When to use bind() when programming with sockets?

Question

I am writing a simple sender and receiver program to transit using UDP so it's connectionless, but I am having a problem figuring out whether my receiver program needs to call bind() or the server and/or both. My receiver program(client) will sit in an infinite loop waiting to receive data from the sender(server) and then it will print out the data. I'm not quite sure what bind() does exactly besides associating an address/port with a specific socket. Why is it that I need to call bind()?

Answer 1

You need to call bind(2) so that the OS knows which application to route network packets to. When you call bind with a specific port for a given protocol (e.g. TCP or UDP), you're asking it "whenever you see a network packet on port XXXXX, please give it to me".

Say, for example, that two copies of your program were running, and they both wanted to listen for UDP packets on the same port. If they both call bind on the same port, then one will succeed and one will fail, since the OS can arbitrate who is bound to each port. Then, any packet received on that port will be given to whichever instance of the program succeeded at binding to that port.

Answer 2

when you want to make a socket a fixed address or/and port, you use bind.

Answer 3

See you when developing a Network Application you need to specify "Address and Port" to Bind because if you want to set it for Localhost your application is not able to communicate with the all over the network its only for your system which its communicating.. If you set it with your Network address it's not able to communicate as localhost Its only communicate with the network and If you set it to 0 then It can be use as both for localhost and Network.