dereference pointer &key index type copy-foreign-object => value
(setf dereference) value pointer &key index type copy-foreign-object => value
An instance of a FLI pointer.
An integer. If
index
is supplied,
dereference
assumes that
pointer
points to one element in an array of object, and returns the element at the
index
position in the array.
The foreign object type that
pointer
points to. If the specified type is different to the actual type,
dereference
returns the value of the object in the format of
type
where possible.
This option is only important when dealing with aggregate FLI types, which cannot be returned by value.
If set to
t
,
dereference
makes a copy of the aggregate object pointed to by
pointer
and returns the copy.
If set to
nil
,
dereference
returns the aggregate object directly.
If set to
:error
then
dereference
signals an error. This is the default value for
copy-foreign-object
.
The function
dereference
accesses and returns the value of the FLI object pointed to by
pointer
, unless
pointer
points to an aggregate type. In the case of aggregates, the return value is specified by using the
copy-foreign-object
option.
An error is signaled if value is an aggregate type and copy-foreign-object is not set accordingly.
The value of an object at
pointer
can be changed using
(setf dereference)
. See the examples section for an example of this.
In the following example a
LONG
type is defined and an instance, pointed to by
point
, with a specified initial value of 10 is created with memory allocated using allocate-foreign-object. The
dereference
function is then used to get the value that
point
points to.
(fli:define-c-typedef LONG :long)
(setq point (fli:allocate-foreign-object
:type 'LONG
:initial-element 10))
(fli:dereference point)
Finally, the value of the object of type
LONG
is changed to 20 using
(setf dereference)
.
(setf (fli:dereference point) 20)
In the next example, a boolean FLI type is defined, but is accessed as a
char
.
(fli:define-c-typedef BOOL (:boolean :int))
(setq point2 (fli:allocate-foreign-object :type 'BOOL))
(fli:dereference point2 :type :char)