主要是如何使用两个函数的返回结构。在gethostbyname函数中，返回hostent，，linux参考手册介绍如下：
struct hostent {h_addrtype;**h_addr_list;/* list of addresses */}
具体用法可以通过以下代码看到：
main(int argc, char* argv[]){char *ptr, **pptr;char str[INET_ADDRSTRLEN];struct hostent * hptr;while (–argc > 0){ptr = *++argv;if ((hptr = gethostbyname(ptr)) == NULL){fprintf(stderr, “gethostbyname error for host%s : %s”,ptr, hstrerror(h_errno));continue;}printf(“official hostname %s\n”, hptr->h_name);for (pptr = hptr->h_aliases; *pptr != NULL; ++pptr)printf(“\talials: %s\n”, *pptr);switch (hptr->h_addrtype){case AF_INET:pptr = hptr->h_addr_list;for (; *pptr != NULL; ++pptr)printf(“\taddress: %s\n”,inet_ntop(hptr->h_addrtype, *pptr,str, sizeof(str)));break;default:fprintf(stderr, “unknown address type”);exit(EXIT_FAILURE);break;}}return 0;}
执行./hostent 后 效果如下：
getaddrinfo函数则更加复杂，但是提供了更好的接口。 这是只展示一个示例程序。
printAddressInfo(const struct addrinfo*);int main(int argc, char* argv[]){int n;struct addrinfo* res, *ressave;struct addrinfo hint;char* serv;if (argc < 2){);exit(EXIT_FAILURE);}if (argc == 2)serv = NULL;elseserv = argv[2];bzero(&hint, sizeof(hint));hint.ai_family = AF_UNSPEC;if ((n = getaddrinfo(argv[1], serv, &hint, &res)) != 0){if (argc > 2)fprintf(stderr, “Cannot get information for “”%s : %s\n\terror:%s\n”,argv[1], serv, gai_strerror(n));,argv[1], gai_strerror(n));exit(EXIT_FAILURE);}ressave = res;while (res != NULL){printAddressInfo(res);res = res->ai_next;}freeaddrinfo(ressave);exit(EXIT_SUCCESS);}void printAddressInfo(const struct addrinfo* addr){char str[INET6_ADDRSTRLEN];short port;printf(“ai_family: “);switch (addr->ai_family){case AF_INET: {struct sockaddr_in* in;printf(“ipv4\n”);in = (struct sockaddr_in *)(addr->ai_addr);port = ntohs(in->sin_port);inet_ntop(AF_INET, &in->sin_addr, str, sizeof(str));break;}case AF_INET6: {struct sockaddr_in6* in6;in6 = (struct sockaddr_in6 *)(addr->ai_addr);port = ntohs(in6->sin6_port);inet_ntop(AF_INET6, &in6->sin6_addr, str, sizeof(str));printf(“ipv6\n”);break;}default:printf(“Unknown\n”);break;}printf(“ai_socktype: “);switch (addr->ai_socktype){case SOCK_STREAM:printf(“stream\n”);break;case SOCK_DGRAM:printf(“dgram\n”);break;case SOCK_SEQPACKET:printf(“seqpacket\n”);break;case SOCK_RAW:printf(“raw\n”);break;default:printf(“others\n”);break;}printf(“protocol: “);switch (addr->ai_protocol){case IPPROTO_TCP:printf(“tcp\n”);break;case IPPROTO_UDP:printf(“udp\n”);break;case IPPROTO_SCTP:printf(“sctp\n”);break;default:printf(“others\n”);break;}printf(“address: %s\n”, str);printf(“port: %d\n”, port);printf(“canonical name: %s\n\n”, addr->ai_canonname);}
上述程序在输入：./getaddrinfo http后，效果如下：
重点在于地址的显示。结构的内容。
选择自己所爱的，爱自己所选择的。
