Using Telnet to test select()

Question

I am fairly new to Linux/socket programming. I am using select to check connections in my server program (it will eventually be a chatroom server). I am using telnet to test it and something weird is happening. When I first run telnet (telnet localhost 5794), select returns 1 and adds the new connection to my master file descriptor list. Everything looks fine.

But then I try to type things in telnet and nothing happens. Select returns 0 unless I open up a new telnet session.

Is select just for finding new connections? I thought I could use it to check for input as well. Below is a copy of my code (It's a little messy at the moment because I've been furiously messing with it for the last couple hours. I'm sorry)

#include "chatpacket.cpp"
#include "serverFunctions.cpp"

#define SERVER_PORT 5794
#define MAX_PENDING 10

int main () {
  fd_set connections;
  fd_set waitingConnections;
  user *clients = new user[50];
  int serverSocket = ServerSetup (SERVER_PORT, MAX_PENDING);
  int maxFD = serverSocket;
  int ConnectionCount;

  struct timeval tv;

  FD_ZERO(&connections);
  FD_SET(0, &connections);
  FD_SET(serverSocket, &connections);

  tv.tv_sec = 1;
  tv.tv_usec = 100;

  bool shutdown = false;
  bool tmpflag = true;
  while(!shutdown) { 

    if (tmpflag == true){printf("in the loop!\n");tmpflag=false;}
    waitingConnections = connections;

    ConnectionCount = select((maxFD+1), &waitingConnections, NULL, NULL, &tv);

    if (ConnectionCount == -1) {
        ///HANDLE ERROR!!!!!!
        printf("Connection Error!");
    }
    else if (ConnectionCount > 0) {
      if (FD_ISSET(serverSocket, &waitingConnections)){
           newConnection(serverSocket, connections, maxFD, clients); //this works fine
      }
      else {
           checkConnections(clients, waitingConnections, maxFD); //the code never gets here
      }
    }

    //check keyboard
    shutdown = checkKeyboard();

  }
}

EDIT: Here is the code for newConnection:

bool newConnection(int serverSocket, fd_set& ConnectionList, int maxFD, user* userGroup){
    printf("in newConnection\n");
    struct sockaddr_storage remoteaddr;

    socklen_t addrlen = sizeof remoteaddr;

    int newFD = accept(serverSocket,(struct sockaddr *)&remoteaddr,&addrlen);
    FD_SET(newFD, &ConnectionList);

    if (newFD > maxFD)
        maxFD = newFD;

    printf("We have a new connection!!! (newConnetcion)\n");

    bool userAdded = false;
    for (int i = 0; i < 50; i++){
      if (userGroup[i].active == false){
            userGroup[i].socket = newFD;
            userGroup[i].active = true;
            userAdded = true;
                        printf("User added in the %ith position of the array.(socket number %i)\n",i,newFD);
            break;
      }
    }
    if (!userAdded)
        printf("new user was not added! (newConnetcion)\n");
}

The checkConnections function has a printf at the beginning of it so I can see whenever it enters the function. It never prints.

Answer 1

Here is the problem.

int main(int argc, char *argv[])
{
    int maxFD = ...;
    ...
    newConnection(..., maxFD, ...);
    ...
}

void newConnection(..., int maxFD, ...)
{
    ...
    if (newFD > maxFD)
        maxFD = newFD;
    ...
}

Note that there are two variables named maxFD: one in the main function and one in the newConnection function. Changing one does not change the other. Recommendation: use a global instead. (Reason: There is only one for the whole application and many functions need to access it.)

This is a very, very basic error. If you don't smack your forehead and say, "D'oh, that's obvious," then you may wish to go back and review an intro to programming book.