);