How to pass environment to Rcpp chunk with knitr?

I'm trying to take the following code and translate it into a knitr chunk (borrowed from Rcpp examples):

library(Rcpp)
library(inline)

openMPCode <- '
   std::vector<double> x = Rcpp::as<std::vector< double > >(xs);
   size_t n = x.size();
   #pragma omp parallel for shared(x, n)
   for (size_t i=0; i<n; i++) {
     x[i] = ::log(x[i]);
   }
   return Rcpp::wrap(x);
'

## modify the plugin for Rcpp to support OpenMP
settings <- getPlugin("Rcpp")
settings$env$PKG_CXXFLAGS <- paste('-fopenmp', settings$env$PKG_CXXFLAGS)
settings$env$PKG_LIBS <- paste('-fopenmp -lgomp', settings$env$PKG_LIBS)
funOpenMP <- rcpp(signature(xs="numeric"), body=openMPCode, settings=settings)

      

        
        
        
      

    

Basically, the main problem is to ensure that the environment is passed into the knitr block so that PKG_LIBS

it is PKG_CXXFLAGS

set appropriately when the code is compiled. An example of what a snippet might look like knitr

:

```{r engine='Rcpp'}
#include <Rcpp.h>
using namespace Rcpp;

// [[Rcpp::export]]
NumericVector openmp_log( NumericVector x ) {
  size_t n = x.size();
  #pragma omp parallel for
  for( size_t i=0; i < n; i++ ) {
    x[i] = ::log10( x[i] );
  }
  return x;
}
```

      

        
        
        
      

    

If I understand correctly, knitr uses sourceCpp

for whatever in the chunk compiles it and passes the parameters specified in engine.opts

- sourceCpp

. Hence, I assume there are two potential directions:

• setting engine.opts=list(env=...)
  
  so that the appropriate environment is transferred; however, I am getting an error trying this ("env" formal argument matched by multiple actual arguments).

• The hook / custom chunk parameter can be used to customize the environment, but I'm not sure how exactly this can be done.

This is with knitr 1.0.11 and Rcpp 0.10.2.