Which user uses which shell on unix in C++11

users_and_their_shells.cpp

#include <iostream>
#include <map>
#include <string>
#include <sys/types.h>
#include <pwd.h>

int
main (int argc, char *argv[])
{ 
  std::map<std::string, std::string> nameshell;
  struct passwd *p;

  setpwent ();
  while ((p = getpwent ()) != NULL)
    nameshell[std::string (p->pw_name)] = std::string (p->pw_shell);
  endpwent ();

  for (const auto& e: nameshell)
    if (e.second.find ("nologin") == std::string::npos)
      std::cout << e.first << " uses " << e.second << std::endl;

  return 0;
}