Question

I know regex and substrings is a common question on here but i can not seem to correlate what I am reading to actual application.

What i want to do:

take a string, look at the last 16 characters of the string, and make sure its alphanumeric. Below is what i have come up with.

 if (Regex.IsMatch(STRINGTOCHECK.ToLower().Substring(16), @"^[a-zA-Z0-9]*$"))

request

some code showing me the right way to accomplish this

or pointing out where my code is wrong

etc.

All help is appreciated!

Answer 1

You need to make sure the last 16 characters are alphanumeric? Just use this regular expression:

[a-zA-Z0-9]{16}$

The problem you have right now is that .Substring(16) will return all characters in the string after and including position 16 – not the last 16 characters. What’s more, you’re already case-insensitive, so:

if(Regex.IsMatch(STRINGTOCHECK, @"[a-zA-Z0-9]{16}$"))

The final $ anchor makes sure the last 16 characters are being matched.