if_nameindex

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  struc-
       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, NULL
       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.

ATTRIBUTES
       For  an  explanation  of  the  terms  used   in   this   section,   see
       attributes(7).

       +-------------------+---------------+---------+
       |Interface          | Attribute     | Value   |
       +-------------------+---------------+---------+
       |if_nameindex(),    | Thread safety | MT-Safe |
       |if_freenameindex() |               |         |
       +-------------------+---------------+---------+

CONFORMING TO
           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 4.04 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       http://www.kernel.org/doc/man-pages/.

GNU                               2015-08-08                   IF_NAMEINDEX(3)
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