bindgen

bindgen automatically generates raw OCaml FFI bindings to C (and some C++) libraries both as OCaml external definitions, types, constants, and the appropriate C shim code.

Non-goals: It does not aim to provide very safe, very idiomatic, pure bindings, but rather give you direct access to the underlying C library with a few conveniences. But you're more than welcome to build idiomatic, type-safe wrappers for bindgen generated libraries.

For example, given the C header doggo.h:

typedef struct Doggo {
    int many;
    char wow;
} Doggo;

void eleven_out_of_ten_majestic_af(Doggo* pupper);

bindgen produces OCaml FFI code allowing you to call into the doggo library's function and use its types:

(* automatically generated by ocaml-bindgen 0.0.1 *)

type doggo = {
  many: int
  wow: char
}

external eleven_out_of_ten_majestic_af : doggo -> unit
    = "caml_eleven_out_of_ten_majestic_af"

And the follow C shim:

/* automatically generated by ocaml-bindgen 0.0.1 */

value caml_Doggo_to_value(struct Doggo *pupper) {
  CAMLparam0();
  CAMLlocal1(caml_pupper);
  event = caml_alloc_tuple(2);
  Store_field(caml_pupper, 0, Val_int(pupper->many));
  Store_field(caml_pupper, 1, Val_char(pupper->wow));
  CAMLreturn(caml_pupper);
}

Doggo* caml_Doggo_of_value(value caml_pupper) {
    Doggo* pupper = malloc(sizeof(struct Doggo));
    pupper.many = Int_val(Field(caml_pupper, 0));
    pupper.wow = Char_val(Field(caml_pupper, 1));
    return pupper
}

CAMLprim value caml_eleven_out_of_ten_majestic_af(value caml_pupper) {
    CAMLparam1(caml_pupper);
    Doggo* pupper = caml_Doggo_of_value(caml_pupper);
    // actual C call
    eleven_out_of_ten_majestic_af(pupper);
    CAMLreturn0();
}