Function

Summary

Accesses and returns the value at a specified point in an array.

Package

fli

Signature

foreign-aref array &rest subscripts => pointer

Arguments

array

An FLI array or a pointer to an FLI array.

subscripts

A list of valid array indices for array .

Values

pointer

A pointer containing the address of the array element being accessed.

Description

The function foreign-aref accesses a specified element in an array and returns its value if the element is an immediate type. If it is an aggregate type, such as a :struct , :union , or :c-array , the function foreign-aref returns a copy of the element. In this case, the copy must be de-allocated after use to reclaim the memory allocated for it by foreign-aref .

The value of an element in an array can be changed using setf and foreign-aref . See the examples section for an example of this.

Example

In the first example, a 3 by 3 integer array is created, and foreign-aref is used with setf to set all the element equal to 42.

(setq array1 (fli:allocate-foreign-object

              :type '(:c-array :int 3 3)))

(dotimes (x 3)

         (dotimes (y 3)

                  (setf (fli:foreign-aref array1 x y)

                        42)))

Next, foreign-aref is used to dereference the value at position 2 2 in array1 . Remember that the count for the indices of an array start at 0 .

(fli:foreign-aref array1 2 2)

In the following example, an array of arrays of integers is created. When an element is dereferenced, a copy of an array of integers is returned.

(setq array2 (fli:allocate-foreign-object

              :type '(:c-array (:c-array :int 3) 3))

(fli:foreign-aref array2 2)

The array returned can be bound to the variable array3 , and accessed using foreign-aref again. This time an integer is returned.

(setq array3 *) (fli:foreign-aref array3 1)

See Also

foreign-array-dimensions

foreign-array-element-type

foreign-array-pointer