On Saturday, November 2, 2013 10:44 PM, Joeish W <joeish80829@yahoo.com> wrote: here is the c code with explanation didn't add all code to keep it short but i know it is still long...if this seems daunting because all the code I added....pls know 1.  I worked on this a long time and added the minimal code i could think to explain the issue 2. if it does seem daunting...if you would be so kind as to look through this and tell me how i could edit my ? to make it easier to answer...with that being said... though this is a very simple post .... Im hoping at the end of the explanation you might be able to help me re-wrap my CV-SEQ struct so i get the same resultt as i do in c

CvSeq* contours;  //hold the pointer to a contour in the memory block

// adds data to CvSeq* contours with &contours call cvFindContours(imgGrayScale, storage, &contours, sizeof(CvContour), CV_RETR_LIST, CV_CHAIN_APPROX_SIMPLE, cvPoint(0,0));

// This is how its supposed to work ....no matter how many times you dereference contours to get the h_next struct member // the value of contours->h_next  is always the same

cout << "c1 = " << endl << " " << contours->h_next << endl << endl;  //output same as next line - see output below cout << "c2 = " << endl << " " << contours->h_next << endl << endl; //output same as above line see output below

// If you assign contours->h_next to a new variable "c" 

CvSeq* c = contours->h_next;

// then cout contours->h_next the output of the below 2 cout's is  still the same as the output of the above 2 - see output below

cout << "c3 = " << endl << " " << contours->h_next << endl << endl; cout << "c4 = " << endl << " " << contours->h_next << endl << endl;

// but  if you assign contours->h_next back to contours the output of the next 2 couts is different than above 4

// see output below

 contours = contours->h_next; cout

cout << "c6 = " << endl << " " << contours->h_next << endl << endl;

here is the cout output

c1 =  0x182f730

c2 =  0x182f730

c3 =  0x182f730

c4 =  0x182f730

c5 =  0x182f560

c6 =  0x182f560

The struct CvSeq is defined as this

#define CV_TREE_NODE_FIELDS(node_type)                               \     int       flags;             /* Miscellaneous flags.     */      \     int       header_size;       /* Size of sequence header. */      \     struct    node_type* h_prev; /* Previous sequence.       */      \     struct    node_type* h_next; /* Next sequence.           */      \     struct    node_type* v_prev; /* 2nd previous sequence.   */      \     struct    node_type* v_next  /* 2nd next sequence.       */   /*    Read/Write sequence.    Elements can be dynamically inserted to or deleted from the sequence. */ #define CV_SEQUENCE_FIELDS()                                              \     CV_TREE_NODE_FIELDS(CvSeq);                                           \     int       total;          /* Total number of elements.            */  \     int       elem_size;      /* Size of sequence element in bytes.   */  \     schar*    block_max;      /* Maximal bound of the last block.     */  \     schar*    ptr;            /* Current write pointer.               */  \     int       delta_elems;    /* Grow seq this many at a time.        */  \     CvMemStorage* storage;    /* Where the seq is stored.             */  \     CvSeqBlock* free_blocks;  /* Free blocks

<< "c5 = " << endl << " " << contours->h_next << endl << endl; list.                    */  \

    CvSeqBlock* first;        /* Pointer to the first sequence block. */   typedef struct CvSeq {     CV_SEQUENCE_FIELDS() } CvSeq;

Im not getting the same thing as in lisp  with my struct like this - SWIG wrapped

(cffi:defcstruct cv-seq   (flags :int)   (header-size :int)   (h-prev :pointer)   (h-next :pointer)   (v-prev :pointer)   (v-next :pointer)   (total :int)   (elem-size :int)   (block-max :pointer)   (ptr :pointer)   (delta-elems :int)   (storage :pointer)   (free-blocks :pointer)   (first :pointer))

with the below code my output is the same for both princ...not newline of course =)

(with-foreign-object (contours '(:pointer (:struct cv-seq)))       (find-contours img-grayscale  storage contours              (size-of cv-contour) +retr-list+              +chain-approx-simple+ (point 0 0))

      (with-foreign-slots ((h-next) contours (:struct cv-seq))     (setf contours  h-next)     (princ contours)     (princ #\newline)     (setf contours  h-next)     (princ contours)))

any help on fixing my struct, my coding or editing this post  =) is much appreciated

Cheers!