Acessing data on `inst/extdata` from Rcpp Catch tests

I am trying to access a data file on a inst/extdata file from a Rcpp Catch2 test. The file tree looks like this:

├── inst
│   └── extdata
│       └── data-sample
├── R
│   ├── catch-routine-registration.R
│   └── RcppExports.R
├── src
    ├── mycode.cpp
    ├── RcppExports.cpp
    ├── Package_types.h
    ├── test-example.cpp
    └── test-runner.cpp

Which would be similar from what you'd get from a new package skeleton using devtools, I believe. Now, I can access this data-sample file from a testthat test pretty easily like this:

system.file(
    "extdata", "data-sample", package = "Package", mustWork = TRUE
)

And use it as needed. I am aware that this uses the global path from the installed package at this point, however I can't find a way to pass this value to my c++ tests. I am currently using a hardcoded path, but that obviously only works on my machine.

This is what I'm currently using:

const std::string DATAFILE = "/my/package/inst/extdata/data-sample";

Since this is a function for reading files I really can't embed this in any way, but I still want to know: how to pass R data to the Rcpp/Catch tests?

Thanks in advance!

Solution

You can get the system.file() path by calling the R function from C++, even if it's not an exported C++ function (this is how I have interpreted your query following comments to the post and to Dirk Eddelbuettel's answer). Consider the following C++ code in print_extdata.cpp:

#include <Rcpp.h>

Rcpp::StringVector get_extdata(){
    Rcpp::Environment base("package:base");
    Rcpp::Function sys_file = base["system.file"];
    Rcpp::StringVector res = sys_file("extdata", "2012.csv",
                                      Rcpp::_["package"] = "testdat");
    return res;
}


// [[Rcpp::export]]
void print_extdata() {
    Rcpp::StringVector path = get_extdata();
    Rcpp::Rcout << path;
}

Then called from R:

> Rcpp::sourceCpp("print_extdata.cpp")
> print_extdata()
"/home/duckmayr/R/x86_64-pc-linux-gnu-library/3.5/testdat/extdata/2012.csv"