: I have an OCAML and C function as follows
:
: **************OCAML side*****************
: let simple_list_test m = m @ [100]
: let _ =
: Callback.register "simple_list_test" simple_list_test;
: ***********************************************
Your function simple_list_test expects a list argument which is represented in
memory as a linked collection of values.
: list = (int *) calloc(10, sizeof(int));
: new_list = call_caml_simple_list_test(list);
This cannot work as you give to "simple_list_test" a C array of ints, not a
linked list as expected by the Ocaml compiler.
Have a look at the reference manual, chapter "Interfacing C with Objective
Caml", section 14.2 "The value type". A list cell is a 3 word object containing
a header, the value of the cell, and a pointer to the next cell.
Here is a way to build a legal 10 element list :
void go()
{
value list, new_list;
int i;
#define nil Val_int(0)
/* builds a list with the 1..10 numbers */
for(list = nil, i = 10; i > 0; i--) {
Begin_roots1(list);
new_list = alloc(2,0);
Field(new_list,0) = Val_int(i);
Field(new_list,1) = list;
End_roots();
list = new_list;
}
/* now calls simple_list_test */
new_list = call_caml_simple_list_test(list);
/* prints the last item */
for (list = new_list; Field(list,1) != nil; list = Field(list,1));
printf("%d\n", Int_val(Field(list,0)));
fflush(stdout);
}
: My understanding ...
: all I have to do is to cast the pointer to a caml 'value' type.
Never cast unless you are absolutely sure the datatypes agree.
-- Michel Quercia 9/11 rue du grand rabbin Haguenauer, 54000 Nancy http://pauillac.inria.fr/~quercia mailto:quercia@cal.enst.fr
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