#include <QGuiApplication>
#include <QImage>

QImage foo(int width, int height)
{
    QImage retVal(width, height, QImage::Format_RGB888);
    for (int i = 0; i < height; ++i) // read each line of the image
    {
        QRgb *lineBuf = reinterpret_cast<QRgb *>(retVal.scanLine(i));
        for (int j = 0; j < width; ++j)
        {
            lineBuf[j] = qRgb(0,0,0);
        }
    }
    return retVal;
}

int main(int argc, char *argv[])
{
    QGuiApplication a(argc, argv);
    {
        QImage test = foo(5,5);
    }
    return a.exec();
}