Question

I am looking for a particular network address using a small snippet like:

  char name[INET_ADDRSTRLEN];
  struct ifaddrs *iflist;
  if (getifaddrs(&iflist) < 0)
    perror("getifaddrs");

  struct in_addr addr;
  for (struct ifaddrs *p = iflist; p; p = p->ifa_next)
    {
      if (strcmp(p->ifa_name, "lo") == 0)
        {
          addr = reinterpret_cast<struct sockaddr_in*>(p->ifa_addr)->sin_addr;
          if (inet_ntop(AF_INET, &addr, name, sizeof(name)) == NULL)
            {
              perror("inet_ntop");
              continue;
            }

          cout << name << " ---> " << if_nametoindex("lo") << " : " << addr.s_addr << endl;
        }
    }

And the output i get is:

1.0.0.0 ---> 1 : 1
127.0.0.1 ---> 1 : 16777343

I don’t understand the first result..this doesnt happen with something like eth# but it does with another interface called bond0. What is this?

Answer 1

getifaddr is non-standard. I suppose you are using it on a linux system. The man page there has the note:

The addresses returned on Linux will usually be the IPv4 and IPv6
addresses assigned to the interface, but also one AF_PACKET address
per
interface containing lower-level details about the interface and its physical layer. In this case, the ifa_data field
may contain a
pointer to a struct net_device_stats, defined in , which contains various interface attributes and
statistics.

You probably should check ifa_addr->sa_family if this has the family that you are expecting.