foreign-slot-offset

foreign-slot-offset Function

Summary

Returns the offset of a slot in a FLI object.

Package

fli

Signature

foreign-slot-offset object-or-type slot-name => offset

Arguments

`object-or-type`⇩	A foreign object, a pointer to a foreign object, or a foreign structure or union type.
`slot-name`⇩	A symbol or a list of symbols identifying the slot to be accessed, as described for foreign-slot-value.

Values

offset

The offset, in bytes, of the slot slot-name in the FLI object object.

Description

The function foreign-slot-offset returns the offset, in bytes, of the slot slot-name in object-or-type. The offset is the number of bytes from the beginning of the object to the start of the slot. For example, the offset of the first slot in any FLI object is 0.

Examples

The following example defines a structure, creates an instance of the structure pointed to by dir, and then finds the offset of the third slot in the object.

(fli:define-c-struct compass
  (east :int)
  (west (:c-array :char 20))
  (north :int)
  (south :int))
 
(fli:foreign-slot-offset 'compass 'north)
 
(setq dir (fli:allocate-foreign-object :type 'compass))
 
(fli:foreign-slot-offset dir 'north)