automational

I am toying with a CMake project for Apknite and in the tutorial, there is a step about system introspection. I tried to do a very simple test which I thought would work but unfortunately, it doesn't. I have a simple module called add which exists in its own module and defines a function called add. directory structure ├── bin ├── cmake_bin ├── CMakeLists.txt ├── src │ ├── add │ │ ├── add.c │ │ ├── add.h │ │ └── CMakeLists.txt │ ├── CMakeLists.txt │ ├── main.c │ ├── main.h │ └── version.h.in src/CMakeLists.txt has the following lines add_executable(main.out main.c) add_subdirectory(add) include(${CMAKE_ROOT}/Modules/CheckFunctionExists.cmake) check_function_exists (add HAVE_ADD) configure_file( "${CMAKE_CURRENT_LIST_DIR}/version.h.in" "${EXECUTABLE_OUTPUT_PATH}/version.h" ) where main.c includes add.h and makes use of the add function. version.h.in contains #cmakedefine HAVE_ADD Can someone help me understand why when version.h is generated it reports looking for add - not found? What I have tried so far is to move the check_function_exists in the src/add/CMakeLists.txt and to use check_symbol_exists(add add.h HAVE_ADD). After a glance at the internetz, I saw that check_function_exists is for system header files but I don't quite get why or how it would distinguish between system files and my source files. Any help is appreciated.