Switching Log and Linear scale, determine which is active

[Lovec47]

Beginner question, I want to make button to switch between Log and Linear axis. How to determine which transformation is active without declaring new variable ?

void HistPlot::switchLogLin()
{
  if(plot->axisScaleDraw(QwtPlot::yLeft)-> ?....== ? )    
    plot->setAxisScaleEngine(QwtPlot::yLeft, new QwtLogScaleEngine);   
  else plot->setAxisScaleEngine(QwtPlot::yLeft, new QwtLinearScaleEngine);
}

void HistPlot::switchLogLin()
{
  if(plot->axisScaleDraw(QwtPlot::yLeft)-> ?....== ? )    
    plot->setAxisScaleEngine(QwtPlot::yLeft, new QwtLogScaleEngine);   
  else plot->setAxisScaleEngine(QwtPlot::yLeft, new QwtLinearScaleEngine);
}

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Thanks

Martin