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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.)

       The  ifa_netmask  field  points  to  a structure containing the netmask
       associated with ifa_addr, if applicable for the address family.

       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 only supported IPv4 addresses; IPv6 support
       was added in glibc 2.3.3.  Support of address families other than  IPv4
       is only available 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  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) {
               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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