C++ boost/asio client doesn't connect to server - c++

Question

I am learning boost/asio ad wrote 2 programs(client and server) from e-book with minor changes.
Basically it should connect to my server.
When i try to connect to outside world(some random http server ) all is good and it works but when i change destination to "localhost:40002" it says invalid argument.
client code:
#include <boost/asio.hpp>
#include <iostream>
int main () {
try {
boost::asio::io_service io_service;
boost::asio::ip::tcp::resolver::query query("localhost", 40002);
boost::asio::ip::tcp::resolver resolver(io_service);
boost::asio::ip::tcp::resolver::iterator destination = resolver.resolve(query);
boost::asio::ip::tcp::resolver::iterator end ;
boost::asio::ip::tcp::endpoint endpoint;
while ( destination != end ) {
endpoint = *destination++;
std::cout<<endpoint<<std::endl;
}
boost::asio::ip::tcp::socket socket(io_service);
socket.connect(endpoint);
}
catch (std::exception& e)
{
std::cerr << e.what() << std::endl;
}
return 0;
}
i did "netstat -l" and it showed that i am truly listening to my port so server i think works to but never less they don't connect
server code:
#include <boost/asio.hpp>
#include <iostream>
#include <string>
#include <ctime>
std::string time_string()
{
using namespace std;
time_t now = time(0);
return ctime(&now);
}
int main () {
try {
boost::asio::io_service io_service;
boost::asio::ip::tcp::acceptor acceptor(io_service, boost::asio::ip::tcp::endpoint(boost::asio::ip::tcp::v4(), 40002));
for (; ;) {
std::cout<<"Listening to"<<std::endl;
boost::asio::ip::tcp::socket socket(io_service);
acceptor.accept(socket);
std::string message = time_string();
boost::system::error_code ignored_error;
boost::asio::write(socket, boost::asio::buffer(message), boost::asio::transfer_all(), ignored_error);
}
}
catch (std::exception& e)
{
std::cerr << e.what() << std::endl;
}
return 0;
}
Can someone hint why connection doesn't happen

Answer 1

The second parameter to ip::tcp::resolver::query is the service name, not a port number:
boost::asio::ip::tcp::resolver::query query("localhost", 40002);
should be
boost::asio::ip::tcp::resolver::query query("localhost", "40002");
fyi, when I compiled your code on my system it failed:
resolve.cc: In function ‘int main()’:
resolve.cc:7: error: invalid conversion from ‘int’ to ‘boost::asio::ip::resolver_query_base::flags’
resolve.cc:7: error: initializing argument 2 of ‘boost::asio::ip::basic_resolver_query<InternetProtocol>::basic_resolver_query(const std::string&, boost::asio::ip::resolver_query_base::flags) [with InternetProtocol = boost::asio::ip::tcp]’
I'm surprised it compiled for you.