struct hostent *host = gethostbyname2([hostName UTF8String], AF_INET);
/**Structuresreturnedbynetworkdatabaselibrary.Alladdressesare*suppliedinhostorder,andreturnedinnetworkorder(suitablefor*useinsystemcalls)网络数据库返回的结构。所有地址都是按主机顺序提供,并以网络顺序返回(适用于在系统调用中使用)。*/structhostent{