ctypes bug description

compile.sh

#!/bin/bash

gcc -ansi -Wall foo_c.c -c -o foo_c.o

ocamlfind ocamlopt \
  -verbose \
  -linkpkg \
  -package ctypes.foreign \
  foo_c.o \
  foo_ml.ml \
  -o foo_ml_linked_o

ar rcs libfoo_c.a foo_c.o

nm libfoo_c.a

ocamlfind ocamlopt \
  -verbose \
  -linkpkg \
  -package ctypes.foreign \
  libfoo_c.a \
  foo_ml.ml \
  -o foo_ml_linked_a

foo_c.c

#include <std

foo_ml.ml

open Ctypes
open Foreign

let my_foo_function = foreign "my_foo_function" (void @-> returning void)

let () =
  Printf.printf "This is printed by OCaml\n%!";
  my_foo_function ();

Depending on the version of gcc, you might need to add -Wl --no-as-needed to the gcc command line; see yallop/ocaml-ctypes#49

Using the C stub generation backend of ctypes avoids this issue (see janestreet/async_ssl as an example myocamlbuild.ml that does this)