[cffi-devel] CFFI malloc free
Hello, 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? How do I deallocate this memory? Should I use `foreign-string-free' or `foreign-free'. Is there any way this deallocation can be made automatic? Say, something similar to clisp's `:malloc-free', or should I copy this foreign string as a lisp string and then free the foreign string. Thanks. -- Surendra Singhi http://www.public.asu.edu/~sksinghi/index.html ,---- | WHY SHOULD WE SAVE TIGER? | Ans: Saving the tiger means saving mankind.. | | Help http://pudang.tripod.com/ | or https://secure.worldwildlife.org/forms/tiger_appeal_1.cfm `----
Surendra Singhi <efuzzyone@netscape.net> 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
Luís Oliveira <luismbo@gmail.com> writes:
Surendra Singhi <efuzzyone@netscape.net> 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 ...)
Thanks. -- Surendra Singhi http://www.public.asu.edu/~sksinghi/index.html ,---- | "All animals are equal, but some animals are more equal than others." | -- Orwell, Animal Farm, 1945 `----
Luís Oliveira <luismbo@gmail.com> writes:
Surendra Singhi <efuzzyone@netscape.net> 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))))
Can the foreign string in the above example contain the null character? Or does cffi assumes that it is a null terminated string? Thanks. -- Surendra Singhi http://www.public.asu.edu/~sksinghi/index.html ,---- | WHY SHOULD WE SAVE TIGER? | Ans: Saving the tiger means saving mankind.. | | Help http://pudang.tripod.com/ | or https://secure.worldwildlife.org/forms/tiger_appeal_1.cfm `----
On 12/19/05, Surendra Singhi <efuzzyone@netscape.net> wrote:
Can the foreign string in the above example contain the null character? Or does cffi assumes that it is a null terminated string?
Yes, yes. See: http://common-lisp.net/project/cffi/manual/html_node/foreign_002dstring_002d... -- Luís Oliveira http://student.dei.uc.pt/~lmoliv/ Equipa Portuguesa do Translation Project http://www.iro.umontreal.ca/translation/registry.cgi?team=pt
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