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Can arguments and return values be passed by reference?

I'm trying to work out how I would bind the following C function:

  int * inc (int *p)
    return p;


  int x = 6;
  assert(x == 8);

(This is a trivial example but is representative of a class of functions
in the C++ API I am trying to bind.)

In my bindings, C ints are represented in Lua as numbers. So, the above C
example would be as follows in lua:

  x = 6
  -- x now equals 8

Any thoughts? If there is no way to pass or return values by reference, do
I just outlaw pointers (and C++ references) in the C++ API?

BTW the binding is automated by way of a SWIG Lua 5.0 language module; if
anyone else is working on one, I would be happy to stop developing it and
be a guinea pig for someone else's.

A real function I'm trying to bind (if the above does not please you) is

        const Vector3 & Vector3::Normalize()
                float mag = Magnitude();

                if(mag == 0.0f)
                        return *this;

                float oo_mag = 1.0f/mag;
                mx *= oo_mag;
                my *= oo_mag;
                mz *= oo_mag;

                return *this;