Boost: how do we specify "any port" for a TCP server?

1. How can I specify "pick any available port" for a TCP based server in Boost?
2. And how do I retrieve the port once a connection is accepted?

UPDATED: By "available port" I mean: the OS can pick any available port i.e. I do not want to s开发者_C百科pecify a port.

---

Question 1: Use port number 0

Question 2: Use acceptor.local_endpoint().port()