Re: Mutable Pointers

Stephen Compall <s11 <at> member.fsf.org> writes:
> Stuart Sierra wrote:
>> I'm working on a CFFI interface to the Perl API (I thought
>> it would be fun - ha!) and I need to be able to do C-style
>> pointer arithmetic.  That is, I have a foreign pointer
>> declared with DEFCVAR and I need to alter the address stored
>> there.  I couldn't see a way to do this with CFFI, so I
>
> You've got one half of the answer already -- `make-pointer'.  Now see
> `pointer-address'
> (http://common-lisp.net/project/cffi/manual/html_node/pointer_002daddress.html).

But POINTER-ADDRESS is not setf-able, is it?  I want to do
this:

  (defcvar "stack_pointer" :pointer)

  (incf (pointer-address *stack-pointer*))

where "stack_pointer" is a global variable in an external
library.  But...

  The function (SETF POINTER-ADDRESS) is undefined.
     [Condition of type UNDEFINED-FUNCTION]

-Stuart