Problem with dynamic_cast

[vratojr]

Hi,even if the following code involves a bit of Qt I post it here because I think it's a more general problem.
The situation is the following:

I have a class that know its position inside an array:

class element{
public: 
 int position(){return pos;}
private:
 int pos
}

class element{
public: 
 int position(){return pos;}
private:
 int pos
}

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A widget that contains it:

class widget : public QWidget{
public:
 widget(element *elem):el(elem){};//I also pass parent to the constructor of qwiget
 element* element(){return el;}
private:
 element* el;
}

class widget : public QWidget{
public:
 widget(element *elem):el(elem){};//I also pass parent to the constructor of qwiget
 element* element(){return el;}
private:
 element* el;
}

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The principal widget is a QTabWidget and it contains a vector of elements.

class main : public QTabWidget{
private:
QVector<element> elements;
}

class main : public QTabWidget{
private:
QVector<element> elements;
}

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Using some slots, I create some elements and add them to the QVector (and coherently I set theirs pos memebers) and then use them to initialize widgets and add them to the tabwidget.

//inside main
addTab(new widget(&elements[i]);

//inside main
addTab(new widget(&elements[i]);

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Now,the problem. If from inside the tabwidget I want to access to *el inside widget (inside a particular tab) I have to use a dynamic cast.
So I use:
widget *w = dynamic_cast<widget*>(QTabWidget::widget(k));
if I then use w->position() to get its position, I sometimes get strange numbers.

It seems that,during the cast the pointer *el inside widget, became dangling...why?

Thanks!