I'm trying to paint some points of my image and I don't know why it doesn't work. I have defined a QImage and I want to modify some points.

QImage *cou= new QImage(height,largeur,QImage::Format_Mono);
    cou->fill(1);
    QPainter *fig=new QPainter (cou);
    for (i=0;i<size_;i++)
    {
        fig-> drawPoint(floor(propa[i]),nbmax[i]);
    }

When I execute the code I obtain 

QPainter::begin: Paint device returned engine == 0, type: 3

and in the following lines:

QPainter::drawPoints: Painter not active
c++ qt qpainter
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