Accessor

Summary

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

Package

fli

Signature

foreign-aref array &rest subscripts => value

setf (foreign-aref array &rest subscripts) value => value

Arguments

array

A FLI array or a pointer to a FLI array.

subscripts

A list of valid array indices for array.

Values

value

An element of array.

Description

The accessor 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, an error is signaled. The function foreign-array-pointer should be used to access such embedded aggregate data.

The value of an element in an array can be changed using the setf form of 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 the setf form of foreign-aref is used to set all the elements 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-array-pointer 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

FLI Types
foreign-array-dimensions
foreign-array-element-type
foreign-array-pointer
foreign-typed-aref