IF_NAMETOINDEX(3)         OpenBSD Programmer's Manual        IF_NAMETOINDEX(3)

NAME
     if_nametoindex, if_indextoname, if_nameindex, if_freenameindex - convert
     interface index to name, and vice versa

SYNOPSIS
     #include <sys/types.h>
     #include <sys/socket.h>
     #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
     These functions map interface indexes to interface names (such as
     ``lo0''), and vice versa.

     The if_nametoindex() function converts an interface name specified by the
     ifname argument to an interface index (positive integer value).  If the
     specified interface does not exist, 0 will be returned.

     if_indextoname() converts an interface index specified by the ifindex ar-
     gument to an interface name.  The ifname argument must point to a buffer
     of at least IF_NAMESIZE bytes into which the interface name corresponding
     to the specified index is returned.  (IF_NAMESIZE is also defined 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 func-
     tion.  If there is no interface corresponding to the specified index,
     NULL is returned.

     if_nameindex() returns an array of if_nameindex structures.  if_nameindex
     is also defined in <net/if.h>, and is as follows:

           struct if_nameindex {
                   unsigned int      if_index;     /* 1, 2, ... */
                   char             *if_name;      /* NUL-terminated name */
           };

     The end of the array of structures is indicated by a structure with an
     if_index of 0 and an if_name of NULL.  The function returns a null point-
     er on error.  The memory used for this array of structures along with the
     interface names pointed to by the if_name members is obtained dynamical-
     ly.  This memory is freed by the if_freenameindex() function.

     if_freenameindex() takes a pointer that was returned by if_nameindex() as
     argument (ptr), and it reclaims the region allocated.

DIAGNOSTICS
     if_nametoindex() returns 0 on error, positive integer on success.
     if_indextoname() and if_nameindex() return NULL on errors.

SEE ALSO
     getifaddrs(3), networking(4)

     R. Gilligan, S. Thomson, J. Bound, and W. Stevens, Basic Socket Interface
     Extensions for IPv6, RFC 2553, March 1999.

STANDARDS
     These functions are defined in ``Basic Socket Interface Extensions for
     IPv6'' (RFC 2533).

OpenBSD 4.1                      May 21, 1998                                2
