Re: template function can't be instantilized (use keyword export?)

I have a small demo with 5 files which describe the problem.

b.h:

#ifndef BB
#define BB
class B
{
public:
    template<typename T> T bf() const;
};
#endif
//////////////////////////
b.cpp:

#include "b.h"
#include <iostream>
using namespace std;
template<> int B::bf<int>() const {cout << "int" << endl;return 10;}
template<> double B::bf<double>() const {cout << "double" <<
endl;return 1.1;}
///////////////////////////////
a.h:

#ifndef AA
#define AA
#include "b.h"
class A
{
public:
   template<typename T> T a() const;
private:
   B mb;
};
#endif
///////////////////////////////////
a.cpp:

#include "a.h"
template<typename T> T A::a() const {return mb.bf<T>();}
//////////////////////////
main.cpp

#include <iostream>
#include "a.h"
using namespace std;
int main()
{
   A *a = new A;
   a->a<double>();
   return 0;
}

///////////////////////
If I compile the project,

g++ a.cpp b.cpp main.cpp

I get a link error:

main.cpp:(.text+0x83): undefined reference to `double A::a<double>()
const'
collect2: ld returned 1 exit status

which means the A::a<double> is not instantilized. I try to use
'export' to solve this problem, but g++ doesn't support this keyword
atm. If I dump all code into one file, then the problem doesn't show
up. So, is there any work around other than this?