IF_NAMETOINDEX(3)

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

LIBRARY
libc

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
The functions map interface index to readable interface name (such as “lo0”), and vice versa.

if_nametoindex() converts readable interface name to interface index

If the specified interface does not exist, 0 will be returned.

if_indextoname() converts interface index to readable 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 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 upon an 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 Interface Extensions for IPv6,'' RFC2553, March 1999.

HISTORY
The implementation first appeared in WIDE Hydrangea IPv6 protocol stack kit.

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