#include <iostream>                /* C++ iostream            C++98/11 */
#include <string>                  /* C++ strings             C++98/11 */
#include <boost/regex.hpp>                           /* RegEx                   Boost  */
#include <boost/algorithm/string.hpp>
int main() {
	std::string str = "\\dir\\dir2\\dir4\\dir4\\dir6";
auto itr = boost::find_nth(str, "\\", 4);
if(itr.empty()) std::cout << "empty";


}