// ==========================
// Usage of gethostbyname()
// Language: C++
// Microsoft Windows 2000 Professional
// Cygwin 1.5.18
// GNU g++ 3.4.4
// -----------------
// Version G-1-1
// -----------------
// Source: gethost.cpp
// ==========================

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

[ gethost.cpp ]
// ==========================
// Usage of gethostbyname()
// Language: C++
// Microsoft Windows 2000 Professional
// Cygwin 1.5.18
// GNU g++ 3.4.4
// -----------------
// Version G-1-1
// -----------------
// Source: gethost.cpp
// ==========================

// --------------------
// ---- 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 <unistd.h>
#include <netdb.h>
#include <sys/socket.h>
#include <arpa/inet.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
             << " - "
             << 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
           << " - "
           << hstrerror(h_errno)
           ;
      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 (*reinterpret_cast<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 ()
{
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");

    return 0;