To use additional packages within the Rcpp ecosystem, the correct header file may not be Rcpp.h
but Rcpp<PACKAGE>.h
(as e.g. for RcppArmadillo). It typically needs to be imported and then the dependency is stated within
// [[Rcpp::depends(Rcpp<PACKAGE>)]]
Examples:
// Use the RcppArmadillo package
// Requires different header file from Rcpp.h
#include <RcppArmadillo.h>
// [[Rcpp::depends(RcppArmadillo)]]
// Use the RcppEigen package
// Requires different header file from Rcpp.h
#include <RcppEigen.h>
// [[Rcpp::depends(RcppEigen)]]