[SOLVED] How do I use Rcpp code in a stand-alone C++ program?

How do I use Rcpp code in a stand-alone C++ program?

I am a Statistician who works a lot with scientists in other fields who are not using R but mostly C++. On occasion I would like to give them a C++ program they can run but that also uses R functionality. Here is a toy example

#include <Rcpp.h>
using namespace Rcpp;
// [[Rcpp::export]]
int mytry() {
  NumericVector x(5);
  x = rnorm(5);
  Rcout<<mean(x)<<"\n";
  return 0;
}

Now when I try to run this in a C++ compiler (I am using Code::Block) I am getting error messages such as

undefined reference to 'Rprintf'

and a list of other similar errors.

I apologize if this is a silly question but I am not an C++ expert. I only use it myself via Rcpp to replace small R code snippets with C++ so they run faster.

Solution

In general you cannot as Rcpp is designed and built as an R extension package that can always assume to be called from R and hence link with many R symbols. In fact, it requires it.

You have two basic options here: the first and more common one is to separate your C++ implementations into 'pure C++' you can hand to your colleagues, along with some remaining 'glue' to call from R / return to R. That is likely your best option---just think, e.g., in terms of std::vector<double> rather than Rcpp::NumericVector. We have ample documentation for working with STL types such as std::vector.

The second is to actually stick R into your C++ application for which you can use CRAN package RInside which also makes heavy use of Rcpp. Both approaches have examples here (you can search among 3000 Rcpp answers by adding [rcpp] to the search term) and at places like the Rcpp Gallery. And of course for all of this, and more, you can always take a look at the Rcpp Introduction vignette which covers this.