ROS报错：CMakeList.txt配置错误——add_dependencies位置错误（难发现）

 这是我的报错：

CMake Error at server_client/CMakeLists.txt:137 (add_dependencies):
  Cannot add target-level dependencies to non-existent target "demo_server".

  The add_dependencies works for top-level logical targets created by the
  add_executable, add_library, or add_custom_target commands.  If you want to
  add file-level dependencies see the DEPENDS option of the add_custom_target
  and add_custom_command commands.

具有普遍性的一句话是：

CMake Error at ？？？？？/CMakeLists.txt:？？？？？ (add_dependencies):
  Cannot add target-level dependencies to non-existent target "?????".

其中问号是根据路径和文件变化的。

原因：

CMakeList.txt文件中add_executable前后都有add_dependencies，如果只认add_dependencies来进行配置的话很容易出现错误。

修改：（注意add_dependencies位置）

修改前：

## Add cmake target dependencies of the library
## as an