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_descriptor_matchers.html?highlight=dmatch#DMatch

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