next up previous contents index
Next: Loading Unix Object Files Up: Alien Objects Previous: External Alien Variables   Contents   Index

Alien Data Structure Example

Now that we have Alien types, operations and variables, we can manipulate foreign data structures. This C declaration can be translated into the following Alien type:

struct foo { int a; struct foo *b[100]; };

$\equiv$

(def-alien-type nil (struct foo (a int) (b (array (* (struct foo)) 100))))

With this definition, the following C expression can be translated in this way:

struct foo f; f.b[7].a

$\equiv$

(with-alien ((f (struct foo))) (slot (deref (slot f 'b) 7) 'a) ;; ;; Do something with f... )

Or consider this example of an external C variable and some accesses:

struct c_struct { short x, y; char a, b; int z; c_struct *n; };

extern struct c_struct *my_struct;

my_struct->x++; my_struct->a = 5; my_struct = my_struct->n;

which can be made be manipulated in Lisp like this:
(def-alien-type nil (struct c-struct (x short) (y short) (a char) (b char) (z int) (n (* c-struct))))

(def-alien-variable "my_struct" (* c-struct))

(incf (slot my-struct 'x)) (setf (slot my-struct 'a) 5) (setq my-struct (slot my-struct 'n))


next up previous contents index
Next: Loading Unix Object Files Up: Alien Objects Previous: External Alien Variables   Contents   Index
Peter Van Eynde 2000-02-08