C automatically assign port

Question

Hi, I just wanted to know how to use C to automatically assign a free port (and see what was used) if a specific port number is not provided.

For example, i'm using this:

struct sockaddr_in address;
address->sin_family = AF_INET;
address->sin_addr.s_addr = INADDR_ANY;
address->sin_port = htons( port );

But how can I replace the sin_port assignment and let C automatically assign for me?

Thanks!

Answer 1

Just use a value of 0.

address->sin_port = 0

Alternatively, you can completely skip the binding step if you don't care which interface you use, either.

Answer 2

Matt has already answered the "how to assign a free port" part (use sin_port = 0).

To answer the second part, i.e. "how to see what was used", use getsockname()