Tooltip in qwt

[Cat]

Hello. I have to do the following: when I point to the value (big dot - qwtSymbol) a coordinate of this value will be appeared . I found on the internet the method realization and I change it a little:

void Monitoring::showToolTip(QMouseEvent* ev){
 
    if(ev == QEvent::MouseMove) {
 
    double distance = 1e99;
    int point_index = first_c->closestPoint(QPoint(ev->x(), ev->y()), &distance); // for my one of my curves
 
    QwtPlotMarker* tooltip = new QwtPlotMarker();
    tooltip->setLabel(QString("hello")); //for debugging
    tooltip->attach(funPlot);
    funPlot->replot();
}

void Monitoring::showToolTip(QMouseEvent* ev){

    if(ev == QEvent::MouseMove) {
    
    double distance = 1e99;
    int point_index = first_c->closestPoint(QPoint(ev->x(), ev->y()), &distance); // for my one of my curves

    QwtPlotMarker* tooltip = new QwtPlotMarker();
    tooltip->setLabel(QString("hello")); //for debugging
    tooltip->attach(funPlot);
    funPlot->replot();
}

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But I don't understand how to call this function. I thought I could call it through the signal-slot construction, but I can't pick up appropriate signal.