How do I check if an externalptr is NULL from within R

Question

I\'m using SWIG to generate wrapper code to access C code from within the R language. The wrapper code uses the R externalptr type to hold references to C pointers

Answer 1

For completeness, here's the solution I used. It required a function on the C side, and one on the R side, as suggested by @DirkEddelbuettel. The C function is:

#include 

SEXP isnull(SEXP pointer) {
  return ScalarLogical(!R_ExternalPtrAddr(pointer));
}

And the wrapper function in R is:

is.null.externalptr <- function(pointer) {
  stopifnot(is(pointer, "externalptr"))
  .Call("isnull", pointer)
}

For an example of use from within R:

> p <- new("externalptr")
> p

> is.null.externalptr(p)
[1] TRUE