Sockets – How to bind to any available port


I need an app that sends an UDP packet to some network server and receives the response. The server replies to the same port number where request came from, so I first need to bind() my socket to any UDP port number.

Hardcoding the UDP port number is a bad idea, as it might be used by any other application running on the same PC.

Is there a way to bind an UDP socket to any port available? IMO it should be an effective way to quickly obtain a free port #, which is used by e.g. accept() function.

If no, then what's the best strategy to try binding and check for WSAEADDRINUSE/EADDRINUSE status: try the ports sequentially starting from from 1025, or 1025+rand(), or some other?

Best Solution

Another option is to specify port 0 to bind(). That will allow you to bind to a specific IP address (in case you have multiple installed) while still binding to a random port. If you need to know which port was picked, you can use getsockname() after the binding has been performed.

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