if_nameindex(3)

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

NAME
       if_nameindex,  if_freenameindex  -  get network interface names and in-
       dexes

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 if_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 if_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 ad-
       dresses.   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  at-
       tributes(7).

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

CONFORMING TO
       POSIX.1-2001, POSIX.1-2008, RFC 3493.

       This function first appeared in BSDi.

EXAMPLES
       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 5.07 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
       https://www.kernel.org/doc/man-pages/.

GNU                               2020-06-09                   IF_NAMEINDEX(3)