Problems with my unix-epoch time converter - c

Question

I wrote a simple function to fill three variables with the current year, month, and day.
However, for some reason it is not working correctly, and I can't seem to find the problem.
void getDate(int *year, int *month, int *date)
{
int epochTime,
monthLength,
functionYear,
functionMonth,
functionDate;
functionYear = 1970;
functionMonth = 1;
functionDate = 1;
epochTime = time(NULL);
while (epochTime > 1 * 365 * 24 * 60 * 60)
{
epochTime -= 1 * 365 * 24 * 60 * 60;
functionYear++;
}
monthLength = findMonthLength(functionYear, functionMonth, false);
while (epochTime > 1 * monthLength * 24 * 60 * 60)
{
printf("%d\n", epochTime);
epochTime -= 1 * monthLength * 24 * 60 * 60;
functionMonth++;
monthLength = findMonthLength(functionYear, functionMonth, false);
printf("functionMonth = %d\n", functionMonth);
}
while (epochTime > 1 * 24 * 60 * 60)
{
printf("%d\n", epochTime);
epochTime -= 1 * 24 * 60 * 60;
functionDate++;
printf("functionDate = %d\n", functionDate);
}
*year = functionYear;
*month = functionMonth;
*date = functionDate;
}
findMonthLength() returns an integer value which the length of the month it is sent. 1 = January, etc. It uses the year to test if it is a leap year.
It is currently April 3, 2013; however, my function finds April 15, and I can't seem to find where my problem is.
EDIT:
I got it. My first problem was that while I remembered to check for leap years when finding the months, I forgot about that when finding each year, which put me several days off.
My second problem was that I didn't convert to the local time zone from UTC

Answer 1

One problem could in this section:
while (epochTime > 1 * 365 * 24 * 60 * 60)
{
epochTime -= 1 * 365 * 24 * 60 * 60;
functionYear++;
}
Each iteration of this loop, a time in seconds corresponding to one normal year is subtracted. This does not account for leap years, where you need to subtract a time corresponding to 366 days.
For that section, you may want:
int yearLength = findYearLength(functionYear + 1);
while (epochTime > 1 * yearLength * 24 * 60 * 60)
{
epochTime -= 1 * yearLength * 24 * 60 * 60;
functionYear++;
yearLength = findYearLength(functionYear + 1);
}
with findYearLength(int year) being a function that returns the length in days of a given year.
One minor issue is that leap seconds are not accounted for. As only 35 of these have been added, that can be safely ignored in a calculation for a given day.

Answer 2

Why not use gmtime() or localtime() and be done with it? They return a structure with everything you need in it.

Answer 3

I made the complete solution based on yours, in Python. I hope it will help someone, someday. Cheers!
Use: getDate(unixtime)
def leapYear(year):
#returns True if the year is a leap year, return False if it isn't
if year % 400 == 0:
return True
elif year % 100 == 0:
return False
elif year % 4 == 0:
return True
else:
return False
def findMonthLength(year, month):
#returns an integer value with the length of the month it is sent.
#1 = January, etc. It uses the year to test if it is a leap year.
months1 = [0,31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
months2 = [0,31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
if (leapYear(year)==True):
return months2[month]
else:
return months1[month]
def findYearLength(year):
#returns an integer value with the length of the year it is sent.
#It uses the year to test if it is a leap year.
if leapYear(year)==True:
return 366
else:
return 365
def getDate(epoch):
SECONDS_PER_YEAR = 0
SECONDS_PER_MONTH = 0
SECONDS_PER_DAY = 24 * 60 * 60
SECONDS_PER_HOUR = 60*60
SECONDS_PER_MIN = 60
epochTime = epoch
monthLength = 0
yearLength = 0
year = 1970
month = 1
day = 1
hour = 0
minu = 0
seg = 0
#Years
yearLength = findYearLength(year)
SECONDS_PER_YEAR = yearLength * SECONDS_PER_DAY
while (epochTime >= SECONDS_PER_YEAR):
epochTime -= SECONDS_PER_YEAR
year += 1
yearLength = findYearLength(year)
SECONDS_PER_YEAR = yearLength * SECONDS_PER_DAY
#Months
monthLength = findMonthLength(year, month)
SECONDS_PER_MONTH = monthLength * SECONDS_PER_DAY
while (epochTime >= SECONDS_PER_MONTH):
epochTime -= SECONDS_PER_MONTH;
month += 1
monthLength = findMonthLength(year, month)
SECONDS_PER_MONTH = monthLength * SECONDS_PER_DAY
#Days
while (epochTime >= SECONDS_PER_DAY):
epochTime -= SECONDS_PER_DAY;
day += 1
#Hours
while (epochTime >= SECONDS_PER_HOUR):
epochTime -= SECONDS_PER_HOUR;
hour += 1
#Minutes
while (epochTime >= SECONDS_PER_MIN):
epochTime -= SECONDS_PER_MIN;
minu += 1
#Seconds
seg = epochTime
print ("%d-%d-%d %d:%d:%d") % (year, month, day, hour, minu, seg)