.net - Regex in C# , Expression in negative lookbehind -


i`m trying write expression mach single code preceded odd number of question marks.

i have found negative look-behind expression match single question mark

pattern (?<!\?)'  aaa?'aaa   match aaa'aaaa   not match aaa??'aaa  match --wrong

but need detect odd number off question marks not one.

i tried put  (?<!\?(??))'  did not work.

the result want is

aaa?'aaaa  match aaa??'aaaa  not match aaa???'aaaa  match aaa????'aaaa  not match aaa?????'aaaa  match

the regex looking (?<=(^|[^?])(\?\?)*\?)'.

let's break lookbehind (i changed positive) down:

(^|[^?]) not question mark (possibly start of string, i.e. nothing) (\?\?)*  number of question mark pairs \?       single question mark

so in order quote match, has preceded these tokens in reverse order. should clear forces number of preceding question marks 2n + 1 n >= 0.


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