Question

Hey everyone,
I need to convert the following format into a new format using NSDateFormatter. I am quite seasoned with this but for some reason I can’t remember the correct formatting information for this foramt:

‘Fri, 25 Mar 2011 10:16:00 -0700’.

I tried using this format:’aaa, dd bbb YYYY HH:MM:SS ZHHMM’ but it doesn’t work, gives me a date way in the past.

I also need to convert it into the Eastern Time Zone when creating a new date. It says ‘+0000’ but what is that normalized to?

Any help appreciated,
Thanks,
~Arash

Answer 1

Typically when you’re getting date strings like that, you know what locale they’re coming from, and you would take an NSDateFormatter, set its locale using setLocale:, set its date and time formatting using setDateStyle: and setTimeStyle: and then use dateFromString:. If you can’t do that because you don’t know the locale, then you can use the UNIX functions:

struct tm  sometime;
const char *formatString = "%a, %d %b %Y %T %z";
strptime_l("Fri, 25 Mar 2011 10:16:00 -0700", formatString, &sometime, NULL);
NSDate *newDate = [NSDate dateWithTimeIntervalSince1970: mktime(&sometime)];

Next, you want to “convert” newDate to Eastern Time. I say “convert” because NSDates don’t contain any information about timezones—they’re just represented as a number of seconds since January 1, 2001—so the idea of conversion makes no sense. When you print out an NSDate you get it in UTC (+0000), but an NSDate is no more associated with that timezone than with any other.

What you want to do instead is to create a dateFormatter with the right timezone and use it to output the date:

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setLocale:[[NSLocale alloc] initWithLocaleIdentifier:@"en_UK"]];
[dateFormatter setTimeZone:[NSTimeZone timeZoneWithAbbreviation:@"EST"]];
[dateFormatter setTimeStyle:NSDateFormatterShortStyle];
[dateFormatter setDateStyle:NSDateFormatterMediumStyle];
NSLog(@"%@",[dateFormatter stringFromDate:newDate]);
// Outputs 25 Mar 2011 13:16