Yes, another Regex question. You're welcome ;-P
This is the first time I've written my own regex for some simple string validation in C#. I think I've got it working but as a learning exercise I was wondering if it could be improved and whether I have made any mistakes.
The strings will all look something like this:
T20160307.0001
Rules:
- Begin with the letter T.
- Date in the format YYYYMMDD.
- A full stop.
- Last 4 characters are always numeric. There should be exactly 4.
Here is my regex (fiddle):
^(?i)[T]20[0-9]{2}[0-1][0-9][0-3][0-9].\d{4}$
^Assert the start of the string.(?i)[T]Check that we have a letter T, case insensitive.20YYYY begins with 20 (I'll be dead by 2100 so I don't care about anything further :-P)[0-9]{2}Any number between 0 and 99 for second part of YYYY.[0-1][0-9]0 or 1 for first part of month, 0-9 for second part of month.[0-3][0-9]0-3 for first part of day, 0-9 for second part of day..Full stop.\d{4}4 numerical characters.$Assert end of string.
One pitfall I can already see is date validation. 20161935 (the 35th day of the 19th month) is considered valid. I've read some / other / posts about achieving this which I believe match on number ranges but I was unable to understand the format.
I would accept an answer that simply solved the date issue if someone would be kind enough to ELI5 how this works, but other improvements would be a welcome bonus.
Edit: To avoid further confusion I should state that I know about DateTime.TryParse etc. As mentioned I'm using this as an opportunity to learn Regex and felt this was a good starting point. Sorry to anyone who's time I wasted, I should have made this clear in the original post.