Is there a way to detect which millennium a NSDate is in? - ios

Question

I have an NSDate from a string of 01/01/14. Unfortunately the strings are saved with two digits so I have no idea if the year is from 1900's or 2000's. But I want create some intelligent code to guess what millennium and century the full year is. I know for a fact (based on the application I'm creating) that the year can't be below 1900 in 99% of cases.
I have converted the date to now show four digits on but it's now being displayed as 01/01/0014.
Is there a way to detect the millennium of the NSDate as 0 and make my changes accordingly?
What I really want to do is something like this (pseudo code):
if (millennium == 0 && decade < 15 && decade > 99)
{
millennium = 2;
century = 0;
// change the date to 2000's here
}
else if (millennium == 00)
{
millennium = 1;
century = 9;
// change the date to 1900's here
}

Answer 1

For starters your pseudocode isn't quite right (the first if statement is an impossible condition as decade can't be less than 15 and more than 99 at the same time).
I have created a basic solution using NSDateComponents and made up my own conditions for when to change the year which you can easily change.
NSDate *date; // this is your date
NSDateComponents* components = [[NSCalendar currentCalendar] components: NSMonthCalendarUnit | NSDateCalendarUnit | NSYearCalendarUnit fromDate:date];
if([components year] < 15) // 2000 to 2015
{
[components setYear:[components year] + 2000];
}
else if([components year] < 100) // 1915 to 1999
{
[components setYear:[components year] + 1900];
}
date = [NSCalendar currentCalendar] dateFromComponents:components];

Answer 2

there is an oldschool stuff (from the 80s) here to convert a year in 2 digits to year in 4 digits.
int finalYear = (19 + (yearIn2Digits < 50)) * 100 + yearIn2Digits;
then you can use that finalYear value to build up the proper NSDate object.
the covered interval is always 100 years and it is up you where you'd like to draw the line. the original idea worked between 1950 and 2049 – as you see in the formula, – but you can refine it for covering better your actual bounds of years.

Answer 3

I wouldn't recommend hardcoding this logic.
what if you want to convert a date which is 1908 , or 2015.
A smarter way to do this is as follows :
-(BOOL)isInCurrentDecade:(NSDate*)date{
// I don't recollect the api to extract year from NSDate
NSInteger tmpYear = [date year];
NSInteger currentYear = [[NSDate date] year];
return tmpYear > currentYear%100
}
What I am doing here is that I compare 87 , 04 , 99 with current year digit's 14. and if it's between 00 and now then its current decade. This code is more robust than your's because it's relative comparison with current date
o/p of the code is as follow as of year 2014 :
87 - > NO // in 90's
99 -> NO
04 - > YES // in 2000's
12 - > YES
Edge case occurs when your date includes 1/1/14 if you want it to be filtered in current decade replace the '>' with ' >=" .

Answer 4

Use NSDateFormatter and its property "twoDigitStartDate". You set this to the earliest date that you want to be able to enter with a two digit year. No complicated logic needed, and easy to update. Now data entry is one thing, but storing a date "with a two digit year", that's criminal.
And it handles things like "I want to be able to store anything starting with the start of the tax year 1985 in two digits, that is April 1st 1985". Then April 1st 85 will be in 1985, while March 31st 85 will be in 2085. With no effort.