QwtPlot derived class

[Marco Trapanese]

Hello,

I want to create a class based upon QwtPlot. I declare it as usual:

#include <Qwt/qwt_plot.h>
 
class myplot : public QwtPlot{
    Q_OBJECT
 
public:
    explicit myplot(QWidget *parent = 0);
 
signals:
 
public slots:
 
};

#include <Qwt/qwt_plot.h>

class myplot : public QwtPlot{
    Q_OBJECT

public:
    explicit myplot(QWidget *parent = 0);
    
signals:
    
public slots:
    
};

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But I get the error:

"During startup program exited with code 0xc0000005".

I know it's an access violation error. But I don't know why it happens only if I create a class derived from QwtPlot. In my application there are several Qwt items and all works fine.

What I should do to find (and fix) the issue?
Thanks in advance
Marco

ps. I get the same behavior if I include the incrementalplot for example