gistfile1.cpp

const int MAX_CORNERS = 500;

int main()
{
	// Load two images and allocate other structures
	IplImage* imgA = cvLoadImage("/d1", CV_LOAD_IMAGE_GRAYSCALE);
	IplImage* imgB = cvLoadImage("d1", CV_LOAD_IMAGE_GRAYSCALE);

	CvSize img_sz = cvGetSize( imgA );
	int win_size = 15;

	IplImage* imgC = cvLoadImage("/d1", CV_LOAD_IMAGE_UNCHANGED);

	// Get the features for tracking
	IplImage* eig_image = cvCreateImage( img_sz, IPL_DEPTH_32F, 1 );
	IplImage* tmp_image = cvCreateImage( img_sz, IPL_DEPTH_32F, 1 );

	int corner_count = MAX_CORNERS;
	CvPoint2D32f* cornersA = new CvPoint2D32f[ MAX_CORNERS ];

	cvGoodFeaturesToTrack( imgA, eig_image, tmp_image, cornersA, &corner_count,
		0.05, 5.0, 0, 3, 0, 0.04 );

	cvFindCornerSubPix( imgA, cornersA, corner_count, cvSize( win_size, win_size ),
		cvSize( -1, -1 ), cvTermCriteria( CV_TERMCRIT_ITER | CV_TERMCRIT_EPS, 20, 0.03 ) );

	// Call Lucas Kanade algorithm
	char features_found[ MAX_CORNERS ];
	float feature_errors[ MAX_CORNERS ];

	CvSize pyr_sz = cvSize( imgA->width+8, imgB->height/3 );

	IplImage* pyrA = cvCreateImage( pyr_sz, IPL_DEPTH_32F, 1 );
	IplImage* pyrB = cvCreateImage( pyr_sz, IPL_DEPTH_32F, 1 );

	CvPoint2D32f* cornersB = new CvPoint2D32f[ MAX_CORNERS ];

	cvCalcOpticalFlowPyrLK( imgA, imgB, pyrA, pyrB, cornersA, cornersB, corner_count, 
		cvSize( win_size, win_size ), 5, features_found, feature_errors,
		 cvTermCriteria( CV_TERMCRIT_ITER | CV_TERMCRIT_EPS, 20, 0.3 ), 0 );

	// Make an image of the results

	for( int i=0; i < 550; i++){
			printf("Error is %f/n", feature_errors[i]);
			continue;
		
		printf("Got it/n");
		CvPoint p0 = cvPoint( cvRound( cornersA[i].x ), cvRound( cornersA[i].y ) );
		CvPoint p1 = cvPoint( cvRound( cornersB[i].x ), cvRound( cornersB[i].y ) );
		cvLine( imgC, p0, p1, CV_RGB(255,0,0), 2 );
	}

	cvNamedWindow( "ImageA", 0 );
	cvNamedWindow( "ImageB", 0 );
	cvNamedWindow( "LKpyr_OpticalFlow", 0 );

	cvShowImage( "ImageA", imgA );
	cvShowImage( "ImageB", imgB );
	cvShowImage( "LKpyr_OpticalFlow", imgC );

	cvWaitKey(0);

	return 0;
}

I have to thank you very much for posting the C++ version of the code here: http://dasl.mem.drexel.edu/~noahKuntz/openCVTut9.html Finding this code really helped me understand this function:)