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# if_nametoindex

    IF_NAMETOINDEX(3)       System Library Functions Manual      IF_NAMETOINDEX(3)

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

    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
         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.

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

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

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

    BSD                              May 21, 1998                              BSD

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