Re: How to call OCaml from C++

[Michael Ekstrand <michael@elehack.net>]

On 02/22/2010 09:11 PM, Jianzhou Zhao wrote:
> Hi,
> 
> Does anyone call OCaml code from C++?
> C can call OCaml with the OCaml foreign interfaces.
> But when we call OCaml from C++, we need to consider ‘extern C'
> stuff, like what we do when call C from C++, because the bridge
> functions between C and OCaml are written in C.
> 
> However, those functions have not been prefixed with 'extern C',
> and some functions, such as caml_alloc_dummy in libasmrun, have not
> been exposed
> in a head file. So it is hard to define a wrapper to let it work in C++.
> When linking C++ and libasmrun, caml_alloc_dummy cannot
> be found by the linker.

If you include your OCaml includes in an 'extern C' block like this:

extern "C" {
#include <caml/mlvalues.h>
/* other OCaml includes */
}

then the C++ compiler should have the right symbol names so that it can
look things up in the runtime.  The headers do not have extern C
declarations in them, but they are able to be imported cleanly in an
extern "C" block.

- Michael