doc/html/boost_asio/example/cpp11/futures/daytime_client.cpp
//
// daytime_client.cpp
// ~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2022 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 <array>
#include <future>
#include <iostream>
#include <thread>
#include <boost/asio/io_context.hpp>
#include <boost/asio/ip/udp.hpp>
#include <boost/asio/use_future.hpp>
using boost::asio::ip::udp;
void get_daytime(boost::asio::io_context& io_context, const char* hostname)
{
try
{
udp::resolver resolver(io_context);
std::future<udp::resolver::results_type> endpoints =
resolver.async_resolve(
udp::v4(), hostname, "daytime",
boost::asio::use_future);
// The async_resolve operation above returns the endpoints as a future
// value that is not retrieved ...
udp::socket socket(io_context, udp::v4());
std::array<char, 1> send_buf = {{ 0 }};
std::future<std::size_t> send_length =
socket.async_send_to(boost::asio::buffer(send_buf),
*endpoints.get().begin(), // ... until here. This call may block.
boost::asio::use_future);
// Do other things here while the send completes.
send_length.get(); // Blocks until the send is complete. Throws any errors.
std::array<char, 128> recv_buf;
udp::endpoint sender_endpoint;
std::future<std::size_t> recv_length =
socket.async_receive_from(
boost::asio::buffer(recv_buf),
sender_endpoint,
boost::asio::use_future);
// Do other things here while the receive completes.
std::cout.write(
recv_buf.data(),
recv_length.get()); // Blocks until receive is complete.
}
catch (std::system_error& e)
{
std::cerr << e.what() << std::endl;
}
}
int main(int argc, char* argv[])
{
try
{
if (argc != 2)
{
std::cerr << "Usage: daytime_client <host>" << std::endl;
return 1;
}
// We run the io_context off in its own thread so that it operates
// completely asynchronously with respect to the rest of the program.
boost::asio::io_context io_context;
auto work = boost::asio::make_work_guard(io_context);
std::thread thread([&io_context](){ io_context.run(); });
get_daytime(io_context, argv[1]);
io_context.stop();
thread.join();
}
catch (std::exception& e)
{
std::cerr << e.what() << std::endl;
}
return 0;
}