Sockets select() question

Hello everyone. I have a question regarding select() function. Imagine i had passed a fd_set* as the readfds parameter. Can i add some fd to the fd_set, using FD_SET, while the thread is blocked in the select call(obviously from another thread), and will that select call monitor those fd, even if they where added after the select call?
Thanks in advance!

No, you cannot modify the FD set while it's waiting on it.

Thank you!