Variables that Provide Information （cmake-variables(7) — CMake 3.0.2 Documentation）

  1： CMAKE_INCLUDE_CURRENT_DIR

       set (CMAKE_INCLUDE_CURRENT_DIR ON)  //自动添加CMAKE_CURRENT_BINARY_DIR和CMAKE_CURRENT_SOURCE_DIR到当前处理的CMakeLists.txt;

 2:    CMAKE_CURRENT_SOURCE_DIR:指的是当前处理的CMakeLists.txt所在的路径；

 3:    CMAKE_CURRENT_BINARY_DIR:如果是in-source编译，则跟CMAKE_CURRENT_SOURCE_DIR一致；如果是out-of-source，指的是target编译目录；

 in-source build 和 out-of-source build 

   in-source build：（源码中构建） in-source是指在顶层CmakeLists.txt中中直接执行

    cmake  .

  out-of-source build:是指在非CmakeLists.txt中目录执行 cmake 

//假设顶层的CMakeLists.txt在bulid同级目录
mkdir build
cd ./build
cmake ../
make