5 Function and Macro Reference

decf-pointer

Function

Summary

Decreases the address held by a pointer.

Package

fli

Signature

decf-pointer pointer &optional delta => number

Arguments

pointer: An FLI pointer.
delta: An integer. The default is 1.

Values

number: The number of bytes the pointer address has decreased by since it was created.

Description

The functiondecf-pointer decreases the address held by the pointer. If delta is not given the address is decreased by the size of the type pointed to by the pointer. The address can be decreased by a multiple of the size of the type by specifying a value for delta.

The functiondecf-pointer is often used to move a pointer through an array of values.

Example

In the following example an array with 10 entries is defined. A copy of the pointer to the array is made, and is incremented and decremented.

(setq array-obj
      (fli:allocate-foreign-object :type :int
        :nelems 10
        :initial-contents '(0 1 2 3 4 5 6 7 8 9)))

(setq point1 (fli:copy-pointer array-obj))

(dotimes (x 9) 
  (fli:incf-pointer point1)
  (print (fli:dereference point1)))

(dotimes (x 9) 
  (fli:decf-pointer point1)
  (print (fli:dereference point1)))

See Also
: incf-pointer