uni/inf1060/hw1/oppg3/oppgave.c

#include "oppgave.h"

#include <stdio.h>
#include <time.h>

void datetime_init(datetime* dt)
{
	dt->date.year = 0;
	dt->date.month = 0;
	dt->date.day = 0;

	dt->time.hours = 0;
	dt->time.minutes = 0;
	dt->time.seconds = 0;
}

// I expect all times to be in UTC, considering there's no timezone information
void datetime_set_date(datetime* dt, int year, int month, int day)
{
	dt->date.year = year;
	dt->date.month = month;
	dt->date.day = day;
}

// I expect all times to be in UTC, considering there's no timezone information
void datetime_set_time(datetime* dt, int hours, int minutes, int seconds)
{
	dt->time.hours = hours;
	dt->time.minutes = minutes;
	dt->time.seconds = seconds;
}

void datetime_diff(datetime* dt_from, datetime* dt_to, datetime* dt_res)
{
	struct tm tm_from = {
		.tm_sec = dt_from->time.seconds,
		.tm_min = dt_from->time.minutes,
		.tm_hour = dt_from->time.hours,
		.tm_mday = dt_from->date.day + 1, // tm is kinda inconsistent here
		.tm_yday = -1,
		.tm_isdst = 0,
		.tm_mon = dt_from->date.month,
		.tm_year = dt_from->date.year - 1900 // tm expects years since 1900
	};
	struct tm tm_to = {
		.tm_sec = dt_to->time.seconds,
		.tm_min = dt_to->time.minutes,
		.tm_hour = dt_to->time.hours,
		.tm_mday = dt_to->date.day + 1, // Still inconsistent
		.tm_yday = -1,
		.tm_isdst = 0,
		.tm_mon = dt_to->date.month,
		.tm_year = dt_to->date.year - 1900 // Not entirely sure why it's 1900
	};

	time_t time_from = mktime(&tm_from);
	time_t time_to = mktime(&tm_to);

	time_t time_res = difftime(time_to, time_from);

	// Still expecting UTC, thus gmtime instead of localtime
	struct tm tm_res = *(gmtime(&time_res));

	dt_res->time.seconds = tm_res.tm_sec;
	dt_res->time.minutes = tm_res.tm_min;
	dt_res->time.hours = tm_res.tm_hour;
	dt_res->date.day = tm_res.tm_mday - 1;
	dt_res->date.month = tm_res.tm_mon;
	dt_res->date.year = tm_res.tm_year - 70; // Because 1970 is UNIX epoch
}

void datetime_print(datetime* dt)
{
	printf("Year: %i, month: %i, day: %i. Hour: %i, minute: %i, second: %i.\n",
		dt->date.year, dt->date.month, dt->date.day,
		dt->time.hours, dt->time.minutes, dt->time.seconds);
}