Rcpp: Question about NumericMatrix & IntergerMatrix

[badbye]

Rcpp::cppFunction('
  void test_pointer(NumericMatrix &m){
      m[0] = 100;
  }
')

a1 = matrix(1:9, 3)
test_pointer(a1) 
a1  # no error and a1 does not change
a2 = a1 + 0.0
test_pointer(a2)  
a2 # a2 changes

I am new to c++ and Rcpp. It seems the test_pointer function does not work on IntergerMatrix input, why it runs successfully without any warning or error?

[HervePerdry]

R creates a temporary NumericMatrix (converting from a1), which is passed to test_pointer, and then lost.

Note that you don’t need to write &m in your function definition, SEXP are references and Rcpp functions can modify their arguments.

[eddelbuettel]

Someone reminded me the other day that we apparently have an entry in the FAQ for this too.