Question

I’m writing a program in C in which the server listens on a well known port, waits for client to connect, and then creates a random port for the client to use and send this port number back to the client. My main difficulty is how to create a “random” port. Should I just be using srand and create a random 4 digit port is the usable range? Or is there a better way to do this? I know that if I use port 0 a port will be chosen for me but the problem here is the fact that I don’t think i can “get/see” the actual value of the port so that I can send this port number back to the client.

Thanks…

Answer 1

Binding port 0 is the solution. It gives you an arbitrary port, not a random port, but this is what many applications do (e.g. FTP etc).

After binding, you can use getsockname to figure out which port you got.