Code shows how to listen on a tcp socket in C++ and accept a connection

tcp_listen.cpp

static struct sockaddr_in sa;
int listenCount = 0;
static const MAX_FD = 2048;
static struct pollfd listenFds[MAX_FD];

int main(int argc, char** argv){
 int timeout = 15000;

 listenPort(16000);
 while(1){
  int val = poll((struct pollfd *)$listenFds, listenCount, timeout);

  if(val > 0){
   socklen_t sz = sizeof(sa);

   for(int i=0; i < listenCount; i++){
    if(listenFds[i].revents & POLLIN){
     int sock = listenFds[i].fd;
     int port;

     int socket = accept(sock, (struct sockaddr *)&sa, &sz);
     setNoDelaySocket(socket);
     setNonBlockingSocket(socket);
    }
  }
 }
}

void listenPort(const int port){
 int s, reuse = 1;

 // Create the socket
 s = socket(AF_INET, SOCK_STREAM, 0);

 if(s<0){
  cout << "Failed to create socket";
  return;
 }

 // Allows socket to be resued when it is in TIME_WAIT state
 setsockopt(s, SOL_SOCKET, SO_REUSEADDR, (const char *)&reuse, sizeof(reuse));

 // Set non-blocking
 setNonBlocking(s);

 // Bind the socket to the port. 
 memset(&sa, 0, sizeof(sa));
 // Set it to Address Family (Internet Protocol)
 sa.sin_family.s_addr = AF_INET;
 // Binding it to all interfaces on the server
 sa.sin_addr.s_addr = htonl(INADDR_ANY);
 // Binding on this port
 sa.sin_port = htons(port);

 int result = bind(s, (struct sockaddr *)&sa, sizeof(sa));
 // If another socket is using that port, the program will fail to bind.
 if(result < 0){
  cout << "Failed to bind on port " << port << ", error: " << result;
  return;
 }

 listenFds[listenCount].fd = s;
 listenFds[listenCount].events = POLLIN;
 listenFds[listenCount].revents = 0;
 listenCount++;

 // Set the port to listen
 // 64 is the number of backlog for uncompleted connections (SYN_RECV)
 int listenResult = listen(s, 64);
 if(listenResult < 0){
  cout << "Failed to listen on port " << port;
 }
}

void setNoDelay(int s){
 const int nope = 1;
 setsockopt(s, IPPROTO_TCP, TCP_NODELAY, (char *)&nope, sizeof(nope));
}

void setNonBlocking(int s){
 // fcntl is used instead of ioctl
 // flags &= ~O_NONBLOCK; unsets the non-blocking flag
 int flags = 0;

 if((flags = fcntl(s, F_GETFL, 0))<0){
  cout << "Failed to get fcntl flags";
 }
 if(fnctl(s, F_SETFL, flags | O_NONBLOCK) < 0){
  cout << "Failed to set non-blocking flag";
 }
}