I'm looking for a regular expression to validate hex colors in asp.net C#. and also looking code for validate in server side
For instance: #CCCCCC
+4
A:
^#(?:[0-9a-fA-F]{3}){1,2}$
Dissection:
^ anchor for start of string
# the literal #
( start of group
?: indicate a non-capturing group that doesn't generate backreferences
[0-9a-fA-F] hexadecimal digit
{3} three times
) end of group
{1,2} repeat either once or twice
$ anchor for end of string
This will match an arbitrary hexadecimal color value that can be used in CSS, such as #91bf4a or #f13.
Joey
2009-10-28 10:22:34
A:
Minor disagreement with the other solution. I'd say
^#([0-9a-fA-F]{2}){3}|([0-9a-fA-F]){3}$
The reason is that this (correctly) captures the individual RGB components. The other expression broke #112233 in three parts, '#' 112 233. The syntax is actually '#' (RR GG BB) | (R G B)
The slight disadvantage is more backtracking is required. When parsing #CCC you don't know that the second C is the green component until you hit the end of the string; when parsing #CCCCCC you don't know that the second C is still part of the red component until you see the 4th C.
MSalters
2009-10-28 13:33:02
This regex would also match #1234 and #12345. However, there can be only either 3 digits or 6 digits. This RE allows anything between 3 and 6 digits. If you truly wanted to capture the correct structure, then you'd have to use `#([1-9a-fA-F]{3}|[1-9a-fA-F]{6})`. If you want to capture the individual color components it gets more complex (your suggestion doesn't do that as well).
Joey
2009-10-28 14:41:54
On second thought, you're right - fixing it.
MSalters
2009-10-28 15:18:51
For pure validation purposes (i. e. whether a value is actually a possible and correct one) however, I find it easier to look at the apparent structure of the string and not at the specified one. At least in this case the resulting RE is simpler.
Joey
2009-10-28 15:26:44