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Allocates memory for an instance of a foreign object.




allocate-foreign-object &key type pointer-type initial-element initial-contents fill nelems size-slot => pointer



a FLI type specifying the type of the object to be allocated. If type is supplied, pointer-type must not be supplied.


A FLI pointer type specifying the type of the pointer object to be allocated. If pointer-type is supplied, type must not be supplied.


A keyword setting the initial value of every element in the newly allocated object to initial-element.


A list of forms which initialize the contents of each element in the newly allocated object.


An integer between 0 to 255.


An integer specifying how many copies of the object should be allocated. The default value is 1.


A symbol naming a slot in the object.


A keyword, either :dynamic or :static.



A pointer to the specified type or pointer-type.


The function allocate-foreign-object allocates memory for a new instance of an object of type type or an instance of a pointer object of type pointer-type.

If allocation is :static then memory is allocated in the C heap and must be explicitly freed using free-foreign-object once the object is no longer needed.

If allocation is :dynamic, then allocate-foreign-object allocates memory for the object and pointer within the scope of the body of with-dynamic-foreign-objects. This is equivalent to using allocate-dynamic-foreign-object.

The default value of allocation is :static.

An integer value of fill initializes all the bytes of the object. If fill is not supplied, the object is not initialized unless initial-element or initial-contents is passed.

If initial-contents is supplied and its length is less than nelems, then the remaining elements are not initialized.

If initial-contents is supplied and its length is greater than nelems, then the length of initial-contents overrides nelems. This is a common case where initial-contents is supplied and nelems is omitted (and hence defaults to 1).

A supplied value of size-slot applies if the type is a struct or union type. The slot size-slot is set to the size of the object in bytes. This occurs after the fill, initial-element and initial-contents arguments are processed. If nelems is greater than 1, then the slot size-slot is initialized in each element. If size-slot is not supplied, then no such setting occurs.


When allocation is :static, memory allocated by allocate-foreign-object is in the C heap. Therefore pointer (and any copy) cannot be used after save-image or deliver.


In the following example a structure is defined and an instance 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, and finally it is freed.

(fli:define-c-typedef LONG :long)
(setq point (fli:allocate-foreign-object
             :type 'LONG
             :initial-element 10))
(fli:dereference point) (fli:free-foreign-object point)
See also

FLI Pointers

LispWorks Foreign Language Interface User Guide and Reference Manual - 16 Feb 2015