如何在CFFI中记忆元对象的输出

Question

我有这个函数标量，它是上面评论的2个函数定义的包装。 我的？我如何记住(scalar 1 2 3 4)的输出，#<CV-SCALAR {10044559D3}> 我认为#<CV-SCALAR {10044559D3}>被称为元对象

    ;; Scalar* cv_create_Scalar(double val0, (double val1, double val2, double val3)
    (defcfun ("cv_create_Scalar" %scalar) scalar
      (val0 :double)
      (val1 :double)
      (val2 :double)
      (val3 :double))


    (define-foreign-type scalar ()
      ((garbage-collect  :reader garbage-collect :initform nil :initarg 
                         :garbage-collect))
      (:actual-type :pointer)
      (:simple-parser scalar))


    (defclass cv-scalar ()
      ((c-pointer :reader c-pointer :initarg :c-pointer)))


    (defmethod translate-to-foreign ((lisp-value cv-scalar) (c-type scalar))
      (c-pointer lisp-value))


    (defmethod translate-from-foreign (c-pointer (c-type scalar))
      (let ((scalar (make-instance 'cv-scalar :c-pointer c-pointer)))
        (when (garbage-collect c-type)
          (tg:finalize scalar (lambda () (del-scalar c-pointer))))
        scalar))

Answer 1

如果你的defclass和defmethods定义如上，你运行(mem-aref (c-pointer a) :int 1)来mem-aref返回值