Cplus2Ruby - Gluing C++ and Ruby together in an OO manner


A major rewrite and lots of new features of Cplus2Ruby lead to a 1.0.0
release, actually the first release ever :slight_smile:
And yes, Cplus2Ruby is different from CplusRuby.



Cplus2Ruby - Gluing C++ and Ruby together in an OO manner


Copyright © 2007, 2008 by Michael N. ([email protected]).
All rights reserved.


Ruby License.


Cplus2Ruby (or “C++Ruby”) makes it easy to mix Ruby and C++ in
a seamless way. You can use the power of the Ruby object model
and where needed switch to C++ methods for ultimate performance!

Cplus2Ruby generates getter and setter methods for C++ properties,
and wrapper methods so that you can call your C++ methods from
Ruby without writing a single line of C++ wrapper code. In the same
way stub methods enable your C++ methods to directly call a Ruby

As mentioned above shortly, the main purpose of Cplus2Ruby is speed.
Accessing instance variables in Ruby is somewhat slow compared to
accessing an C++ attribute. Calling a C++ method is as well a lot
faster than calling a Ruby method. Cplus2Ruby now allows you to
write your performance critical methods in C++, which can call other
C++ methods and access C++ attributes with native C++ performance.


gem install cplus2ruby


  • gem install facets
  • C++ compiler and make


Take a look at the following example. You should also take a look
at the generated C++ source file (work/*.cc). Note that properties
are actually members of a C++ class, not instance variables, and as
such, their access from C++ is very fast. As calling a method is
quite slow in Ruby, a method defined in C++ (“method”) can be called
directly from C++, which again is very fast!

 $LOAD_PATH.unshift './lib'
 require 'rubygems'
 require 'cplus2ruby'

 class NeuralEntity; cplus2ruby
   property :id

 class Neuron < NeuralEntity
   property :potential,       :float
   property :last_spike_time, :float
   property :pre_synapses

   method :stimulate, {:at => :float},{:weight => :float}, %{
     // This is C++ Code
     @potential += at*weight;

     // call a Ruby method

   stub_method :log, {:pot => :float}

   def log(pot)
     puts "log(#{pot})"

   def initialize
     self.pre_synapses = []

 if __FILE__ == $0
   # Generate C++ code, compile and load shared library.

   n = Neuron.new
   n.id = "n1"
   n.potential = 1.0
   n.stimulate(1.0, 2.0)
   p n.potential # => 3.0


You can disable the substitution of “@” to “this->” in the generated
C++ source code with:

   Cplus2Ruby.settings :substitute_iv_ats => false

A method signature to return a value (in our case an integer) looks

 method :abc, {:arg1 => :int}, {:arg2 => :float}, {:returns => 

:int}, %{


Mixins can be used:

 module Mixin; cplus2ruby
   property :a

 class C; cplus2ruby
   include Mixin

They don’t generate a C++ class, instead get inlined into the class
into which they are mixed in.

You can use type aliases:

 Cplus2Ruby.add_type_alias 'MyIntegerType' => 'unsigned int'

After that Cplus2Ruby knows about this type and how to convert it
(if it knows how to convert the ‘unsigned int’ type) and you can
use it wherever you want.

Inline, static and virtual methods can be declared like this:

 method :abc, {:a1 => :int}, %{
 }, :inline => true, :static => true, :virtual => true

There is also a static_method short-cut for static methods, so

 method :abc, {:a1 => :int}, %{
 }, :static => true

you can write:

 static_method :abc, {:a1 => :int}, %{

To mark a method in a class hierarchy forever as virtual, you can

 virtual :method1, :method2

You can also define a class that is purely used from within C++.
If you don’t want to generate wrapper code etc. specify:

 cplus2ruby :no_wrap => true

You can use Strings, Symbols and Classes for types in signatures or
in property declarations. There is no distinction between Strings and
Symbols. If you specify a class, it must be known to Cplus2Ruby,
either explicitly:

 class A
   cplus2ruby # marks it known to Cplus2Ruby

Or using inheritance:

 class A
   cplus2ruby # marks it known to Cplus2Ruby

 class B < A  # implicit by inheritance

Global code (mostly type declarations etc.) can be added as shown

 Cplus2Ruby << %q{
   #include <assert.h>
   #include <math.h>

   #define real_exp expf
   #define real_fabs fabsf

   #define THROW(str) rb_raise(rb_eRuntimeError, str)

Compilation flags etc.:

 Cplus2Ruby.startup(module_name, force_compilation, cflags, ldflags)

For example:

 # force_compilation => true regenerates and recompiles the
 # C++ code every time.
 Cplus2Ruby.startup("work/mymodule", true, '-DNDEBUG -Winline

-Wall’, ‘-lm’)


  • I get an “illegal instruction” (sig 4) when the C++ code is
    with -pthread. This is the default in the ports on FreeBSD 7.0 even
    when WITH_PTHREAD is defined. It is somehow related to the GC,
    because when I disable the GC everything is fine (except memory
    usage :).


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