Escape Left Bracket C# Regex

Question

I have a string in the following format:

prm.Add( "blah", "blah" ); 

I am looking to use regex to extract the first "blah". To do this I am carving the front half off and then the back half.

The regex I'm using to get rid of "prm.Add( " is:

"prm.Add\([ ]*"

Other threads seem to indicate that escape characters before paranthesis would be acceptable. However VS complains that I have an invalid escape charcter sequence "(". If I use:

"prm.Add([ ]*" 

The application errors as there is no closing paranthesis.

I realise I can get around this by using Regex.Escape on the "prm.Add(". But this isn't really very elegant.

Have I got my regex syntax wrong or does VS2010 not accept escapes of brackets?

Solution 1

You just have to escape the backslash as well for the compiler to understand: "prm.Add\\([ ]*" or @"prm.Add\([ ]*"

Otherwise the compiler couldn't understand things like "\n" - what does the author want? A line break or the string "\n" as-is?

But I'd try to make it more dynamic, e.g. not assuming a space character being there.

Solution 2

When you escape in patterns (which are strings) you have to use two escape sequences:

"prm.Add\\([ ]*"

This is because if you only use one escape, the system tries to find a character that evaluates to \(, that doesn't exist - others that you surely know are e.g. \r or \n.

So, by using two \, you actually escape the \ - leaving it in the pattern that is interpreted. And inside that pattern, you then esapce the regex-meaning of (

Comments

[Damien_The_Unbeliever]

Side note - you'll want to escape the . also, unless you want to match any character at that position.

[Fraser Connor]

Did the trick thanks very much! Also I was under the impression that standard usage of * would imply 0 or more so would get rid of any whitespace even if it didn't exist?

[Mario]

Yes, but there's even a special character class for whitespaces: \s which will match any white space (space, tab, etc.).