if_indextoname.c

#include <net/if.h>
#include <stdlib.h>
#include <stdio.h>

int main(int argc, char **argv)
{
        char ifname[IF_NAMESIZE+1];
        int ifindex = atoi(argv[1]);
        if (if_indextoname( ifindex, ifname) != NULL)
                puts(ifname);
}