Socket structs

addrinfo

-----------
addrinfo
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|
sockaddr
|

struct addrinfo 
{
  int ai_flags;          // AI_PASSIVE, AI_CANONNAME, etc.
  int ai_family;         // AF_INET, AF_INET6, AF_UNSPEC
  int ai_socktype;       // SOCK_STREAM, SOCK_DGRAM
  int ai_protocol;       // use 0 for "any"
  size_t ai_addrlen;     // size of ai_addr in bytes
  struct sockaddr *ai_addr; // struct sockaddr_in or _in6
  char *ai_canonname;    // full canonical hostname
  struct addrinfo *ai_next; // linked list, next node
};

Адреси

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

или

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
};