From: Jason Roelofs <jameskilton@...>
Date: 2011-07-11T21:32:39+09:00
Subject: Re: FFI with a C++ Library

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On Jul 9, 2011, at 1:16 AM, Michael Edgar wrote:

> On Jul 9, 2011, at 12:40 AM, Mike Bethany wrote:
>> This may be more of a C++ question but here goes:
>>=20
>> I'm trying to use Ruby FFI with a CPP library but when I compile my =
CPP
>> library and look at the method names there's always a __Z5, __Z4, or =
__Z3 in
>> front of the method name. I see this when I run nm against the dynlib =
file.
>>=20
>> Oddly when I compile a C file it works fine but I can use a C file =
because
>> I'm using some CPP libraries in my library.
>=20
> This is due to what's called "name mangling" - it's how C++
> differentiates different functions with the same name based on
> namespace, overloads, etc. You can learn more on
> Wikipedia [0].
>=20
> To resolve this, you need to specify the functions being
> called with C linkage. Wrap the necessary function as
> follows in your .cpp/.cc file:
>=20
> extern "C" {
>  void foo(...) {
>  }
> }
>=20
> This will give foo the external name "foo" instead of how
> it would be defined with C++ linkage.
>=20
> If you have C headers and see them being used from
> C++ and wish to keep the unmangled names, you can
> add this to the top of your C header:
>=20
> #ifdef __cplusplus
> extern "C" {
> #endif
>=20
> and this at the bottom:
>=20
> #ifdef __cplusplus
> }
> #endif
>=20
>=20
> [0] http://en.wikipedia.org/wiki/Name_mangling
>=20
> Michael Edgar
> adgar@carboni.ca
> http://carboni.ca/

Another solution is to use the Rice library (http://rice.rubyforge.org/) =
to build C++ bindings. That said, depending on the size of the C++ code =
you're working with, it's probably simpler to go with your own code =
inside an extern C { } as Michael explained above and from that you can =
use FFI.

Jason=

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