FLI type descriptor

Summary

Converts between a Lisp object and a C struct .

Package

fli

Syntax

:struct &rest slots

slots ::= { symbol | ( symbol slot-type )}*

slot-type ::= type | (:bit-field integer-type size )

Arguments

slots

A sequence of one or more slots making up the structure.

symbol

A symbol naming the slot.

type

The slot type. If no type is given it defaults to an :int .

integer-type

An integer type. Only :int , (:unsigned :int) and (:signed :int) are guaranteed to work on all platforms.

size

An integer specifying a number of bits for the field.

Description

The FLI :struct type is an aggregate type, and converts between a Lisp object and a C struct type. The FLI structure consists of a collection of one or more slots. Each slot has a name and a type. A structure can also contain bit fields, which are integers with a specified number of bits.

The foreign-slot-names, foreign-slot-type, and foreign-slot-value functions can be used to access and change the slots of the structure. The convenience FLI function define-c-struct is provided to simplify the definition of structures.

Example

In the following example a structure for passing coordinates to Windows functions is defined.

(fli:define-c-struct tagPOINT (x :long) (y :long))

An instance of the structure is allocated and bound to the Lisp variable place .

(setq place 

      (fli:allocate-foreign-object :type 'tagPOINT))

Finally, the x slot of place is set to be 4 using fli:foreign-slot-value .

(seft (fli:foreign-slot-value place 'x) 4)

See also

define-c-struct
foreign-slot-names
foreign-slot-offset
foreign-slot-pointer
foreign-slot-type
foreign-slot-value