NSDateFormatter: how to convert date string with 'GMT' to local NSDate?

Question

I need to convert a date string retrieved from a server, to local NSDate, the string looks like:

"Fri, 30 Nov 2012 00:35:18 GMT"

But now it is Friday, 30th Nov, 11:36 AM, so how do I convert the string to a meaningful local NSDate?

I found:

iPhone: NSDate convert GMT to local time

But looks like it does the opposite.

Answer 1

Note that NSDate's always store the date, internally, in GMT. You then use a date formatter to create a string in your local time zone. In this case, you are starting with a string so need to use the date formatter to create the date in the first place, and then use it again to create a string in your local time zone (which it defaults to when the timezone is not specified).

NSString *dateString           = @"Fri, 30 Nov 2012 00:35:18 GMT";

NSDateFormatter *dateFormatter = [NSDateFormatter new];
dateFormatter.dateFormat       = @"EEE, dd MM yyyy HH:mm:ss zzz";

NSDate *date                   = [dateFormatter dateFromString:dateString];
NSString *localDateString      = [dateFormatter stringFromDate:date];

NSLog(@"%@", localDateString);
// Results:  Thu, 29 11 2012 19:35:18 EST

Answer 2

Just use NSDateFormatter with the formatting string eee, dd MMM yyyy HH:mm:ss zzz. The Zs at the end cause it to read the time zone from the string.

So, given QA1480, sample code:

NSLocale *usLocale = [[[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"] autorelease];
NSDateFormatter *formatter = [[[NSDateFormatter alloc] init] autorelease];
[formatter setLocale:usLocale];
[formatter setDateFormat:@"eee, dd MMM yyyy HH:mm:ss zzz"];
_createdAt = [formatter dateFromString:dateString];