Comments on: Advanced Regular Expressions in C#

By: Holystream

Holystream — Fri, 02 Oct 2009 17:14:36 +0000

Just noticed Richard said the same thing

By: Holystream

Holystream — Fri, 02 Oct 2009 16:50:45 +0000

Because we have added a lot of spaces and new lines to our expression we need to tell Regex about them by specifying the RegexOptions.Multiline and RegexOptions.IgnorePatternWhitespace options.

This is incorrect. RegexOptions.Multiline changes the behavior of the matching against the target string. It does not have anything to do with breaking the regular expression into multiple lines. For example, if your option is RegexOptions.Singleline, then ^ matches the start of the entire string, $ matches the end of the entire string, while in RegexOptions.Multiline, ^ matches start of the beginning of the line after the last carriage return, and $ matches before the carriage return.

All you need is RegexOptions.IgnorePatternWhitespace, if you broke your regular expression into multiple lines.

By: paul heintz

paul heintz — Thu, 27 Aug 2009 11:24:02 +0000

Excellent, I’ve used them for years and yes after coming back to my code to modify many a time have I crossed my eyes trying to remember why and what I did.

This is extremely helpful at structuring code

Thank you,

By: Martin Sykora

Martin Sykora — Mon, 15 Jun 2009 17:49:31 +0000

Wow, this is a sweet little intro to regex, good blog writing my friend!

Keep it up!! I am looking forward to other topics you will cover

By: Link Love | Kaeli's Space

Link Love | Kaeli's Space — Sun, 12 Apr 2009 13:44:19 +0000

[...] Advanced Regular Expressions in C# – neat tricks, including how to comment the expression [...]

By: Richard

Richard — Fri, 13 Mar 2009 17:34:13 +0000

“Because we have added a lot of spaces and new lines to our expression we need to tell Regex about them by specifying the RegexOptions.Multiline and RegexOptions.IgnorePatternWhitespace options.”

RegexOptions.Multiline doesn’t do what you think it does. Rather than specifying that the pattern is on multiple lines, it changes the meaning of ^ and $ so they match at the beginning and end, respectively, of any line, and not just the beginning and end of the entire string.

RegexOptions.IgnorePatternWhitespace is enough to tell the engine to ignore the white-space – including new-lines – within your pattern.

By: Gareth

Gareth — Thu, 12 Mar 2009 14:42:53 +0000

I like to learn something every day. And I never knew you could use “#” to comment regular expressions in conjunction with RegexOptions.IgnorePatternWhitespace. Thanks!

By: Martijn

Martijn — Thu, 12 Mar 2009 02:15:54 +0000

Hi George,

Many thanks for the feedback! You are not missing things — I was so focused on using index entries that I forgot to check if a name would work as well. I will fix the example as this makes things that much cleaner.

Cheers,
Martijn

By: georg

georg — Wed, 11 Mar 2009 21:22:52 +0000

Nice series! Clean and easy to follow – even if I’ve used regular expressions for some time now, there’s always something new to pick up. One question though: At line 36 in the fourth listing you say “// The only drawback to named groups is that we need to look up their
// index offset in the group table.”

And then you use the index when fetching the named group values. Isn’t it the same thing to use the name of the group directly or am I missing something here, e.g:

your line(#28): return match.Groups[of_Username].Value
could be: return match.Groups["Username"].Value

or…..?

regards,
George