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

   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
   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

   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 appropriately.


   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.


   For   an   explanation   of   the  terms  used  in  this  section,  see

   │InterfaceAttributeValue   │
   │getifaddrs(), freeifaddrs() │ Thread safety │ MT-Safe │


   Not in POSIX.1.  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       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>

   Program source

   #define _GNU_SOURCE     /* To get defns of NI_MAXSERV and NI_MAXHOST */
   #include <arpa/inet.h>
   #include <sys/socket.h>
   #include <netdb.h>
   #include <ifaddrs.h>
   #include <stdio.h>
   #include <stdlib.h>
   #include <unistd.h>
   #include <linux/if_link.h>

   int main(int argc, char *argv[])
       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);



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


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