.\"	$KAME: if_indextoname.3,v 1.10 2000/11/24 08:13:51 itojun Exp $
.\"	BSDI	Id: if_indextoname.3,v 2.2 2000/04/17 22:38:05 dab Exp
.\"
.\" Copyright (c) 1997, 2000
.\"	Berkeley Software Design, Inc.  All rights reserved.
.\"
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.\" modification, are permitted provided that the following conditions
.\" are met:
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.\"	$FreeBSD: src/lib/libc/net/if_indextoname.3,v 1.2.2.6 2002/07/29 18:33:18 ume Exp $
.\"	$DragonFly: src/lib/libc/net/if_indextoname.3,v 1.3 2006/05/26 19:39:37 swildner Exp $
.\"
.Dd "July 11, 1997"
.Dt IF_NAMETOINDEX 3
.Os
.Sh NAME
.Nm if_nametoindex ,
.Nm if_indextoname ,
.Nm if_nameindex ,
.Nm if_freenameindex
.Nd provide mappings between interface names and indexes
.Sh SYNOPSIS
.In 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
.Fn if_nametoindex
function maps the interface name specified in
.Ar ifname
to its corresponding index.
If the specified interface does not exist, it returns 0.
.Pp
The
.Fn if_indextoname
function maps the interface index specified in
.Ar ifindex
to it corresponding name, which is copied into the
buffer pointed to by
.Ar ifname ,
which must be of at least IFNAMSIZ bytes.
This pointer is also the return value of the function.
If there is no interface corresponding to the specified
index, NULL is returned.
.Pp
The
.Fn if_nameindex
function returns an array of
.Nm if_nameindex
structures, one structure per interface, as
defined in the include file
.In net/if.h .
The
.Nm if_nameindex
structure contains at least the following entries:
.Bd -literal
    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
.Nm if_index
of 0 and an
.Nm if_name
of NULL.
A NULL pointer is returned upon an error.
.Pp
The
.Fn if_freenameindex
function frees the dynamic memory that was
allocated by
.Fn if_nameindex .
.Sh RETURN VALUES
Upon successful completion,
.Fn if_nametoindex
returns the index number of the interface.
If the interface is not found, a value of 0 is returned and
.Va errno
is set to
.Er ENXIO .
A value of 0 is also returned if an error
occurs while retrieving the list of interfaces via
.Xr getifaddrs 3 .
.Pp
Upon successful completion,
.Fn if_indextoname
returns
.Ar ifname .
If the interface is not found, a NULL pointer is returned and
.Va errno
is set to
.Er ENXIO .
A NULL pointer is also returned if an error
occurs while retrieving the list of interfaces via
.Xr getifaddrs 3 .
.Pp
The
.Fn if_nameindex
returns a NULL pointer if an error
occurs while retrieving the list of interfaces via
.Xr getifaddrs 3 ,
or if sufficient memory cannot be allocated.
.Sh SEE ALSO
.Xr getifaddrs 3 ,
.Xr networking 4
.Sh STANDARDS
The
.Fn if_nametoindex ,
.Fn if_indextoname ,
.Fn if_nameindex ,
and
.Fn if_freenameindex
functions conform to RFC 2553.
.Sh HISTORY
The implementation first appeared in BSDI BSD/OS.