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

int main(int argc, char** argv){
        uid_t effective, real, saved;
        getresuid(&real,&effective,&saved);

        printf("Real UID : %d, Effective UID : %d, Saved UID : %d\n",real,effective,saved);
        //printf("Real UID : %d, Effective UID : %d, Saved UID : %d\n",getuid(),geteuid(),0);
        seteuid(1000);
        getresuid(&real,&effective,&saved);
        printf("Real UID : %d, Effective UID : %d, Saved UID : %d\n",real,effective,saved);
        setuid(0);
        getresuid(&real,&effective,&saved);
        printf("Real UID : %d, Effective UID : %d, Saved UID : %d\n",real,effective,saved);
}