/* See https://www.netmeister.org/blog/epoch.html for context. */
#include <err.h>
#include <stdio.h>
#include <stdlib.h>
#include <strings.h>
#include <time.h>

int main() {
	struct tm t;

	time_t epoch = 1483228798;
	int s = 58;
	char buf[BUFSIZ];

	printf("From epoch to time, via gmtime(3) to strftime(3):\n");
	for (int i = 0; i<3; i++) {
		struct tm *gmt;
		if ((gmt = gmtime(&epoch)) == NULL) {
			err(EXIT_FAILURE, "gmtime");
			/* NOTREACHED */
		}
		(void)strftime(buf, BUFSIZ, "%Y-%m-%dT%H:%M:%S", gmt);
		(void)printf("%ld %s\n", epoch, buf);
		epoch++;
	}

	(void)printf("\nFrom time to epoch, via strptime(3) to mktime(3):\n");
	for (int i = 0; i<3; i++) {
		bzero(buf, BUFSIZ);
		snprintf(buf, BUFSIZ, "2016-12-31T23:59:%02d", s);
		s++;
		strptime(buf, "%Y-%m-%dT%H:%M:%S", &t);
		printf("%s is %ld\n", buf, mktime(&t));
	}

	bzero(buf, BUFSIZ);
	strptime("2017-01-01T00:00:00", "%Y-%m-%dT%H:%M:%S", &t);
	printf("2017-01-01T00:00:00 is %ld\n", mktime(&t));

	return 0;
}