Regex Nested quantifier +

Question

I'm trying to replace c++ with c++ in the following string:

"Select the projects entry and then select VC++ directories. Select show"

I want it to be

"Select the projects entry and then select V<b>C++</b> directories. Select show"

Im using this code :

string cssOld = Regex.Replace(
   "Select the projects entry and then select VC++ directories. Select show",
   "c++", "<b>${0}</b>", RegexOptions.IgnoreCase);

I get the following error :
System.ArgumentException: parsing "c++" - Nested quantifier +.

This code works fine with other text(!c++). It seems like the + operator cause the Regex library to throw an exception.

SLaks · Accepted Answer · 2012-03-18 16:47:14Z

4

+ is a special character in regexes; it means "match one or more of the preceding character".

To match a literal + character, you need to escape it by writing \+ (inside an @"" literal)

To match arbitrary literal characters, use Regex.Escape.

answered Mar 18, 2012 at 16:47

SLaks

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2 Comments

chosenOne Thabs Over a year ago

Okay thanks a lot. Do i only have to cater for + operator or are there any other operators(*,&,\ etc) that can cause this exception as well?

chosenOne Thabs Over a year ago

Oh thanks. Regex.Escape did do the job as well. So i changed my code to: string cssOld = Regex.Replace(Regex.Escape("Select the projects entry and then select VC++ directories. Select show "),Regex.Escape("c++"), "${0}", RegexOptions.IgnoreCase); And it works fine. Thank you all.

Olivier Jacot-Descombes · Accepted Answer · 2012-03-18 17:22:15Z

2

You should escape special characters in regex:

string cssOld = Regex.Replace(
    "Select the projects entry and then select VC++ directories. Select show ",
    @"c\+\+", "${0}", RegexOptions.IgnoreCase);

edited Mar 18, 2012 at 17:22

Olivier Jacot-Descombes

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answered Mar 18, 2012 at 16:49

ionden

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3 Comments

chosenOne Thabs Over a year ago

Okay thanks a lot. Do i only have to cater for + operator or are there any other operators(*,&,\ etc) that can cause this exception as well?

ionden Over a year ago

You can check this for other special characters: stackoverflow.com/questions/399078/… . Among them are the following: (\, *, +, ?, |, {, [, (,), ^, $,., #, and white space)

chosenOne Thabs Over a year ago

Oh thanks. Regex.Escape did do the job as well. So i changed my code to: string cssOld = Regex.Replace(Regex.Escape("Select the projects entry and then select VC++ directories. Select show "),Regex.Escape("c++"), "${0}", RegexOptions.IgnoreCase); And it works fine. Thank you all.

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