nodename
    Points to a network node name, alias, or numeric host address
    (for example, an IPv4 dotted-decimal address or an IPv6
    hexadecimal address). An IPv6 nonglobal address with an intended
    scope zone may also be specified. This is a null-terminated
    string or NULL. NULL means the service location is local to the
    caller. The nodename and servname arguments must not both be
    NULL.
 servname
    Points to a network service name or port number. This is a null-
    terminated string or NULL; NULL returns network-level addresses
    for the specified nodename. The nodename and servname arguments
    must not both be NULL.
 hints
    Points to an addrinfo structure that contains information about
    the type of socket, address family, or protocol the caller
    supports. The NETDB.H header file defines the addrinfo structure.
    If hints is a null pointer, the behavior is the same as if
    addrinfo contained the value 0 for the ai_flags, ai_socktype
    and ai_protocol members and AF_UNSPEC for the ai_family member.
 res
    Points to a linked list of one or more addrinfo structures.