echo_server_by_select.c

int sock = socket(PF_INET, SOCK_STREAM);
bind(sock, addr);
listen(sock);

allsock.add(sock);

while ( 1 ) {
    result = select(sock);
    if ( result > 0 ) {
        int new_sock = accept(sock, &addr);
        allsock.add(new_sock);
    }
    foreach ( sock = allsock ) {
        result = select(sock);
        if ( result > 0 ) {
            char buf[100];
            size_t size = read(new_sock, buf, 100);
            if ( size == 0 ) {
                close(new_sock);
            }
            else {
                write(new_sock, buf, size);
            }
        }
    }
}