Calling C++ (not C) from Common Lisp?

Question

I am wondering if there is some way to call C++ code from Common Lisp (preferably portably, and if not, preferably in SBCL, and if not, well, then Clozure, CLisp or ECL).

The C++ would be called inside loops for numeric computation, so it would be nice if calls were fast.

CFFI seems to not support this:

"The concept can be generalized to other languages; at the time of writing, only CFFI's C support is fairly complete, but C++ support is being worked on."

(chapter 4 of the manual)

SBCL's manual doesn't mention C++ either; it actually says

This chapter describes SBCL's interface to C programs and libraries (and, since C interfaces are a sort of lingua franca of the Unix world, to other programs and libraries in general.)

The C++ code uses OO and operator overloading, so it really needs to be compiled with g++.

And as far as I know, I can have a C++ main() function and write wrappers for C functions, but not the other way around -- is that true?

Anyway... Is there some way to do this?

Thank you!

Answer 1

After compiling, most C++ functions actually boil down to regular C function calls. Due to function overloading and other features, C++ compilers use name mangling to distinguish between similarly named functions. Given an object dump utility and sufficient knowledge about your C++ compiler, you can call C++ code directly from the outside world.

Having said that though, you may find it easier to write a C-compatible layer between Lisp and your C++ code. You would do that using extern "C" like this:

extern "C" Foo *new_Foo(int x)
{
    return new Foo(x);
}

This makes the new_Foo() function follow the C calling convention so that you can call it from external sources.