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I'm using free-form dates as part of a search syntax. I need to parse dates from strings, but only preserve the parts of the date that are actually specified. For instance, "november 1, 2010" is a specific date, but "november 2010" is the range of dates "november 1, 2010" to "november 30, 2010".
Unfortunately, DateTime.Parse and friends parse these dates to the same DateTime:
DateTime.Parse("November 1, 2010") // == {11/1/2010 12:00:00 AM}
DateTime.Parse("November, 2010") // == {11/1/2010 12:00:00 AM}
I need to know which parts of the DateTime were actually parsed and which were guessed by the parser. Essentially, I need DateTime.Parse("November, 2010") == {11/-1/2010 -1:-1:-1}; I can then see that the day portion is missing and calculate the range of dates covering the whole month.
(Internally, C# has the DateTimeParse and DateTimeResult classes that parse the date and preserve exactly the information I need, but by the time the date gets back to the public interfaces it's been stripped off. I'd rather avoid reflecting into these classes, unless that's really the only route.)
Is there some way to get DateTime.Parse to tell me which format it used to parse the date? Or can the returned DateTime have placeholders for unspecified parts? I'm also open to using another date parser, but I'd like it to be as reliable and locale-flexible as the internal one. Thanks in advance.
EDIT: I've also tried ParseExact, but enumerating all of the formats that Parse can handle seems nearly impossible. Parse actually accepts more formats than are returned by DateTimeFormatInfo.GetAllDateTimePatterns, which is about as canonical a source as I can find.
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The Parse method tries to convert the string representation of a date and time value to its DateTime equivalent. It tries to parse the input string completely without throwing a FormatException exception.
The DateTime. ParseExact(String, String, IFormatProvider) method parses the string representation of a date, which must be in the format defined by the format parameter.
Python has a built-in method to parse dates, strptime . This example takes the string “2020–01–01 14:00” and parses it to a datetime object. The documentation for strptime provides a great overview of all format-string options.
print(new DateFormat('yyyy/MM/dd'). parse(null)); That's how to parse a String to a DateTime in Dart.
You could try using TryParseExact(), which will fail if the data string isn't in the exact format specified. Try a bunch of different combinations, and when one succeeds you know the format the date was in, and thus you know the parts of the date that weren't there and for which the parser filled in defaults. The downside is you have to anticipate how the user will want to enter dates, so you can expect exactly that.
You could also use a Regex to digest the date string yourself. Again, you'll need different regexes (or a REALLY complex single one), but it is certainly possible to pull the string apart this way as well; then you know what you actually have.
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