objective c - iOS Regex: Unknown escape sequence "\|" -
I am getting a strange warning, and as a result my regex search is not working. Here's the line: NSRang R = [HTML categoryoffstring: @ "\ | (*. *) \ |" Options: NSRegularExpressionSearch]; Where html is a string which I'm sure is a single match for regex above. The warning only You are getting a warning because \ | Objective-C (or C or C ++ for that matter) does not have a valid Escape sequence. The compiler is ignoring it and instead a raw | is using the character, so the string you are actually passing is @ "| (. *)." . You want to get the behavior, you have to run backslash in your source code so that the regex engine can see the literal backslash and | Alternately translate the character as a translation, such as @ "\\ | (* * * \\ |" .