表头文件: #include

struct addrinfo
{
int ai_flags;
int ai_family; //AF_INET,AF_INET6,UNIX etc
int ai_socktype; //STREAM,DATAGRAM,RAW
int ai_protocol; //IPPROTO_IP, IPPROTO_IPV4, IPPROTO_IPV6 etc
size_t ai_addrlen;//length of ai_addr
char* ai_canonname; //full hostname
struct sockaddr* ai_addr; //addr of host
struct addrinfo* ai_next;
}

value of ai_falgs:
AI_PASSIVE: Socket address is intended for `bind'.
AI_CANONNAME:Request for canonical name.
AI_NUMERICHOST: Don't use name resolution.
AI_V4MAPPED: IPv4 mapped addresses are acceptable.
AI_ALL: Return IPv4 mapped and IPv6 addresses.
AI_ADDRCONFIG:Use configuration of this host to choose

定义函数:
int getaddrinfo( const char *hostname, const char *service, const struct addrinfo *hints,
struct addrinfo **result );

定义函数:const char *gai_strerror( int error );
函数说明:
该函数以getaddrinfo返回的非0错误值的名字和含义为他的唯一参数，返回一个指向对应的出错信息串的指针。

定义函数: void freeaddrinfo( struct addrinfo *ai );
函数说明:
由getaddrinfo返回的所有存储空间都是动态获取的，这些存储空间必须通过调用freeaddrinfo返回给系统。

例子：