What is wrong in this code?

[Angelo Graziosi]

Dear All,

I have found a build problem with an application which I have reduced to the 
following test case:

$ cat foomain.cc
//
// g++ foomain.cc foo01.cc foo02.cc -o foo.out
//
// g++ -c foomain.cc
// g++ -c foo01.cc
// g++ -c foo02.cc
//
// g++ foomain.o foo01.o foo02.o -o foo.out
//
int main()
{
  return 0;
}

$ cat foo01.cc
#include "foo.hh"

MYCLASS_INSTANTIATE_TYPES

$ cat foo02.cc
#include "foo.hh"

MYCLASS_INSTANTIATE_TYPES

$ cat foo.hh
#ifndef ONCE_FOO_H_
#define ONCE_FOO_H_

template<typename Value_t>
class MyClassBase
{
 public:

  class ClassWrapper;

  MyClassBase();
  ~MyClassBase();
};

template<typename Value_t>
class MyClassBase<Value_t>::ClassWrapper
{
    friend class MyClassBase<Value_t>;

 public:
    ClassWrapper() {}
};

#define MYCLASS_INSTANTIATE(g) g(int)

#define MYCLASS_INSTANTIATE_BASE(type) \
    template class MyClassBase<type>;

#define MYCLASS_INSTANTIATE_TYPES \
  MYCLASS_INSTANTIATE(MYCLASS_INSTANTIATE_BASE)

#endif

This test should be build as

g++ foomain.cc foo01.cc foo02.cc -o foo.out

or

g++ -c foomain.cc
g++ -c foo01.cc
g++ -c foo02.cc

g++ foomain.o foo01.o foo02.o -o foo.out


Now what happens is this:

Building on *** MAC OSX *** with gcc45, gcc46, gcc47 installed by means of 
MacPorts, fails as

$ g++ foomain.o foo01.o foo02.o -o foo.out
duplicate symbol MyClassBase<int>::ClassWrapper::ClassWrapper() in:
    foo01.o
    foo02.o
duplicate symbol MyClassBase<int>::ClassWrapper::ClassWrapper() in:
    foo01.o
    foo02.o
ld: 2 duplicate symbols for architecture x86_64
collect2: error: ld returned 1 exit status

instead it builds (on MAC OSX) using clang++,

$ clang++ foomain.o foo01.o foo02.o -o foo.out
$

It also builds on Cygwin with gcc-4.5.3 and gcc-4.8 snapshot.

It builds on GNU/Linux (K)Ubuntu with gcc-4.6.3

So the question is: does the above code violate some C++ standard?

Maybe is it wrong the way as the inline (the class ClassWrapper constructor in 
the above code) functions are used?

TIA,
 Angelo.