Question

所以我试图了解我的一个C ++项目出了什么问题。基本上，项目1工作正常，一切都很好。在项目的主头文件中我有

#include "spdlog/spdlog.h"

我将spdlog作为项目1中的子项目。此外，在项目1的CMake中，我有include_directories(spdlog/include)。现在，我正在构建项目2，它依赖于项目1并将其作为子项目。但是，当我尝试添加spdlog时，它不允许我，并希望我制作完整的../project1/spdlog/include/spdlog.h。组织此依赖关系并包含标头的正确方法是什么？

Answer 1

您应该寻找现代的cmake资源。在现代cmake样式中，您可以为spdlog创建一个Imported目标，然后您可以在其他任何地方使用它。

让我们假设以下结构

external/spdlog
external/CMakeLists.txt
project1/CMakeLists.txt
project2/CMakeLists.txt
CMakeLists.txt

你写的external/CMakeLists.txt中的

## add the imported library which is 
##   an INTERFACE (ie header only)
##   IMPORTED (ie third party - no compilation necessary)
##   GLOBAL (you can reference it from everywhere 
##           even if the target is not in the same scope
##           which is the case for project1 and project2 because 
##           the spdlog  target is not in their parent folder)
add_library(spdlog INTERFACE IMPORTED GLOBAL)
## set the include directory which is to be associated with this target
## and which will be inherited by all targets which use 
## target_link_libraries(<target> spdlog)
target_include_directories(spdlog INTERFACE spdlog/include)

在根CMakeLists.txt中编写解决方案配置（示例）

project(mysolution)
add_subdirectory(external)
add_subdirectory(project1)
add_subdirectory(project2)

在您的项目CMakeLists.txt中，您现在可以使用在external

中创建的目标

PROJECT1 /的CMakeLists.txt

add_library(project1 ${Sources})
## this will set the include directories configured in the spdlog target (library) 
## and also ensure that targets depending on target1 will have access to spdlog  
## (if PUBLIC were changed to PRIVATE then you could only use spdlog in 
## project1 and dependeing targets like project2 would not 
## inherit the include directories from spdlog it wouldn't 
target_link_libraries(project1 PUBLIC spdlog)

项目2 /的CMakeLists.txt

add_library(project2 ${Sources})
## this will link project1 which in return also links spdlog
## so that now project2 also has the include directories (because it was inherited)
## also targets depending on project2 will inherit everything from project1 
## and spdlog because of the PUBLIC option
target_link_libraries(project2 PUBLIC project1)

来源：

[0] https://cmake.org/cmake/help/v3.9/command/add_library.html

[1] https://cmake.org/cmake/help/v3.9/command/target_link_libraries.html?highlight=target_link_libraries

[2] http://thetoeb.de/2016/08/30/modern-cmake-presentation/（见幻灯片20开头的演示文稿）

CMake - 如何组织依赖项

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