What's Wrong With This Regex?

Question

I have some text of which the following is a sample:

  2_Chief Ships.Niobe 2 0 2 1.0
  3_Chief Vehicles.WillisMB_US 1
[0_Chief_Road]
  77704.27 140254.33 120.00 0 2 9.166666984558105
  100653.84 140379.05 120.00
[2_Chief_Road]
  76911.77 139996.94 120.00 0 2 3.8583335876464844
  100446.47 140028.61 120.00

I want to retrieve this part under [0_Chief_Road]:

77704.27 140254.33 120.00 0 2 9.166666984558105
100653.84 140379.05 120.00

I'm using this code:

System.Text.RegularExpressions.Regex reg = null;
string routeTitle = "[0_Chief_Road]";  //  this is hard coded for StackOverflow
reg = new System.Text.RegularExpressions.Regex(@"(?<=" + routeTitle + @")[\d\.\s]+(?=\[)");
string routeText = reg.Match(chiefsSection).Captures[0].ToString();

The result I'm getting is:

4.27 140254.33 120.00 0 2 9.166666984558105
  100653.84 140379.05 120.00

...which is everything after the first zero! I've tried changing the values and it always returns everything after the first zero. I don't get why!!

Can anyone help out here? Thank you!

Gregg

Tim Pietzcker · Accepted Answer · 2010-12-15 08:03:08Z

2

The problem is that routeTitle contains brackets that, when used in a regular expression, will be interpreted as a character class. You need to escape any literal string before inserting it into a regular expression.

So you should use string routeTitle = @"\[0_Chief_Road\]";

Or use the Regex.Escape() function:

string routeTitle = "[0_Chief_Road]";  //  this is hard coded for StackOverflow
reg = new System.Text.RegularExpressions.Regex(@"(?<=" + Regex.Escape(routeTitle) + @")[\d\.\s]+(?=\[)");

Be aware that the CRLF after [0_Chief_Road] will also be part of the match - if you don't want that, add a \s+ at the end of the lookbehind assertion.

edited Dec 15, 2010 at 8:03

answered Dec 15, 2010 at 7:56

Tim Pietzcker

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1 Comment

MrGreggles Over a year ago

Yep, that's it. Thanks for waking me up!

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