parse static method Null safety

DateTime parse(
  1. String formattedString
)

Constructs a new DateTime instance based on formattedString.

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 cannot 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"

This method accepts out-of-range component values and interprets them as overflows into the next larger component. For example, "2020-01-42" will be parsed as 2020-02-11, because the last valid date in that month is 2020-01-31, so 42 days is interpreted as 31 days of that month plus 11 days into the next month.

To detect and reject invalid component values, use DateFormat.parseStrict from the intl package.

Implementation

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);
  }
}