/* * Structure used by kernel to store most * addresses. */struct sockaddr {        u_short sa_family;              /* address family */        char    sa_data[14];            /* up to 14 bytes of direct address */};/* * Socket address, internet style. */struct sockaddr_in {        short   sin_family;        u_short sin_port;        struct  in_addr sin_addr;        char    sin_zero[8];};//// IPv4 Internet address// This is an ‘on-wire‘ format structure.//typedef struct in_addr {        union {                struct { UCHAR s_b1,s_b2,s_b3,s_b4; } S_un_b;                struct { USHORT s_w1,s_w2; } S_un_w;                ULONG S_addr;        } S_un;#define s_addr  S_un.S_addr /* can be used for most tcp & ip code */#define s_host  S_un.S_un_b.s_b2    // host on imp#define s_net   S_un.S_un_b.s_b1    // network#define s_imp   S_un.S_un_w.s_w2    // imp#define s_impno S_un.S_un_b.s_b4    // imp ##define s_lh    S_un.S_un_b.s_b3    // logical host} IN_ADDR, *PIN_ADDR, FAR *LPIN_ADDR;