left of '.push_back' must have class/struct/union

Question

Why can't I use the vector? Is it not initialized? can't I access the member data in a static function?

#include<iostream>
#include<boost/thread.hpp> 
#include<vector>
#include<boost/asio.hpp> 
#include <ctime>
#include <string>

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

std::string make_daytime_string()
{
    using namespace std; // For time_t, time and ctime;
    time_t now = time(0);
    return ctime(&now);
}

class maintain_overlay{

public:
    maintain_overlay():thread_(&maintain_overlay::member_list_server)
    {
        thread_.join();
    }
    static void member_list_server(){
        boost::asio::io_service io_service;

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

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

            member_list.push_back(socket.remote_endpoint());

            std::string message = make_daytime_string();

            boost::system::error_code ignored_error;
            boost::asio::write(socket, boost::asio::buffer(message),
                boost::asio::transfer_all(), ignored_error);


        }
    }

private:
    std::vector<tcp::endpoint> member_list;
    boost::thread thread_;

};

-----edit---

my server wants to maintain a list of all the incoming tcp conections? What is the best way to do this? Should I declare member_list static? When I do that I get an error error LNK2001: unresolved external symbol

Answer 1

member_list is not a static variable and is being accessed in the static member function member_list_server() . member_list can only be accessed via an instance of maintain_overlay .

Example fix using boost::bind (which Andy posted first, as I had to compile and be certain before posting):

maintain_overlay() :
    thread_(boost::bind(&maintain_overlay::member_list_server, this))

void member_list_server(){

Answer 2

Your member_list_server() function is static, and you are trying to access a data member.

That would only be possible if your member function were not static, so that it would receive an implicit this pointer on which to access the member_list data member.

You should make your function non-static and use boost::bind() when constructing your thread object:

#include <boost/bind.hpp>

maintain_overlay()
    :
    thread_(boost::bind(&maintain_overlay::member_list_server, this))
//          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
{
    thread_.join();
}

void member_list_server() {
// ...
}

Alternatively, if that is appropriate for the semantics of your class, you may make member_list a static data member. In that case, do not forget to provide a definition for it at namespace scope:

class maintain_overlay
{
    // ...
private:
    static std::vector<tcp::endpoint> member_list; // DECLARATION
//  ^^^^^^
};

std::vector<tcp::endpoint> maintain_overlay::member_list; // DEFINITION