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IF_NAMETOINDEX(3)        BSD Library Functions Manual        IF_NAMETOINDEX(3)

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

     #include <net/if.h>

     unsigned int
     if_nametoindex(const char *ifname);

     char *
     if_indextoname(unsigned int ifindex, char *ifname);

     struct if_nameindex *

     if_freenameindex(struct if_nameindex *ptr);

     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
     argument to an interface name.  The ifname argument must point to a
     buffer of at least IF_NAMESIZE bytes into which the interface name corre-
     sponding to the specified index is returned.  (IF_NAMESIZE is also
     defined in <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, NULL is returned.

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

     struct if_nameindex {
         unsigned int   if_index;  /* 1, 2, ... */
         char          *if_name;   /* null terminated name: "le0", ... */

     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
     pointer on error.  The memory used for this array of structures along
     with the interface names pointed to by the if_name members is obtained
     dynamically.  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.

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

     R. Gilligan, S.  Thomson, J. Bound, and W. Stevens, ``Basic Socket Inter-
     face Extensions for IPv6,'' RFC2553, March 1999.

     These functions are defined in ``Basic Socket Interface Extensions for
     IPv6'' (RFC2533).

BSD                              May 21, 1998                              BSD