Visual C++ :: Drawing A Rubber Band Rectangle

I am trying to draw a rubber band rectangle. I have got a following code from a site but its giving an error:

Code:
class CSampleView: Public CView{
...
public:
CrectTracker m_tracker;//Changed to CRectTracker
...
};

Secondly, in the constructor to initialize the object CRectTracker document class:

CSampleDoc :: CSampleDOC () {
// Initialize tracker position, size and style.
m_tracker.m_rect.SetRect (0, 0, 10, 10);
m_tracker.m_nStyle = CRectTracker :: resizeInside |
CRectTracker :: dottedLine;
}

The error is:

error C2065: 'm_tracker' : undeclared identifier

How to get rid of this error??