Question

I’m getting this error in C++ and I really don’t know how to get to the bottom of it:

g++ proxy.cpp -lboost_thread -lboost_filesystem -lboost_system

/tmp/ccUHa2s3.o: In function `main’:
proxy.cpp:(.text+0x1d8): undefined reference to `server::server(std::deque<boost::shared_ptr<boost::asio::io_service>, std::allocator<boost::shared_ptr<boost::asio::io_service> > > const&, int)‘
collect2: ld returned 1 exit status

I have the following source code (which I copied off http://alexott.net/common/asio-proxy-async/proxy-conn.cpp.html):

//proxy.cpp:
#include "proxy-server.hpp"

int main(int argc, char** argv) {
    try {
        int thread_num=2;
        if(argc > 1)
            thread_num=boost::lexical_cast<int>(argv[1]);
        ios_deque io_services;
        std::deque<ba::io_service::work> io_service_work;

        boost::thread_group thr_grp;

        for (int i = 0; i < thread_num; ++i) {
            io_service_ptr ios(new ba::io_service);
            io_services.push_back(ios);
            io_service_work.push_back(ba::io_service::work(*ios));
            thr_grp.create_thread(boost::bind(&ba::io_service::run, ios));
        }
        server server(io_services);   //apparently there's some error here?
        thr_grp.join_all();
    } catch (std::exception& e) {
        std::cerr << e.what() << std::endl;
    }


    return 0;
}



//proxy-server.hpp:
#ifndef _PROXY_SERVER_H
#define _PROXY_SERVER_H 1

#include "common.h"
#include "proxy-conn.hpp"

#include <deque>

typedef std::deque<io_service_ptr> ios_deque;

class server {
public:
    server(const ios_deque& io_services, int port=10001);

private:
    void start_accept();
    void handle_accept(connection::pointer new_connection, const bs::error_code& error);

    ios_deque io_services_;
    ba::ip::tcp::acceptor acceptor_;
};


#endif /* _PROXY-SERVER_H */


//proxy-server.cpp:
#include "proxy-server.hpp"

server::server(const ios_deque& io_services, int port)
    : io_services_(io_services),
      acceptor_(*io_services.front(), ba::ip::tcp::endpoint(ba::ip::tcp::v4(), port)) {
    start_accept();
}

void server::start_accept() {
    // Round robin.
    io_services_.push_back(io_services_.front());
    io_services_.pop_front();
    connection::pointer new_connection = connection::create(*io_services_.front());

    acceptor_.async_accept(new_connection->socket(),
                           boost::bind(&server::handle_accept, this, new_connection,
                                       ba::placeholders::error));
}

void server::handle_accept(connection::pointer new_connection, const bs::error_code& error) {
    if (!error) {
        new_connection->start();
        start_accept();
    }
}

Can someone please point me in the right direction as to how to fix this error?

---

Edit

I now get the following error:

g++ proxy.cpp proxy-server.cpp -lboost_thread -lboost_filesystem -lboost_system

/tmp/ccl3DHn7.o: In function `server::handle_accept(boost::shared_ptr<connection>, boost::system::error_code const&)‘:
proxy-server.cpp:(.text+0x250): undefined reference to `connection::start()‘
/tmp/ccl3DHn7.o: In function `connection::create(boost::asio::io_service&)‘:
proxy-server.cpp:(.text._ZN10connection6createERN5boost4asio10io_serviceE[connection::create(boost::asio::io_service&)]+0x29): undefined reference to `connection::connection(boost::asio::io_service&)‘
collect2: ld returned 1 exit status`

Answer 1

It means it cannot find the implementation of the server constructor. Have you written one which you do not show above?

EDIT: Ok, so you’ve written one, but you’re not passing it to the compiler. You need to have proxy-server.cpp in your g++ line.

EDIT 2: It is not enough to just compile the file containing main and include the header files. You need to provide all the cpp files to g++, or it will not be able to link your program.

g++ proxy.cpp proxy-server.cpp proxy-conn.cpp -lboost_thread -lboost_filesystem -lboost_system