Regex issue

[John B]

I am trying to do a pretty simple pattern match using regex.

The pattern is ^(?:(?<Item>.*?)@:@)*$.

This should return a match for test123@:@ but does not, instead it never
returns when I call Regex.Match, I have to kill the thread.

The code is below, The Regulator (some will know it) returns the correct
results, I cannot work out why.

RegexOptions options = RegexOptions.IgnoreCase |
RegexOptions.IgnorePatternWhitespace | RegexOptions.Multiline;
Regex matcher = new Regex(@"^(?:(?<Item>.*?)@:@)*$", options);
Match match = matcher.Match(@"test123@:@"); //Never returns from here.

I have tried this on two machines, it just doesnt work.

TIA

JB

[Jesse Houwing]

Hello John,

I am trying to do a pretty simple pattern match using regex.

The pattern is ^(?:(?<Item>.*?)@:@)*$.

This should return a match for test123@:@ but does not, instead it
never returns when I call Regex.Match, I have to kill the thread.

The code is below, The Regulator (some will know it) returns the
correct results, I cannot work out why.

RegexOptions options = RegexOptions.IgnoreCase |
RegexOptions.IgnorePatternWhitespace | RegexOptions.Multiline; Regex
matcher = new Regex(@"^(?:(?<Item>.*?)@:@)*$", options); Match match =
matcher.Match(@"test123@:@"); //Never returns from here.

I have tried this on two machines, it just doesnt work.

TIA

JB

^(?:(?<Item>.*?)@:@)*$

I'd giess that the problem lies in the last *, but I'm unsure why it would
hang the parser. I've seen these kinds of problems before where a lot of
backtracking is possible.

a better pattern would be: ^(?<item>.*)@:@$

The extra ? after the first .* isn't really needed, unless there are more
than one @:@ signs in your text at the end of a line (which I doubt). But
as you've not sent us the text you're trying to extract your pattern from
I'd have to guess that.

Another pattern that would probably work would be:

^(?<item>[^@]*)@:@$ but in there I assume that @ does not precede the @:@
at all.

I hope this helps. If not, please add some sample input.

Another possible problem might be that your input is simply too large. The
engine isn't very good at reading multiple megabytes of text at once. As
you're looking at the lines one by one, you could use that to your advantage
and load a couple of lines, try to match and load the next couple of lines.
A StringReader would be ideal for that purpose.

--
Jesse Houwing
jesse.houwing at sogeti.nl

[Mike Blake-Knox]

In article <46***********************@news.optusnet.com.au> , John B wrote:

This should return a match for test123@:@ but does not, instead it never*
returns when I call Regex.Match, I have to kill the thread.

It sounds as if you are running your code under the debugger. I had what
sounds like the same problem a few weeks ago involving regular expressions
that worked fine using a regex test tool (in my case Expresso). I noticed
that if I set the breakpoint on the line after the match, the breakpoint
was reached. Eventually, I discovered that if the "Autos" window wasn't
open, Visual Studio was able to step though the code including the Match
line.

I suspect that Visual Studio has some problems with some of the objects in
the Match/Regular expression objects. This might be because the VS debugger
actually uses an object's ToString(format,format Provider) to display
values. If the object's ToString() routine takes an exception, it must be
very difficult for the debugger to handle. Any window that shows an
object's value might have the same problem.

Hope this helps.

Mike