quick little program that takes a network interface at argv[1] and gets the Linux interface id

resolve-net-interface-index.c

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

#ifndef NULL
#define NULL 0
#endif

int main(int argc, char *argv[]) {

    char *name = (argc < 2) ? "eth0" : argv[1];
    unsigned int idx = if_nametoindex(name); 

    if (idx == 0) {
        printf("Oh no THAT WAS NOT A VALID INTERFACE the world shall end and thus errno was set to %d!\n", errno);
    }

    else
        printf("CONGRATULATIONS you win the lottery for the index of %s was %d.\n", name, idx);

    return 0;
}