IPv6、IPv4中的四个地址结构：sockaddr、sockaddr_in、sockaddr_in6、addrinfo的对比

struct sockaddr {
      unsigned short sa_family;     /* address family, AF_xxx */
      char sa_data[14];                  /* 14 bytes of protocol address */
};

struct sockaddr_in {
      short int sin_family;                /* Address family AF_INET */
      unsigned short int sin_port;    /* Port number */
      struct in_addr sin_addr;         /* Internet address */
      unsigned char sin_zero[8];     /* Same size as struct sockaddr */
};
struct in_addr {
      unsigned long s_addr;           /* Internet address */
};

struct sockaddr_in6 {
      sa_family_t sin6_family;         /* AF_INET6 */
      in_port_t sin6_port;               /* transport layer port # */
      uint32_t sin6_flowinfo;           /* IPv6 traffic class & flow info */
      struct in6_addr sin6_addr;    /* IPv6 address */
      uint32_t sin6_scope_id;        /* set of interfaces for a scope */
};
struct in6_addr {
      uint8_t s6_addr[16];            /* IPv6 address */
};

struct addrinfo{
      int ai_flags;                         /* AI_PASSIVE,AI_CANONNAME,AI_NUMERICHOST */
      int ai_family;                        /* AF_INET,AF_INET6 */
      int ai_socktype;                   /* SOCK_STREAM,SOCK_DGRAM */
      int ai_protocol;                   /* IPPROTO_IP, IPPROTO_IPV4, IPPROTO_IPV6 */
      size_t ai_addrlen;               /* Length */
      char *ai_cannoname;         /* */
      struct sockaddr *ai_addr;   /* struct sockaddr */
      struct addrinfo *ai_next;      /* pNext */
}