interface to C++

interface to C++

[christ]

Hi.

Please help me answer a question. Is the 'camlc -custom' link
command able to work with C++ objects? I would guess it is not,
but would appreciate any ideas for linking with C++. The startup
code would have to run the extra initializer functions, so it's
mostly a factor of what compiler is used I think. Again, thank
you for any help.

Thanks, Chris

P.S. Thanks for making caml available. It's a great alternative
to SMLNJ. Nice job.

Chris Tilt				    chris.tilt@tek.com
Tektronix, Inc.				Beaverton, Oregon, USA

Re: interface to C++

[Xavier Leroy]

> Please help me answer a question. Is the 'camlc -custom' link
> command able to work with C++ objects?

I can't provide definitive answers, as I'm not an expert in C++. It
seems that the key point is how your C/C++ compiler allows C++
functions to be called from C. You may want to check first the
compiler docs or hotline, or post a query on comp.compilers. I had a
look at the gcc/g++ documentation, and it doesn't say anything about
this, unfortunately.

The Caml Light runtime system is basically a big set of C functions
that is entered at main() and eventually calls the user-provided C
functions. If you can link that with your C++ code so that
initializers get called correctly, then main() is called, the only
remaining problem is to understand how the names of your C++ functions
appear from the C side (I understand most C++ compilers "mangle" names
by adding type information or whatever to the function name.) Then,
just put the mangled names in the Caml "value" declarations, and
everything should work fine. To get your C++ compiler to be called
instead of the standard C compiler for building the custom executable,
use
        camlc -cc <the C++ compiler> -custom ...

or just hack the camlc command itself, it's a shell script.

It may be needed to define main() in C++ that just calls
Caml's main(), suitably renamed. It will take some more hacking in
camlc and maybe in libcaml.a.

If your compiler has different, incompatible calling conventions for C
and C++, then maybe it provdes some kind of pragma or declaration
to declare an external C++ function in a C file. Then, camlc will have
to edit /tmp/camlprim.$$.c to insert the correct C++ declarations.

Let me know how it works.

- Xavier Leroy

Re: interface to C++

[Stefan Monnier]

Xavier Leroy <Xavier.Leroy@inria.fr> wrote:
> by adding type information or whatever to the function name.) Then,
> just put the mangled names in the Caml "value" declarations, and
> everything should work fine. To get your C++ compiler to be called

Rather than mess around with the mangled names, you might be better off trying
to compile caml-light with your C++ compiler so that the name (de)mangling
is all done by your compiler. Since C++ is an approximate superset of ANSI C,
it might work.
(but don't ask me how to interface caml-light with C++ objects and methods.
I have no idea how easy it can be to add custom-made types)


	Stefan

Re: interface to C++

[Jean-Marie Geffroy]

Stefan Monnier <stefan.monnier@epfl.ch> wrote

> Rather than mess around with the mangled names, you might be better
> off trying to compile caml-light with your C++ compiler so that the
> name (de)mangling is all done by your compiler. Since C++ is an
> approximate superset of ANSI C, it might work.

Right. The Windows version (1) is in fact already compiled this way:
the standard caml system is written in pure C but compiled with a C++
compiler. The graphical interface is written in C++ and uses the
MFC. It exports 5 or 6 functions through extern "C" declarations such
as:

extern "C" ui_xxx(...){...}

The C modules contain standard extern declarations:

extern ui_xxx(...);

Linking C++ functions is thus completely straightforward and there's no
messing around with names.

Hope this helps !

    Jean-Marie


(1) soon available !