Error parsing regex pattern

Question

I'm writing a simple regex in c# to locate backslashes not preceded or followed by any backslashes:

Regex reg = new Regex(".*(?<!\\)\\(?!\\).*");

However, this statment generates an ArgumentException: "parsing ".(?" - Not enough )'s"

The group parentheses seem to match. Can anyone spot the problem?

John Fisher · Accepted Answer · 2009-09-24 18:54:12Z

16

Put the @ symbol in front of your string, otherwise you need to double-escape the slashes (once for C#, and once for Regex).

Regex reg = new Regex(@".*(?<!\\)\\(?!\\).*");

or

Regex reg = new Regex(".*(?<!\\\\)\\\\(?!\\\\).*");

answered Sep 24, 2009 at 18:54

John Fisher

22.8k2 gold badges43 silver badges67 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

thank goodness for string literals, double escaping just makes these more difficult to parse (for humans that is)

Hasani Blackwell · Accepted Answer · 2009-09-24 18:55:07Z

4

use the string literal @

Regex reg = new Regex(@".*(?<!\\)\\(?!\\).*");

answered Sep 24, 2009 at 18:55

Hasani Blackwell

2,0561 gold badge14 silver badges10 bronze badges