remove of all QwtPlotCurves

[gyre]

Hi I was trying to remove all curves from QwtPLot...I did not succed (otherwise I wouldnt write here )
I thought this would do that for me:

trendPlot->detachItems(QwtPlotItem::Rtti_PlotCurve, true);

trendPlot->detachItems(QwtPlotItem::Rtti_PlotCurve, true);

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I was wrong...so I tried to reimplement detachItems method...but did not succed ...
Anyone help pls ?
Thanks