RE/flex is a free and open-source alternative to the fast lexical analyzer
Flex. RE/flex generates fast lexical analyzers for C++, also known as
"scanners", "lexers", or "tokenizers". RE/flex offers many new useful features
including Unicode support, indent/nodent/dedent anchors, word boundaries, lazy
quantifiers (non-greedy, lazy repeats), and performance tuning options. The
RE/flex software also includes a very fast stand-alone regex library for C++.

WWW: https://www.genivia.com/reflex.html