Parse ISO8601 date in Objective-C (iPhone OS SDK)

Question

How do I parse "2010-04-30T00:45:48.711127" into an NSDate? (and maintain all precision)

Answer 1

It seems the NSDate only has millisecond precision.

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"yyyy-MM-dd'T'hh:mm:ss.SSSSSS"];

    NSDate *date = [dateFormatter dateFromString:@"2010-04-30T00:45:48.711127"];

    NSLog(@"%@", date);

    NSString *string = [dateFormatter stringFromDate:date];

    NSLog(@"%@", string);

    [pool drain];
    return 0;
}

That code yields the following console output:

Program loaded.
run
[Switching to process 27202]
Running…
2010-05-08 20:02:46.342 TestNSDate[27202:a0f] 2010-04-30 00:45:48 -0700
2010-05-08 20:02:46.344 TestNSDate[27202:a0f] 2010-04-30T12:45:48.711000

Debugger stopped.
Program exited with status value:0.

So "2010-04-30T00:45:48.711127" turning into "2010-04-30T00:45:48.711000" is probably not what you have in mind.

Answer 2

You have your work cut out for you.

NSDate will throw out any values past 3 decimal places for seconds. You can create a subclass of NSDate to hold on to that precision but you'll also need to implement your own parsing and custom formatters to input and display it since NSDateFormatter and CFDateFormatter, which it is built on, will also truncate precision after 3 decimal places. Depending on what you're doing though that shouldn't be all that hard.

This is a simple subclass (not implementing NSCoding or NSCopying) that will hold on to all the precision you give it.

@interface RMPreciseDate : NSDate {
    double secondsFromAbsoluteTime;
}

@end

@implementation RMPreciseDate

- (NSTimeInterval)timeIntervalSinceReferenceDate {
    return secondsFromAbsoluteTime;
}

- (id)initWithTimeIntervalSinceReferenceDate:(NSTimeInterval)secsToBeAdded {
    if (!(self = [super init]))
        return nil;

    secondsFromAbsoluteTime = secsToBeAdded;

    return self;
}

@end

You can then ask for the -timeIntervalSince1970 to get UNIX epoch time.

There is an ISO8601 date/time parser class already out there, but since it's using NSDateComponents to generate its date it's limited to full-second precision currently, but you could use it as a starting point perhaps to create more precise representations.