Winsock binding on the same port

Question

So I recently decided to dabble into winsock and network programming a bit by using a guide I found and searching the net, but I have run into a problem which I am not really sure how i should solve.

I'm trying to make a very simple chat system, I've got a working server program and client program, and if I only use on client (sending the message back to the same client) It seems to work perfectly fine. The problem appears when I try to have multiple clients connect. I get error 10048 from WSAgetlasterror and it seems to be the bind function that is the source, more specificly the fact that I am trying to bind on the same port twice, (once for each client). From looking around on msdn and forums it seems to be possible to get around this problem by using setsockopt, but I'm not really sure what changes I should make, and also if this is the smartest solution.

I mean I want the clients to connect to the same port don't I? How else will the client program know what to connect to? Or am I just missing something? As I said I have no prior experience with winsock or any other network programming so I might be doing things in a stupid way.

int listenOnPort(int portno, SOCKET& reciever, SOCKET s){
int error = WSAStartup(0x0202, &w);

if (error)
{
    cout << "Error starting WSA";
    return false; //for some reason we couldn't start Winsock
}

if (w.wVersion != 0x0202) //Wrong Winsock version?
{
    cout << "Wrong Winsock version";
    WSACleanup();
    return false;
}

SOCKADDR_IN addr; // The address structure for a TCP socket

addr.sin_family = AF_INET; // Address family
addr.sin_port = htons(portno); // Assign port no to this socket

//Accept a connection from any IP using INADDR_ANY
//You could pass inet_addr("0.0.0.0") instead to accomplish the 
//same thing. If you want only to watch for a connection from a 
//specific IP, specify that //instead.
addr.sin_addr.s_addr = htonl(INADDR_ANY);

s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP); // Create a socket

if (s == INVALID_SOCKET)
{
    cout << "Couldn't create the socket";
    return false; //Don't continue if we couldn't create a //socket!!
}

if (bind(s, (LPSOCKADDR)&addr, sizeof(addr)) == SOCKET_ERROR)
{
    //We couldn't bind (this will happen if you try to bind to the same  
    //socket more than once)
    cout << "Error binding the socket";
    return false;
}

//Now we can start listening (allowing as many connections as possible to  
//be made at the same time using SOMAXCONN). You could specify any 
//integer value equal to or lesser than SOMAXCONN instead for custom 
//purposes). The function will not //return until a connection request is 
//made
listen(s, 1);

reciever = accept(s, NULL, NULL);
cout << "connection established\n\n";

//Don't forget to clean up with CloseConnection()!}



int main(){
e = WSAGetLastError();
listenOnPort(1337, r1, s1);
cout << "First Client connected\n\n";
e = WSAGetLastError();

listenOnPort(1338, r2, s2);
cout << "Second Client connected\n\n";
e = WSAGetLastError();

std::thread com1(communicate, r1, r2);
std::thread com2(communicate, r2, r1);

com1.join();
com2.join();

//system("pause");

closeConnection();}

For TCP you only create one single passive listening socket and bind it to your port. The clients all connect to the same port and then you accept these new connections on that single passive socket. You don't need to open one passive socket per client. — Some programmer dude

eritiro eritiro · Accepted Answer · 2015-03-08T19:18:15

You have to have 1 thread in the server dedicated to accept new connections.

The process listens to new connections and assigns a new port (in the server) for that connection, making the default port available for new connections.

in the server you will have N+1 socket ports open at any time when N is the number of clients the server has and 1 is the socket listening to new connections.

Take a look at this: http://www.codeproject.com/Articles/7785/Single-Server-With-Multiple-Clients-a-Simple-C-Imp

Winsock binding on the same port

1 Answers