此项目中使用了以下变量，但它们设置为 NOTFOUND

Question

我是第一次使用 CMake，但有一些理解上的问题。谁能向我解释一下 ERROR 是什么意思，为什么以及如何解决它？

对于我的项目，我下载了 git-libraries "libubox-master" 和 "ubus-head" 并将它们分别放入我的项目目录中的文件夹 "libubox" 和 "ubus" 中。这些库已经有不同的 CMakeList.txt 文件。 在我的项目目录中，我自己创建了文件 client.c、server.c、server.h 和 CMakeLists.txt。

我的文件夹结构：

project/
--------cmake-build-debug/ ...
--------libubox/ ... provided files and folders, including CMakeFiles
--------ubus/ ... provided files and folders, including CMakeFiles
--------client.c
--------CMakeLists.txt
--------server.c
--------server.h

我的 CMakeList.txt 文件如下所示：

   cmake_minimum_required(VERSION 3.7)
   project (ubusDemo)

   add_subdirectory(libubox)
   add_subdirectory(ubus)

   add_executable(Client client.c)
   add_executable(Server server.c)

所以这只是一个简单的文件 - 我是不是忘记了一些必要的东西？

我得到的错误信息：

CMake Error: The following variables are used in this project, but they are set to NOTFOUND.
Please set them or make sure they are set and tested correctly in the CMake files:
blob_library
    linked by target "ubusd" in directory /home/matthias/Workspace/ubusDemo/ubus
    linked by target "cli" in directory /home/matthias/Workspace/ubusDemo/ubus
    linked by target "server" in directory /home/matthias/Workspace/ubusDemo/ubus/examples
ubox_include_dir
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus/lua
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus/lua
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus/lua
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus/lua
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus/lua
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus/lua
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus/lua
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus/examples
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus/examples
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus/examples
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus/examples
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus/examples
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus/examples
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus/examples
   used as include directory in directory /home/matthias/Workspace/ubusDemo/ubus/examples
ubox_library
    linked by target "ubus" in directory /home/matthias/Workspace/ubusDemo/ubus
    linked by target "ubusd" in directory /home/matthias/Workspace/ubusDemo/ubus
    linked by target "cli" in directory /home/matthias/Workspace/ubusDemo/ubus
    linked by target "server" in directory /home/matthias/Workspace/ubusDemo/ubus/examples
    linked by target "client" in directory /home/matthias/Workspace/ubusDemo/ubus/examples

我必须在哪里进行更改？ 就在我的 CMakeLists.txt 文件中，还是我必须在其他 CMakeLists.txt 文件中添加一些依赖项？

我如何使用一些头文件，例如libubox 像我的client.c 文件中的blob.h 吗？ 写#include <libubox/blob.h>对吗？

不幸的是，我以前没有使用过 Makefiles（既不是 CMake 也不是 Make）。 我希望，有人可以帮助我。

Answer 1

在每个外部存储库中搜索这些未设置的变量后，我在ubus CMake 文件中找到了它们here：

IF(BUILD_STATIC)
  FIND_LIBRARY(ubox_library NAMES ubox.a)
  FIND_LIBRARY(blob_library NAMES blobmsg_json.a)
ELSE(BUILD_STATIC)
  FIND_LIBRARY(ubox_library NAMES ubox)
  FIND_LIBRARY(blob_library NAMES blobmsg_json)
ENDIF(BUILD_STATIC)

FIND_PATH(ubox_include_dir libubox/usock.h)
INCLUDE_DIRECTORIES(${ubox_include_dir})

ubus 中的这段代码正在寻找由libubox 包提供的头文件和构建 库文件。它假定libubox 已安装在您的机器上，并且搜索到的组件可以在标准系统路径中找到。

使用add_subdirectory() 将libubox 包含在您的CMake 项目中将无法构建它很快；相反，当您调用add_subdirectory(ubus) 时，需要构建和安装libubox。

因此，在运行 CMake 项目之前，您必须手动单独构建和安装 libubox 包。或者，您可以尝试让 CMake 在您的项目中处理这些步骤，如 ExternalProject_Add() 和 execute_process 或 FetchContent，如 this question 的一些答案中所述。如果您选择后者，我鼓励您逐一研究以确定哪种解决方案最适合您的项目。

另外，如果刚刚开始使用 CMake，CMake tag 有一些有用的 CMake 教程和资源。