Re: [Chicken-users] What happens to a (non-simple) Scheme object sent to a foreign function?

[felix winkelmann]

On 2/4/07, Thomas Christian Chust <address@hidden> wrote:
> the address of the C function wrapping the define-external'ed Scheme
> procedure is unproblematic, because it will never change. The pointer to
> the C string data may become invalid, though, once the program returns
> from the library call. In order to make this safe, you would have to
> duplicate the string in the C heap (for example using strdup) or you
> would have to create a non-garbage-collected copy of the Scheme string
> (for example using object-copy) to pass that to the library routine. In
> either case you would have to release the string data later on when it
> is no longer needed.

Exactly.

Another option would be to create a GC root (CHICKEN_new_gc_root)
and keep it on the C-side (you have to pass the argument string as
a scheme-object, then create the GC-root from it). Later, you can
access the gc root (CHICKEN_gc_root_ref) and use the string. The
gc root will be updated on every garbage collection. You just have
to make sure you free it eventually (or just reuse it).


cheers,
felix