getifaddrs

       #include <sys/types.h>
       #include <ifaddrs.h>

       int getifaddrs(struct ifaddrs **ifap);

       void freeifaddrs(struct ifaddrs *ifa);

DESCRIPTION
       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
       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.

       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).

VERSIONS
       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.

ATTRIBUTES
       For   an   explanation   of   the  terms  used  in  this  section,  see
       attributes(7).

       +----------------------------+---------------+---------+
       |Interface                   | Attribute     | Value   |
       +----------------------------+---------------+---------+
       |getifaddrs(), freeifaddrs() | Thread safety | MT-Safe |
       +----------------------------+---------------+---------+

CONFORMING TO
       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.

NOTES
       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.

EXAMPLE
       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)

       #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) {
               perror("getifaddrs");
               exit(EXIT_FAILURE);
           }

           /* 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)
                   continue;

               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",
                      ifa->ifa_name,
                      (family == AF_PACKET) ? "AF_PACKET" :
                      (family == AF_INET) ? "AF_INET" :
                      (family == AF_INET6) ? "AF_INET6" : "???",
                      family);

               /* 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));
                       exit(EXIT_FAILURE);
                   }

                   printf("\t\taddress: <%s>\n", host);

               } else if (family == AF_PACKET && ifa->ifa_data != NULL) {

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

COLOPHON
       This page is part of release 4.04 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       http://www.kernel.org/doc/man-pages/.

GNU                               2015-07-23                     GETIFADDRS(3)
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