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       getifaddrs, freeifaddrs - get interface addresses


       #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 describing 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 flags).

       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 pointer.

       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  for  the  address  family)  or  ifa_dstaddr  will
       contain the destination address of the point-to-point interface.

       The  ifa_data field points to a buffer containing address-family-specific data; this field
       may be NULL if there is no such data for this interface.

       The data returned by getifaddrs() is dynamically  allocated  and  should  be  freed  using
       freeifaddrs() when no longer needed.


       On  success,  getifaddrs()  returns  zero;  on  error,  -1  is  returned, and errno is set


       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


       Not in POSIX.1-2001.  This function first appeared in BSDi  and  is  present  on  the  BSD
       systems,  but  with  slightly  different  semantics  documented—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      address family: 17 (AF_PACKET)
           eth0    address family: 17 (AF_PACKET)
           lo      address family: 2 (AF_INET)
                   address: <>
           eth0    address family: 2 (AF_INET)
                   address: <>
           lo      address family: 10 (AF_INET6)
                   address: <::1>
           eth0    address family: 10 (AF_INET6)
                   address: <fe80::2d0:59ff:feda:eb51%eth0>

   Program source

       #include <arpa/inet.h>
       #include <sys/socket.h>
       #include <netdb.h>
       #include <ifaddrs.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>

       main(int argc, char *argv[])
           struct ifaddrs *ifaddr, *ifa;
           int family, s;
           char host[NI_MAXHOST];

           if (getifaddrs(&ifaddr) == -1) {

           /* Walk through linked list, maintaining head pointer so we
              can free list later */

           for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) {
               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("%s  address family: %d%s\n",
                       ifa->ifa_name, family,
                       (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("\taddress: <%s>\n", host);



       bind(2), getsockname(2), socket(2), packet(7), ifconfig(8)


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