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Linux 2.6 - man page for if_nameindex (linux section 3)

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

NAME
       if_nameindex, if_freenameindex - get network interface names and indexes

SYNOPSIS
       #include <net/if.h>

       struct if_nameindex *if_nameindex(void);
       void if_freenameindex(struct if_nameindex *ptr);

DESCRIPTION
       The  if_nameindex()  function returns an array of if_nameindex structures, each containing
       information about one of the network interfaces on the  local  system.	The  if_nameindex
       structure contains at least the following entries:

	       unsigned int if_index; /* Index of interface (1, 2, ...) */
	       char	   *if_name;  /* Null-terminated name ("eth0", etc.) */

       The  if_index  field contains the interface index.  The ifa_name field points to the null-
       terminated interface name.  The end of the array is indicated by entry with  if_index  set
       to zero and ifa_name set to NULL.

       The data structure returned by if_nameindex() is dynamically allocated and should be freed
       using if_freenameindex() when no longer needed.

RETURN VALUE
       On success, if_nameindex() returns pointer to the array;  on  error,  a	NULL  pointer  is
       returned, and errno is set appropriately.

ERRORS
       if_nameindex() may fail and set errno if:

       ENOBUFS
	      Insufficient resources available.

       if_nameindex()  may  also  fail	for  any  of the errors specified for socket(2), bind(2),
       ioctl(2), getsockname(2), recvmsg(2), sendto(2), or malloc(3).

VERSIONS
       The if_nameindex() function first appeared in glibc  2.1,  but  before  glibc  2.3.4,  the
       implementation  supported only interfaces with IPv4 addresses.  Support of interfaces that
       don't have IPv4 addresses is available only on kernels that support netlink.

CONFORMING TO
       RFC 3493, POSIX.1-2001.

       This function first appeared in BSDi.

EXAMPLE
       The program below demonstrates the use of the functions described on this page.	An  exam-
       ple of the output this program might produce is the following:
	   $ ./a.out
	   1: lo
	   2: wlan0
	   3: em1

   Program source
       #include <net/if.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>

       int
       main(int argc, char *argv[])
       {
	   struct if_nameindex *if_ni, *i;

	   if_ni = if_nameindex();
	   if (if_ni == NULL) {
	       perror("if_nameindex");
	       exit(EXIT_FAILURE);
	   }

	   for (i = if_ni; ! (i->if_index == 0 && i->if_name == NULL); i++)
	       printf("%u: %s\n", i->if_index, i->if_name);

	   if_freenameindex(if_ni);

	   exit(EXIT_SUCCESS);
       }

SEE ALSO
       getsockopt(2),  setsockopt(2), getifaddrs(3), if_indextoname(3), if_nametoindex(3), ifcon-
       fig(8)

COLOPHON
       This page is part of release 3.55 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					    2012-11-21				  IF_NAMEINDEX(3)


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