re2c is a tool for generating C-based recognizers from regular
expressions.  re2c-based scanners are efficient:  for programming
languages, given similar specifications, an re2c-based scanner is
typically almost twice as fast as a flex-based scanner with little or no
increase in size (possibly a decrease on cisc architectures).  Indeed,
re2c-based scanners are quite competitive with hand-crafted ones.

WWW: http://re2c.sourceforge.net/