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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?
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Binding to port 0 is the official documented way to bind to a OS-assigned random port. It is in the bind() documentation: "if the port is specified as zero, the service provider assigns a unique port to the application from the dynamic client port range.
Bind can be used to attach names to a sockets. Thus, say you create a software that uses a particular TCP port, you need to bind it and then, you will know the TCP port it is using.
A port binding is the configuration information that determines where and how a message will be sent or received. Depending on its type, a port binding might refer to physical locations, pipelines, or other orchestrations.
What this means is that if you bind on port 0 and actually bind to port 55441, then the next process that tries to bind to port 0 will probably get port 55442 (if it's available), and the next process will get port 55443, and so on.
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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Call sendto without calling bind first, the socket will be bound automatically (to a free port).
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