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GETIFADDRS(3)              Linux Programmer's Manual             GETIFADDRS(3)



NAME
       getifaddrs, freeifaddrs - get interface addresses

SYNOPSIS
       #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 describing the net-
       work 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 sub-field 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 interface.

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

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

ERRORS
       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 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.

CONFORMING TO
       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.

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  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 getname-
       info(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: <127.0.0.1>
           eth0    address family: 2 (AF_INET)
                   address: <10.1.1.4>
           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>

       int
       main(int argc, char *argv[])
       {
           struct ifaddrs *ifaddr, *ifa;
           int family, s;
           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; ifa != NULL; ifa = ifa->ifa_next) {
               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("%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));
                       exit(EXIT_FAILURE);
                   }
                   printf("\taddress: <%s>\n", host);
               }
           }

           freeifaddrs(ifaddr);
           exit(EXIT_SUCCESS);
       }

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

COLOPHON
       This page is part of release 3.22 of the Linux man-pages project.  A description of
       the  project, and information about reporting bugs, can be found at http://www.ker-
       nel.org/doc/man-pages/.



GNU                               2009-01-23                     GETIFADDRS(3)

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