parsing date from string, nsdate, objective c - objective-c

Question

Below is a string represented a date
NSString *dateStr = #"2011-07-06";
And when I am trying to convert it to NSDate by doing :
NSDateFormatter *format = [[NSDateFormatter alloc] init];
[format setDateFormat:#"yyyy-MM-dd"];
NSDate *tmp = [format dateFromString:dateStr];
NSLog(#"tmp is %#",[tmp description]);
What I am getting from the console is
tmp is 2011-07-06 04:00:00 +0000
I dont understand why I am getting extra info :04:00:00 +0000 for the result
Please help if you experienced it before

Answer 1

Your code
NSString *dateStr = #"2011-07-06";
NSDateFormatter *format = [[NSDateFormatter alloc] init];
[format setDateFormat:#"yyyy-MM-dd"];
NSDate *tmp = [format dateFromString:dateStr]
will result in a NSDate object, that represents your local time at 0:00 — the beginning of the day.
but if you print a plain date object, it will result in a string that represents the time in GMT timezone, as internally all dates are normalized to that timezone.
As your string is 4 hours ahead, we can tell, that you most likely are in East Europe, maybe Moscow.
So if you want to see the string in your timezone, you need to use a NSDateFormatter to create it from the date object.
NSLog(#"tmp is %#",[formatter stringFromDate:tmp]);
to check, if it is correct, what I said, change the format to contain the time components.
formatter.format = [#"yyyy-MM-dd HH:mm"];
NSLog(#"tmp is %#",[formatter stringFromDate:tmp]);
The formatter will also take "oddities" like Leap Day, Leap Month (yes — those exits), Daylight Saving Times, Leap Seconds … in account — accordantly to the current calendar.
A great WWDC 2011 Video: Performing Calendar Calculations — a must-see for every cocoa developer.
BTW: to print a object with NSLog you dont need to call -description on it to pass in a string. NSLog will do this internally.
NSLog(#"tmp is %#", tmp);
is just fine.

Answer 2

The answer is simple, NSLog just converts the NSDate to a NSString, using its formatter with GMT (zero) timezone.
Your formatter is by default set to your default time zone, which is probably -4:00. When you print it out, NSLog converts it to 0:00, adding 4 hours.
In general, it's unsafe to parse dates without specifying their timezone.