使用CMAKE添加图书馆（CLI11）下载了GitHub的表单

Question

我想在我的C ++项目中添加一个库。我不知道该怎么做 这是我的项目树

├── build
├── build.sh
├── CMakeLists.txt
├── include
│   └── CLI11.hpp
└── src
    └── main.cc

，这是我的cmakelists，

cmake_minimum_required(VERSION 3.16.3)

project(yup)


set(CMAKE_CXX_STANDARD 20)

# add cli11

if (NOT DEFINED CLI11_DIR)
    set(CLI11_DIR "/usr/local/lib/CLI11" CACHE STRING "cli11 git repo")
endif()

# src/
include_directories(${PROJECT_SOURCE_DIR}/src)

include_directories(${CLI11_DIR}/include)
include_directories(${PROJECT_SOURCE_DIR}/include/)

add_executable(yup 
    src/main.cc
)

target_link_libraries(CLI11::CLI11)

为什么这不起作用？为什么在C ++中很难添加外部依赖性？