C# .NET Regex problem

Question

I am trying to find out a solution to an issue I'm having. If I execute the following C# code:

Regex r = new Regex("[\\r\\n]*");
Match m = r.Match("\\r\\n");

If I examine the value of m.Success, I get a value of true, which is correct. But if I examine the value of m.Length, I get a value of 0. If I examine m.Value, I also get a blank value. Am I missing something in my Regex? I am under the impression that either m.Success needs to be false and m.Length is 0 or else m.Success needs to be true and m.Length needs to be greater then 0. Any help on clearifing this would be appreciated!

shouldn't the second line be Match m = r.Match("\r\n"); ? I imagine this is a string with actual cr/lf chars, not escaped ? — Steve B
– Steve B, Commented Jul 6, 2011 at 4:54
if you leave out one '\', it does do the job... But I do not know if that is what is intended... — Flawless
– Flawless, Commented Jul 6, 2011 at 4:56

Peter O. · Accepted Answer · 2020-08-29 03:54:24Z

6

Match.Success returns true because the Regex is supposed to match "zero or more" instances of "\r" or "\n", that is, carriage return or line feed, (as indicated by the "*" symbol). However, the string you gave (within Match) instead contains backslash, r, backslash, n, which is neither a carriage return nor a line feed, so the length of the match was zero. (Within the regular expression, the "backslash, n" is treated as a single character, line feed).

To avoid further confusion in the future, try prefixing the regular expression with an "@" symbol to possibly avoid some confusion with how the backslashes work in regular expressions, like this:

 @"[\r\n]*"

Hopefully this makes it a little clearer that "\r" stands for a carriage return and "\n" for a line feed. The related regular expression:

 @"[\\rn]*"

Would match zero or more instances of backslashes, r, and/or n. (The doubled backslash is necessary because that symbol is treated specially in regular expressions.)

edited Aug 29, 2020 at 3:54

answered Jul 6, 2011 at 4:53

Peter O.

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1 Comment

Icemanind Over a year ago

Such a frickin' obvious mistake on my part. Thanks Peter

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