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           #include <sys/types.h>
           #include <ifaddrs.h>
           int getifaddrs(struct ifaddrs **ifap);
           void freeifaddrs(struct ifaddrs *ifa);


           The  getifaddrs() function creates a linked list of structures describ-
           ing the network interfaces of the local system, and stores the  address
           of  the  first item of the list in *ifap.  The list consists of ifaddrs
           structures, defined as follows:
               struct ifaddrs {
                   struct ifaddrs  *ifa_next;    /* Next item in list */
                   char            *ifa_name;    /* Name of interface */
                   unsigned int     ifa_flags;   /* Flags from SIOCGIFFLAGS */
                   struct sockaddr *ifa_addr;    /* Address of interface */
                   struct sockaddr *ifa_netmask; /* Netmask of interface */
                   union {
                       struct sockaddr *ifu_broadaddr;
                                        /* Broadcast address of interface */
                       struct sockaddr *ifu_dstaddr;
                                        /* Point-to-point destination address */
                   } ifa_ifu;
               #define              ifa_broadaddr ifa_ifu.ifu_broadaddr
               #define              ifa_dstaddr   ifa_ifu.ifu_dstaddr
                   void            *ifa_data;    /* Address-specific data */
           The ifa_next field contains a pointer to  the  next  structure  on  the
           list, or NULL if this is the last item of the list.
           The ifa_name points to the null-terminated interface name.
           The  ifa_flags  field  contains the interface flags, as returned by the
           SIOCGIFFLAGS ioctl(2) operation (see netdevice(7) for a list  of  these
           The  ifa_addr  field  points  to  a  structure containing the interface
           address.  (The sa_family subfield should be consulted to determine  the
           format  of  the  address  structure.)   This  field  may contain a null
           The ifa_netmask field points to  a  structure  containing  the  netmask
           associated  with  ifa_addr, if applicable for the address family.  This
           field may contain a null pointer.
           Depending on whether the bit IFF_BROADCAST or IFF_POINTOPOINT is set in
           ifa_flags  (only  one  can be set at a time), either ifa_broadaddr will
           contain the broadcast address associated with ifa_addr  (if  applicable


           getifaddrs() may fail and set errno for any of the errors specified for
           socket(2),  bind(2),  getsockname(2), recvmsg(2), sendto(2), malloc(3),
           or realloc(3).


           The getifaddrs() function first appeared in glibc 2.3, but before glibc
           2.3.3,  the  implementation supported only IPv4 addresses; IPv6 support
           was added in glibc 2.3.3.  Support of address families other than  IPv4
           is available only on kernels that support netlink.


           Not  in  POSIX.1-2001.   This  function  first  appeared in BSDi and is
           present on the BSD systems, but with slightly different semantics docu-
           mented--returning  one entry per interface, not per address.  This means
           ifa_addr and other fields can actually be NULL if the interface has  no
           address,  and no link-level address is returned if the interface has an
           IP address assigned.  Also, the way of choosing either ifa_broadaddr or
           ifa_dstaddr differs on various systems.


           The  addresses  returned  on  Linux  will  usually be the IPv4 and IPv6
           addresses assigned to the interface, but also one AF_PACKET address per
           interface  containing  lower-level  details about the interface and its
           physical layer.  In this case, the ifa_data field may contain a pointer
           to a struct rtnl_link_stats, defined in <linux/if_link.h> (in Linux 2.4
           and earlier, struct net_device_stats, defined in  <linux/netdevice.h>),
           which contains various interface attributes and statistics.


           The  program below demonstrates the use of getifaddrs(), freeifaddrs(),
           and getnameinfo(3).  Here is what we see when running this  program  on
           one system:
               $ ./a.out
               lo       AF_PACKET (17)
                               tx_packets =        524; rx_packets =        524
                               tx_bytes   =      38788; rx_bytes   =      38788
               wlp3s0   AF_PACKET (17)
                               tx_packets =     108391; rx_packets =     130245
                               tx_bytes   =   30420659; rx_bytes   =   94230014
               em1      AF_PACKET (17)
                               tx_packets =          0; rx_packets =          0
                               tx_bytes   =          0; rx_bytes   =          0
               lo       AF_INET (2)
                               address: <>
               wlp3s0   AF_INET (2)
                               address: <>
               lo       AF_INET6 (10)
                               address: <::1>
               wlp3s0   AF_INET6 (10)
                               address: <fe80::7ee9:d3ff:fef5:1a91%wlp3s0>
               struct ifaddrs *ifaddr, *ifa;
               int family, s, n;
               char host[NI_MAXHOST];
               if (getifaddrs(&ifaddr) == -1) {
               /* Walk through linked list, maintaining head pointer so we
                  can free list later */
               for (ifa = ifaddr, n = 0; ifa != NULL; ifa = ifa->ifa_next, n++) {
                   if (ifa->ifa_addr == NULL)
                   family = ifa->ifa_addr->sa_family;
                   /* Display interface name and family (including symbolic
                      form of the latter for the common families) */
                   printf("%-8s %s (%d)\n",
                          (family == AF_PACKET) ? "AF_PACKET" :
                          (family == AF_INET) ? "AF_INET" :
                          (family == AF_INET6) ? "AF_INET6" : "???",
                   /* For an AF_INET* interface address, display the address */
                   if (family == AF_INET || family == AF_INET6) {
                       s = getnameinfo(ifa->ifa_addr,
                               (family == AF_INET) ? sizeof(struct sockaddr_in) :
                                                     sizeof(struct sockaddr_in6),
                               host, NI_MAXHOST,
                               NULL, 0, NI_NUMERICHOST);
                       if (s != 0) {
                           printf("getnameinfo() failed: %s\n", gai_strerror(s));
                       printf("\t\taddress: <%s>\n", host);
                   } else if (family == AF_PACKET && ifa->ifa_data != NULL) {
                       struct rtnl_link_stats *stats = ifa->ifa_data;
                       printf("\t\ttx_packets = %10u; rx_packets = %10u\n"
                              "\t\ttx_bytes   = %10u; rx_bytes   = %10u\n",
                              stats->tx_packets, stats->rx_packets,
                              stats->tx_bytes, stats->rx_bytes);

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