In UDP communication, there is accually no server or client.
A computer binds its own port and use recvfrom(), the others computer just sendto the computer IP and port without bind().

1. initialize a socket
2. bind its own port and IP(INADDR_ANY)
3. recvfrom via its own port(can get clientaddr)

1. initialize a socket
2. assign server IP and port
3. sendto the above server IP and port

In a PC whose IP is 192.168.1.126, run

g++ server.cc -o server
./server

In a PC whose IP is another, run

g++ client.cc  -o client -std=c++14 -pthread
./client

You can use lsof -i:port in client PC to verify if the port output from server.cc is consistent.