Yes, it seems you're right.  I just need the "extern" annotation
around the includes.

extern "C" {
#include <caml/mlvalues.h>
#include <caml/memory.h>
#include <caml/callback.h>
}

Thanks to everyone for the helpful comments.

 - Aaron

On Tue, Dec 15, 2009 at 8:59 AM, Mark Shinwell <mshinwell@janestreet.com> wrote:
> On Tue, Dec 15, 2009 at 08:50:33AM -0500, Aaron Bohannon wrote:
>> On Tue, Dec 15, 2009 at 1:59 AM, Robert Roessler <roessler@rftp.com> wrote:
>> > Aaron Bohannon wrote:
>> >>
>> >> How do I link C++ code with OCaml?
>>
>> > You might try (when mixing C++ and OCaml) wrapping the whole thing in an
>> > 'extern "C" {...}' block (*including* the #includes and the entire main
>> > function).
>>
>> Thanks for the tip.  This does resolve the missing caml symbols (even
>> when naming the file with a cpp extension).  However, my real program
>> actually uses some C++ features.  I think I could convert it to a real
>> C program, but I assumed there would be some other way.
>
> I suspect it will work if only the #include directives pertaining to Caml
> header files are marked as 'extern "C"'.  You just need to tell the compiler to
> use the C linkage convention rather than the C++ name mangling convention for
> the external Caml functions that your program (implicitly or explicitly) calls.
> This is done at the function prototype site, not the call site.  Everything
> else in the program should be unaffected.
>
> Xavier, could the headers have the guards added?  (I only spot-checked one,
> mlvalues.h, and that didn't appear to have it).
>
> Mark
>