域名系统(Domain Name System,DNS)主要用于主机名字与IP地址之间的映射。
#include <netdb.h>
const char *hstrerror(int err); //全局h_errno被设置错误信息
struct hostent
{
char *h_name; //地址的正式名称
char **h_aliases; //地址的预备名称的指针
int h_addrtype; //地址类型
int h_length; //地址的比特长度
char **h_addr_list; //主机网络地址指针,网络字节顺序
};
struct hostent *gethostbyname(const char *hostname);
struct hostent *gethostbyname_r(const char *hostname, struct hostent *result, char *buf, int buflen/*8192*/, int *h_errnop);
struct hostent *gethostbyaddr(const char *addr, socklen_t len, int family);
struct hostent *gethostbyaddr_r(const char *addr, int len, int type, struct hostent *result, char* buf, int buflen/*8192*/, int* h_errnop);
struct servent
{
char *s_name; //正规的服务名
char **s_aliases; //一个以空指针结尾的可选服务名队列
int s_port; //连接该服务时需要用到的端口号,返回的端口号是以网络字节顺序排列的
char *s_proto; //连接该服务时用到的协议名
};
struct servent* getservbyname(const char *servname, const char *protoname);
struct servent* getservbyport(int port, const char* protoname);
struct addrinfo
{
int ai_flags; /*in*/
int ai_family; /*in*/
int ai_socktype; /*in*/
int ai_protocol; /*in*/ /*IPPROTO_TCP/IPPROTO_UDP*/
socklen_t ai_addrlen;
struct sockaddr *ai_addr;
char *ai_canonname;
struct addrinfo *ai_next;
};
int getaddrinfo(const char *hostname, const char *service, const struct addrinfo *hints, struct addrinfo **result);
const char* gai_strerror(int error); //getaddrinfo的返回值做参数
void freeaddrinfo(struct addrinfo* ai); //形参是链表头
int getnameinfo(const struct sockaddr* sockaddr, socklen_t addrlen, char* host, socklen_t hostlen, char* serv, socklen_t servlen, int flags);