NTP client in C++ using boost::asio

For your convenience, I wrote a simple NTP client using nothing but standard C++ and the boost::asio library. The code for it is attached below. Using the static method NtpClient::GetTime(), the current time as reported by pool.ntp.org is retreaved as in the following program:

#include <iostream>
#include "NtpClient.hpp"
#include <boost/date_time/posix_time/posix_time.hpp> // Need I/O.
int main(int argc,char** argv)
{
   if( 1 == argc )
   {
      std::cout << NtpClient::GetTime() << '\n';
   }
   else if( 2 == argc )
   {
      std::cout << NtpClient::GetTime( argv[1] ) << '\n';
   }
   else
   {
      std::cerr
        << "Usage: " << argv[0]
        << " NTP-server\n  NTP-server is pool.ntp.org if not specified\n";
      return 1;
   }
   return 0;
}

The NtpClient class is coded as follows:

// NTP client uaing Boost::Asio.
// 2010-05-11
// Jansson Consulting
// http://www.p-jansson.com
// Dedicated to the Public Domain.
#ifndef NTPCLIENT_HPP
#define NTPCLIENT_HPP
#include <boost/asio.hpp>
#include <boost/date_time/posix_time/posix_time_types.hpp>
class NtpClient
{
   public:
      static boost::posix_time::ptime GetTime()
      {
         return GetTime("pool.ntp.org");
      };
      static boost::posix_time::ptime GetTime( const char* ntpServer )
      {
         using boost::asio::ip::udp;
         boost::asio::io_service io_service;

         udp::resolver resolver(io_service);
         udp::resolver::query query(udp::v4(), ntpServer, "ntp");
         udp::endpoint receiver_endpoint = *resolver.resolve(query);

         udp::endpoint sender_endpoint;

         boost::uint8_t data[48] = {
            0x1B,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
            0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0
         };

         udp::socket socket(io_service);
         socket.open(udp::v4());

         socket.send_to(
               boost::asio::buffer(data),
               receiver_endpoint);
         socket.receive_from(
               boost::asio::buffer(data),
               sender_endpoint);

         typedef boost::uint32_t u32;
         const u32 iPart(
               static_cast<u32>(data[40]) << 24
               | static_cast<u32>(data[41]) << 16
               | static_cast<u32>(data[42]) << 8
               | static_cast<u32>(data[43])
               );
         const u32 fPart(
               static_cast<u32>(data[44]) << 24
               | static_cast<u32>(data[45]) << 16
               | static_cast<u32>(data[46]) << 8
               | static_cast<u32>(data[47])
               );

         using namespace boost::posix_time;
         const ptime pt(
               boost::gregorian::date(1900,1,1),
               milliseconds(
                  iPart * 1.0E3
                  + fPart * 1.0E3 / 0x100000000ULL )
               );
         return pt;
      };
};
#endif

When linking, you have to include the boost_date_time and boost_system libraries.

Update 2010-06-15: I have built this program for Microsoft Windows in another post.