Undefined reference to signal

[chinalski]

Hi all,
I have a problem that could be very stupid, but I'm not able to solve it.
I'm tring to be aware when an operator click with mouse on a qwtPlot, and have a class informed with a signal of the mouse position on the plot where he clicked.

These are the pieces of code.
Header:

#include <QMouseEvent>
#include <QDebug>
#include <qwt_plot.h>
 
class QwtPlotMy : public QwtPlot
{
public:
    QwtPlotMy(int idPlotValue = 0);
 
signals:
    void clickSignal();
 
private:
    void mousePressEvent(QMouseEvent * event);
 
    int idPlot;
};

#include <QMouseEvent>
#include <QDebug>
#include <qwt_plot.h>

class QwtPlotMy : public QwtPlot
{
public:
    QwtPlotMy(int idPlotValue = 0);

signals:
    void clickSignal();

private:
    void mousePressEvent(QMouseEvent * event);

    int idPlot;
};

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Cpp:

#include "qwtplotmy.h"
 
QwtPlotMy::QwtPlotMy(int idPlotValue) :
    QwtPlot()
{
    idPlot = idPlotValue;
 
    return;
}
 
void QwtPlotMy::mousePressEvent(QMouseEvent * event)
{
    emit (clickSignal());
    qDebug() << "Into qwtplot"<<idPlot;
    qDebug() << "x"<< event->x() << " - y"<< event->y() ;
    return;
}

#include "qwtplotmy.h"

QwtPlotMy::QwtPlotMy(int idPlotValue) :
    QwtPlot()
{
    idPlot = idPlotValue;

    return;
}

void QwtPlotMy::mousePressEvent(QMouseEvent * event)
{
    emit (clickSignal());
    qDebug() << "Into qwtplot"<<idPlot;
    qDebug() << "x"<< event->x() << " - y"<< event->y() ;
    return;
}

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The problem is: compiling I get the message error:

undefined reference to 'QwtPlotMy::clickSignal()'

undefined reference to 'QwtPlotMy::clickSignal()'

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If I comment the "emit (clickSignal())" line everything works well and I have the mouse position in the debug messages. Where I missed something?

Thank you very much in advance,
Carlo