C Protocol-Independent Sockets

[Xx r3negade]

I am learning the C interface to protocol-independent sockets, and I'm very confused. For example I keep reading in tutorials to not use sockaddr_in and sockaddr_in6 (since these are protocol-dependent structures), but I *need* to use them in order to use getaddrinfo(). So to start out: below is a function for a host name lookup. Is there any practical way to do this without using the nasty switch statements and the protocol-dependent structures?

vector<string> DnsLookup(const string& hostString, const int& IPproto=PROTO_UNDEF) // Perform a DNS lookup
{
    struct addrinfo *res /* host information */, *p /* pointer to host information for iterating */;
    struct addrinfo hints;
    vector<string> ip_addrs; // list of IP addresses to be returned

    // Set data in the hints struct
    memset(&hints, 0, sizeof(hints));

    // Set the protocol in the hints struct
    hints.ai_socktype = SOCK_STREAM;
    switch (IPproto)
    {
    case PROTO_UNDEF:
        hints.ai_family = AF_UNSPEC;
        break;
    case IPV4:
        hints.ai_family = AF_INET;
        break;
    case IPV6:
        hints.ai_family = AF_INET6;
        break;
    }

    // Perform the lookup
    int lookup;
    if ((lookup = getaddrinfo(hostString.c_str(), NULL, &hints, &res)) != 0)
    {
       throw SockErr::SocketError(SockErr::BAD_RESOLV);
    }

    // Get all the resulting addresses, convert them to a std::string, and add them to the list of addresses
    for (p = res; p != NULL; p = p->ai_next)
    {
        char *ipver, ip_addr_buff[INET6_ADDRSTRLEN];
        void *addr;

        if (p->ai_family == AF_INET)
        { //IPv4
            struct sockaddr_in *ipv4 = reinterpret_cast<struct sockaddr_in*>(p->ai_addr);
            addr = &(ipv4->sin_addr);
            ipver = "IPv4";
        }
        else
        { //IPv6
            struct sockaddr_in6 *ipv6 = reinterpret_cast<struct sockaddr_in6*>(p->ai_addr);
            addr = &(ipv6->sin6_addr);
            ipver = "IPv6";
        }

        inet_ntop(p->ai_family, addr, ip_addr_buff, sizeof(ip_addr_buff));
        ip_addrs.push_back(static_cast<string>(ip_addr_buff));
    }

    freeaddrinfo(res);

    return ip_addrs;
}