得到的就是struct hostent的指针。h_addr_list就是地址列表,最后用0结尾。
struct hostent {
char *h_name; /* canonical name of host */
char **h_aliases; /* alias list */
int h_addrtype; /* host address type */
int h_length; /* length of address */
char **h_addr_list; /* list of addresses */
};