.\" $OpenBSD: if_indextoname.3,v 1.16 2015/11/21 07:48:10 jmc Exp $ .\" Copyright (c) 1983, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" 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. 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 .\" .Dd $Mdocdate: November 21 2015 $ .Dt IF_NAMETOINDEX 3 .Os .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 .In sys/types.h .In sys/socket.h .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 These functions map interface indexes to interface names (such as .Dq lo0 ) , and vice versa. .Pp The .Fn if_nametoindex function converts an interface name specified by the .Fa ifname argument to an interface index (positive integer value). If the specified interface does not exist, 0 will be returned. .Pp .Fn if_indextoname converts an interface index specified by the .Fa ifindex argument to an 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. .Pf ( Dv IF_NAMESIZE is also defined in .In net/if.h and its value includes a terminating NUL byte at the end of the interface name.) 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 .Vt if_nameindex structures. .Vt if_nameindex is also defined in .In net/if.h , and is as follows: .Bd -literal -offset indent struct if_nameindex { unsigned int if_index; /* 1, 2, ... */ char *if_name; /* NUL-terminated name */ }; .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 null pointer on 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 .Xr getifaddrs 3 , .Xr netintro 4 .Sh STANDARDS .Rs .%A R. Gilligan .%A S. Thomson .%A J. Bound .%A J. McCann .%A W. Stevens .%D February 2003 .%R RFC 3493 .%T Basic Socket Interface Extensions for IPv6 .Re