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.\" Copyright (c) 1983, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
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.\" modification, are permitted provided that the following conditions
.\" are met:
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.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the University of
.\" California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" From: @(#)rcmd.3 8.1 (Berkeley) 6/4/93
.\" $Id: if_indextoname.3,v 1.2 1999/07/03 21:43:12 deraadt Exp $
.\"
.Dd May 21, 1998
.Dt IF_NAMETOINDEX 3
.Os KAME
.Sh NAME
.Nm if_nametoindex ,
.Nm if_indextoname ,
.Nm if_nameindex ,
.Nm if_freenameindex
.Nd convert interface index to name, and vice versa
.Sh SYNOPSIS
.Fd #include <net/if.h>
.Ft "unsigned int"
.Fn if_nametoindex "const char *ifname"
.Ft "char *"
.Fn if_indextoname "unsigned int ifindex" "char *ifname"
.Ft "struct if_nameindex *"
.Fn if_nameindex "void"
.Ft "void"
.Fn if_freenameindex "struct if_nameindex *ptr"
.Sh DESCRIPTION
The functions map interface index to readable interface name
.Po
such as
.Li ``lo0''
.Pc
, and vice versa.
.Pp
.Fn if_nametoindex
converts readable interface name to interface index
.Pp positive integer value .
If the specified interface does not exist, 0 will be returned.
.Pp
.Fn if_indextoname
converts interface index to readable interface name.
The
.Fa ifname
argument must point to a buffer of at least
.Dv IF_NAMESIZE
bytes into which the interface name corresponding to the specified index is
returned.
.Po
.Dv IF_NAMESIZE
is also defined in
.Li <net/if.h>
and its value includes a terminating null byte at the end of the
interface name.
.Pc
This pointer is also the return value of the function.
If there is no interface corresponding to the specified index,
.Dv NULL
is returned.
.Pp
.Fn if_nameindex
returns an array of
.Fa if_nameindex
structures.
.Fa if_nametoindex
is also defined in
.Li <net/if.h> ,
and is as follows:
.Bd -literal -offset
struct if_nameindex {
unsigned int if_index; /* 1, 2, ... */
char *if_name; /* null terminated name: "le0", ... */
};
.Ed
.Pp
The end of the array of structures is indicated by a structure with
an
.Fa if_index
of 0 and an
.Fa if_name
of
.Dv NULL .
The function returns a
.Dv NULL
pointer upon an error.
The memory used for this array of structures along with the interface
names pointed to by the
.Fa if_name
members is obtained dynamically.
This memory is freed by the
.Fn if_freenameindex
function.
.Pp
.Fn if_freenameindex
takes a pointer that was returned by
.Fn if_nameindex
as argument
.Pq Fa ptr ,
and it reclaims the region allocated.
.Sh DIAGNOSTICS
.Fn if_nametoindex
returns 0 on error, positive integer on success.
.Fn if_indextoname
and
.Fn if_nameindex
return
.Dv NULL
on errors.
.Sh SEE ALSO
R. Gilligan, S. Thomson, J. Bound, and W. Stevens,
``Basic Socket Interface Extensions for IPv6,'' RFC2553, March 1999.
.Sh STANDARDS
These functions are defined in ``Basic Socket Interface Extensions for IPv6''
.Pq RFC2533 .
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