Get random port for UDP socket

Question

I need to create a program that will communicate with other programs on the same computer via UDP sockets. It will read commands from stdin, and some of this commands will make it to send/recieve packets without halting execution. I've read some information out there, but since I'm not familiar with socket programming and need to get this done quickly, I have the following questions:

1. I need to get a random unused port for the program to listen to, and reserve it so other programs can communicate with this and also the port isn't reserved by another program. I also need to store the port number on a variable for future usage.
2. Since the communication is across processes on the same machine, I'm wondering if I can use PF_LOCAL.

Also a code sample of the setup of such socket would be welcome, as well as an example of sending/recieving character strings.

Answer 1

Call bind() specifying port 0. That will allow the OS to pick an unused port. You can then use getsockname() to retreive the chosen port.