#include <iostream>
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>

using namespace std;

void MyID(string header) {

   uid_t real, effective, saved;

   cout << endl;
   cout << "*****************************************" << endl;
   cout << header << endl;
   cout << "real user id " << getuid() << endl;
   cout << "effecitve  user id " << geteuid() << endl;
   getresuid(&real, &effective, &saved);
   cout << "saved user id " << saved << endl;
   cout << "*****************************************" << endl;
   cout << endl;
}

int main(int argc, char * argv[]) {

     int targetID = 1001;
     string phrase ;

     if (argc > 1) {
         targetID = atoi(argv[1]);
	 cout << "The targetID is " << targetID << endl;
     }

     MyID("At start of process");

     if (setuid(1000) != 0) {
        perror("setuid(1000) failed: ");
	return -1;
     }

     MyID("After a call to setuid(1000)");

     if (setuid(targetID) != 0) {
        perror("setuid failed");
	return -1;
     }

  
     cout << "called setuid " << targetID << endl;
     MyID("After a call to setuid()");

     return 0;
}