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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | EXAMPLES | SEE ALSO | COLOPHON |
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if_nameindex(3) Library Functions Manual if_nameindex(3)
if_nameindex, if_freenameindex - get network interface names and
indexes
Standard C library (libc, -lc)
#include <net/if.h>
struct if_nameindex *if_nameindex(void);
void if_freenameindex(struct if_nameindex *ptr);
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.
On success, if_nameindex() returns pointer to the array; on error,
NULL is returned, and errno is set to indicate the error.
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).
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ if_nameindex(), if_freenameindex() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
POSIX.1-2008, RFC 3493.
glibc 2.1. POSIX.1-2001. BSDi.
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.
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(void)
{
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);
}
getsockopt(2), setsockopt(2), getifaddrs(3), if_indextoname(3),
if_nametoindex(3), ifconfig(8)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.15 2025-05-17 if_nameindex(3)
Pages that refer to this page: if_nametoindex(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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