3.5.1 Allocating an integer

To allocate an integer in C:

(int *)malloc(sizeof(int))

You can allocate the integer from LispWorks using the :type argument:

(fli:allocate-foreign-object :type :int)

      => #<Pointer to type :INT = #x007E1A60>

Alternatively you can allocate the integer from LispWorks using the :pointer-type argument:

(fli:allocate-foreign-object

                  :pointer-type '(:pointer :int))

      => #<Pointer to type :INT = #x007E1A60>

3.5.2 Allocating a pointer to a pointer to a void

Suppose you need to call a C function that takes a void ** argument, defined as follows:

struct arg_struct

{

int val;

};

void func_handle_init(void **h)

{

  struct arg_struct *handle = NULL;

  handle = (struct arg_struct *)malloc(sizeof(struct arg_struct));

  memset(handle, 0, sizeof(struct arg_struct));

  handle->val = 12;

  *h = handle;

}

With this foreign function definition:

(fli:define-foreign-function

    (func-handle-init "func_handle_init"

                      :source)

    ((handle (:pointer (:pointer :void))))

  :result-type :void

  :language :ansi-c)

you could simply do:

(setq handle

      (fli:allocate-foreign-object :type :pointer))

(func-handle-init handle)

but do not forget to also free the pointer:

(fli:free-foreign-object handle)

Another approach is to allocate the pointer on the stack. In this case you do not need to free it explicitly:

(fli:with-dynamic-foreign-objects ((handle :pointer))

  (func-handle-init handle))

Yet another approach is to define the foreign function like this:

(fli:define-foreign-function

    (func-handle-init "func_handle_init"

                      :source)

    ((:ignore (:reference-return (:pointer :void))))

  :result-type :void

  :language :ansi-c)

Then call the function like this:

(func-handle-init)

and it will return the handle. This works because the :reference-return type allocates the temporary void ** within the function and returns its contents.