Joeish W joeish80829@yahoo.com writes:
I have this C wrapper
DMatch* cv_create_DMatch3(int _queryIdx, int _trainIdx, float _distance) { return new DMatch(_queryIdx, _trainIdx, _distance); }
it is a wrapper for these struct members
http://docs.opencv.org/modules/features2d/doc/common_interfaces_of_descripto...
here is my lisp wrapper for it:
(defctype dmatch :pointer)
(defcfun ("cv_create_DMatch3" dmatch3) (:pointer dmatch) "DMatch constructor" (-query-idx :int) (-train-idx :int) (-distance :float))
In C I can do this:
DMatch* a = cv_create_DMatch3(1, 2, 3.0); cout << a->distance ;
and the output is 3
but in lisp when I do this:
(defparameter a (dmatch3 1 2 3f0))
LCV> (mem-aref a :int 0) 1 LCV> (mem-aref a :int 1) 2 LCV> (mem-aref a :float 2) #<SINGLE-FLOAT quiet NaN> <--- this is output
Any help on figuring out the reason would be much appreciated
This is not really suprising. You are treating the resulting pointer `a` as an untyped pointer. When you do `(mem-aref a :float 2)` you are basically saying:
1. Assume a is a pointer to an array of floats 2. Give me the third element (element at index 2).
Unfortunately `a` is not a pointer to an array of floats, but a pointer to a struct DMatch.
You should lookup `defcstruct` in the CFFI documentation:
http://common-lisp.net/project/cffi/manual/html_node/defcstruct.html#defcstr...
Wim Oudshoorn.