🚀 go-pugleaf

Below is the source for a program and a DLL such as you are asking about, a
program which provides no body for the templated function and a DLL that
provides a body for the templated function specialized for the type used to
call the function in the main program.

.  Ed

----------------------------------------------
#ifndef THEDLLH
#define THEDLLH

// header file used by both the DLL and the program using the DLL
class IntType
  {
public:
  IntType(int i = 0) : value(i)
    {
    }
  ~IntType()
    {
    }
  void swap(IntType & a)
    {
    value ^= a.value;
    a.value ^= value;
    value ^= a.value;
    }
  int Value() const
    {
    return value;
    }

private:
  int value;
  };


#ifdef __BUILDING_DLL
 #define __EXPORT_TYPE _declspec(dllexport)
#else
 #define __EXPORT_TYPE _declspec(dllimport)
#endif


__EXPORT_TYPE
template <class T>
void ClearContainer(T& x);

#endif

----------------------------------------------

// main program source

#include <windows.h>
#include "thedll.h"

void ShowContainer(const char * title, const IntType & c)
  {
  char buffer[128];

  wsprintf(buffer, "Container value is %d", c.Value());
  MessageBox(HWND_DESKTOP, buffer, title, MB_OK);
  }


int WINAPI WinMain(HINSTANCE, HINSTANCE, LPSTR, int)
  {
  IntType container(12);

  ShowContainer("Starting", container);
  ClearContainer(container);
  ShowContainer("After Calling ClearContainer", container);
  return 0;
  }

----------------------------------------------
// DLL source

#include <windows.h>

#define __BUILDING_DLL
#include "thedll.h"


int WINAPI DllEntryPoint(HINSTANCE, unsigned long, void*)
  {
  return 1;
  }


// specialization of ClearContainer for T == IntType
__EXPORT_TYPE template <>
void ClearContainer<IntType>(IntType& x)
  {
  IntType y;
  y.swap(x);
  };


// dummy function used to force compiler to create an
// instance of ClearContainer specialized for T == IntType
__EXPORT_TYPE void NeverCalled(IntType& x)
  {
  ClearContainer(x);
  }

----------------------------------------------

> Gene wrote in message
> news:486fa525$1@newsgroups.borland.com...
>
> Hello,
>
> I got a new problem for Dll calling from BCB2007. The Dll calling is ok in
> BCB6. That code is as in below:
>
> In the Dll header:
>
> #ifdef __BUILDING_DLL
>  #define __EXPORT_TYPE __export
> #else
>  #define __EXPORT_TYPE __import
> #endif
>
> template <class T>
> void __EXPORT_TYPE ClearContainer(T& x) { T y; y.swap(x); };
>
>
> Then I include the header in my main cpp file, and call the function. The
> Dll project build is ok, but when I try to build the main project. It says
> "Link32 error: unresolved external function..." Does any one know what
> causes that and what should I do to get around?
>
> Any suggestion will be appreciated.