cmake does not create rules to create .lib target.

Usage
1

Hi

I have a build that is very simple and essentially creates a shared library (an Emacs module).

The subdirectory CMakeLists.txt file just contains the following. The top CMakeLists.txt just contains, essentially, the definition of EMACS_MODULE_INCLUDE_DIR.

add_library(platel_emacs_module SHARED platel_emacs_module.c platel.c)

set_target_properties(platel_emacs_module PROPERTIES PREFIX “”)

target_include_directories(platel_emacs_module
INTERFACE
${CMAKE_CURRENT_SOURCE_DIR}
)

target_include_directories(platel_emacs_module
PUBLIC
“${EMACS_MODULE_INCLUDE_DIR}”
)

On Mac OS things work as advertised (following Steps 1-3 of the Tutorial). But on Windows with VS I get this error. Yes, the VS environment is set up properly. It appears that cmake creates a spurious target for which no build instructions are given; this seems to be for “testing”.

C:\Users\marco\Projects\Lang\ELisp\platel\platel_build>cmake --build .
MSBuild version 17.12.12+1cce77968 for .NET Framework

1>Checking Build System
Building Custom Rule C:/Users/marco/Projects/Lang/ELisp/platel/c/CMakeLists.txt
platel_emacs_module.c
platel.c
Generating Code…
platel_emacs_module.vcxproj → C:\Users\marco\Projects\Lang\ELisp\platel\platel_build\c\Debug\platel_emacs_module.dll
Building Custom Rule C:/Users/marco/Projects/Lang/ELisp/platel/CMakeLists.txt
platel_test.c
LINK : fatal error LNK1104: cannot open file ‘c\Debug\platel_emacs_module.lib’ [C:\Users\marco\Projects\Lang\ELisp\plat****el\platel_build\platel_check.vcxproj]

C:\Users\marco\Projects\Lang\ELisp\platel\platel_build>

Any ideas about what could be done to fix this?

Thanks

Marco

2

Does your DLL actually export any symbols? An import .lib is only created if any symbols are exported from the DLL.

3

AFAIU no. I do not “export” any symbols.

The question is that cmake seems to create a target, without analyzing the spec (I do not pretend it analyzed the code), but it does so without any warning.

What am I after? A single spec that generated makefiles in a platform dependent way, and AFAIU, the Tutorials do not work on Windows.

MA

4

See this blog: https://www.kitware.com/create-dlls-on-windows-without-declspec-using-new-cmake-export-all-feature/. For C++ on Windows, you need to export symbols or you don’t get an import library.

5

Does it help if you use MODULE instead of SHARED for add_library()?

6

Thank you. That helps. However, no mention of it (I may be wrong) is made in the Tutorial. Hence, if you try the tutorial on a Windows machine with VS installed (no other UN*X-like stuff), you are going to get stumped.

Let me do some more tests…

All the best

Marco

7

Thanks. Yes, but that is not the problem.

The problem is that the tutorial assumes a UN*X setup and Windows DLLs cannot be simply built.
Plus IMHO the MSVC build system generator is somewhat broken; it appears to create a project file which contains a broken .lib dependency: it should know better IMHO.

MA

8

Exactly where in the Tutorial? The Tutorial code is tested on all platforms.

9

Hi Bill

I think I reconstructed my personal issue with the Tutorial. Actually there are two. The first one is that, unlike my wife, I read a bit and then I try things; she reads everything beforehand.

Apart from that, I followed the tutorial and tried to build a SHARED library. Alas, the Tutorial (Step 2) does not build a SHARED library, but just links in an object, static, one.

Here is the catch: if you add SHARED to Step 2, TODO 1, the compilation on Windows with MSBuild fails with the error reported before (in an empty Step2_build folder; if you built the object file before and then just add SHARED to the MathFunctions/CMakeLists.txt add_library, the build would succeed (obviously)).

How to fix it? Add a note saying that to build SHARED libraries, especially on Windows, you need to RTMF about tarket_link_libraries. As it is now, you can run the tutorial Step 2 without problems on UN*X, but you need to add things on Windows.

Yes. A note in the Tutorial would suffice.

Nope. I have not yet figured out how to fix the issue.

All the best

MA