function trouble upgrading from c to c++

edit

I have a very small simple function using opencv libraries which takes a source image and stamps it to a location on a destination image. No matter what I try I am getting nowhere trying to update it to a c++ format. Here is the original.

void coriolus::stamp(IplImage * src, IplImage *dst, CvRect r)
{
      IplImage * mask = cvCloneImage(src);
      cvNot(mask,mask);
      cvSetImageROI(dst, r);
      cvCopy(src,dst,mask); 
      cvResetImageROI(dst); 
      cvReleaseImage(&mask);    
}

I actually thought it would be something simple like

void stamp(Mat src, Mat dst, Rect r)
{
    Mat mask = src.clone();
    bitwise_not(mask,mask);
    dst.adjustROI( Rect(r) );
    src.copyTo(dst,mask);
}

what am I missing?