20 minutes ago, Neil Toronto wrote:
> 1. Is there a way to associate a prop:custom-write to _cpointers or
> instances of ctypes defined using define-cstruct? [...]
No, it's just a thin wrapper around the C data. But you can create
the C type that you need to talk to the library and a racket
struct (with anything you want there). Make the racket struct hold
the C value in it, and write a ctype for it that translates trivially
to/from the lower level type.
> where mpfr constructs instances of _mpfr_t from Racket reals. As it is,
> I'm defining a struct wrapper,
Uh, that.
> which seems like a pointless indirection.
(I don't see why, either way you need some pointer going to some
data.)
> 2. There are a few cases where MPFR (the C library) allocates arrays and
> returns pointers to them. I want to interpret them as strings, lists,
> and vectors, but I also have to call "special free" functions to
> deallocate the memory. This is the way I'm doing it (simplified):
>
> (define gimme-string
> (get-ffi-obj 'gimme_string libmpfr (_fun -> _pointer)))
>
> @c{
> char* cstr_id(char* p)
> {
> return p;
> }
> }
>
> (define cstr->string
> (get-ffi-obj-from-this 'cstr_id (_fun _pointer -> _string)))
>
> (define cstr (gimme-string))
> (define str (cstr->string cstr))
> (special-free cstr)
>
> It's silly. But I can't figure out another way to have the FFI
> library interpret a char* pointer as a string AND give me access to
> the pointer itself so I can free the memory. I get the impression
> that it's possible, but I don't know the right incantations yet.
Why aren't you using a byte string directly?
--
((lambda (x) (x x)) (lambda (x) (x x))) Eli Barzilay:
http://barzilay.org/ Maze is Life!
_________________________________________________
For list-related administrative tasks:
http://lists.racket-lang.org/listinfo/users
