ROI Assertion failed (C++ and openCV) - c++

Question

I have a Student class and an imagehandler class (which as the opencv image handler)
Student object has a field:
imagehandler img;
and in the imagehandler class there is a function to copy image from one image to another into a certain location.
void imagehandler::copy_paste_image(imagehandler& dst, int xLoc, int yLoc){
cv::Rect roi(xLoc, yLoc, m_image.size().width, m_image.size().height);
cv::Mat imageROI (dst.m_image, roi);
m_image.copyTo(imageROI);
}
and the imagehandler class has a Mat object m_image:
private:
cv::Mat m_image;
Now in the main, I have declared a new image through the imagehandler specified constructor.
the constructor I use to make the image:
imagehandler::imagehandler(int width, int height)
: m_image(width, height, CV_8UC3){
}
in the main, I declare the image like this:
imagehandler CSImg((4*300), (320 * ceil((float)(numOfCSStudents/4))));
Trust me on this one: CSImg is way bigger than all of the images I want to input in it.
Now I want to copy a certain student's picture and input it into CS Img. That's what I do:
studentsVector.at(i)->getImg().copy_paste_image(CSImg, CSWidthCount*300, CSHeightCount*320);
And I get this error:
OpenCV Error: Assertion failed (0 <= roi.x && 0 <= roi.width && roi.x + roi.width <= m.cols && 0 <= roi.y && 0 <= roi.height && roi.y + roi.height <= m.rows) in Mat, file /build/buildd/opencv-2.3.1/modules/core/src/matrix.cpp, line 303
terminate called after throwing an instance of 'cv::Exception'
what(): /build/buildd/opencv-2.3.1/modules/core/src/matrix.cpp:303: error: (-215) 0 <= roi.x && 0 <= roi.width && roi.x + roi.width <= m.cols && 0 <= roi.y && 0 <= roi.height && roi.y + roi.height <= m.rows in function Mat
I've noticed that this happens in roi, I have no clue why. I -am- a total beginner at openCV and I am doing this for homework.
Thank you.
If you need any further info please ask.

Answer 1

I'm not sure about C++ API but this is what I did in C API;
CvRect ROI = cvRect(x, y, width, height);
cvSetImageROI(srcImg, ROI);
IplImage* cropImg = cvCreateImage(cvGetSize(srcImg), IPL_DEPTH_8U, 1);//this part very important
cvCopy(srcImg, cropImg);
cvResetImageROI(srcImg);