How to check for valid Date in yyyyMM format

Question

I have an internal business process that my finance dept runs. To kick it off they input a Date in the format of yyyyMM or 201009. I want to check for a valid date from that string but so far I got nothing.

I am currently exploring breaking the string up, taking the first 4 and checking that they are between 1990 and 2050(as example) and then the last 2 and checking that it is between 01 and 12.

Is there a better way?

Answer 1

You can use DateTime.TryParseExact to see if it can be parsed correctly:

bool isValid = false;
DateTime dateValue;
if(DateTime.TryParseExact("201009", "yyyyMM", CultureInfo.InvariantCulture, 
                       DateTimeStyles.None, out dateValue))
{
   // DateTime parsed, dateValue contains the parsed DateTime

   // Can validate dateValue against business rules at this point
   isValid = (dateValue <= DateTime.Now && dateValue >= DateTime.Now.AddYears(-5));
}

If you would rather get an exception, you can use DateTime.ParseExact:

// Next line throws exception if format not correct
DateTime.ParseExact("201009", "yyyyMM", CultureInfo.InvariantCulture);

Answer 2

The problem here is that the format "yyyyMM" cannot represent a specific DateTime. So the parsing methods built in to DateTime will do you no good.

Update: Never mind; I stand corrected. DateTime.TryParseExact will work just fine (which is ironic, if you ask me); it'll interpret your string to represent the first day of the given month.

I would do what you're describing: parsing the string into the two numeric components and simply compare those values to whatever range you require them to fall within.

Answer 3

I would go with DateTime.ParseExact:

DateTime d = DateTime.ParseExact("201009", "yyyyMM", System.Globalization.CultureInfo.InvariantCulture);

Answer 4

You can use a regular expression:

if (Regex.IsMatch(input, @"^(199\d|20[0-5]\d)(0[1-9]|1[0-2])$")) {
  // valid input between 199001 and 205912
}

Answer 5

I'd be tempted perform this as a number range problem:

UInt32 val;
if (input.Length != 6
   || !UInt32.TryParse(input, out val)
   || val > 205012
   || val < 199001
   || val % 100 > 12
   || val % 100 == 0) {
  // Invalid...
}