Question

I have an R script with some inline C++, and I’d like to include a header file in the same directory. I can get the following to work:

library(Rcpp)
library(inline)

code <- '
   // my C++ code here
   '

settings=getPlugin("Rcpp")
settings$env$PKG_CXXFLAGS='-I /hard/coded/path/to/header/'

myfunction <- cxxfunction(signature(x="numeric"),
                          plugin="Rcpp",  include='#include "myheader.hpp"',
                          settings=settings, body=code)

But it seems like there should be a convenient way to include a header file in the same directory. I just can’t see what it is. I’d really like a way to include c++ files which are located in the same directory.

(Also apologies: I’m not a c++ (or R) ninja, so I may be missing something very obvious.

Answer 1

Can you clarify what directory you refer to when you say “in the same directory”? Same as what?

If it is the current directory, you still need -I. as that directory may not added as a default. But if that is indeed the directory you want, then its relative path (saying “current dir”) is more general than the absolute -I/hard/coded/path/to/header.

Otherwise, what you have done is the correct way to modify the plugin to provide extra flags to the compiler.

Edit: Made a test or two and it turns out that the inline package always use R’s tempdir to compile — so -I. makes no sense as we generally do not know where that is.

That leaves you with two choices:

1. Use an absolute path as you have done.

2. Use R to read the content of the header file into a variable passed to the include= argument.

Edit 2: Turns out that we do that in one of the examples shipped with Rcpp itself:

settings <- getPlugin("Rcpp")
settings$env$PKG_CXXFLAGS <- paste("-I", getwd(), sep="")

and then uses settings=settings in the call to cxxfunction.