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.\" Copyright (c) 2012 YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
.\" and Copyright (c) 2012 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of
.\" this manual under the conditions for verbatim copying, provided that
.\" the entire resulting derived work is distributed under the terms of
.\" a permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume
.\" no responsibility for errors or omissions, or for damages resulting
.\" from the use of the information contained herein. The author(s) may
.\" not have taken the same level of care in the production of this
.\" manual, which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\" %%%LICENSE_END
.\"
.TH IF_NAMEINDEX 3 2012-11-21 "GNU" "Linux Programmer's Manual"
.SH NAME
if_nameindex, if_freenameindex \- get network interface names and indexes
.SH SYNOPSIS
.nf
.B #include <net/if.h>
.sp
.BI "struct if_nameindex *if_nameindex(void);
.BI "void if_freenameindex(struct if_nameindex *" "ptr" );
.fi
.SH DESCRIPTION
The
.BR if_nameindex ()
function returns an array of
.I if_nameindex
structures, each containing information
about one of the network interfaces on the local system.
The
.I if_nameindex
structure contains at least the following entries:
.sp
.in +4n
.nf
unsigned int if_index; /* Index of interface (1, 2, ...) */
char *if_name; /* Null-terminated name ("eth0", etc.) */
.fi
.in
.PP
The
.I if_index
field contains the interface index.
The
.I ifa_name
field points to the null-terminated interface name.
The end of the array is indicated by entry with
.I if_index
set to zero and
.I ifa_name
set to NULL.
.PP
The data structure returned by
.BR if_nameindex ()
is dynamically allocated and should be freed using
.BR if_freenameindex ()
when no longer needed.
.SH RETURN VALUE
On success,
.BR if_nameindex ()
returns pointer to the array;
on error, NULL is returned, and
.I errno
is set appropriately.
.SH ERRORS
.BR if_nameindex ()
may fail and set
.I errno
if:
.TP
.B ENOBUFS
Insufficient resources available.
.PP
.BR if_nameindex ()
may also fail for any of the errors specified for
.BR socket (2),
.BR bind (2),
.BR ioctl (2),
.BR getsockname (2),
.BR recvmsg (2),
.BR sendto (2),
or
.BR malloc (3).
.SH VERSIONS
The
.BR 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.
.SH CONFORMING TO
RFC\ 3493, POSIX.1-2001.
This function first appeared in BSDi.
.SH 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:
.in +4n
.nf
$ \fB./a.out\fI
1: lo
2: wlan0
3: em1
.fi
.in
.SS Program source
.nf
#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);
}
.fi
.SH SEE ALSO
.BR getsockopt (2),
.BR setsockopt (2),
.BR getifaddrs (3),
.BR if_indextoname (3),
.BR if_nametoindex (3),
.BR ifconfig (8)
.SH COLOPHON
This page is part of release 3.74 of the Linux
.I 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/.
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