I think the issue is with my callback function but not 100% when i run the c code and print with these 2 lines(from c callback):

cout << "a = " << "(" << "" << "," << _a << ")" << endl ;           cout << "b = " << "(" << "" << "," << _b << ")" << endl;

i get 53 elements printed not icluding the other printf output and  in the lisp code i converterd

when i print with this line(from lisp defcallback):

(format t "~%x~a~%b~a" _a _b)

in the defcallback  i get 114 elements

Hoping someone can look at my code and tell me if my coding is off ....the functions you wont recognize are opencv functions with correctly lispified names  i/e cvSeqSort = seq-sort ...  If requested will post the wrappers .... the -> is a macro for with-foreign-slots (and if not a pointer just a getf for a plist)

;;;;;;;;C CODE;;;;;;;;;;;;;;;;;;;       #include <cv.h>       #include <highgui.h>       using namespace std;

static int cmp_func( const void* _a, const void* _b, void* userdata )       {         //cout << "test";       //cout <<_a << _b;           CvPoint* a = (CvPoint*)_a;           CvPoint* b = (CvPoint*)_b;           cout << "a = " << "(" << "" << "," << _a << ")" << endl ;           cout << "b = " << "(" << "" << "," << _b << ")" << endl;           int y_diff = a->y - b->y;           int x_diff = a->x - b->x;           return y_diff ? y_diff : x_diff;       }

int main()       {           CvMemStorage* storage = cvCreateMemStorage(0);           CvSeq* seq = cvCreateSeq( CV_32SC2, sizeof(CvSeq), sizeof(CvPoint), storage );           int i;               printf("\n=== Test sequence sorting ===");

for( i= 0; i < 10; i++ )           {               CvPoint pt;               pt.x = rand() % 1000;  // 1000 以内的随机数               pt.y = rand() % 1000;               cvSeqPush( seq, &pt );           }               printf("\nOriginal point set:\n");           for( i = 0; i < seq->total; i++ )           {               CvPoint* pt = (CvPoint*)cvGetSeqElem( seq, i );               printf( "(%d,%d)\n", pt->x, pt->y );           }

cvSeqSort( seq, cmp_func, 0 /* userdata is not used here */ );               /* print out the sorted sequence */           printf("\nAfter sorting:\n");           for( i = 0; i < seq->total; i++ )           {               CvPoint* pt = (CvPoint*)cvGetSeqElem( seq, i );               printf( "(%d,%d)\n", pt->x, pt->y );           }               cvClearSeq( seq );   // Sequence clearing should be done before storage clearing           cvReleaseMemStorage( &storage );       }

;;;;;;;;;;;;;;;;;;;;;;;;;LISP CODE;;;;;;;;;;;;;;;;;;;; (defcallback cmp-func :void  ((_a :pointer) (_b :pointer) (user-data :pointer) (a :int) (b :int) (y-diff :int) (x-diff :int))   (format t "~%x~a~%b~a" _a _b)   (setf a (mem-aref _a '(:struct cv-point)))   (setf b (mem-aref _b '(:struct cv-point)))                     ;(format t "~%a~a~%b~a" a b)   (setf y-diff (- (-> cv-point a y) (-> cv-point b y)))   (setf x-diff (- (-> cv-point a x) (-> cv-point b x)))   (if y-diff y-diff x-diff))

(defun seq-sort-example ()   (let* ((storage (create-mem-storage 0))      (seq (create-seq +32sc2+ (size-of cv-seq) (size-of cv-point) storage)))     (format t "~%=== Test sequence sorting ===")     (with-foreign-object (pt '(:struct cv-point))       (dotimes (i 10)     (setf (foreign-slot-value pt '(:struct cv-point) 'x) (random 1000)           (foreign-slot-value pt '(:struct cv-point) 'y) (random 1000))     (seq-push seq pt)))

(with-foreign-object (pt '(:pointer (:struct cv-point)))       (format t "~%Original point set:~%")       (dotimes (i (-> cv-seq seq total))     (setf pt (get-seq-elem seq i))     (format t "(~a, ~a)~%" (-> cv-point pt x) (-> cv-point pt y)  )))     (seq-sort seq (callback cmp-func) (null-pointer))     (with-foreign-object (pt '(:pointer (:struct cv-point)))       (format t "~%After sorting:~%")       (dotimes (i (-> cv-seq seq total))     (setf pt (get-seq-elem seq i))     (format t "(~a, ~a)~%" (-> cv-point pt x) (-> cv-point pt y)  )))     (clear-seq seq)     (release-mem-storage storage)))