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.
An error is signaled if pointer is a null pointer. You can use null-pointer-p to detect null pointers.
64-bit integer types such as
(:long :long)
,
:int64
and
:uint64
are now supported for type in dereference
in 32-bit LispWorks. In 32-bit LispWorks 6.1 and earlier versions, these types could only be used by define-foreign-function.
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)
allocate-foreign-object
free-foreign-object
foreign-slot-value
null-pointer-p
FLI Types
Pointer dereferencing and coercing
Calling a C function that takes an array of strings
LispWorks Foreign Language Interface User Guide and Reference Manual - 16 Feb 2015