sizeof(struct sockaddr_in) : sizeof(struct sockaddr_in6), host, NI_MAXHOST, NULL, 0, NI_NUMERICHOSTsizeof(struct sockaddr_in) : sizeof(struct sockaddr_in6), host, NI_MAXHOST, NULL, 0, NI_NUMERICHOSTstructure (of type sockaddr_in or sockaddr_in6 ) of size addrlen that holds the input