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POAdding a single character to my .NET RegEx causes it to hang
 

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  1. POAdding a single character to my .NET RegEx causes it to hang
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    <p>Here is the input data:</p> <pre><code> *** INVOICE *** THE BIKE SHOP 1 NEW ROAD, TOWNVILLE, SOMEWHERE, UK, AB1 2CD TEL 01234-567890 To: COUNTER SALE No: 243529 Page: 1 Date: 04/06/10 12:00 Ref: Aiden Cust No: 010000 </code></pre> <p>Here is a regex that works (Options: singleline, ignorewhitespace, compiled) - it matches immediately and the groups are properly populated:</p> <pre><code>\W+INVOICE\W+ (?&lt;shopAddr&gt;.*?)\W+ To:\W+(?&lt;custAddr&gt;.*?)\W+ No:\W+(?&lt;invNo&gt;\d+).*? Date:\W+(?&lt;invDate&gt;[0-9/ :]+)\W+ Ref:\W+(?&lt;ref&gt;[\w ]*?)\W+ Cust </code></pre> <p>As soon as I add the 'N' out of Cust No into the rex, parsing the input hangs forever:</p> <pre><code>\W+INVOICE\W+ (?&lt;shopAddr&gt;.*?)\W+ To:\W+(?&lt;custAddr&gt;.*?)\W+ No:\W+(?&lt;invNo&gt;\d+).*? Date:\W+(?&lt;invDate&gt;[0-9/ :]+)\W+ Ref:\W+(?&lt;ref&gt;[\w ]*?)\W+ Cust N </code></pre> <p>If I add something like "any character" :</p> <pre><code>\W+INVOICE\W+ (?&lt;shopAddr&gt;.*?)\W+ To:\W+(?&lt;custAddr&gt;.*?)\W+ No:\W+(?&lt;invNo&gt;\d+).*? Date:\W+(?&lt;invDate&gt;[0-9/ :]+)\W+ Ref:\W+(?&lt;ref&gt;[\w ]*?)\W+ Cust . </code></pre> <p>It works, but as soon as I add a fixed character, the rex hangs again:</p> <pre><code>\W+INVOICE\W+ (?&lt;shopAddr&gt;.*?)\W+ To:\W+(?&lt;custAddr&gt;.*?)\W+ No:\W+(?&lt;invNo&gt;\d+).*? Date:\W+(?&lt;invDate&gt;[0-9/ :]+)\W+ Ref:\W+(?&lt;ref&gt;[\w ]*?)\W+ Cust ..: </code></pre> <p>Can anyone advise why adding something so trivial would cause it to fall over? Can I enable some kind of tracing to watch the matching activity to see if it is getting stuck in a catastrophic backtrack?</p>
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    1. COLol repro'd. Freaky.
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    2. CONote: I couldnt even get the RegEx to match if I use this as a pattern: Cust No ..yes literally just the words "Cust No" couldnt be found in the input. I hexedited the file to see if there was anything weird about it but it's just plain ASCII. Can someone else put that data as input, and try to even just match "Cust No" as a pattern?
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    3. COI also note that it doesnt hang if I don't rely on the word "Cust" and simply change the last lines of the regex to: Ref:\W+(?<ref>[\w ]*?).*?No:
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