5 Function and Macro Reference

dereference

Function

Summary

Accesses and returns the value of a foreign object.

Package

fli

Signature

dereference pointer &key index type copy-foreign-object => value

Arguments

pointer

An instance of an FLI pointer.

index

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.

type

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.

copy-foreign-object

This option is only important when dealing with aggregate FLI types, which cannot be returned by value.

If set tot,dereference makes a copy of the aggregate object pointed to by pointer and returns the copy.

If set tonil,dereference returns the aggregate object directly.

If set toerror thendereference signals an error. This is the default value for copy-foreign-object.

Values

value: The value of the dereferenced object at pointer.

Description

The functiondereference 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 usingsetf anddereference. See the examples section for an example of this.

Example

In the following example aLONG type is defined and an instance, pointed to bypoint, with a specified initial value of 10 is created with memory allocated usingallocate-foreign-object. Thedereference function is then used to get the value thatpoint 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 typeLONG is changed to 20 usingsetf.

(setf (fli:dereference point) 20)

: In the next example, a boolean FLI type is defined, but is accessed as achar.

(fli:define-c-typedef BOOL (:boolean :int))

(setq point2 (fli:allocate-foreign-object :type 'BOOL))

(fli:dereference point2 :type :char)

See Also
: allocate-foreign-object
: free-foreign-object
: foreign-slot-value