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 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 destina-
       tion 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 VALUE

       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),  mal-
       loc(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 sup-
       port 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  docu-
       mented--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_broad-
       addr 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>, 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	   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
",
		       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
", gai_strerror(s));
		       exit(EXIT_FAILURE);
		   }
		   printf("	address: <%s>
", 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 3.44 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

GNU
								    2012-07-07							     GETIFADDRS(3)