Question

I’m getting some strange output from a NSDateFormatter. I’m converting a date from GMT to the system time zone, which is EDT. This should be -4 hours from GMT.

-(NSDate*)parseDate:(NSString*)inStrDate {

NSLog(@"Date To Parse %@", inStrDate);
NSDateFormatter* dtFormatter = [[NSDateFormatter alloc] init];
[dtFormatter setLocale:[NSLocale systemLocale]];
[dtFormatter setTimeZone:[NSTimeZone systemTimeZone]];
[dtFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss +0000"];
NSDate* dateOutput = [dtFormatter dateFromString:inStrDate];
NSLog(@"Parsed Date %@ %@", dateOutput, [NSTimeZone systemTimeZone]);

return dateOutput;

}

Log output:

2012-09-15 22:32:53.358 Date To Parse 2012-09-16 02:32:53 +0000
2012-09-15 22:32:53.360 Parsed Date 2012-09-16 06:32:53 +0000 America/New_York (EDT) offset -14400 (Daylight)

But it’s returning +4 hours instead of -4. So where it should output 22.30 EDT (02.30 GMT) it’s actually returning 06.30 EDT. Which is 8 hours in the future.

Can anyone help me understand if I’m going wrong somewhere here? I’m scratching my head but I can’t figure out why this wont seem to work.

Thanks

Answer 1

You just got the dateFormatter the wrong way around.
When you do

[dtFormatter setTimeZone:[NSTimeZone systemTimeZone]];

you’re telling it that the input Date is in terms of your time zone. Therefore, it converts it to GMT and outputs the time +4 hours. To do it the other way around you can use this:

NSDateFormatter* df_local = [[NSDateFormatter alloc] init];
[df_local setTimeZone:[NSTimeZone timeZoneWithName:@"America/New_York"]];
[df_local setDateFormat:@"yyyy.MM.dd' 'HH:mm:ss zzz"];

NSDate* dateOutput = [dtFormatter dateFromString:dateString];
NSLog(@"Parsed Date in GMT %@", dateOutput);
NSString *yourLocalDate = [df_local stringFromDate:dateOutput];
NSLog(@"in EDT %@",yourLocalDate);

This logs

2012-09-16 05:23:53.297 TestingApplication[10109:c07] Date To Parse 2012-09-16 02:32:53 +0000
2012-09-16 05:23:53.302 TestingApplication[10109:c07] Parsed Date in GMT 2012-09-16 02:32:53 +0000
2012-09-16 05:23:53.304 TestingApplication[10109:c07] in EDT 2012.09.15 22:32:53 EDT