Okay, thank you, now it's clear. The Visual Studio solutions has Header files and Resource files folder, and does this process automatically. But I need to do that manually in this case, or modify the compile.bat / compile64.bat to do that.

To still though enforce it automatically, the not-elegant and the very-non-standard solution is writing the declarations and definitions in different files, then include them independently from each other.

We have the
- func_declaration.cpp
- func_definition.cpp
- obj_declaration.cpp
- obj_definition.cpp

Then:
in func_definition.cpp I start with including the func_declaration.cpp and obj_declaration.cpp, then obj_definition.cpp.
in obj_definition.cpp I also start with including the func_declaration.cpp and obj_declaration.cpp, then func_definition.cpp.
Every file with the #pragma once command.

Therefore it automatically compiles everything with just one click in Zorro UI, without modifying compile.bat, and I can also separate the code parts. But as I see it would be much cleaner to compile the object files then link them together.