Após corrigir a função, chegamos a nova função abaixo:
#include <Rcpp.h>
#using namespace Rcpp;
#using namespace std;
#// [[Rcpp::export]]
#NumericVector Cquantile(NumericVector x, NumericVector probs) {
# Environment stats("package:stats");
# Function quantile = stats["quantile"];
# int npr = probs.size();
# NumericVector res(npr);
# for(int i=0; i<npr; i++){
# res[i] = as<double>(quantile(x, probs[i]));
# }
# return res;
#}
Testando a função
## Testando no R
#set.seed(22)
# Cquantile(rnorm(1000000,0,1),c(0.025,0.975))
#[1] -1.963335 1.960857