[Rcpp-devel] Question about Rcpp and boost

Hello,

I know this question has been answered before (and I have searched for
it), but I cannot figure out a solution:

I want to use boost with Rcpp, basically to be able to use numbers with a
higher precision than a double. I am comfortable using the inline package
for small c++ functions, I have never used Rccp per se. I have created a
skeleton with convolve, and it works. I have added a new function:

// We can now use the BH package
// [[Rcpp::depends(BH)]]

#include <Rcpp.h>
#include <boost/math/common_factor.hpp>

using namespace Rcpp;

// [[Rcpp::export]]
int computeGCD(int a, int b) {
    return boost::math::gcd(a, b);
}

and when I try to compile, it fails (basically, the compiler does not find
where boost is). I have then run in R:

Sys.setenv("PKG_CXXFLAGS"="-I C:/Program~Files/boost/boost_1_57_0/")

which allows me to go a bit more into the build, but the compile fails
when reaching the #include <boost/math/common_factor.hpp>  above, since
it does not know where boost is (boost is at C:/Program~Files/boost/boost_1_57_0/
I have not compiled it, but just extracted with 7-zip and copied and pasted
the corresponding files into this subfolder).

From reading the attribute document of Dirk Eddelbuettel, it seems as if
adding the comments // [[Rcpp::export]] and // [[Rcpp::depends(BH)]]
would do the job. But for me, it does not work. What do I need to do?
Thanks and sorry for the basic question, I have tried to read everything I
could before asking this list.