CMake如何避免递归add_subdirectory？

Question

我的工作区结构如下

workspace
  library1
  library2
  library3

library3依赖于library2和library1

library2依赖于library1

在library3 CMakeLists.txt中

cmake_minimum_required (VERSION 3.9)
add_subdirectory(../library2 ${CMAKE_CURRENT_SOURCE}/../library2/build)
add_subdirectory(../library1 ${CMAKE_CURRENT_SOURCE}/../library1/build)

在library2 CMakeLists.txt中

cmake_minimum_required (VERSION 3.9)
add_subdirectory(../library1 ${CMAKE_CURRENT_SOURCE}/../library1/build)

library2中的cmake会抛出一个错误，指出library1/build已经包含cmake文件。

CMake Error at C:/Users/me/workspace/Library2/CMakeLists.txt:12 (add_subdirectory):
  The binary directory

    C:/Users/me/workspace/Library1/build

  is already used to build a source directory.  It cannot be used to build
  source directory

    C:/Users/me/workspace/Library1

  Specify a unique binary directory name.

Answer 1

我个人会这样做，在workspace中，我有一个根CMakeList.txt文件来设置项目：

# Set the minimum version of cmake required
cmake_minimum_required(VERSION 3.9)
project(MyProject)
add_subdirectory(library1)
add_subdirectory(library2)
add_subdirectory(library3)

(这就是您真正需要的，您的根CMakeLists.txt文件根本不需要很长)。

然后，对于需要依赖项的库，使用add_dependencies( \[\]...)来确保依赖项目标在当前目标之前构建，而不是调用相对路径add_subdirectory()调用。

因此，在library3/CMakeLists.txt中，在add_library/add_executable和target_link_libraries调用(如果适用)之后添加：

add_dependencies(library3 general path/to/library2 general path/to/library1

作为一个例子。