udp poll sockets and multicast in C++ - c++

Question

1) I am trying to make a simple game server using UDP. Would my code be the correct way to check if there is any reads from a single socket?
2) I want to recieve data from one user on a request ( he wants to move left), then update where the server thinks he or she is located, then broadcast the x , y coordinates. How would I implement a multicast reply with a different socket?
void run()
{
//logging file
ofstream log;
log.open("server_log.txt", ios::out | ios::app);
struct sockaddr_in myaddr; // our address
struct sockaddr_in remaddr; // remote address
socklen_t addrlen = sizeof(remaddr);
int recvlen;
int fd; // server socket that listens
int fd_reply; // this will be used to reply to all users
char buf[BUFSIZE]; // receive buffer
memset((char *)&myaddr, 0, sizeof(myaddr));
myaddr.sin_family = AF_INET;
myaddr.sin_addr.s_addr = htonl(INADDR_ANY);
myaddr.sin_port = htons(PORT);
if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
std::time_t result = std::time(nullptr);
log << "Error: cannot create socket! " << "TIMESTAMP: " << std::asctime(std::localtime(&result)) << endl;
log.close();
return 0;
}
if (bind(fd, (struct sockaddr *)&myaddr, sizeof(myaddr)) < 0) {
std::time_t result = std::time(nullptr);
log << "Error: bind failed " << "TIMESTAMP: " << std::asctime(std::localtime(&result)) << endl;
log.close();
return 0;
}
pollfd fds;
memset(fds, 0, sizeof(fds));
fds[0].fd = fd;
fds[0].events = POLLIN;
while (1)
{
int rv = poll(ufds, 1, 3500);
if (rv == -1)
{
// error occured
}
else if (rv == 0)
{
//time out
}
else
{
//check for events on fd
if (fds.revents & POLLIN)
{
recvlen = recvfrom(fd, buf, BUFSIZE, 0, (struct sockaddr *)&remaddr, &addrlen);
}
}
}
}

Answer 1

Yes it looks okay.
Keep a list of all clients, and then in a loop send to all of them. To populate this list, all clients need to contact the server the first thing they do.