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.\"     From: @(#)rcmd.3        8.1 (Berkeley) 6/4/93

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.Dd May 21, 1998

.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

.Fd #include 

.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

.Aq Pa net/if.h

and its value includes a terminating null 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

.Fa if_nameindex

structures.

.Fa if_nametoindex

is also defined in

.Aq Pa 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 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

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 .