Short version:
link to your lib file.

Long version:
A recent project I'm working on requires me to make a plugin for a native C++ application. So I need to create a dll that exposes C functions thru dllexport. As a .Net guy, I've my business model and UI written in .Net and a C++/CLI project serves as a glue project between .net and the native C++ application. The solution looks like this:

- plugin.dll (C++/CLI, used by native C++ application, depends on businesslogic.dll)
- businesslogic.dll (C++/CLI, contains a native C++ class that will get called by plugin.dll)
- ui.dll (C#, used by businesslogic.dll)

After coding everything, I find out that all dll compiles fine except pluging.dll: it complains about LINK2028 & LNK2019. I know the linker error usually tells me that something is missing its definition. But I'm still scratching my head because A: I have the header file included and B: I have the dll added to the project reference. In .net the project should build fine. But it turns out that since businesslogic.dll is a mixed dll, to use with plugin.dll, I should also link to the businesslogic.lib file.

It took me about 30 minutes to figure out that I need to link to the lib file of my own C++/CLI project. I know, I'm not that familiar with native programming. Anyway, if you google "LNK2028" you'll find a lot of questions asked, either with no answer or answers doesn't make sence. So I'd like to share this post with everyone, hopefully can save someone's time. (especially .net programmer)

BTW: here is a similar error with the same solution.