main.c

#include <arpa/inet.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char* argv[])
{
    if (argc < 2)
	exit(1);

    struct addrinfo* hints = calloc(0, sizeof(struct addrinfo));
    hints->ai_socktype = SOCK_STREAM;
    hints->ai_flags |= AI_CANONNAME;

    struct addrinfo* res;
    int ecode = getaddrinfo(argv[1], NULL, hints, &res) != 0;
    if (ecode != 0) {
	printf("error: %s\n", gai_strerror(ecode));
	return ecode;
    }

    while (res) {
	void* ptr;
	switch (res->ai_family) {
	case AF_INET:
	    ptr = &((struct sockaddr_in*)res->ai_addr)->sin_addr;
	    break;
	case AF_INET6:
	    ptr = &((struct sockaddr_in6*)res->ai_addr)->sin6_addr;
	    break;
	}
	char addr[INET6_ADDRSTRLEN];
	inet_ntop(res->ai_family, ptr, addr, sizeof(addr));
	printf("IPv%d address: %s (%s)\n", res->ai_family == PF_INET6 ? 6 : 4,
	    addr, res->ai_canonname);
	res = res->ai_next;
    }

    return 0;
}