How to know the value of a point on the graph?

[oddytz1989]

I corrected:

picker_m = new QwtPickerClickPointMachine();
picker_m->setState(QwtPickerMachine::PointSelection);
d_picker = new QwtPlotPicker(QwtPlot::xBottom, QwtPlot::yLeft,
         QwtPlotPicker::CrossRubberBand, QwtPicker::AlwaysOn,
       myPlot->canvas());
d_picker->setStateMachine(picker_m);
 
connect(d_picker, SIGNAL(selected(const QPointF &pos)), SLOT(UpdVizir()));

picker_m = new QwtPickerClickPointMachine();
picker_m->setState(QwtPickerMachine::PointSelection);
d_picker = new QwtPlotPicker(QwtPlot::xBottom, QwtPlot::yLeft,
         QwtPlotPicker::CrossRubberBand, QwtPicker::AlwaysOn,
       myPlot->canvas());
d_picker->setStateMachine(picker_m);

connect(d_picker, SIGNAL(selected(const QPointF &pos)), SLOT(UpdVizir()));

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But anyway, nothing has changed.