foreign name typ exposes the C function of type typ named by name as an OCaml value.

The argument ?from, if supplied, is a library handle returned by Dl.dlopen.

The argument ?stub, if true (defaults to false), indicates that the function should not raise an exception if name is not found but return an OCaml value that raises an exception when called.

The value ?check_errno, which defaults to false, indicates whether Unix.Unix_error should be raised if the C function modifies errno. Please note that a function that succeeds is allowed to change errno. So use this option with caution.

The value ?release_runtime_lock, which defaults to false, indicates whether the OCaml runtime lock should be released during the call to the C function, allowing other threads to run. If the runtime lock is released then the C function must not access OCaml heap objects, such as arguments passed using Ctypes.ocaml_string and Ctypes.ocaml_bytes, and must not call back into OCaml.

• raises Dl.DL_error

  if name is not found in ?from and ?stub is false.

foreign_value name typ exposes the C value of type typ named by name as an OCaml value. The argument ?from, if supplied, is a library handle returned by Dl.dlopen.

Construct a function pointer type from a function type.

The ctypes library, like C itself, distinguishes functions and function pointers. Functions are not first class: it is not possible to use them as arguments or return values of calls, or store them in addressable memory. Function pointers are first class, and so have none of these restrictions.

The value ?check_errno, which defaults to false, indicates whether Unix.Unix_error should be raised if the C function modifies errno.

The value ?runtime_lock, which defaults to false, indicates whether the OCaml runtime lock should be released during the call to the C function, allowing other threads to run. If the runtime lock is released then the C function must not access OCaml heap objects, such as arguments passed using Ctypes.ocaml_string and Ctypes.ocaml_bytes, and must not call back into OCaml. If the function pointer is used to call into OCaml from C then the ?runtime_lock argument indicates whether the lock should be acquired and held during the call.

• raises Dl.DL_error

  if name is not found in ?from and ?stub is false.

A note on lifetime: this function ties the lifetime of the C function to the associated OCaml closure, so that the C function may be used only while the closure is still live.

The dynamic_funptr function is an alternative to funptr with explicit lifetime management.

Construct a function pointer type from a function type.

This behaves like funptr, except that null pointers appear in OCaml as None.

A closure passed to C was collected by the OCaml garbage collector before it was called.

Define a type representation for passing OCaml functions to C with explicit lifetime management.

(val (dynamic_funptr (foo @-> returning bar))) corresponds to the C type bar( * )(foo).

Example:

  module Progress_callback =
    (val (dynamic_funptr (int @-> int @-> ptr void @-> returning void)))
  let keygen = foreign "RSA_generate_key"
    (int @-> int @-> Progress_callback.t @-> ptr void @-> returning rsa_key)
  let secret_key =
    Progress_callback.with_fun
      (fun a b _ -> printf "progress: a:%d, b:%d\n" a b)
      (fun progress ->
         keygen 2048 65537 progress null)

Hook called on collection of closures associated with dynamic_funptr values that have not been deallocated with free.

By default the ctypes library retains closures associated with function pointers that have not been freed and prints a warning to stderr.

You can use this hook to change how these error messages are reported.