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1.\" $OpenBSD: if_indextoname.3,v 1.5 2002/03/07 22:41:12 millert Exp $
2.\" Copyright (c) 1983, 1991, 1993
3.\" The Regents of the University of California. All rights reserved.
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33.\" From: @(#)rcmd.3 8.1 (Berkeley) 6/4/93
34.\"
35.Dd May 21, 1998
36.Dt IF_NAMETOINDEX 3
37.Os
38.Sh NAME
39.Nm if_nametoindex ,
40.Nm if_indextoname ,
41.Nm if_nameindex ,
42.Nm if_freenameindex
43.Nd convert interface index to name, and vice versa
44.Sh SYNOPSIS
45.Fd #include <net/if.h>
46.Ft "unsigned int"
47.Fn if_nametoindex "const char *ifname"
48.Ft "char *"
49.Fn if_indextoname "unsigned int ifindex" "char *ifname"
50.Ft "struct if_nameindex *"
51.Fn if_nameindex "void"
52.Ft "void"
53.Fn if_freenameindex "struct if_nameindex *ptr"
54.Sh DESCRIPTION
55These functions map interface indexes to interface names (such as
56.Dq lo0 ) ,
57and vice versa.
58.Pp
59The
60.Fn if_nametoindex
61function converts an interface name specified by the
62.Fa ifname
63argument to an interface index (positive integer value).
64If the specified interface does not exist, 0 will be returned.
65.Pp
66.Fn if_indextoname
67converts an interface index specified by the
68.Fa ifindex
69argument to an interface name.
70The
71.Fa ifname
72argument must point to a buffer of at least
73.Dv IF_NAMESIZE
74bytes into which the interface name corresponding to the specified index is
75returned.
76.Pf ( Dv IF_NAMESIZE
77is also defined in
78.Aq Pa net/if.h
79and its value includes a terminating null byte at the end of the
80interface name.)
81This pointer is also the return value of the function.
82If there is no interface corresponding to the specified index,
83.Dv NULL
84is returned.
85.Pp
86.Fn if_nameindex
87returns an array of
88.Fa if_nameindex
89structures.
90.Fa if_nametoindex
91is also defined in
92.Aq Pa net/if.h ,
93and is as follows:
94.Bd -literal -offset
95struct if_nameindex {
96 unsigned int if_index; /* 1, 2, ... */
97 char *if_name; /* null terminated name: "le0", ... */
98};
99.Ed
100.Pp
101The end of the array of structures is indicated by a structure with
102an
103.Fa if_index
104of 0 and an
105.Fa if_name
106of
107.Dv NULL .
108The function returns a null pointer on error.
109The memory used for this array of structures along with the interface
110names pointed to by the
111.Fa if_name
112members is obtained dynamically.
113This memory is freed by the
114.Fn if_freenameindex
115function.
116.Pp
117.Fn if_freenameindex
118takes a pointer that was returned by
119.Fn if_nameindex
120as argument
121.Pq Fa ptr ,
122and it reclaims the region allocated.
123.Sh DIAGNOSTICS
124.Fn if_nametoindex
125returns 0 on error, positive integer on success.
126.Fn if_indextoname
127and
128.Fn if_nameindex
129return
130.Dv NULL
131on errors.
132.Sh SEE ALSO
133.Xr getifaddrs 3 ,
134.Xr networking 4
135.Pp
136R. Gilligan, S. Thomson, J. Bound, and W. Stevens,
137``Basic Socket Interface Extensions for IPv6,'' RFC2553, March 1999.
138.Sh STANDARDS
139These functions are defined in ``Basic Socket Interface Extensions for IPv6''
140.Pq RFC2533 .