[R] accesing slots of S4 class in C code

[Douglas Bates]

On 8/17/05, Aniko Szabo <aniko.szabo at hci.utah.edu> wrote:
> 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);
> 
> }

Your C code is set for the .Call interface, not the .C interface. 
Change the R code to

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


> 
> 
> 
> 
> 
> 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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