Replacement for lookbehind in std::regex

Question

I need a regex to match tokens for a syntax highlighter, which should match full words when surrounded by non-alphanumeric characters or string boundaries. The regex I initially came up with is:

(?<=[^\w]|^)TOKEN(?=[^\w]|$)

Where TOKEN is the token I'm searching for. This works in regex testers, but c++'s regex doesn't support lookbehinds. Omitting the lookbehind causes the regex to match the character before the token as well, which causes issues. I'm aware boost::regex supports lookbehinds, but I'd like to keep to std::regex if possible.

My question is: can I change my regex to exclude the character before the token from the match?

Answer 1

The pattern is missing a closing ] at the end, and \w also matches \d

You might use an alternation asserting either the start of the string, or a position where \b does not match and assert not a word char to the right.

(?:^|\B)TOKEN(?!\w)

Regex demo

After the update of the question, you can write (?<=[^\w]|^)TOKEN(?=[^\w]|$) as (?<=\W|^)TOKEN(?=\W|$) or in short without the lookbehind:

\bTOKEN(?!\w)