Maybe you have to add 
#include <stdio.h>
#include <R.h>
to your C++ source code.
Massimiliano Tripoli
Il giorno mer, 20/04/2011 alle 22.06 +0200, Sascha Vieweg ha scritto:
> #include <iostream>
> using namespace std;
> void foo (double* x, double* y, double* out)
> {
>         out[0] = x[0] + y[0];
> }
> 
>