include(FetchContent) FetchContent_Declare(json GIT_REPOSITORY https://github.com/ArthurSonzogni/nlohmann_json_cmake_fetchcontent GIT_TAG v3.10.2) FetchContent_GetProperties(json) if(NOT json_POPULATED) FetchContent_Populate(json) add_subdirectory(${json_SOURCE_DIR} ${json_BINARY_DIR} EXCLUDE_FROM_ALL) endif()