if_indextoname(3)

NAME
     if_indextoname, if_nametoindex, if_nameindex, if_freenameindex -
     functions for converting interface index to name, and vice versa.

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/types.h>
     #include <sys/socket.h>
     #include <net/if.h>

     char *if_indextoname(unsigned int ifindex, char *ifname);
     unsigned int if_nametoindex(const char *ifname);
     struct 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_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 and
     errno is set to ENXIO.  If there was a system error (such as running out
     of memory), errno is set to ENOMEM.

     if_nametoindex converts readable interface name to interface index
     positive integer value.  If the specified interface does not exist, 0
     will be 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;   /* 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 and errno is set to the approprate value.  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.

STANDARDS
     These functions are defined in "Basic Socket Interface Extensions for
     IPv6" (RFC2553).