Good tools for creating a C/C++ parser/analyzer

What are some good tools for getting a quick start for parsing and analyzing C/C++ code?

In particular, I'm looking for open source tools that handle the C/C++ preprocessor and language. Preferably, these tools would use lex/yacc (or flex/bison) for the grammar, and not be too complicated. They should handle the latest ANSI C/C++ definitions.

Here's what I've found so far, but haven't looked at them in detail (thoughts?):

  • CScope - Old-school C analyzer. Doesn't seem to do a full parse, though. Described as a glorified 'grep' for finding C functions.
  • GCC - Everybody's favorite open source compiler. Very complicated, but seems to do it all. There's a related project for creating GCC extensions called GEM, but hasn't been updated since GCC 4.1 (2006).
  • PUMA - The PUre MAnipulator. (from the page: "The intention of this project is to provide a library of classes for the analysis and manipulation of C/C++ sources. For this purpose PUMA provides classes for scanning, parsing and of course manipulating C/C++ sources."). This looks promising, but hasn't been updated since 2001. Apparently PUMA has been incorporated into AspectC++, but even this project hasn't been updated since 2006.
  • Various C/C++ raw grammars. You can get c-c++-grammars-1.2.tar.gz, but this has been unmaintained since 1997. A little Google searching pulls up other basic lex/yacc grammars that could serve as a starting place.
  • Any others?

I'm hoping to use this as a starting point for translating C/C++ source into a new toy language.

Thanks! -Matt

(Added 2/9): Just a clarification: I want to extract semantic information from the preprocessor in addition to the C/C++ code itself. I don't want "#define foo 42" to disappear into the integer "42", but remain attached to the name "foo". This, unfortunately, excludes several solutions that run the preprocessor first and only deliver the C/C++ parse tree)


Parsing C++ is extremely hard because the grammar is undecidable. To quote Yossi Kreinin:

Outstandingly complicated grammar

"Outstandingly" should be interpreted literally, because all popular languages have context-free (or "nearly" context-free) grammars, while C++ has undecidable grammar. If you like compilers and parsers, you probably know what this means. If you're not into this kind of thing, there's a simple example showing the problem with parsing C++: is AA BB(CC); an object definition or a function declaration? It turns out that the answer depends heavily on the code before the statement - the "context". This shows (on an intuitive level) that the C++ grammar is quite context-sensitive.

You can look at clang that uses llvm for parsing.

Support C++ fully now link

The ANTLR parser generator has a grammar for C/C++ as well as the preprocessor. I've never used it so I can't say how complete its parsing of C++ is going to be. ANTLR itself has been a useful tool for me on a couple of occasions for parsing much simpler languages.

Depending on your problem GCCXML might be your answer. Basically it parses the source using GCC and then gives you easily digestible XML of parse tree. With GCCXML you are done once and for all.

pycparser is a complete parser for C (C99) written in Python. It has a fully configurable AST backend, so it's being used as a basis for any kind of language processing you might need.

Doesn't support C++, though. Granted, it's much harder than C.

Update (2012): at this time the answer, without any doubt, would be Clang - it's modular, supports the full C++ (with many C++-11 features) and has a relatively friendly code base. It also has a C API for bindings to high-level languages (i.e. for Python).

Have a look at how doxygen works, full source code is available and it's flex-based.

A misleading candidate is GOLD which is a free Windows-based parser toolkit explicitly for creating translators. Their list of supported languages refers to the languages in which one can implement parsers, not the list of supported parse grammars.

They only have grammars for C and C#, no C++.

Parsing C++ is a very complex challenge.

There's the Boost/Spirit framework, and a couple of years ago they did play with the idea of implementing a C++ parser, but it's far from complete.

Fully and properly parsing ISO C++ is far from trivial, and there were in fact many related efforts. But it is an inherently complex job that isn't easily accomplished, without rewriting a full compiler frontend understanding all of C++ and the preprocessor. A pre-processor implementation called "wave" is available from the Spirit folks.

That said, you might want to have a look at pork/oink (elsa-based), which is a C++ parser toolkit specifically meant to be used for source code transformation purposes, it is being used by the Mozilla project to do large-scale static source code analysis and automated code rewriting, the most interesting part is that it not only supports most of C++, but also the preprocessor itself!

On the other hand there's indeed one single proprietary solution available: the EDG frontend, which can be used for pretty much all C++ related efforts.

Personally, I would check out the elsa-based pork/oink suite which is used at Mozilla, apart from that, the FSF has now approved work on gcc plugins using the runtime library license, thus I'd assume that things are going to change rapidly, once people can easily leverage the gcc-based C++ parser for such purposes using binary plugins.

So, in a nutshell: if you the bucks: EDG, if you need something free/open source now: else/oink are fairly promising, if you have some time, you might want to use gcc for your project.

Another option just for C code is cscout.

The grammar for C++ is sort of notoriously hairy. There's a good thread at Lambda about it, but the gist is that C++ grammar can require arbitrarily much lookahead.

For the kind of thing I imagine you might be doing, I'd think about hacking either Gnu CC, or Splint. Gnu CC in particular does separate out the language generation part pretty thoroughly, so you might be best off building a new g++ backend.

Actually, PUMA and AspectC++ are still both actively maintained and updated. I was looking into using AspectC++ and was wondering about the lack of updates myself. I e-mailed the author who said that both AspectC++ and PUMA are still being developed. You can get to source code through SVN or you can get regular binary builds at As with a lot of excellent c++ projects these days, the author doesn't have time to keep up with web page maintenance. Makes sense if you've got a full time job and a life.

Elsa beats everything else I know hands down for C++ parsing, even though it is not 100% compliant. I'm a fan. There's a module that prints out C++, so that may be a good starting point for your toy project.

how about something easier to comprehend like tiny-C or Small C

See our C++ Front End for a full-featured C++ parser: builds ASTs, symbol tables, does name and type resolution. You can even parse and retain the preprocessor directives. The C++ front end is built on top of our DMS Software Reengineering Toolkit, which allows you to use that information to carry out arbitrary source code changes using source-to-source transformations.

DMS is the ideal engine for implementing such a translator.

Having said that, I don't see much point in your imagined task; I don't see much value in trying to replace C++, and you'll find building a complete translator an enormous amount of work, especially if your target is a "toy" language. And there is likely little point in parsing C++ using a robust parser, if its only purpose is to produce an isomorphic version of C++ that is easier to parse (wait, we postulated a robust C++ already!).

EDIT May 2012: DMS's C++ front end now handles GCC3/GCC4/C++11,Microsoft VisualC 2005/2010. Robustly.

EDIT Feb 2015: Now handles C++14 in GCC and MS dialects.

EDIT August 2015: Now parses and captures both the code and the preprocessor directives in a unified tree.

A while back I attempted to write a tool that will automatically generate unit tests for c files.

For preprosessing I put the files thru GCC. The output is ugly but you can easily trace where in the original code from the preprocessed file. But for your needs you might need somthing else.

I used Metre as the base for a C parser. It is open source and uses lex and yacc. This made it easy to get up and running in a short time without fully understanding lex & yacc.

I also wrote a C app since the lex & yacc solution could not help me trace functionality across functions and parse the structure of the entire function in one pass. It became unmaintainable in a short time and was abandoned.

What about using a tool like GNU's CFlow, that can analyse the code and produce charts of call-graphs, here's what the opengroup(man page) has to say about cflow. The GNU version of cflow comes with source, and open source also ...

Hope this helps, Best regards, Tom.

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