[cffi-devel] Calling function expecting char**

[James Bielman]

On Wed, 2005-12-28 at 00:59 +0700, JoeSB COE9 wrote:

> ;; Lisp side
> (cffi:with-foreign-object (argv :pointer 2)
>            (setf (cffi:mem-ref argv :pointer 0)
> (cffi:foreign-string-alloc "Hello"))
>            (setf (cffi:mem-ref argv :pointer 1)
> (cffi:foreign-string-alloc "Hello"))
>            (cffi:foreign-funcall "expect_charpp" :pointer argv))
> 
> And I got a memory fault error in SBCL.

You want to use MEM-AREF here, not MEM-REF.  The optional third argument
to MEM-REF is a byte offset to add to the pointer, whereas the third
argument to MEM-AREF is an array index.

I admit this is a little confusing---I wonder if MEM-AREF might be
better given a more generic name and documented as the default accessor
for foreign pointers.  I don't think user code will need to use the more
primitive features of MEM-REF directly very often...

James