// ==========================
// Usage of gethostbyname()
// Language: C++
// Microsoft Windows XP Professional
// Microsoft C++ Compiler Version 13.10.3077 for 80x86
// ==========================

// --------------------
// ---- C-includes ----
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cerrno>
#include <cassert>
// --------------------

// --------------------
// --- C++-includes ---
#include <iostream>
#include <iomanip>
#include <string>
#include <vector>
using namespace std;
// --------------------

// --------------------
// --- System calls ---
// ----- includes -----
#include <sys/types.h>
#include <winsock2.h>
// --------------------

// ====================
#define CERR cerr << "[" << __FILE__ << ", " << setw (3) << __LINE__ <<
"] ERROR: "

// ====================
enum {H_NAME, H_ALIASES, H_ADDR_LIST, SIZE_OF_HOSTBYNAME_INFO };
const char* e_names[] = {"h_name", "h_aliases", "h_addr_list" };

// ====================
string get_hostname()
{
char host_name [256];
const int ret_code = gethostname (host_name, sizeof (host_name));
    if (ret_code != 0)
    {
        CERR << ""
             << "Unable to perform gethostname(): "
             << "ret_code = "
             << ret_code
             << ", errno = "
             << errno
             << ", "
             << "WSAGetLastError() = "
             << WSAGetLastError()
             << " - "
             << strerror (errno)
             << endl;
       return string();
    }
    assert (strlen (host_name) < sizeof (host_name));

    return string (host_name);

// ====================
vector<vector<string> > get_hostbyname(const string& host_name_i =
string())
{
const hostent * const p_host = gethostbyname (host_name_i.c_str());
  if (p_host == 0)
  {
      CERR << ""
           << "Unable to perform gethostbyname("
           << host_name_i
           << "): "
           << "h_errno = "
           << h_errno
           << ", "
           << "WSAGetLastError() = "
           << WSAGetLastError()
           << " - "
           << strerror(WSAGetLastError())
           ;
      return vector<vector<string> > ();
  }

vector<vector<string> > ret_vvect (SIZE_OF_HOSTBYNAME_INFO);

  ret_vvect[H_NAME].push_back (p_host->h_name);

  for (int i = 0; p_host->h_aliases[i]; i++)
  {
      ret_vvect[H_ALIASES].push_back (p_host->h_aliases[i]);
  }
  for (int i = 0; p_host->h_addr_list[i]; i++)
  {
      ret_vvect[H_ADDR_LIST].push_back (inet_ntoa (*(struct in_addr
*)p_host->h_addr_list[i]));
  }

  return ret_vvect;

// ====================
void show_hostbyname(const string& host_name_i = string())
{
   cout << endl;
   cout << endl;
   cout << "====== " << "gethostbyname(" << host_name_i << ")" << "
======" << endl;

const vector<vector<string> > result = get_hostbyname (host_name_i);

   for (size_t i = 0; i < result.size(); i++)
   {
     cout << e_names[i] << endl;
     if (!result[i].empty())
     {
       for (size_t k = 0; k < result[i].size(); k++)
       {
         cout << "* " << result[i][k] << endl;
       }
     }
     else
     {
       cout << "! None" << endl;
     }
     cout << endl;
   }

// ====================
int main ()
{
WSADATA            wsaData;
    WSAStartup(MAKEWORD(2,2), &wsaData);

int ret_code;
const string host_name = get_hostname();
    if (!host_name.empty())
    {
        cout << "gethostname() returns host_name  = " << host_name << endl;
    }
    else
    {
        cout << "gethostname() can't return host_name" << endl;
    }

    // --------------------
    show_hostbyname ();

    show_hostbyname ("localhost");

    if (!host_name.empty())
    {
      show_hostbyname (host_name);
    }
    show_hostbyname ("dummy");

    WSACleanup();

    return 0;

Alex Vinokur
     email: alex DOT vinokur AT gmail DOT com
     http://mathforum.org/library/view/10978.html
     http://sourceforge.net/users/alexvn