[ please post back to the list, not private email ] It looks like you are confused about the difference in CFFI between a pointer to a struct and a pointer to a pointer to a struct. Unfortunately, CFFI pointers are untyped so you don't get errors by doing the wrong thing.
To call cvFindContours as in the example, you need a pointer to a pointer to a struct (&contour in the C code). Whenever you want to translate C code that uses &variable, you need to allocate a pointer to hold the value and then dereference it after calling the function. E.g. something like this (untested): (cffi:with-foreign-object (contour-ptr (:pointer (:struct cv-seq))) ;; contour-ptr has foreign type (:pointer (:pointer (:struct cv-seq))) (cv-find-contours ... contour-ptr ...) (mem-ref contour-ptr '(:pointer (:struct cv-seq)))) __Martin >>>>> On Wed, 23 Oct 2013 17:04:07 -0700 (PDT), Joeish W said: > > well I'm trying to learn about Sequences in opencv. So this was practice at > making the code at this link > > http://opencv-srf.blogspot.com/2011/09/object-detection-tracking-using-contours.html > > under the > > Shape Detection & Tracking using Contours > heading . in that code there is this line CvSeq* contours; since i dont > know how to initialize a struct pointer in lisp as it is done there ive been > using CvSeq* contours = cvCreateSeq(0, > sizeof(CvSeq),sizeof(CvPoint),storage); which also initializes a CvSeq* and > works in that example. if you could advise me initializing structs I would be > most grateful.....Basically I'm starting off by mastering the CvSeq parts of > the code. > . > > > > On Wednesday, October 23, 2013 3:23 AM, Martin Simmons <mar...@lispworks.com> > wrote: > >>>>> On Tue, 22 Oct 2013 15:48:50 -0700 (PDT), Joeish W said: > > > >> > >> take this for instance > >> > >> CvPoint points[2]; > >> > >> > >> id like to be able to cast points[2] to the CvPoint struct more info > >> here > >> http://docs.opencv.org/modules/core/doc/old_basic_structures.html?highlight=cvpoint#CvPoint > >> > >> > >> here is my struct which works for other things > >> > >> > >> > >> ;; (cffi:foreign-type-size '(:struct cv-point)) = 8 > >> (cffi:defcstruct cv-point > >> (x :int) > >> (y :int)) > >> > >> > >> put in a defparameter you cant just go > >> > >> (defparameter points (cffi:foreign-alloc :int :count 2)) > >> > >> (defparameter a ((:struct cv-point) points)) > >> > >> > >> you get an illegal function call error...any help is appreciated > > > >Your example is inconsistent -- in C, your points variable is an array of two > >CvPoints, but in Lisp it is an array of two ints. > > > >What are you really trying to do? > > > >I suggest you post the C code that you are trying to convert. The opencv doc > >for CvPoint doesn't use casting or arrays of ints. > > > >__Martin > > > > > > > > > > >
