Include C++ DLL, error in ...: C symbol name not in load table

Hello R experts

I am googling and reading around, however, I can't get it working
(perhaps because I do not understand much C, however, I'll give it
a try). I am trying to include C++ code into an R routine, where
the C++ code looks:

#include<iostream>
using namespace std;
void foo (double* x, double* y, double* out)
{
  	out[0] = x[0] + y[0];
}

Back in R, the command

R CMD SHLIB --preclean -o xplusy

works fine resulting in two new files, xplusy.o and xplusy.so. The
wrapper in R is:

dyn.load("xplusy.so")
xplusy<- function(x, y){
    .C("foo", as.double(x), as.double(y), out=double(1))$out
}
xplusy(1, 2)
dyn.unload("xplusy.so")

Now, dyn.load() works and xplusy also shows up in getLoadedDLLs().
However, when invoking the function, xplusy(1, 2), R complains:

Error in .C("foo", as.double(x), as.double(y), out = double(1)): C
symbol name "foo" not in load table

I found some hints concerning Fortran code producing this error
message, but no help concerning C code.

Any help tips?

Thanks, *S*

$. uname -a
Darwin * 10.7.3 Darwin Kernel Version 10.7.3[...]

$: c++ --version
i686-apple-darwin10-g++-4.2.1 (GCC) 4.2.1 (Apple Inc. build 5666)
(dot 3)

platform       i386-apple-darwin9.8.0
arch           i386
os             darwin9.8.0
system         i386, darwin9.8.0
status
major          2
minor          12.2
year           2011
month          02
day            25
svn rev        54585
language       R
version.string R version 2.12.2 (2011-02-25)

On 20 April 2011 at 16:24, Duncan Murdoch wrote:
| On 20/04/2011 4:06 PM, Sascha Vieweg wrote:
|>  Hello R experts
|>
|>  I am googling and reading around, however, I can't get it working
|>  (perhaps because I do not understand much C, however, I'll give it
|>  a try). I am trying to include C++ code into an R routine, where
|>  the C++ code looks:
|>
|>  #include<iostream>
|>  using namespace std;
|>  void foo (double* x, double* y, double* out)
|>  {
|>    	out[0] = x[0] + y[0];
|>  }
|>
|>  Back in R, the command
|>
|>  R CMD SHLIB --preclean -o xplusy
|>
|>  works fine resulting in two new files, xplusy.o and xplusy.so. The
|>  wrapper in R is:
|>
|>  dyn.load("xplusy.so")
|>  xplusy<- function(x, y){
|>      .C("foo", as.double(x), as.double(y), out=double(1))$out
|>  }
|>  xplusy(1, 2)
|>  dyn.unload("xplusy.so")
|>
|>  Now, dyn.load() works and xplusy also shows up in getLoadedDLLs().
|>  However, when invoking the function, xplusy(1, 2), R complains:
|>
|>  Error in .C("foo", as.double(x), as.double(y), out = double(1)): C
|>  symbol name "foo" not in load table
|>
|>  I found some hints concerning Fortran code producing this error
|>  message, but no help concerning C code.
|
| You have C++ code, not C code.  C++ normally mangles names of exports.
|
| To get this to work, you should surround your declarations with
|
| extern "C" {
| }
|
| Another possibility is to use the Rcpp package; it writes the interface
| code for you.

I believe Duncan refers to the 'inline' package, rathern than 'Rcpp' (which
itself uses 'inline').

#include <iostream>
using namespace std;
void foo (double* x, double* y, double* out)
{
        out[0] = x[0] + y[0];
}