a.c

#include <sys/types.h>

#include <arpa/inet.h>
#include <netdb.h>
#include <netinet/in.h>
#include <sys/socket.h>

#include <err.h>
#include <stdio.h>
#include <string.h>

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

	int err;
	struct addrinfo hints, *res, *p;
	const char *host = "pkg.freebsd.org";
	const char *service = "http";
	void *addr;
	char *ipver;
	struct sockaddr_in *ipv4;
	struct sockaddr_in6 *ipv6;
	char ipstr[INET6_ADDRSTRLEN];

	memset(&hints, 0, sizeof(hints));
	hints.ai_family = AF_UNSPEC;
	hints.ai_socktype = SOCK_STREAM;
	hints.ai_flags = AI_ADDRCONFIG;

	err = getaddrinfo(host, service, &hints, &res);
	if (err != 0)
		errx(err, "getaddrinfo: %s", gai_strerror(err));

	for (p = res; p != NULL; p = p->ai_next) {

		if (p->ai_family == AF_INET) {
			ipv4 = (struct sockaddr_in *)p->ai_addr;
			addr = &(ipv4->sin_addr);
			ipver = "IPv4";
		} else if (p->ai_family == AF_INET6) {
			ipv6 = (struct sockaddr_in6 *)p->ai_addr;
			addr = &(ipv6->sin6_addr);
			ipver = "IPv6";
		} else {
			printf("unknown ai_family\n");
		}

		inet_ntop(p->ai_family, addr, ipstr, sizeof(ipstr));
		printf(" %s: %s\n", ipver, ipstr);
	}

	return 0;
}