This tutorial program shows how to use asio to implement a server application with TCP.

#include <ctime>
#include <iostream>
#include <string>
#include <asio.hpp>

using asio::ip::tcp;

We define the function make_daytime_string() to create the string to be sent back to the client. This function will be reused in all of our daytime server applications.

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
  {
    asio::io_context io_context;

A ip::tcp::acceptor object needs to be created to listen for new connections. It is initialised to listen on TCP port 13, for IP version 4.

    tcp::acceptor acceptor(io_context, tcp::endpoint(tcp::v4(), 13));

This is an iterative server, which means that it will handle one connection at a time. Create a socket that will represent the connection to the client, and then wait for a connection.

    for (;;)
    {
      tcp::socket socket(io_context);
      acceptor.accept(socket);

A client is accessing our service. Determine the current time and transfer this information to the client.

      std::string message = make_daytime_string();

      std::error_code ignored_error;
      asio::write(socket, asio::buffer(message), ignored_error);
    }
  }

Finally, handle any exceptions.

  catch (std::exception& e)
  {
    std::cerr << e.what() << std::endl;
  }

  return 0;
}

See the full source listing

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