Hi Phil,
Can't you wrap the array and size in a struct. For example in
https://github.com/polyml/polyml/tree/cb1b36caa242fc6ea9f74b015158466efac68d66/mlsource/extra/CInterface/Examples
we have :
---------------------------------
//ForeignTest.c
typedef struct _tree {
struct _tree *left, *right;
int nValue;
} *tree;
int SumTree(tree t)
{
if (t == NULL) return 0;
else return t->nValue + SumTree(t->left) + SumTree(t->right);
}
---------------------------------
and
---------------------------------
(*ForeignTest.sml*)
val sumTree = CInterface.call1 ( CInterface.load_sym mylib "SumTree") TREE
INT;
---------------------------------
So you just write a FreeTree function, which is modelled after the FreeIt
function in ForeignTest.c :
void FreeIt(void *p)
{
printf("Freed object at %p\n", p);
fflush(stdout);
free(p);
}
, which then reads nValue and passes it on to the relevant gtk function?
On Mon, Sep 14, 2015 at 10:36 PM, Phil Clayton <[email protected]>
wrote:
> I am trying to create an SML binding to a C function that returns an array
> that the caller must free. Usually, there is a free function that takes
> just the array (as a pointer) which can be attached as a finalizer with
> CInterface.setFinal. I have encountered a case [1] where the caller must
> also pass the size of the array, returned when the array is created, to the
> free function.
>
> Simplifying the example, we have, for some C type Elem:
>
> Elem *new (..., int *n_elems); /* n_elems is an 'out' parameter */
> void free (Elem *elems, int n_elems);
>
> and want an SML function like
>
> val new : ... -> elem vector
>
> Unfortunately, the function given to CInterface.setFinal is called with
> only one argument, the vol that is being finalized. Therefore this free
> function cannot be used. Does the current FFI architecture allow a variant
> of setFinal that passes extra arguments to the finalization function? For
> example:
>
> val setFinal1 : sym -> 'a Conversion -> vol -> 'a -> unit
>
> This isn't particularly common so is probably not a show-stopper. Another
> benefit could be enabling use of functions g_slice_alloc and g_slice_free1
> that needs the number of bytes to free:
> https://developer.gnome.org/glib/stable/glib-Memory-Slices.html
>
> Thanks,
> Phil
>
>
> 1. The C function in question is gtk_target_table_new_from_list that
> returns an array and its size. The array should be freed with
> gtk_target_table_free which should be passed the size. See:
> -
> https://developer.gnome.org/gtk3/stable/gtk3-Selections.html#gtk-target-table-new-from-list
> -
> https://developer.gnome.org/gtk3/stable/gtk3-Selections.html#gtk-target-table-free
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