Unresolved external symbol error when creating Armadillo DLL

Question

I am trying to create a dynamic library of the Armadillo linear algebra library, which is originally a header-only library, using VC++ 2010 on Win XP. I created a new project, added the source files, and created a .def file specifying to export only one Armadillo function (the Col class), and I get the LNK2001 error for the Col class. I can create a main and use Col just fine, so I think Col is being included correctly.

I have also tried using "__declspec(dllexport)" on the function definition and it compiles, but the function is not exported since using dumpbin shows nothing, and I can not use the .dll sucessfully. Am I missing something here?

Answer 1

As Armadillo is a C++ template library that uses expression templates, I don't think it's possible to create a DLL out of it.

The expression templates are executed (run) at compile-time by the C++ compiler, whenever compiling code that uses Armadillo classes. Whenever a C++ library uses expression templates (part of template metaprogramming), the library can be thought of as an extension to the C++ compiler.

All the Armadillo code is in headers. As such, even if you managed to export one of the classes (eg. the Col class), none of the associated mathematical machinery (eg. addition, multiplication, etc) would be exported, which is defined all throughout the other parts of the library.