c++ - Using Eigen Lib in my Cmake project?

Question

I am having difficulty using a header-only library (Eigen) in my CMake project. When i take off all the portion related to Eigen library it compiles, but not sure how to build with (Eigen). Note that Eigen has a CmakeLists.txt in Eigen folder, and it has /src folder having (*.h and *.cpp) related to Matrix operation etc...

The structure of my program is as follow

Myproject (folder) is composed of :

• CmakeLists.txt
• /Build
• /Source

The Source folder has bunch of my files (*.h and *.cpp) and the /Eigen (folder).

what i did is :

FIND_PACKAGE(PkgConfig REQUIRED)
PKG_CHECK_MODULES(GTK3 REQUIRED gtk+-3.0)
LIST(APPEND CMAKE_CXX_FLAGS 
    "-std=c++0x
     -pthread 
     ${CMAKE_CXX_FLAGS} 
     -g 
    -Wall -Wextra ")

ADD_LIBRARY(Eigen ${CMAKE_SOURCE_DIR}/Eigen)
TARGET_INCLUDE_DIRECTORIES(Eigen INTERFACE
 $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src>
 $<INSTALL_INTERFACE:include/Eigen>
)

INCLUDE_DIRECTORIES(${GTK3_INCLUDE_DIRS})
ADD_DEFINITIONS(${GTK3_CFLAGS_OTHERS})
INCLUDE_DIRECTORIES(include)
ADD_LIBRARY(RTT 
        Def.cpp 
        Def.h       
        krnel.cpp 
        krnel.h 
        Mesh.cpp 
        Mesh.h 
        Mcom.cpp 
        Mcom.h 
        timer.h 
        Identifier.h)       

ADD_EXECUTABLE(Rdrtst main.cpp)
TARGET_LINK_LIBRARIES(Rdrtst RTT ${GTK3_LIBRARIES} Eigen)

When i cd to /Build and type (Cmake ../Source )

I get the following :

[/../Build]$ cmake ../Source
-- Configuring done
CMake Error: Cannot determine link language for target "Eigen".
CMake Error: CMake can not determine linker language for target:Eigen
-- Generating done
-- Build files have been written to: /../../MyProject/Build

The eigen folder has the CMakeLists.txt with the following content :

include(RegexUtils)
test_escape_string_as_regex()

file(GLOB Eigen_directory_files "*")

escape_string_as_regex(ESCAPED_CMAKE_CURRENT_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}")

foreach(f ${Eigen_directory_files})
  if(NOT f MATCHES "\.txt" AND NOT f MATCHES "${ESCAPED_CMAKE_CURRENT_SOURCE_DIR}/[.].+" AND NOT f MATCHES "${ESCAPED_CMAKE_CURRENT_SOURCE_DIR}/src")
    list(APPEND Eigen_directory_files_to_install ${f})
  endif()
endforeach(f ${Eigen_directory_files})

install(FILES
  ${Eigen_directory_files_to_install}
  DESTINATION ${INCLUDE_INSTALL_DIR}/Eigen COMPONENT Devel
  )

add_subdirectory(src)

Answer 1

You are trying to include Eigen as a compiled library. However, as you have stated, Eigen is really a header only library and does not need to be compiled, just included. There should be no .cpp files at all.

Remove the line

ADD_LIBRARY(Eigen ${CMAKE_SOURCE_DIR}/Eigen)

as that is meant for static or shared libraries. Now that you're not building Eigen, you can remove the line

TARGET_INCLUDE_DIRECTORIES(Eigen ...

The Eigen CMakeLists file really just copies the Eigen header files to an include directory and doesn't compile anything. See this link for an example of how to use Eigen with CMake.