C# Regex to match hexadecimal number between 0 to FE

Question

I want a regex in c# that validates the hexadecimal number between 0 to FE (i.e. 0 to 254 in decimal)(Case insensitive).

here user can enter the single digit number in two digit. For example number 9 as 09.

any help is appreciated.

Note: We don't need to validate '0x' here,just a range between 0 to FE.

Possible duplicate of [How to convert numbers between hexadecimal and decimal in C#?](http://stackoverflow.com/questions/74148/how-to-convert-numbers-between-hexadecimal-and-decimal-in-c) — zimdanen, Feb 18 '16 at 13:22
Suggest you attempt to convert to an int (see above link) and check the link. Use TryParse, in case the string is incorrect. — zimdanen, Feb 18 '16 at 13:24
I don't want to convert the string,I ant a regex pattern to validate the string. — Mahendra, Feb 18 '16 at 13:25
@Mahendra But why? Typically, you would use `Parse` or `Convert` or `TryParse` - even just to validate. `Regex` is often "overkill" for most scenarios - it may even perform slower than, let say, `TryParse`. Anyway, if you really need things to check the `string` without actually converting the `string`, I once have such wish too. For some special case, it is indeed beneficial. Check this out: http://stackoverflow.com/questions/34392763/tryparse-without-actual-parsing-or-any-other-alternative-for-checking-text-forma perhaps you want to explain your context too... — Ian, Feb 18 '16 at 13:31

Alex Kopachov · Accepted Answer · 2016-02-18T14:02:34.270

4

Try this

^(([fF][0-9a-eA-E])|([0-9a-eA-E]?[0-9a-fA-F]))$

Some explanations:

This regex contains 2 logical parts. First ([fF][0-9a-eA-E]) matches cases when number starts with "f" or "F", as per original criteria, in that case only 0-9 and A-E is available, to reject "FF". Second part ([0-9a-eA-E]?[0-9a-fA-F]) handles all other cases, first symbol is 0-9 or A-E (F is covered by first part) or absent (to cover single symbol numbers), and second symbol is any valid for hexdecimal (0-9 A-F).

edited Feb 18 '16 at 14:02

answered Feb 18 '16 at 13:32

Alex Kopachov

723
4
9

Thanks Alex,I was testing it with various numbers and it succeeded.Can you please explain this regex it a bit? – Mahendra Feb 18 '16 at 13:46
I've added few explanations. – Alex Kopachov Feb 18 '16 at 14:04

score 0 · Answer 2 · answered Feb 18 '16 at 13:44

0

You can use

^(?:[0-9a-eA-E]?[0-9a-fA-F]|[fF][0-9a-eA-E])$

It will work with or without leading zero, uppercase or lowercase characters.

Explanation

Visualization

answered Feb 18 '16 at 13:44

Gediminas Masaitis

3,172
14
35

kionay · Answer 3 · 2016-02-18T14:46:13.137

-1

Maybe this is what you want?

([0-9A-F]{1}[0-9A-E]{1})

edited Feb 18 '16 at 14:46

answered Feb 18 '16 at 13:33

kionay

135
4

This requires the use of two characters. So this would fail a valid input of `8`. – ryanyuyu Feb 18 '16 at 13:42
It also matches a comma (`,`) – Steven Doggart Feb 18 '16 at 13:49
And without anchors, it matches any string that contains something that could pass as a 2-digit hex number (such as `nnnnnnn0000000000`). – ryanyuyu Feb 18 '16 at 13:52
@ryanyuyu I must've misread the original, i thought it **had** to be 2 digits. And from what it seemed like Mahendra wanted the input would only ever be 2 characters. – kionay Feb 18 '16 at 14:17

C# Regex to match hexadecimal number between 0 to FE

3 Answers3