precompiled header issue with cmake

[usergoodvery]

Hi
i tried to include the header file as precompiled in a cmake file, but the linker is not happy, with endless stream of: ld.lld: error: duplicate symbol: xxxxx

I used the directive: target_precompile_headers(${EXEC_NAME} PRIVATE easy_memory.h)

With the above directive, cmake will force-include the header into every file.
I glanced over your header and you seem to have the right guardrails in there like extern and inlines etc...

Have you tried to use your header as precombiled header before?

[gooderfreed]

Hi!

Thank you for bringing this up and pointing out the issue.

To be completely honest, I am not a CMake expert as I mostly rely on Makefiles for my projects, so any additional information you can share to help me understand your setup would be highly appreciated.

If possible, could you share a simplified layout of your project (or your CMakeLists.txt) so I can try to replicate the exact error locally?

Also, could you please check if you defined EASY_MEMORY_IMPLEMENTATION globally as a compile definition? For example, using something like:

target_compile_definitions(${EXEC_NAME} PRIVATE EASY_MEMORY_IMPLEMENTATION)

If that is the case, compiling it as a precompiled header would force-include the full implementation into every source file, which indeed leads to the duplicate symbol errors.

As a quick workaround, you can try defining EM_STATIC alongside the implementation in your CMake:

target_compile_definitions(${EXEC_NAME} PRIVATE 
    EM_STATIC 
    EASY_MEMORY_IMPLEMENTATION
)
target_precompile_headers(${EXEC_NAME} PRIVATE easy_memory.h)

Defining EM_STATIC will force the library functions to use static linkage instead of extern. This will make local copies of the functions for each translation unit, which should resolve the duplicate symbol conflicts.

Please let me know if this workaround helps, or if you can share more details about your setup so we can find a cleaner solution!

[usergoodvery]

Thanks for looking into this issue. I have a fairly complex project setup, with multiple modules controlled by their own cMakeLists.txt file.
I abandoned the idea of precompiled header and opted instead for a single translation unit as far as the library header file is concerned. cmake's default behaviour for precompiled headers proved too heavy-handed.
I am outlining my solution below--feel free to share it in your main docs:

In my cMakeList.txt file where the header lives I created an object library just to encapsulate the header. With that I just simply include the library in the final executable linking process--just like any other library.

1. Define object library (i using clang below)

add_library(compiled_easy_memory_header OBJECT)
target_sources(compiled_easy_memory_header PRIVATE easy_memory.h)
set_source_files_properties(easy_memory.h PROPERTIES
        HEADER_FILE_ONLY FALSE
        LANGUAGE C
        COMPILE_OPTIONS "$<$<C_COMPILER_ID:Clang>:-xc>"
        COMPILE_DEFINITIONS "EASY_MEMORY_IMPLEMENTATION" 
)

2. Executable linking:

target_link_libraries(${EXEC_NAME} LINK_PUBLIC compiled_easy_memory_header other_libs....)

3. Global definition of 'DEM_STATIC'

[gooderfreed]

Thanks for sharing this solution.

This approach is actually very similar to the compilation method described in the README, where the header is compiled directly as a C translation unit using -x c and -DEASY_MEMORY_IMPLEMENTATION.

With this setup, please make sure that EASY_MEMORY_IMPLEMENTATION is not defined in any of your other source files when including the header.

Also, you should no longer need the global EM_STATIC flag. Without it, your other modules can normally link to the extern symbols exported by this object library.

I will add this CMake object library method to the documentation. Thanks again for your feedback!

[usergoodvery]

The clang directive 'set_source_files_properties(easy_memory.h PROPERTIES ...' ensures the EASY_MEMORY_IMPLEMENTATION definition is only applied to the compiled version of the easy_memory.h file. So, no issues there. It is not defined elsewhere except here.

And yes, you are right DEM_STATIC is no longer needed. it was a hold-over from my prior jihad, trying to get cmake to work with this setup :)