C# Regex Range in Reverse order

Question

I have got list of ASCII Codes of character which are allowed in the name.So, I am trying to build regex patter using range(-) hypen operator and string length should be 40.

Finally, I have ended up by creating following pattern.

^([\x20-\x21\x23-\x25\x28-\x2E\x30-\x3B\x3F-\x7E\xA0-\xFF]){0,40}$

with this pattern I am specifying the range of character's ASCII codes allowed in the string.

But it throws exception of Range in reverse order. I have gone through couple of question. I have found that it happens because of hypen(-) character. So, In order to remove this problem I have to use escape sequence (-) instead of(-).

After adding escape sequence although it doesn't throw exception but it doesn't give the desire result.

So, I want to know is my pattern is correct or Is it right away to specify ASCII Code character range.

Yes it was typo, but If I correct it. Still it doesn't give desired result — Yogesh
– Yogesh, Commented Nov 18, 2015 at 9:09
What is the desired result? String must be exactly 40 symbols long? Remove 0,. And remove ( and ), no need grouping 1 symbol. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Nov 18, 2015 at 9:10
\x19 is not valid character so, it should not match. Regex.IsMatch() should return false — Yogesh
– Yogesh, Commented Nov 18, 2015 at 9:11

Wiktor Stribiżew · Accepted Answer · 2015-11-18 09:50:03Z

3

You need to use a negated character class, remove the grouping, quantifier, anchors and fix the typo:

[^\x20-\x21\x23-\x25\x28-\x2E\x30-\x3B\x3F-\x7E\xA0-\xFF]

See the regex demo (1 match is found before here) and use it as shown in the below C# demo:

var str = "  some text here ";
if (str.Length > 40 || Regex.IsMatch(str, @"[^\x20-\x21\x23-\x25\x28-\x2E\x30-\x3B\x3F-\x7E\xA0-\xFF]"))
    Console.WriteLine("The line is too long or contains invalid char(s)!");

Note that a negated character class is formed with the help of [^....] notation and matches all characters other than those specified in the character class.

If performance is key, you need to declare the regex as a static readonly field with RegexOptions.Compiled flag. Have a look at the Kurt Schindler's Regular expression performance comparisons blog.

edited Nov 18, 2015 at 9:50

answered Nov 18, 2015 at 9:19

Wiktor Stribiżew

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6 Comments

Yogesh Over a year ago

Ya it works fine but I had to add check length of string should be between lower limit 0 and upper limit 40. So, I had to add {0,40}$ in the end of expression

Wiktor Stribiżew Over a year ago

Why do you need a regex for that? Just check the string length. It is possible to do with regex , but why should you sacrifice performance? Add str.Length > 40 ||.

Yogesh Over a year ago

Yes I agree with you that it would have performance hit but in my case I would be using the same expression so many places. So, Instead of using extra code, I wan to do with the help of regex. I have read that {0,40}$ it should work perfectly fine for me but with the conjuction of above pattern it is not working. Moreover, its going to be very small string. So, no risk of performance hits

Wiktor Stribiżew Over a year ago

Please check this demo showing that @"^[\x20-\x21\x23-\x25\x28-\x2E\x30-\x3B\x3F-\x7E\xA0-\xFF]{0,40}$" should be working for you.

Yogesh Over a year ago

I have found out that already in-fact this is the same what I had started

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