Limit the number of decimal and length of number with regex in c#

Question

I have been trying to validate a number that limits the decimal point to 3 points and the length of the number (including the dot) to 6, but couldn't get it to validate properly. This is so far what I have:

^([0-9]([.][0-9]{1,3})?){1,6}$

How could I change the regex above to validate properly? Thanks.

Answer 1

You can use this lookahead based regex for checking length:

^(?=[0-9.]{1,6}$)[0-9]+(?:\.[0-9]{1,3})?$

RegEx Demo

Answer 2

For the total length I would just check the string length:

if(s.Length <= 6 && Regex.IsMatch(s, @"^[0-9]+(\.[0-9]{1,3})?$")) {

}

Because the {1,6} at the end of your expression means 0 to 6 repetitions of the term preceeding it (in your case, the whole number). It does not limit the length of the string.