Using regex to match date format in yyyymmdd

Question

The regular expression must match valid dates in a string in the format YYYYMMDD . For example, aaa_20150327_bbb should be matched, but aaa_20150229_bbb not because 2015 is not a leap year.

Only the year 2000 to 2099 should be considered.

Answer 1

General Madness (years 0-9999)

The following (based on this answer) works for many years between 0 and 9999.

 (?<!\d)(?:(?:(?:1[6-9]|[2-9]\d)?\d{2})(?:(?:(?:0[13578]|1[02])31)|(?:(?:0[1,3-9]|1[0-2])(?:29|30)))|(?:(?:(?:(?:1[6-9]|[2-9]\d)?(?:0[48]|[2468][048]|[13579][26])|(?:(?:16|[2468][048]|[3579][26])00)))0229)|(?:(?:1[6-9]|[2-9]\d)?\d{2})(?:(?:0?[1-9])|(?:1[0-2]))(?:0?[1-9]|1\d|2[0-8]))(?!\d) 

(check out the demo )

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General insanity simplified (years 2000-2099)

If you want, you can simplify it to work only for many years between 2000 and 2099.

 (?<!\d)(?:(?:20\d{2})(?:(?:(?:0[13578]|1[02])31)|(?:(?:0[1,3-9]|1[0-2])(?:29|30)))|(?:(?:20(?:0[48]|[2468][048]|[13579][26]))0229)|(?:20\d{2})(?:(?:0?[1-9])|(?:1[0-2]))(?:0?[1-9]|1\d|2[0-8]))(?!\d) 

But, as you can see, this is not much easier.

(check demo )

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The smart way (years *)

To maintain common sense, you should stick with a very simple regular expression and then test it with code.

 (20\d{2})(\d{2})(\d{2}) 

(check out the demo )

Answer 2

My way (not a smart way)

 (((\d{4})(0[13578]|10|12)(0[1-9]|[12][0-9]|3[01]))|((\d{4})(0[469]|11)(0[1-9]|[12][0-9]|30))|((\d{4})(02)(0[1-9]|1[0-9]|2[0-8]))|([0-9][0-9][02468]40229)|([0-9][0-9][02468]80229)|([0-9][0-9][13579]20229)|([0-9][0-9][13579]60229)|([0-9][0-9][02468]00229)) 

With vb.net (easier to understand, I think so)

  Dim meses31 As String = "((\d{4})(0[13578]|10|12)(0[1-9]|[12][0-9]|3[01]))" Dim meses30 As String = "((\d{4})(0[469]|11)(0[1-9]|[12][0-9]|30))" Dim febrero28 As String = "((\d{4})(02)(0[1-9]|1[0-9]|2[0-8]))" Dim febrero29 As String = "([0-9][0-9][02468]40229)|([0-9][0-9][02468]80229)|([0-9][0-9][13579]20229)|([0-9][0-9][13579]60229)|([0-9][0-9][02468]00229)" Dim patternFecha As String = String.Concat("(", meses31, "|", meses30, "|", febrero28, "|", febrero29, ")")