convert Rcpp::CharacterVector to std::string

Question

I am trying to open a file within an Rcpp function, so I need the file name as a char* or std::string.

So far, I have tried the following:

#include <Rcpp.h>
#include <boost/algorithm/string.hpp>
#include <fstream>
#include <string>

RcppExport SEXP readData(SEXP f1) {
    Rcpp::CharacterVector ff(f1);
    std::string fname = Rcpp::as(ff);
    std::ifstream fi;
    fi.open(fname.c_str(),std::ios::in);
    std::string line;
    fi >> line;
    Rcpp::CharacterVector rline = Rcpp::wrap(line);
    return rline;
}

But apparently, as does not work for Rcpp::CharacterVector as I get a compile time error.

foo.cpp: In function 'SEXPREC* readData(SEXPREC*)':
foo.cpp:8: error: no matching function for call to 'as(Rcpp::CharacterVector&)'
make: *** [foo.o] Error 1

Is there a simple way to get a string from the argument or somehow open a file from the Rcpp function argument?