CMake finds more than one main function - c++

Question

I am trying to compile a project that has only one main function, but CMake find more.
My CMakeLists.txt is like:
cmake_minimum_required(VERSION 2.8)
project(my_proj)
include_directories(".")
add_subdirectory(main)
add_subdirectory(resources)
find_package(OpenCV REQUIRED)
find_package(Boost REQUIRED COMPONENTS system regex program_options)
include_directories(${Boost_INCLUDE_DIRS})
file(GLOB_RECURSE SRC_FILES ${PROJECT_SOURCE_DIR}/*.cpp)
file(GLOB_RECURSE HDR_FILES ${PROJECT_SOURCE_DIR}/*.hpp)
add_executable(my_proj ${SRC_FILES} ${HDR_FILES})
target_link_libraries(my_proj ${OpenCV_LIBS})
target_link_libraries(my_proj ${OpenCV_LIBS}
${Boost_PROGRAM_OPTIONS_LIBRARY}
${Boost_REGEX_LIBRARY}
${Boost_FILESYSTEM_LIBRARY}
${Boost_SYSTEM_LIBRARY})
I have more folders with .hpp and .cpp files that is why I have added file(GLOB_RECURSE... statements and also include_directories(".").
I get an error after it compiles all files that says:
CMakeFiles/my_proj.dir/CMakeFiles/CompilerIdCXX/CMakeCXXCompilerId.cpp.o: In function `main':
/media/N/my_proj/build/CMakeFiles/CompilerIdCXX/CMakeCXXCompilerId.cpp:209: multiple definition of `main'
CMakeFiles/my_proj.dir/main.cpp.o:/media/N/my_proj/main.cpp:10: first defined here
CMakeFiles/my_proj.dir/main/solution2/sources/CRunSolution2.cpp.o: In function `boost::filesystem3::path::codecvt()':
/usr/include/boost/filesystem/v3/path.hpp:377: undefined reference to `boost::filesystem3::path::wchar_t_codecvt_facet()'
Has anyone met something like that? If yes, how to fix it?

Answer 1

In your executable you simply have 2 main functions (print out SRC_FILES by MESSAGE(${SRC_FILES})). One is in main.cpp and one in CMakeCXXCompilerId.cpp (which is a file that CMake generates to test if your CXX compiler works correctly). The GLOB_RECURSE probably finds and adds both of these files to SRC_FILES
Using FILE(GLOB ...) is tricky:
We do not recommend using GLOB to collect a list of source files from your source tree. If no CMakeLists.txt file changes when a source is added or removed then the generated build system cannot know when to ask CMake to regenerate.
You should list your source and header files in your CMakeLists.txt directly