Surendra Singhi <[EMAIL PROTECTED]> writes:
> If I have a C function which allocates memory for a C string and returns a
> pointer to this memory (return type char *).
>
> Should the return type of this function be :string or :pointer?
Either :pointer or :string+ptr. The :string+ptr type will return a list
with two values: a lisp string and a pointer to the C string.
> How do I deallocate this memory? Should I use `foreign-string-free' or
> `foreign-free'.
I have been meaning to look into this. Right now, you'd have to use
something like (foreign-funcall "free" :pointer <your-pointer>)
> Is there any way this deallocation can be made automatic?
Not that I know of. However, I suspect that, in your case, something like
this would suffice:
(defcfun your-foreign-function :pointer ...)
(defun your-wrapper-around-the-foreign-function (...)
(let ((ptr (your-foreign-function ...)))
(unwind-protect
(foreign-string-to-lisp ptr)
(foreign-funcall "free" :pointer ptr))))
Or you could define a new type to do this:
(defctype my-string :pointer)
(define-type-translator my-string :from-c (value)
"Converts a foreign string to lisp, and frees it."
(once-only (value)
`(unwind-protect (foreign-string-to-lisp ,value)
(foreign-funcall "free" :pointer ptr))))
(defcfun your-foreign-function my-string ...)
--
Luís Oliveira
luismbo (@) gmail (.) com
Equipa Portuguesa do Translation Project
http://www.iro.umontreal.ca/translation/registry.cgi?team=pt
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