Static linking search for dynamic symbols (VS 2015)

Question

I'm trying to compile a project and link it with a static library that I compiled before. My file compile, however it doesn't link.

I'm getting these messages (I truncated it, otherwise it's too long):

error LNK2019: unresolved external symbol __imp_flann_build_index referenced in function ....
error LNK2019: unresolved external symbol __imp_flann_find_nearest_neighbors_index referenced in function ...
error LNK2019: unresolved external symbol __imp_flann_free_index referenced in function ...
error LNK2019: unresolved external symbol __imp_DEFAULT_FLANN_PARAMETERS referenced in function ...

From my understanding is that __imp_ symbols means the linker is trying to find the dll. However, I compiled the library as static, and I properly set the 'Additional Library directories' and 'Additional Dependencies'.

My library is compiled with /MD as my executable. I tried to switch to /MT but because I have other dependencies etc... it just starts messing everything up.

I checked in the library and the symbols are there, but without the __imp_ prefix.

I also put my library at the end so it should resolve symbols, but it still doesn't work.

I don't know what's going on here. Any help is welcome.

Thanks.

Edit: Actually it's a bit less straight forward than I mentionned. Here is what I have:

FLANN library ---> file1.cpp  --
                   file1.h     | ---> files.lib ----    
                   file2.cpp   |                   |
                   file2.h    --                   |---> program.exe
FLANN.lib ------------------------------------------

Basically I have files using FLANN library (include headers and call functions of the FLANN library). I want to create a static library of these files, and link it to myprogram.exe (and this is where I get the errors mentionned earlier). But I noticed that already in files.lib I have the symbols __imp_ . I don't understand why it uses the dynamic symbols there though.

What I'm trying to do is to tell files.lib to use the static symbols of FLANN.lib, because this is what I will link myprogram.exe to, but so far, it seems the linker doesn't care, and just assume FLANN will be a dynamic library.

Answer 1

I finally figure it out.

It turns out that the compiler cannot know in advance if I will be linking FLANN with a static or dynamic library.

So I looked into FLANN library itself, and deep there, there is a MACRO (FLANN_STATIC) that should be passed as a compile definition (target_compile_definitions in cmake) to let the compiler know that it will be a static library (as we say, by default, it assumes it will be a dynamic library).

Then I had to add into my CMakeLists.txt for files.lib:

target_compile_definitions(files.lib PUBLIC FLANN_STATIC)

and it worked. I know nobody answered, but it took me hours to find this, so hopefully someday, it might save somebody's hours !!