if_nameindex man page on ElementaryOS

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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	strucā€
       tures,  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 example 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), ifconfig(8)

COLOPHON
       This  page  is  part of release 3.54 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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