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 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 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

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

       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 4.15 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/.