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 5.10 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)
Generated by dwww version 1.14 on Fri Jan 24 09:26:06 CET 2025.