parse method Null safety

DateTime parse (
  1. String formattedString
)

Constructs a new DateTime instance based on formattedString.

The formattedString must not be null. Throws a FormatException if the input string cannot be parsed.

The function parses a subset of ISO 8601 which includes the subset accepted by RFC 3339.

The accepted inputs are currently:

  • A date: A signed four-to-six digit year, two digit month and two digit day, optionally separated by - characters. Examples: "19700101", "-0004-12-24", "81030-04-01".
  • An optional time part, separated from the date by either T or a space. The time part is a two digit hour, then optionally a two digit minutes value, then optionally a two digit seconds value, and then optionally a '.' or ',' followed by at least a one digit second fraction. The minutes and seconds may be separated from the previous parts by a ':'. Examples: "12", "12:30:24.124", "12:30:24,124", "123010.50".
  • An optional time-zone offset part, possibly separated from the previous by a space. The time zone is either 'z' or 'Z', or it is a signed two digit hour part and an optional two digit minute part. The sign must be either "+" or "-", and can not be omitted. The minutes may be separated from the hours by a ':'. Examples: "Z", "-10", "+01:30", "+1130".

This includes the output of both toString and toIso8601String, which will be parsed back into a DateTime object with the same time as the original.

The result is always in either local time or UTC. If a time zone offset other than UTC is specified, the time is converted to the equivalent UTC time.

Examples of accepted strings:

  • "2012-02-27"
  • "2012-02-27 13:27:00"
  • "2012-02-27 13:27:00.123456789z"
  • "2012-02-27 13:27:00,123456789z"
  • "20120227 13:27:00"
  • "20120227T132700"
  • "20120227"
  • "+20120227"
  • "2012-02-27T14Z"
  • "2012-02-27T14+00:00"
  • "-123450101 00:00:00 Z": in the year -12345.
  • "2002-02-27T14:00:00-0500": Same as "2002-02-27T19:00:00Z"

Implementation

// TODO(lrn): restrict incorrect values like  2003-02-29T50:70:80.
// Or not, that may be a breaking change.
static DateTime parse(String formattedString) {
  var re = _parseFormat;
  Match? match = re.firstMatch(formattedString);
  if (match != null) {
    int parseIntOrZero(String? matched) {
      if (matched == null) return 0;
      return int.parse(matched);
    }

    // Parses fractional second digits of '.(\d+)' into the combined
    // microseconds. We only use the first 6 digits because of DateTime
    // precision of 999 milliseconds and 999 microseconds.
    int parseMilliAndMicroseconds(String? matched) {
      if (matched == null) return 0;
      int length = matched.length;
      assert(length >= 1);
      int result = 0;
      for (int i = 0; i < 6; i++) {
        result *= 10;
        if (i < matched.length) {
          result += matched.codeUnitAt(i) ^ 0x30;
        }
      }
      return result;
    }

    int years = int.parse(match[1]!);
    int month = int.parse(match[2]!);
    int day = int.parse(match[3]!);
    int hour = parseIntOrZero(match[4]);
    int minute = parseIntOrZero(match[5]);
    int second = parseIntOrZero(match[6]);
    int milliAndMicroseconds = parseMilliAndMicroseconds(match[7]);
    int millisecond =
        milliAndMicroseconds ~/ Duration.microsecondsPerMillisecond;
    int microsecond = milliAndMicroseconds
        .remainder(Duration.microsecondsPerMillisecond) as int;
    bool isUtc = false;
    if (match[8] != null) {
      // timezone part
      isUtc = true;
      String? tzSign = match[9];
      if (tzSign != null) {
        // timezone other than 'Z' and 'z'.
        int sign = (tzSign == '-') ? -1 : 1;
        int hourDifference = int.parse(match[10]!);
        int minuteDifference = parseIntOrZero(match[11]);
        minuteDifference += 60 * hourDifference;
        minute -= sign * minuteDifference;
      }
    }
    int? value = _brokenDownDateToValue(years, month, day, hour, minute,
        second, millisecond, microsecond, isUtc);
    if (value == null) {
      throw FormatException("Time out of range", formattedString);
    }
    return DateTime._withValue(value, isUtc: isUtc);
  } else {
    throw FormatException("Invalid date format", formattedString);
  }
}