How to validate DateTime format?

Question

I am suppose to let the user enter a DateTime format, but I need to validate it to check if it is acceptable. The user might enter \"yyyy-MM-dd\" and it would be fine, but t

Answer 1

Unless I am remembering incorrectly, the only invalid DateTime format strings are one character long. You can assume any 2 or more character DateTime format string is valid.

DateTime.ParseExact("qq", "qq", null) == DateTime.Today
DateTime.ParseExact("myy", "501", null) == "05/01/2001"

Standard (1 character)
Custom (>1 character)

For reference, allowed single character strings as formats:

d,D,f,F,g,G,m,M,o,O,r,R,s,T,u,U,y,Y

Any other character, such as q, by itself is invalid. All other strings will be successfully parsed as formatting strings.