#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <net/if.h>
#include <unistd.h>
#include <stropts.h>
#include <sys/sockio.h>

int main(int argc, char **argv)
{
	const int s = socket(AF_INET, SOCK_DGRAM, 0);
	struct ifconf ifc;
	const struct ifreq *p;
	const size_t guess = 100;   /* hope no more than this # of interfaces */
	size_t n;                   /* actual number of interfaces */

	if (s < 0) {
		perror(argv[0]);
		return 1;
	}

	ifc.ifc_len = guess * sizeof (struct ifreq);
	ifc.ifc_buf = malloc(ifc.ifc_len);
	if (ifc.ifc_buf == NULL) {
		perror(argv[0]);
		return 2;
	}

	if (ioctl(s, SIOCGIFCONF, &ifc) < 0) {
		perror(argv[0]);
		return 3;
	}

	n = ifc.ifc_len / sizeof (struct ifreq);
	if (n > guess) {
		fprintf(stderr,
			"%s: increase guess to at least %d and try again.\n",
			argv[0], n);
		return 4;
	}

	for (p = ifc.ifc_req; p < ifc.ifc_req + n; ++p) {

		const struct sockaddr_in *const address =
			(struct sockaddr_in *)&p->ifr_addr;

		char dotted[INET6_ADDRSTRLEN];
		if (inet_ntop(address->sin_family, &address->sin_addr, dotted,
			sizeof dotted) == NULL) {
			fprintf(stderr, "%s: inet_ntop failed\n", argv[0]);
			return 5;
		}

		printf("%s %d %s\n", p->ifr_name, address->sin_family, dotted);
	}

	return EXIT_SUCCESS;
}