The FLI provides the
:struct
and
:union
types to interface Lisp objects with the C
struct
and
union
types.
To define types to interface with C structures, the FLI macro define-c-struct is provided. In the next example it is used to define an FLI structure,
tagpoint
:
(fli:define-c-struct tagpoint
(x :long)
(y :long)
(visible (:boolean :byte))
This structure would interface with the following C structure:
typedef struct tagPOINT {
LONG x;
LONG y;
BYTE visible;
} POINT;
The various elements of a structure are known as
slots
, and can be accessed using the FLI foreign slot functions, foreign-slot-names, foreign-slot-type, and foreign-slot-value. For example, the next commands set
point
equal to an instance of
tagPOINT
, and set the Lisp variable
names
equal to a list of the names of the slots of
tagPOINT
.
(setq point (fli:allocate-foreign-object :type 'tagpoint))
(setq names (fli:foreign-slot-names point))
The next command finds the type of the first element in the List
names
, and sets the variable
name-type
equal to it.
(setq name-type (fli:foreign-slot-type point (car names)))
Finally, the following command sets
point-to
equal to a pointer to the first element of
point
, with the correct type.
(setq point-to (fli:foreign-slot-pointer point (car names)
:type name-type))
The above example demonstrates some of the functions used to manipulate FLI structures. The FLI :union type is similar to the :struct type, in that the FLI slot functions can be used to access instances of a union. The convenience FLI function define-c-union is also provided for the definition of specific union types.