why date gets changed when i try to change formate? [duplicate] - iphone

Question

This question already has an answer here:
NSDateFormatter not giving me correct
(1 answer)
Closed 9 years ago.
this is the code that i am using for changing date formate
NSLog(#"newBirthDates%#",_newwBirthDates);
NSDateFormatter *Form = [[NSDateFormatter alloc] init];
[Form setDateFormat:#"MM/dd"];
NSDate *date1 =[NSDate date];
NSString *string =[Form stringFromDate:date1];
NSLog(#"string%#",string);
NSDate *todaydate =[Form dateFromString:string];
NSLog(#"todaydate%#",todaydate);
this is what i get as output
newBirthDates(
"05/22",
"07/11",
"10/07",
"02/20"
)
newBirthDates(
"05/22",
"07/11",
"10/07",
"02/20"
)
string03/18
todaydate1970-03-17 18:30:00 +0000
now my question is why 3/18 become 03/17?? why one day get decreases

Answer 1

The answer is simple - time zones.
Take a close look at what NSLog prints out
1970-03-17 18:30:00 +0000
By default, a NSDateFormatter is set to your local timezone. That means, if your time zone is +5:30 giving it a date "1970/18/3" results in 1970-03-18 00:00:00 +0530.
However, NSLog always prints dates in GMT (zero) time zone, adding/substracting the time zone difference (5 hours and 30 minutes).
Basically, there is nothing to fix, you just have to understand how NSLog works if you want to use it to check NSDate values.

Answer 2

Your Log is showing as per string value, eliminating all important timezone differences.
Log of NSDate shows you the time from GMT.
And both the values are correct.
The sole primitive method of NSDate, timeIntervalSinceReferenceDate,
provides the basis for all the other methods in the NSDate interface.
This method returns a time value relative to an absolute reference
date—the first instant of 1 January 2001, GMT.
You must read NSDate Documentation.

Answer 3

for getting correct date you can use this one,
NSDateFormatter *Form = [[NSDateFormatter alloc] init];
[Form setDateFormat:#"MM/dd"];
[Form setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0]];
NSDate *date1 =[NSDate date];
NSString *string =[Form stringFromDate:date1];
NSLog(#"string%#",string);
NSDate *todaydate =[Form dateFromString:string];
NSLog(#"todaydate%#",todaydate);
above code will give the correct date.

Answer 4

The Main thing is TimeZone : [Form setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0]];
This is the Correct Code :
NSDateFormatter *Form = [[NSDateFormatter alloc] init];
[Form setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0]];
[Form setDateFormat:#"MM/dd"];
NSDate *date =[NSDate date];
NSString *string =[Form stringFromDate:date];
NSDate *todaydate = [Form dateFromString:string];
NSLog(#"todaydate %#",todaydate);