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Regex.IsMatch returns two different results in C #

I am trying to find a match between a string and a pattern using Regex.IsMatch (). I created a regex and tested it with regex101.com, it works great. Now the problem is that Regex.IsMatch(filename, curSetting.RegExMatch.ToString());

returning true curSetting.RegExMatch.IsMatch(filename))

returns false for the same filename. Can anyone explain how this is different and what is the difference between the two?

RegExMatch

is my object regex member curSetting

. The test data in my case is Pattern

Gen(?!.*(?:erallog))(?<SerialNo>.+?)-(?<Year>(?:\d{2}))(?<Month>\d{2})(?<Day>\d{‌2})(?<Other>.*?\.log‌)

String 1_GeneralLog1370013-170403.log

.

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It is understood that yours is curSetting.RegExMatch

compiled with the flag RegexOptions.IgnoreCase

: is (?!.*(?:erallog))

treated case insensitively and matches eralLog

in your input string 1_GeneralLog1370013-170403.log

, so the negative reverse lookup pattern finds a match and a complete match.

So, there are 2 outputs (depending on what you want):



  • Either remove RegexOptions.IgnoreCase

    from the regex object initialization, or

  • Add a custom option (?i)

    to case:

    (?i)Gen(?!.*(?:erallog))(?<SerialNo>.+?)-(?<Year>(?:\d{2}))(?<Mo‌nth>\d{2})(?<Day>\d{2})(?<Other>.*?\.log)

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