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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

       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.


       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       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)
                      (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
", gai_strerror(s));

                   printf("		address: <%s>
", host);

               } else if (family == AF_PACKET && ifa->ifa_data != NULL) {
                   struct rtnl_link_stats *stats = ifa->ifa_data;

                   printf("		tx_packets = %10u; rx_packets = %10u
                          "		tx_bytes   = %10u; rx_bytes   = %10u
                          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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       description of the project, and information about reporting  bugs,  can
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