get a line from csv (Rcpp)

readaline.cpp

#include "RcppArmadillo.h"
// [[Rcpp::depends(RcppArmadillo)]]
#include <iostream>
#include <string>
#include <vector>
using namespace Rcpp;

// [[Rcpp::export]]
std::vector<double> readaline(std::string readtxt, int ind_n) { 
  std::ifstream file(readtxt);
  std::string str;
  std::vector<double> result;
  int index = 0;
  while (std::getline(file, str))
  {
    if(index == ind_n){
      std::stringstream ss(str);
      while( ss.good() )
      {
        std::string substr;
        getline(ss, substr, ',');
        result.push_back( stod(substr) );
      }
    }
    index++;
    if(index>ind_n){
      break;
    }
  }
  return result;
}