Question about getaddrinfo() function in socket programming

Below is a sample invoking of getaddrinfo()

status = getaddrinfo("www.example.net","1234", &hints, &server_info);

After that, the ser开发者_开发问答ver_info will point to a linked list with all kinds of address information.

I have the following questions:

Since I have clearly specified the host name and port number, the only address infos I can think of are IPv4 and IPv6 addresses. So, the length of the linked list should be 2. Is there any other kind of address info besides them?

Thanks.

The name could resolve to more than one IPv4 or IPv6 address, there is nothing to say that only one IPv4 address will be returned, for example (try it with "www.google.com" for example, you'll likely get more than one IPv4 address).

But in any case, I think the basic premise of your question is wrong. Even if there was no possibility to return more than one IPv4 and one IPv6 address today, the function is documented to return an arbitrarily-long linked list of addrinfo objects. Therefore, even if your code worked today in every situation, there is no guarantee that it would continue to work tomorrow. If the function is documented to return an arbitrarily-long linked list, then you need to be able to handle that.

You want to disconnect the physical configuration of machines with names in your mind. DNS merely maps a name to a set of addresses. A lot of hosts will only have one interface. Many hosts will have multiple (called multi-homing). DNS doesn't care about what the configuration of the machine or machines that the addresses it maps a name to is. As simple examples often a server will have interfaces on multiple networks with different addresses that will all map to the same name. Sometimes when collapsing services from different machines onto one different names will map to the same address. So don't assume any sort of 1:1 mapping between names and machines much less interfaces.