Visual Studio dll export issue for class and function template instantiations

Question

I am using VS2008 in win7 and g++ 4.7 in CentOS 18. The issue is only seen on Windows when I used dynamically shared library. When I convert it static library the program li

Answer 1

I worked out the problem. Under windows class template and function template are exported differently and there is a interesting reading on the net.

VS compilers exports class template symbols if class template is instantiated on the translation unit (.cpp).

However, in the case of function template, the keyword '__declspec(dllexport)' needs to be present explicitly for the symbols to be present on the dynamic library.

e.g

template EXPORT void HelpingRegistration<double>( double );
//EXPORT is defined as __declspec(dllexport) 

It's just another case where VS decide to things differently. There is interesting reading here: http://www.codesynthesis.com/~boris/blog/2010/01/18/dll-export-cxx-templates/

Answer 2

I believe this is because compiler creates specialized code for template class when the template class is first used with a specific parameters. Since compiler uses only the included header files (.h) when compling a compilation unit (.cpp files) all the tmplate code must be available in .h files. You can export specialized template classes from a dll but not the template classes themselves.

Answer 3

I believe you need to export the specializations. Have you tried this in your .cpp file:

template class EXPORT TemplatedStaticLib<double>;
template class EXPORT TemplatedStaticLib<std::string>;

and pretty much the same in your header:

template class EXPORT TemplateStaticLib<double>;
template class EXPORT TemplateStaticLib<std::string>;

I think that will work with your EXPORT macro (assuming the .cpp file see __declspec(dllexport) and the header sees __declspec(dllimport)). I admit I'm not an expert with Windows' __declspec.

I admit that I drew my answer from this other answer on the intarwebs: http://social.msdn.microsoft.com/Forums/vstudio/en-US/4fd49664-e28e-4f23-b1eb-b669d35ad264/function-template-instantation-export-from-dll (scroll all the way to the bottom for Franjo555's final version.)