oc code:

NSDate *date = [NSDate date];

NSTimeZone *zone = [NSTimeZone timeZoneWithName:@"GMT"];

[NSTimeZone setDefaultTimeZone:zone];

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];

dateFormatter.dateFormat = @"EEE,d MMM yyyy HH:mm:ss 'GMT'";

dateFormatter.locale = [[NSLocal alloc] initWithLocalIdentifier:@"en_US"];

NSString *dateString = [dateFormatter stringFromDate:date];

output:

Wed, 1 Apr 2016 12:51:39 GMT