问使用敞开式CV迭代器分段故障

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// This is basically a matrix that needs to have a bunch of images as rows.
Mat data(numImages, IMAGE_SIZE * IMAGE_SIZE, CV_8UC1);
// I also replaced CV_8U by images[0].type() and CV_8U. no change
MatIterator_<unsigned short> iter = data.begin<unsigned short> (),
                             iter_end = data.end<unsigned short> (), 
                             iter2;

for (i = 0; i < numImages; ++i)
{
    MatIterator_<unsigned short> begin = images[i].begin<unsigned short> ();
    MatIterator_<unsigned short> end = images[i].end<unsigned short> ();
    for (iter2 = begin; iter2 != end; iter2++)
    {
        *iter = *iter2; // Segfault is here.
        if (iter != iter_end) // safety check
            iter++;
        else
            perror("Screwed!\n"); // This does not execute!
    }
}