Static member variable in template, with multiple dlls

Question

My code is built to multiple .dll files, and I have a template class that has a static member variable.

I want the same instance of this static member variable to be available in all dlls, but it doesn't work: I see different instance (different value) in each of them.

When I don't use templates, there is no problem: initialize the static member in one of the source files, and use __declspec(dllexport) and __declspec(dllimport) directives on the class. But it doesn't work with templates. Is there any way to make it work?

I saw some proposed solutions that use "extern", but I think I can't use it because my code is supposed to work with visual studio 2002 and 2005.

Thank you.

Clarification: I want to have a different instance of static variable per each different type of template instantiation. But if I instantiate the template with the same type in 2 different dlls, I want to have the same variable in the both of them.

Answer 1

There exists the following solution, as well:

• in the library: explicitly instantiate some template specialization and share them with dllexport
• in the main program:
  • if the specialization is available it will be used from the library
  • if the specialization is not available it is compiled in the main program

The desciption in detail how you can do this:

Anteru's blog Explicit template instantiation

Answer 2

The problem is that each different template instantiation is a different type with its own static variable that is not shared with other instances that have different template parameters. You could provide a non-template base class that contains the static variable.

Answer 3

Create template specialization and then export the static members of the specialization.