Hi Jaap
I was in contact with the original developer of QCustomPlot. According to his statement, this warning is a false-positive, as it cannot occur with real numbers.
Maybe I'm wrong but I read
20769 result[i*2+0].setX(valueAxis->coordToPixel(0));
and the issue is within coordToPixel() called with 0. As far as I recall, qcustomplot is "amalgamated" (QCustomPlot uses code amalgamation to generate the single .h/.cpp pair from its source tree). Maybe the error is in the amalgamation routine not the code itself. Just guessing.
