C++: BOOST-ASIO No server causes client to crash?

Question

The following code crashes at the connector boost::asio::connect(s, iterator); with the output:

before connector:
This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.

Process returned 3 (0x3)   execution time : 1.281 s
Press any key to continue.

I don't have a server running at port 4001 with the localhost connected and I wondered if there is a way to prevent this crash from occurring in case the server isn't running for some reason yet the client can still run the software somewhat. In other words is there a way to see if a server exists without crashing the program?

Heres the code

//
// blocking_tcp_echo_client.cpp
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2012 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 <cstdlib>
#include <cstring>
#include <iostream>
#include <boost/asio.hpp>

using boost::asio::ip::tcp;

enum { max_length = 1024 };

int main(int argc, char* argv[])
{
  //try
 // {
    //if (argc != 3)
    //{
    //  std::cerr << "Usage: blocking_tcp_echo_client <host> <port>\n";
    //  return 1;
    //}

    boost::asio::io_service io_service;

    tcp::resolver resolver(io_service);
    //tcp::resolver::query query(tcp::v4(), argv[1], argv[2]);
    tcp::resolver::query query(tcp::v4(), "127.0.0.1", "4001");
    tcp::resolver::iterator iterator = resolver.resolve(query);

    tcp::socket s(io_service);
    std::cout << "before connector: ";
    boost::asio::connect(s, iterator);
    std::cout << "after connector: ";
    using namespace std; // For strlen.
    std::cout << "Enter message: ";
    char request[max_length];
    std::cin.getline(request, max_length);
    size_t request_length = strlen(request);
    boost::asio::write(s, boost::asio::buffer(request, request_length));

    char reply[max_length];
    size_t reply_length = boost::asio::read(s,
        boost::asio::buffer(reply, request_length));
    std::cout << "Reply is: ";
    std::cout.write(reply, reply_length);
    std::cout << "\n";
  //}
  //catch (std::exception& e)
  //{
  //  std::cerr << "Exception: " << e.what() << "\n";
  //}

  return 0;
}

Answer 1

boost::asio::connect throws on error. So the try {} block and the catch { } block that are commented out would be useful for detecting the error rather than crashing.

resolver.resolve(query) returns .end() instead of a valid iterator if the port is not found, so you could test the iterator first before attempting to call connect

From boost documentation:

• @throws boost::system::system_error Thrown on failure. If the sequence is
• empty, the associated @c error_code is boost::asio::error::not_found.
• Otherwise, contains the error from the last connection attempt.