if_nametoindex(3)

NAME

if_nametoindex, if_indextoname, if_nameindex,

if_freenameindex - provide
mappings between interface names and indexes

SYNOPSIS

#include <net/if.h>
unsigned int
if_nametoindex(const char *ifname);
char *
if_indextoname(unsigned int ifindex, char *ifname);
struct if_nameindex *
if_nameindex(void);
void
if_freenameindex(struct if_nameindex *ptr);

DESCRIPTION

The if_nametoindex() function maps the interface name speci

fied in ifname
to its corresponding index. If the specified interface does

not exist,
it returns 0.

The if_indextoname() function maps the interface index spec

ified in
ifindex to it corresponding name, which is copied into the

buffer pointed
to by ifname, which must be of at least IFNAMSIZ bytes.

This pointer is
also the return value of the function. If there is no in

terface corresponding to the specified index, NULL is returned.

The if_nameindex() function returns an array of if_nameindex

structures,
one structure per interface, as defined in the include file

The
if_nameindex structure contains at least the following en

tries:

unsigned int if_index; /* 1, 2, ... */
char *if_name; /* null terminated name:

"le0", ... */

The end of the array of structures is indicated by a struc

ture with an
if_index of 0 and an if_name of NULL. A NULL pointer is re

turned upon an
error.

The if_freenameindex() function frees the dynamic memory

that was allocated by if_nameindex().

RETURN VALUES

Upon successful completion, if_nametoindex() returns the in

dex number of
the interface. If the interface is not found, a value of 0

is returned
and errno is set to ENXIO. A value of 0 is also returned if

an error
occurs while retrieving the list of interfaces via getifad

drs(3).

Upon successful completion, if_indextoname() returns ifname.

If the
interface is not found, a NULL pointer is returned and errno

is set to
ENXIO. A NULL pointer is also returned if an error occurs

while retrieving the list of interfaces via getifaddrs(3).

The if_nameindex() returns a NULL pointer if an error occurs

while
retrieving the list of interfaces via getifaddrs(3), or if

sufficient
memory cannot be allocated.

SEE ALSO

getifaddrs(3), networking(4)

STANDARDS

The if_nametoindex(), if_indextoname(), if_nameindex(), and if_freenameindex() functions conform to RFC 2553.

HISTORY

The implementation first appeared in BSDi BSD/OS.

BSD July 15, 2002

BSD