Created: 2008-04-20 21:38
Updated: 2017-10-15 17:51
License: mit


What is rbgccxml?

RbGCCXML allows one to easily parse out and query C++ code. This library uses CastXML to parse out the C++ code into XML, and then nokogiri for parsing and querying.

CastXML (https://github.com/CastXML/CastXML) is an application that takes takes the parse tree of g++ and constructs a very parsable and queryable XML file with all related information. CastXML currently only works with code declarations; there currently are no plans to support code bodies.

Note: For those familiar with pygccxml, the similarities are minimal. Outside of the purpose of both libraries, rbgccxml was built from scratch to provide a Ruby-esque query API instead of being a port. However, many thanks to Roman for his work, without which this library would also not exist.


  • nokogiri
  • castxml


gem install rbgccxml

RbGCCXML will work on all platforms that CastXML supports, which includes Windows, Mac, and *nix.

The Project

RbGCCXML's source is in a git repository hosted on github:

Project page:


Clone with:

git clone git://github.com/jasonroelofs/rbgccxml.git



All rbgccxml parses start with the RbGCCXML.parse method:

# Parse a single header file

# Parse out all files that match a given glob

# Parse out a specified set of files"
RbGCCXML.parse(["/path/to/file1.h", "/path/to/file2.h", ...])

# Parse out multiple globs
RbGCCXML.parse(["/my/headers/**/*.h", "/other/headers/*.hpp"])


As CastXML runs on top of Clang, it will need to know about locations of other header files that may be included by the header files being parsed out. Adding these paths is simple:

RbGCCXML.parse(..., :includes => *directories)

where directories can be a single directory string or an array of directories, just like RbGCCXML.parse.

Also, if there are other CXXFLAGS that need to be added to the command line for CastXML to properly parse the source headers (say, -D defines), add those via the :cxxflags option.

RbGCCXML.parse(..., :cxxflags => *flags)

RbGCCXML tries to intelligently find the location of the castxml and clang++ binaries, but if these binaries cannot be found, you can specify an exact path using the :castxml_path and :clangpp_path options respectively.

Querying By Name

Once the header files have been parsed, RbGCCXML.parse returns a Namespace node that references the global namespace "::". From here, all the function, class, etc declarations are easily queryable.

source = RbGCCXML.parse("header.h")  #=> <Namespace ...>

Each major C++ node (class, struct, function, method, argument (of functions, methods, and constructors)) have a related query method that can be called in various ways:

# Get all classes in the current scope

# Explicitly call #find on these classes

# Or use a short cut, if you're just looking for a class by a given name

# Find supports regular expressions as well

These queries are also nestable as long as there's more code available to query. To find the class "Math" inside the namespace "core::utils", you can do:


or in a short-hand / C++ qualified form:


# or

Querying with #find

Of course, querying for names is only the tip of the powerful querying that RbGCCXML supports.

What if you want to find all methods on a class that return an int and have three arguments of any type? This is easy with RbGCCXML:

source.classes("TheClass").methods.find(:returns => :int, :arguments => [nil, nil, nil])

The keys :returns and :arguments can be used on their own or together as seen above. The :arguments option must be an array, and if the type of the argument doesn't matter, placing 'nil' in it's place acts as a wildcard. QueryResult#find is also chainable, provided that there are always more than one result. Otherwise, if there is just one result, only that Node will be returned and any further chained QueryResult#find methods will fail with NoMethodError.

The Next Step

See RbGCCXML::Node for all methods available on all C++ nodes.

See RbGCCXML::QueryResult for the full run-down on #find

Additional Notes

Querying for unsigned types is currently not implemented.

Cookies help us deliver our services. By using our services, you agree to our use of cookies Learn more