'\" t
.\" Copyright (c) 2012 YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH if_nametoindex 3 2023-03-30 "Linux man-pages 6.04"
.SH NAME
if_nametoindex, if_indextoname \- mappings between network interface
names and indexes
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <net/if.h>
.PP
.BI "unsigned int if_nametoindex(const char *" "ifname" );
.BI "char *if_indextoname(unsigned int ifindex, char *" ifname );
.fi
.SH DESCRIPTION
The
.BR if_nametoindex ()
function returns the index of the network interface
corresponding to the name
.IR ifname .
.PP
The
.BR if_indextoname ()
function returns the name of the network interface
corresponding to the interface index
.IR ifindex .
The name is placed in the buffer pointed to by
.IR ifname .
The buffer must allow for the storage of at least
.B IF_NAMESIZE
bytes.
.SH RETURN VALUE
On success,
.BR if_nametoindex ()
returns the index number of the network interface;
on error, 0 is returned and
.I errno
is set to indicate the error.
.PP
On success,
.BR if_indextoname ()
returns
.IR ifname ;
on error, NULL is returned and
.I errno
is set to indicate the error.
.SH ERRORS
.BR if_nametoindex ()
may fail and set
.I errno
if:
.TP
.B ENODEV
No interface found with given name.
.PP
.BR if_indextoname ()
may fail and set
.I errno
if:
.TP
.B ENXIO
No interface found for the index.
.PP
.BR if_nametoindex ()
and
.BR if_indextoname ()
may also fail for any of the errors specified for
.BR socket (2)
or
.BR ioctl (2).
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR if_nametoindex (),
.BR if_indextoname ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH STANDARDS
POSIX.1-2008, RFC\ 3493.
.SH HISTORY
POSIX.1-2001.
BSDi.
.SH SEE ALSO
.BR getifaddrs (3),
.BR if_nameindex (3),
.BR ifconfig (8)