//
// server.cpp
// ~~~~~~~~~~
//
// Copyright (c) 2003-2016 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
#include <ctime>
#include <iostream>
#include <string>
#include <boost/array.hpp>
#include <boost/asio.hpp>
using boost::asio::ip::udp;
std::string make_daytime_string()
{
  using namespace std; // For time_t, time and ctime;
  time_t now = time(0);
  return ctime(&now);
}
int main()
{
  try
  {
    boost::asio::io_service io_service;
    udp::socket socket(io_service, udp::endpoint(udp::v4(), 13));
    for (;;)
    {
      boost::array<char, 1> recv_buf;
      udp::endpoint remote_endpoint;
      boost::system::error_code error;
      socket.receive_from(boost::asio::buffer(recv_buf),
          remote_endpoint, 0, error);
      if (error && error != boost::asio::error::message_size)
        throw boost::system::system_error(error);
      std::string message = make_daytime_string();
      boost::system::error_code ignored_error;
      socket.send_to(boost::asio::buffer(message),
          remote_endpoint, 0, ignored_error);
    }
  }
  catch (std::exception& e)
  {
    std::cerr << e.what() << std::endl;
  }
  return 0;
}

Возврат кDaytime.5 - синхронный UDP дневной сервер