gistfile1.txt

#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <arpa/inet.h>

int main(int argc, char **argv)
{
    if (argc < 2)
    {
      printf("Usage: %s hostname\n", argv[0]);
      exit(-1);
    }

    printf("GetHostByName results:\n");

    // gethostbyname
    struct hostent *hp = gethostbyname(argv[1]);

    if (hp == NULL) 
    {
      printf("gethostbyname() failed\n");
      printf("%s: %d\n", hstrerror(h_errno), h_errno);
      char buffer[500];
      strerror_r(h_errno, buffer, 500);
      printf("strerror_r: %s", buffer);
      printf("\n");
    } 
    else
    {
      printf("%s = ", hp->h_name);
      unsigned int i=0;
      while (hp->h_addr_list[i] != NULL)
      {
        printf("%s ", inet_ntoa(*(struct in_addr*)(hp->h_addr_list[i])));
        i++;
      }

      printf("\n");
    }

    printf("GetAddrInfo results:\n");

    // getaddrinfo
    struct addrinfo *result, *rp, hints;

    memset(&hints, 0, sizeof(struct addrinfo));
    hints.ai_family = AF_UNSPEC;    
    hints.ai_flags = 0x02;
    hints.ai_protocol = 0;          

    int s = getaddrinfo(argv[1], NULL, &hints, &result);
    if (s != 0)
    {
      printf("getaddrinfo() failed\n");
      printf("%s %d\n", gai_strerror(s), s);
      char buffer[500];
      strerror_r(h_errno, buffer, 500);
      printf("strerror_r: %s", buffer);
      printf("\n");
    }
    else
    {
      printf("%s = ", result->ai_canonname);
      char str[INET6_ADDRSTRLEN];
      for (rp = result; rp != NULL; rp = rp->ai_next)
      {
        inet_ntop(AF_INET6, rp->ai_addr->sa_data, str, INET6_ADDRSTRLEN);
        printf("%s ", str);
      }
    }

    printf("\n");
    freeaddrinfo(result);
    return 0;
}