accesing slots of S4 class in C code

I am trying to use a custom S4 object in my C code and I cannot get the
access to its slots working.



The following is a toy example, but even this crashes.



In R I have:



setClass("pd", representation(data="numeric"))

x <- new("pd", data=1:5)



test <- function(pd.obj) {

  res <- .C("TestFun", pd.obj)

  res}



test(x)



(Of couse I load the DLL as well.)



The corresponding C file has:



SEXP TestFun(SEXP pd_obj)

{

 SEXP t=R_NilValue;

 PROTECT(t = GET_SLOT(pd_obj, install("data")));

 UNPROTECT(1);

 return(t);

}





What I hope to get as a result is the (1:5) vector.

In the long term, the vector will be a multi-dimensional array and I
will want to do calculations using its contents in the C program.



Thanks for any help,



Aniko


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