c++ how to use select to see if a socket has closed

Question

Can someone provide me an example of how to use select() to see if a client has closed the connection on a socket?

FYI. I\'m using linux.

Thanks!

Answer 1

You don't need to do a select() followed by ioctl(). You can instead do a non-blocking peek on the socket to see if it returns 0.

bool isclosed (int sock) {
    char x;
interrupted:
    ssize_t r = ::recv(sock, &x, 1, MSG_DONTWAIT|MSG_PEEK);
    if (r < 0) {
        switch (errno) {
        case EINTR:     goto interrupted;
        case EAGAIN:    break; /* empty rx queue */
        case ETIMEDOUT: break; /* recv timeout */
        case ENOTCONN:  break; /* not connected yet */
        default:        throw(errno);
        }
    }
    return r == 0;
}