Importing explicitly instantiated template class from dll.

Being a dll newbie I have to ask the allmighty SO about something.

Say I explicitly instantiate a template class like this:

template class __declspec(dllexport) B<int>;

How do I use import this templated class again?

I've tried the adding the code below in my .cpp file where I want to use B

template class __declspec(dllimport) B<int>;

From stackoverflow

• When you instantiate a template fully -- you have a complete type. It is no different from any other types. You need to include the header for B and also compile-time linking in with a lib file or dynamically load the dll to link to the definition.

  Have you read this article: http://support.microsoft.com/kb/168958 ?

  Here's a brief summary of what I tested (and it worked):

  ---

  Create a dummy DLL project

  • Used the Win32 Console application wizard to generate the dll header/source files called: template_export_test
  • Added the following:

  file: template_export_test.h

  ---

  #ifndef EXP_STL
  #define EXP_STL
  #endif 
  
  #ifdef EXP_STL
  #    define DECLSPECIFIER __declspec(dllexport)
  #    define EXPIMP_TEMPLATE
  #else
  #    define DECLSPECIFIER __declspec(dllimport)
  #    define EXPIMP_TEMPLATE extern
  #endif
  
  EXPIMP_TEMPLATE template class DECLSPECIFIER CdllTest<int>;
  

  ---

  file: template_export_test.cpp

  ---

  template<class T>
  CdllTest<T>::CdllTest(T t)
  : _t(t)
  {
      std::cout << _t << ": init\n";
  }
  

  ---

  Create the test application

  • Use the wizard to create a Win32 Console application called: driver
  • Edit the Linker project settings of this project:
    • Add to Linker > General > Additional Library Directories: path to template_export_test.lib
    • Add to Linker > Input > Additional Dependencies: template_export_test.lib
  • Include the template_export_test.h in the main cpp file

  ---

  #include "c:\Documents and Settings\...\template_export_test.h"
  using namespace std;
  
  int main(int argc, char** argv) {
      CdllTest<int> c(12);
  }
  

  ---

  • Compile and go!
  Nailer : I've tried : extern template class __declspec(dllimport) B; Didn't work.

• It seems, even with explicit instatiation of the template, problems may arise that lead to run-time errors. Take a look at this interesting article to C4251 (especially the "Conclusion").