CMake cannot link executable -ljsoncpp: no such file using github submodules

I am working in a project which uses jsoncpp for parsing and cmake for compilation. I added the jsoncpp official git repository as a submodule to my project with git submodule add REPO_URL external/jsoncpp, so as to keep every dependency together.

When running cmake -B out/build, it works normally. But when I do make, I get the following error:

/usr/bin/ld: cannot find -ljsoncpp: No such file or directory.

The files are organized the following way:

- root
    - out/build
    - external
        - jsoncpp (cloned repo)
    - include
        foo.h
        bar.h
    - src
        foo.cpp
        bar.cpp
        main.cpp
    CMakeLists.txt

The CMakeLists.txt is like this:

cmake_minimum_required(VERSION 3.22.1)
project(ants)


# ".cpp" files in folder "src" into cmake variable "SOURCE"
file(GLOB SOURCE "src/*.cpp")

# Executable
add_executable(${PROJECT_NAME} ${SOURCE})

# Directory where cmake will look for include files
include_directories(include)

# Tells cmake to compile jsoncpp
add_subdirectory(external/jsoncpp)
# Tells cmake where to look for jsoncpp include files
target_include_directories(${PROJECT_NAME} 
    PUBLIC external/jsoncpp/include 
)

target_link_libraries(${PROJECT_NAME} jsoncpp)

Solution

The jsoncppConfig.cmake defines property INTERFACE_INCLUDE_DIRECTORIES for targets jsoncpp_lib and jsoncpp_lib_static.

You need to query the target property and set it manually:

get_target_property(JSON_INC_PATH jsoncpp_lib INTERFACE_INCLUDE_DIRECTORIES)
include_directories(${JSON_INC_PATH})

Linking is done via:

target_link_libraries(${PROJECT_NAME} jsoncpp_lib)

Source.

Try this:

cmake_minimum_required(VERSION 3.22.1)
project(ants)

# ".cpp" files in folder "src" into cmake variable "SOURCE"
file(GLOB SOURCE "src/*.cpp")

# Executable
add_executable(${PROJECT_NAME} ${SOURCE})

# Directory where cmake will look for include files
include_directories(include)

# Tells cmake to compile jsoncpp
add_subdirectory(external/jsoncpp)
get_target_property(JSON_INC_PATH jsoncpp_lib INTERFACE_INCLUDE_DIRECTORIES)
include_directories(${JSON_INC_PATH})

target_link_libraries(${PROJECT_NAME} jsoncpp_lib)