RE/flex (regex-centric, fast lexical analyzer) is a free and open source computer program written in C++ that generates fast lexical analyzers (also known as "scanners" or "lexers") in C++. RE/flex offers full Unicode support, indentation anchors, word boundaries, lazy quantifiers (non-greedy, lazy repeats), and performance tuning options. RE/flex accepts Flex lexer specifications and offers options to generate scanners for Bison parsers. RE/flex includes a fast C++ regular expression library.