NSDateFormatter and Strings with Timezone Format "+HH:mm"

This question is a bit old, but I was having the same problem. I came up with some code which is an answer and might be useful to others...

I use a regex to parse an ISO-8601 string and grab the output into a bunch of strings you can then use to create your own string to pass into NSDateFormatter (i.e. removing colons etc) or if you always are going to want the same output string, just create that from the results of a call to NSRegularExpression.

//    ISO-8601 regex: 
//        YYYY-MM-DDThh:mm[:ss[.nnnnnnn]][{+|-}hh:mm]
// Unfortunately NSDateFormatter does not parse iso-8601 out of the box,
// so we need to use a regex and build up a date string ourselves.
static const char * REGEX_ISO8601_TIMESTAMP = 
            "\\A(\\d{4})-(\\d{2})-(\\d{2})T(\\d{2}):(\\d{2})" // Mandatory - YYYY-MM-DDThh:mm
            "(?:"
            ":(\\d{2})"                                       // Optional - :ss
            "(?:"
            "[.](\\d{1,6})"                                   // Optional - .nnnnnn
            ")?"
            ")?"
            "(?:"
            "([+-])(\\d{2}):(\\d{2})|Z"                       // Optional -[+-]hh:mm or Z
            ")?\\z";

// Extract all the parts of the timestamp
NSError *error = NULL;
NSString *regexString = [[NSString alloc] initWithUTF8String:REGEX_ISO8601_TIMESTAMP];

NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:regexString
                                                                       options:NSRegularExpressionCaseInsensitive
                                                                         error:&error];

NSArray *matches = [regex matchesInString:timestamp
                              options:0
                                range:NSMakeRange(0, [timestamp length])];

// Groups:
//
// elements start at 1 in the array returned from regex, as [0] contains the original string.
//
// MANDATORY - must exist as per ISO standard
//  1  - YYYY
//  2  - MM
//  3  - DD
//  4  - hh
//  5  - mm
// OPTIONAL (each one can be optional)
//  6  - ss
//  7  - nn (microseconds)
//  8  - offset sign (+/-)
//  9  - offset hour
//  10 - offset min
// put the parts into a string which will then be recognised by NSDateFormatter
// (which is acutally RFC822 format)

// mandatory init'd to nil, optional set to defaults.
NSString *YYYY, *MM, *DD, *hh, *mm, *ss, *nn, *sign, *Zhh, *Zmm;
NSRange tempRange;

for (NSTextCheckingResult *match in matches) {
    NSRange matchRange = [match range];
    NSInteger matchCount = [match numberOfRanges] - 1;
    NSUInteger idx = 1;

    if (idx < matchCount) {
        tempRange = [match rangeAtIndex:idx++];
        YYYY = tempRange.location != NSNotFound ? [timestamp substringWithRange:tempRange] : nil;
    }

    if (idx < matchCount) {
        tempRange = [match rangeAtIndex:idx++];
        MM   = tempRange.location != NSNotFound ? [timestamp substringWithRange:tempRange] : nil;
    }

    if (idx < matchCount) {
         tempRange = [match rangeAtIndex:idx++];
         DD   = tempRange.location != NSNotFound ? [timestamp substringWithRange:tempRange] : nil;
    }

    if (idx < matchCount) {
        tempRange = [match rangeAtIndex:idx++];
        hh   = tempRange.location != NSNotFound ? [timestamp substringWithRange:tempRange] : nil;
    }

    if (idx < matchCount) {
        tempRange = [match rangeAtIndex:idx++];
        mm   = tempRange.location != NSNotFound ? [timestamp substringWithRange:tempRange] : nil;
    }

    if (idx < matchCount) {
        tempRange = [match rangeAtIndex:idx++];
        ss   = tempRange.location != NSNotFound ? [timestamp substringWithRange:tempRange] : nil;
    }

    if (idx < matchCount) {
        tempRange = [match rangeAtIndex:idx++];
        nn = tempRange.location != NSNotFound ? [timestamp substringWithRange:tempRange] : nil;
    }

    if (idx < matchCount) {
        tempRange = [match rangeAtIndex:idx++];
        sign = tempRange.location != NSNotFound ? [timestamp substringWithRange:tempRange] : nil;
    }

    if (idx < matchCount) {
        tempRange = [match rangeAtIndex:idx++];
        Zhh  = tempRange.location != NSNotFound ? [timestamp substringWithRange:tempRange] : nil;
    }

    if (idx < matchCount) {
        tempRange = [match rangeAtIndex:idx++];
        Zmm  = tempRange.location != NSNotFound ? [timestamp substringWithRange:tempRange] : nil;
    }
}

Hope this helps someone!

Old question, but I found the right answer on someone's gist :

https://gist.github.com/soffes/840291

It parses and creates ISO-8601 Strings, and it's quicker than NSDateFormatter

Here is the code:

+ (NSDate *)dateFromISO8601String:(NSString *)string {
    if (!string) {
        return nil;
    }

    struct tm tm;
    time_t t;    

    strptime([string cStringUsingEncoding:NSUTF8StringEncoding], "%Y-%m-%dT%H:%M:%S%z", &tm);
    tm.tm_isdst = -1;
    t = mktime(&tm);

    return [NSDate dateWithTimeIntervalSince1970:t + [[NSTimeZone localTimeZone] secondsFromGMT]];
}


- (NSString *)ISO8601String {
    struct tm *timeinfo;
    char buffer[80];

    time_t rawtime = [self timeIntervalSince1970] - [[NSTimeZone localTimeZone] secondsFromGMT];
    timeinfo = localtime(&rawtime);

    strftime(buffer, 80, "%Y-%m-%dT%H:%M:%S%z", timeinfo);

    return [NSString stringWithCString:buffer encoding:NSUTF8StringEncoding];
}