4. Jumping from IPv4 to IPv6

But I just want to know what to change in my code to get it going with IPv6! Tell me now!

Ok! Ok!

Almost everything in here is something I've gone over, above, but it's the short version for the impatient. (Of course, there is more than this, but this is what applies to the guide.)

1. First of all, try to use getaddrinfo() to get all the struct sockaddr info, instead of packing the structures by hand. This will keep you IP version-agnostic, and will eliminate many of the subsequent steps.
2. Any place that you find you're hard-coding anything related to the IP version, try to wrap up in a helper function.
3. Change AF_INET to AF_INET6.
4. Change PF_INET to PF_INET6.

5. Change INADDR_ANY assignments to in6addr_any assignments, which are slightly different:

   struct sockaddr_in sa;
   struct sockaddr_in6 sa6;
   
   sa.sin_addr.s_addr = INADDR_ANY;  // use my IPv4 address
   sa6.sin6_addr = in6addr_any; // use my IPv6 address

   Also, the value IN6ADDR_ANY_INIT can be used as an initializer when the struct in6_addr is declared, like so:

   struct in6_addr ia6 = IN6ADDR_ANY_INIT;

6. Instead of struct sockaddr_in use struct sockaddr_in6, being sure to add "6" to the fields as appropriate (see structs, above). There is no sin6_zero field.
7. Instead of struct in_addr use struct in6_addr, being sure to add "6" to the fields as appropriate (see structs, above).
8. Instead of inet_aton() or inet_addr(), use inet_pton().
9. Instead of inet_ntoa(), use inet_ntop().
10. Instead of gethostbyname(), use the superior getaddrinfo().
11. Instead of gethostbyaddr(), use the superior getnameinfo() (although gethostbyaddr() can still work with IPv6).
12. INADDR_BROADCAST no longer works. Use IPv6 multicast instead.

Et voila!