1 /*This program is modified from CSAPP: hostinfo.c 2  */ 3 #include <stdio.h> 4 #include <stdlib.h> 5 #include <unistd.h> 6 #include <string.h> 7 #include <ctype.h> 8 #include <setjmp.h> 9 #include <signal.h>10 #include <sys/time.h>11 #include <sys/types.h>12 #include <sys/wait.h>13 #include <sys/stat.h>14 #include <fcntl.h>15 #include <sys/mman.h>16 #include <errno.h>17 #include <math.h>18 #include <pthread.h>19 #include <semaphore.h>20 #include <sys/socket.h>21 #include <netdb.h>22 #include <netinet/in.h>23 #include <arpa/inet.h>24 #include <netinet/in.h>25 #include <netdb.h>26 27 void dns_error(char * msg)28 {29   fprintf(stderr, "%s: DNS error %d\n", msg, h_errno);30 }31 32 struct hostent *Gethostbyaddr(const char * addr, int len, int flag)33 {34   struct hostent *p;35   if ((p = gethostbyaddr(addr, len, flag)) == NULL)36     dns_error("Gethostbyaddr error");37   return p;38 }39 40 struct hostent *Gethostbyname(const char * name)41 {42   struct hostent *p;43   if ((p = gethostbyname(name)) == NULL)44     dns_error("Gethostbyname error");45   return p;46 }47 48  int main(int argc, char ** argv)49 {50   char **pp;51   struct in_addr addr;52   struct hostent *hostp;53 54   if (argc != 2) {55     fprintf(stderr, "usage: %s <domain name or dotted-decimal>\n",56     argv[0]);57     exit(0);58     }59   int af_inet = AF_INET;60   if (inet_aton(argv[1], &addr) != 0)61     hostp = Gethostbyaddr((const char *)&addr, sizeof(addr), AF_INET);62   else63     hostp = Gethostbyname(argv[1]);64 65   if (hostp == NULL)66     exit(0);67 68   printf("official hostname: %s\n", hostp->h_name);69 70   for (pp = hostp->h_aliases;*pp != NULL;pp++)71     printf("alias: %s\n", *pp);72 73   for (pp = hostp->h_addr_list;*pp != NULL; pp++) {74      addr.s_addr = ((struct in_addr *)*pp)->s_addr;75     printf("address: %s\n", inet_ntoa(addr));     76   }77   exit(0);78 }