Question

I’m working on a cross-platform c++/qt project with a plugin system, we are using so files on linux and dll on windows. We are using gcc on Linux and Visual Studio 2010 on Windows through cmake.
The problem is our plugins sometimes need to call a function from the application source code, which is working fine on Linux with gcc by just including the header files. But on Visual Studio, we got unresolved external symbol errors.

Is it because so and dll files works differently?

thank you.

Answer 1

The default behaviour for exporting symbols from dlls on Windows is exactly opposite: by default, symbols are invisible, you need to export them explicitly. With VC++ this is done by __declspec(dllexport) declarators.

EDIT (Information added): You are entering a region of non-standardized, system specific behaviour… There are much more problems associated with writing cross-platform “pluggable” component systems in C++ than you might be expecting. On Windows there are so called import libraries, which define all symbols exported from a dll. You have to link against these libraries in order to resolve these symbols. This is called implicit linking. You can also link explicitly which means loading dll and its exported symbols at run-time. However all these are just technical details compared to so called binary compatibility issues, which will almost certainly kill you, if not considered during the design of your component system.

I am wondering about one thing: You said you’re using Qt. Qt application framework has got it’s own cross platform conventions and rules for writing and building pluggable components. Why don’t you stick with these…?