c++ - CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS does not cover global variables

Question

Porting a C++ library, under CMake, to Windows.

• Option 1: Decorate the API with __declspec(dllexport).
• Option 2: set(CMAKE_WINDOWS_EXPORT_ALL_SYMBOLS ON).

We go for option 2, since it seems much easier, and leaves our sources intact. Works like a charm: our application compiles and gets linked with the library dll.

However, it ensures only the export of classes and functions. What needs to be done to export global variables? Like in:

lib_source.cpp:
    int my_secret;

app.cpp:
    extern int my_secret;

Answer 1

For global data symbols, __declspec(dllimport) must still be used when compiling against the code in the .dll.

src: https://cmake.org/cmake/help/latest/prop_tgt/WINDOWS_EXPORT_ALL_SYMBOLS.html