5 Function and Macro Reference

foreign-slot-pointer

Function

Summary

Returns a pointer to a specified slot of an object.

Package

fli

Signature

foreign-slot-pointer object slot-name &key type => pointer

Arguments

object: A foreign object, or a pointer to a foreign object.
slot-name: The name of a slot in object.
type: The type of the slot slot-name.

Values

pointer: A pointer to slot-name.

Description

The functionforeign-slot-pointer takes a foreign object, a slot within the object, and optionally the type of the slot, and returns a pointer to the slot.

Example

In the following example a structure type calledCOMPASS is defined. An instance of the structure is allocated usingallocate-foreign-object, pointed to bypoint1. Thenforeign-slot-pointer is used to get a pointer, calledpoint2, to the second slot of the foreign object.

(fli:define-c-struct COMPASS
  (west :int)
  (east :int))

(setq point1 (fli:allocate-foreign-object :type 
                                          'COMPASS))

(setq point2 (fli:foreign-slot-pointer point1 'east 
                                       :type :int))

: The:type keyword can be used to return the value stored in the slot as a different type, providing the type is compatible. In the next example,point3 is set to be a pointer to the same address aspoint2, but it expects the value stored there to be a boolean.

(setq point3 (fli:foreign-slot-pointer point1 'east
              :type '(:boolean :int)))

: Usingdereference the value can be set as an integer usingpoint2 and read as a boolean usingpoint3.

(setf (fli:dereference point2) 0)

(fli:dereference point3)

(setf (fli:dereference point2) 1)

(fli:dereference point3)

See Also
: decf-pointer
: incf-pointer
: make-pointer