Question

I am a novice with Regex usage in C#. I want a regex to find the next keyword from a given list but which is not surrounded by the quotes.

e.g. if i have a code which looks like:

            while (t < 10)             {                 string s = 'get if stmt';                 u = GetVal(t, s);                 for(;u<8;u++)                 {                     t++;                 }              } 

i tried using the Regex as @'(.*?)\s(FOR|WHILE|IF)\s’ but it gives me the ‘if’ as next keyword. whereas, i want to get the next keyword after while as ‘for’ and not as ‘if’ which is surrounded by quotes.

Can it be done in anyway using Regex? Or i will have to use conventional programming?

Answer 1

Try the following RegEx (Edit: fixed).

(?:[^\']|(?:(?:.*?\'){2})*?)(?: |^)(?<kw>for|while|if)[ (] 

Note: Because this RegEx literal includes quotes, you can’t use the @ sign before the string. Remember that if you add any RegEx special chars to the string, you’ll need to double-escape them appropiatlye (e.g. \w). Insure that you also specify the Multiline parameter when matching with the RegEx, so the caret (^) is treated as the start of a new line.

This hasn’t been tested, but should do the job. Let me know if there’s any problems. Also, depending on what more you want to do here, I might recommend using standard text-parsing (non-RegEx), as it will quickly become more readable depending on how much data you want to extract from the code. Hope that helps anyway.

Edit: Here’s some example code, which I’ve tested and am pretty confident that it works as intended.

var input = 'while t < 10 loop\n s => 'this is if stmt'; for u in 8..12 loop \n}';  var pattern = '(?:[^\']|(?:(?:.*?\'){2})*?)(?: |^)(?<kw>for|while|if)[ (]'; var matches = Regex.Matches(input, pattern); var firstKeyword = matches[0].Groups['kw'].Value; // The following line is a one-line solution for .NET 3.5/C# 3.0 to get an array of all found keywords. var keywords = matches.Cast<Match>().Select(match => match.Groups['kw'].Value).ToArray(); 

Hopefully this should be your complete solution now…