Problem building C++ code with Eigen3 and CMake eigen3/Eigen/Core' file not found

Question

I have simple C++ project that is organized like this:

project
|-- Input
|     |-- data.cpp          <-- this file used eigen3
|     |--- CmakeLists.txt
|--- main.cpp
|--- CmakeLists.txt

Basically I am trying to create .so library from input and have main.cpp calls functions in it. CMake under project looks like this

cmake_minimum_required(VERSION 3.20)
project(myProj)

find_package (Eigen3 REQUIRED)

# Dependencies paths
set(EIGEN_INC_DIR  ${EIGEN3_INCLUDE_DIR})

if (TARGET Eigen3::Eigen)
  message("Eigen was found").  <--- I do see this message so Eigen3 package is found
endif (TARGET Eigen3::Eigen) 
add_subdirectory(Input)
<more cmake commands to link with main.cpp>

CMake under Input looks like this

cmake_minimum_required(VERSION 3.20)
set(TARGET_LIB_INPUT input_data)

set(SRC_FILES
    Data.cpp
)

set(INC_DIRS
    ${EIGEN_INC_DIR}
)

include_directories(${INC_DIRS})

add_library (${TARGET_LIB_INPUT} SHARED ${SRC_FILES})
target_link_libraries (${TARGET_LIB_INPUT} Eigen3::Eigen)

in file data.cpp, I do the following include to eigen3

#include <eigen3/Eigen/Core>

But I keep getting the error fatal error: 'eigen3/Eigen/Core' file not found I see the build command clearly include eigen directory: -I /usr/local/include/eigen3

Anybody knows what am I missing here? Thanks for help

Answer 1

The include directory defined in Eigen3::Eigen already includes eigen3 (eg, /usr/include/eigen3 on Ubuntu). So you should use #include <Eigen/Core> .

You can check this by:

find_package(Eigen3 REQUIRED CONFIG)

# checking property of the target
get_target_property(inc_dir Eigen3::Eigen INTERFACE_INCLUDE_DIRECTORIES)
message("[DEBUG] inc_dir: ${inc_dir}")

# or checking the Eigen variable
message("[DEBUG] EIGEN3_INCLUDE_DIRS: ${EIGEN3_INCLUDE_DIRS}")

EIGEN3_INCLUDE_DIRS is defined in here .