Undefined reference to function CMake

Question

I am trying to learn CMake, but I get a undefined reference to ... linker error I have a directory with a subdirectory. each of them has its own CMakeLists.txt

test
|----main.cpp
|----CMakeLists.txt
|----test2
     |----foo.hpp
     |----foo.cpp
     |----CMakeLists.txt

the CMakeLists.txt for test is:

cmake_minimum_required(VERSION 3.5)
project(tests)

add_subdirectory(test2)
set(SOURCE_FILES main.cpp)
add_executable(tests ${SOURCE_FILES})

the CMakeLists.txt for test2 is:

set(test2_files
        foo.cpp
        foo.hpp
        )
add_library(test2 ${test2_files})

foo.cpp implements a function which is defined in foo.hpp for this function I am getting the undefined reference error. What am I doing wrong? How can I get rid of this linker error

EDIT: My CMakeLists.txt now looks like this, but I still get the linker error:

project(tests)

cmake_minimum_required(VERSION 2.8)

set(SOURCE_FILES main.cpp)

include_directories(test2)
link_directories(test2)

add_subdirectory(test)

add_executable( ${PROJECT_NAME} ${SOURCE_FILES} )

target_link_libraries(${PROJECT_NAME} test2)

I also tried it with the absolute path instead of test2

EDIT: solved it it was only a typo in the CMakeLists.txt of test2.

Answer 1

Make sure that your test CMakeLists.txt links to the created library.

project(test)

cmake_minimum_required(VERSION 2.8)

set(SOURCE_FILES main.cpp)

include_directories( test2 )

#here
link_directories(test2)

add_subdirectory(test2)

add_executable( ${PROJECT_NAME} ${SOURCE_FILES} )

#and here
target_link_libraries( ${PROJECT_NAME} test2 )

Answer 2

Function add_subdirectory($dir) does not automatically add $dir to include directories and link directories. To use library test2 you should do it manually in CMakeLists.txt of test directory:

include_directories(test2/)
link_directories(test2/)

Then, link your executable with test2 library to get functions definitions. Add to CMakeLists.txt of test directory:

target_link_libraries(tests test2)