Re: [Haskell-cafe] GHCi fails to load C++ object files (missing symbol)

7 Mar 2012


      Sorry for the double post, but I forgot to mention I'm using GHC 7.4 and
gcc/libstdc++ 4.5.2.
(Running Ubuntu 11.04 Natty Narwhal).

2012/3/7 Yves Parès 
...
Hi, I'm trying to have GHCi load a haskell file that depends on a C++
object file, which causes GHCi to fail because of an unknown symbol (*and
I did link with **libstdc++*), whereas the link into an executable with
ghc works and runs perfectly.
I've reduced my code to the smallest one that produces the problem:
The C++ part defines a mere class and C externals that enable
communication with Haskell:
// Header Stuff.hpp
class Base {
    public:
        Base();
        ~Base();
}
extern "C" {
    Base* mkthing();
    void delthing(Base*);
}
-----------
// Source Stuff.cpp
#include <iostream>
#include "Stuff.hpp"
using namespace std;
Base::Base()
{
    cout << "Base created" << endl;
}
Base::~Base()
{
    cout << "Base deleted" << endl;
}
extern "C" {
    Base* mkthing()
    {
        return new Base();
    }
void delthing(Base* b)
    {
        delete b;
    }
}
Haskell code (just for reference, but I'm not sure it's relevant), Main.hs:
{-# LANGUAGE ForeignFunctionInterface #-}
import Foreign
import Foreign.C
foreign import ccall unsafe "mkthing"
  mkthing :: IO (Ptr ())
foreign import ccall unsafe "delthing"
  delthing :: Ptr () -> IO ()
main = do
  p <- mkthing
  delthing p
I then compile it with:
g++ -c Stuff.cpp
ghci Main.hs Stuff.o -lstdc++
And then the error is:
Loading object (static) Stuff.o ... done
Loading object (dynamic)
/usr/lib/i386-linux-gnu/gcc/i686-linux-gnu/4.5.2/libstdc++.so ... done
final link ... ghc: Stuff.o: unknown symbol `__dso_handle'
linking extra libraries/objects failed
Whereas 'ghc Main.hs Stuff.o -lstdc++' works just fine.
Does GHCi lacks a link directive that regular GHC has?