From: Tim Pease <tim.pease@...>
Date: 2007-04-14T23:39:11+09:00
Subject: Re: Nuby question on using C++ with Swig - issues with cout

On 4/13/07, james.d.masters@gmail.com <james.d.masters@gmail.com> wrote:
> I am looking into using Swig to bring some C++ libraries into Ruby.
> I'm not extremely C++ proficient, but know the basics.  Anyway, I'm
> having issues with using "cout" within Swig.  I've put together a
> small test case here:
>
> === hello.h ===
> #include <iostream>
> void hello_world() {
>   std::cout << "hello world";
> }
>
> === hello.i ===
> %module example
> %{
> #include "hello.h"
> %}
> %include "hello.h"
>
> === extconf.rb ===
> require 'mkmf'
> $libs = append_library($libs, "supc++")
> create_makefile('hello')
>
> Commands:
>
> % swig -c++ -ruby hello.i
> % ruby extconf.rb
> % make
> % ruby -e 'require "hello"'
> ./hello.so: ./hello.so: undefined symbol: _ZSt4cout - ./hello.so
> (LoadError)
>         from -e:1
>
> Please help me on this... is this an issue with dynamic linking?

C++ name mangling problem.  You need to put extern "C" around your method.

=== hello.h ===
#include <iostream>

#ifdef __cplusplus
extern "C" {
#endif

void hello_world() {
 std::cout << "hello world";
}

#ifdef __cplusplus
}
#endif


Blessings,
TwP