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Lexer generator for C, C++ and Go.

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re2c is a free and open-source lexer generator for C, C++ and Go.

Its main goal is generating fast lexers: at least as fast as their reasonably optimized hand-coded counterparts. Instead of using traditional table-driven approach, re2c encodes the generated finite state automata directly in the form of conditional jumps and comparisons. The resulting programs are faster and often smaller than their table-driven analogues, and they are much easier to debug and understand. re2c applies quite a few optimizations in order to speed up and compress the generated code.

Another distinctive feature is its flexible interface: instead of assuming a fixed program template, re2c lets the programmer write most of the interface code and adapt the generated lexer to any particular environment.


Official re2c website is It has a lot of examples.


Release tarballs:

Source code:

$ git clone
$ git clone

Github is the main repo, sourceforge is a mirror and can be slightly outdated.


re2c is an Open Source, community-driven project. See for details about contributions to this repository.


See or the online docs for instructions how to build re2c.




Mailing lists:

IRC channels:


You are welcome to ask for help or share your thoughts and ideas.


Re2c was originally written by Peter Bumbulis [email protected]. Since then many people contributed to the project. The current maintainer is Ulya Trofimovich [email protected].

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