CMake 配置以从根目录或子目录构建项目

Question

我最近开始使用 CMake（2.8.12.2，包含在 CentOS 6.8 中的那个），我认为它足够强大，可以帮助完成我想要的，但我无法弄清楚如何 :-) ，所以我呼吁您的智慧来帮助我找到缺失的点。

我有一个这样的项目布局：

BaseDir
|
+-->bin (generated by the process)
|    |
|    +-->Debug
|    +-->Release
|
+-->lib (generated by the process)
|    |
|    +-->Debug
|    +-->Release
|    
+-->CMakeLists.txt
|
+-->Library_A
|    |
|    +-->CMakeLists.txt
|    +-->include
|    +-->src
|    |    |
|    |    +-->CMakeLists.txt
|    |
|    +-->test # Small binary to test solely the library functions 
|        |
|        +-->CMakeLists.txt
|
+-->Library_B (depends on Library_A)
|    |
|    +-->CMakeLists.txt
|    +-->include
|    +-->src
|    |    |
|    |    +-->CMakeLists.txt
|    |
|    +-->test # Small binary to test solely the library functions 
|        |
|        +-->CMakeLists.txt
|
+-->Application_1 (depends on Library_B, hence transitivitely depends on Library_A)
|    |
|    +-->CMakeLists.txt
|    +-->include
|    +-->src
|        |
|        +-->CMakeLists.txt
|
+-->Application_2 (depends on Library_A)
    |
    +-->CMakeLists.txt
    +-->include
    +-->src
        |
        +-->CMakeLists.txt

当我将自己置于 BaseDir 下并运行“cmake .”时，它就像一个魅力。 Application_1、Application_2、Library_A 和 Libray_B 都以正确的顺序构建、链接等。

但是，我的想法是也能够在任何子目录（Application_、Library_）下进行构建，并且在这种情况下，只构建与其相关的代码（即自身，它的测试及其依赖项）。例如，当站在 Library_A 中时，仅构建该文件夹，而从 Library_B 中，也会构建 Library_A，当站在 Application_1 或 Application_2 下时发生的等效情况。另外，独立于我站在哪里触发 cmake 过程，构建结果（库或 bin）必须始终放在 BaseDir/{lib|bin}/{Debug/Release/etc} 下，永远不要放在库或应用程序子目录下.例如，这意味着 Library_B（依赖于 Library_A）或 Application_1（依赖于 Library_A 和 B）的链接必须查看 BaseDir/lib/{Debug/Release}。

我的目标是在 BaseDir 下拥有许多应用程序，因此如果不是真的需要，我希望避免每次都构建它们，只需要我想要的单个应用程序。

我查看了CMakeLists.txt files for multiple libraries and executables 和CMake and finding other projects and their dependencies，但这与我在这里尝试实现的情况并不完全相同。

我尝试过类似以下的方法：

BaseDir/CMakeLists.txt
|
|    cmake_minimum_required (VERSION 2.8)
|    project (BASE_DIR)
|
|    add_subdirectory (Library_A)     # No local dependencies
|    add_subdirectory (Library_B)     # Depends on A
|    add_subdirectory (Application_1) # Depends on A and B
|    add_subdirectory (Application_2) # Depends on A
|
|    # I want all binary outputs (executables and libraries) placed under BaseDir/{lib|bin}/{Debug|Release}
|    set(CMAKE_RUNTIME_OUTPUT_DIRECTORY "${CMAKE_SOURCE_DIR}/bin/${CMAKE_BUILD_TYPE}") # For the executables
|    set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY "${CMAKE_SOURCE_DIR}/lib/${CMAKE_BUILD_TYPE}") # For the static libraries
|    set(CMAKE_LIBRARY_OUTPUT_DIRECTORY "${CMAKE_SOURCE_DIR}/lib/${CMAKE_BUILD_TYPE}") # For the dynamic libraries
|
+-->BaseDir/Library_A/CMakeLists.txt (again, no dependencies)
|    |
|    |    cmake_minimum_required (VERSION 2.8)
|    |    project (LIB_A)
|    |    
|    |    # In case CMake is run from within BaseDir/Library_A and not from BaseDir, I still want the outputs being placed under BaseDir/{lib|bin}/{Debug|Release}
|    |    set(CMAKE_RUNTIME_OUTPUT_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/../bin/${CMAKE_BUILD_TYPE}") # For the test executables
|    |    set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/../lib/${CMAKE_BUILD_TYPE}") # For the static libraries
|    |    set(CMAKE_LIBRARY_OUTPUT_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/../lib/${CMAKE_BUILD_TYPE}") # For the dynamic libraries
|    |
|    |    include_directories(include)
|    |    add_subdirectory (src)
|    |    add_subdirectory (test)
|    |    set(${PROJECT_NAME}_INCLUDE_DIRECTORIES ${PROJECT_SOURCE_DIR}/include CACHE INTERNAL "${PROJECT_NAME}: Include Directories" FORCE)
|    |
|    +-->BaseDir/Library_A/src/CMakeLists.txt
|    |
|    |        cmake_minimum_required (VERSION 2.8)
|    |
|    |        # add all files in the current directory
|    |        file(GLOB LIB_A_SRCS "*.h" "*.cpp")
|    |
|    |        # Create a library called libA.a
|    |        add_library(A ${LIB_A_SRCS})
|    |
|    +-->BaseDir/Library_A/test/CMakeLists.txt
|    
|            cmake_minimum_required (VERSION 2.8)
|    
|            # add all files in the current directory
|            file(GLOB TEST_A_SRCS "*.h" "*.cpp")
|    
|            # Create an executable file from sources
|            add_executable(TEST_A ${TEST_A_SRCS})
|    
|            # Link this executable to the library it's testing
|            target_link_libraries(TEST_A A)
|    
+-->BaseDir/Library_B/CMakeLists.txt (dependency on A)
|    |    
|    |    cmake_minimum_required (VERSION 2.8)
|    |    project (LIB_B)
|    |    
|    |    # In case CMake is run from within BaseDir/Library_B and not from BaseDir, I still want the outputs being placed under BaseDir/{lib|bin}/{Debug|Release}
|    |    set(CMAKE_RUNTIME_OUTPUT_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/../bin/${CMAKE_BUILD_TYPE}") # For the test executables
|    |    set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/../lib/${CMAKE_BUILD_TYPE}") # For the static libraries
|    |    set(CMAKE_LIBRARY_OUTPUT_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/../lib/${CMAKE_BUILD_TYPE}") # For the dynamic libraries
|    |
|    |    include_directories(include)
|    |    add_subdirectory (src)
|    |    add_subdirectory (test)
|    |    set(${PROJECT_NAME}_INCLUDE_DIRECTORIES ${PROJECT_SOURCE_DIR}/include CACHE INTERNAL "${PROJECT_NAME}: Include Directories" FORCE)
|    |
|    +-->BaseDir/Library_B/src/CMakeLists.txt
|    |
|    |        cmake_minimum_required (VERSION 2.8)
|    |
|    |        # add all files in the current directory
|    |        file(GLOB LIB_B_SRCS "*.h" "*.c")
|    |
|    |        # Create a library called libB.a
|    |        add_library(B ${LIB_B_SRCS})
|    |        
|    |        # Add a dependency to Library_A
|    |        find_library(LIBRARY_A A PATHS ${CMAKE_CURRENT_SOURCE_DIR}/../../Library_A)
|    |        include_directories("$LIB_A_INCLUDE_DIRECTORIES")
|    |        target_link_libraries(B ${LIBRARY_A}) 
|    |
|    +-->BaseDir/Library_B/test/CMakeLists.txt
|
|            cmake_minimum_required (VERSION 2.8)
|
|            # add all files in the current directory
|            file(GLOB TEST_B_SRCS "*.h" "*.cpp")
|
|            # Create an executable file from sources, for both versions of the library
|            add_executable(TEST_B ${TEST_B_SRCS})
|            
|            # Link this executable to the library it's testing
|            target_link_libraries(TEST_B B)
|
+-->BaseDir/Application_1/CMakeLists.txt
|    |
|    |    cmake_minimum_required (VERSION 2.8)
|    |    project (APP_1)
|    |    
|    |    # In case CMake is run from within BaseDir/Application_1 and not from BaseDir, I still want the outputs being placed under BaseDir/{lib|bin}/{Debug|Release}
|    |    # In this case, only executables are generated.
|    |    set(CMAKE_RUNTIME_OUTPUT_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/../bin/${CMAKE_BUILD_TYPE}")
|    |
|    |    include_directories(include)
|    |    add_subdirectory (src)
|    |
|    +-->BaseDir/Application_1/src/CMakeLists.txt
|
|            cmake_minimum_required (VERSION 2.8)
|
|            # add all files in the current directory
|            file(GLOB APP_1_SRCS "*.cpp")
|
|            # Create an executable file from sources
|            add_executable(EXE_1 ${APP_1_SRCS})
|            
|            # This should automatically bring Library_A
|            find_library(LIBRARY_B B PATHS ${CMAKE_CURRENT_SOURCE_DIR}/../../Library_B)
|            include_directories(${LIB_B_INCLUDE_DIRECTORIES})
|            target_link_libraries(EXE_1 ${LIBRARY_B})
|
+-->BaseDir/Application_2/CMakeLists/CMakeLists.txt
    |
    |    cmake_minimum_required (VERSION 2.8)
    |    project (APP_2)
    |    
    |    # In case CMake is run from within BaseDir/Application_2 and not from BaseDir, I still want the outputs being placed under BaseDir/{lib|bin}/{Debug|Release}
    |    # In this case, only executables are generated.
    |    set(CMAKE_RUNTIME_OUTPUT_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/../bin/${CMAKE_BUILD_TYPE}")
    |
    |    include_directories(include)
    |    add_subdirectory (src)
    |
    +-->BaseDir/Application_2/src/CMakeLists.txt

            cmake_minimum_required (VERSION 2.8)

            # add all files in the current directory
            file(GLOB APP_2_SRCS "*.cpp")

            # Create an executable file from sources
            add_executable(EXE_2 ${APP_2_SRCS})

            # Link this executable to the library it needs
            find_library(LIBRARY_A A PATHS ${CMAKE_CURRENT_SOURCE_DIR}../../Library_A)
            include_directories(${LIB_A_INCLUDE_DIRECTORIES})
            target_link_libraries(EXE_2 ${LIBRARY_A})

但没有运气，因为当我从子目录（例如，BaseDir/Application_1）运行时，我只得到：

CMake 错误：此项目中使用了以下变量，但它们设置为 NOTFOUND。 请设置它们或确保它们在 CMake 文件中正确设置和测试： LIBRARY_B

我猜 "find_library()" 调用不足以满足我的要求，它基本上是加载库项目中包含的所有设置，不仅包括库本身，还包括该库添加的包含目录。 find_library() 的具体用法是什么，将其指向创建库的项目的位置，或实际生成的库（“.a”或“.so”）？

所以，我的主要疑问是：这种布局可行吗？如果是这样，我错过了什么？我应该使用 find_package() 还是 find_path() 之类的东西？如何从另一个“相同级别”CMakeLists.txt 触发解析 CMakeLists.txt 配置文件？

PS：我真的需要考虑在任何时候使用 "add_dependencies()" 吗？如果不是，该命令有什么意义？

Answer 1

首先，一条一般建议：在 CMake 中，您总是希望尝试将构建目录与源目录严格分开。特别是，您不应该将文件写回源目录作为构建过程的一部分。编写脚本，以便它们也可以与安装在只读文件系统上的源目录一起使用。虽然一开始这似乎是一个随意的限制，但从长远来看，它实际上可以帮助您避免很多麻烦。

至于你的实际问题：find_library 是一个非常低级的解决依赖问题的工具。这里的想法基本上是您在系统的某个位置安装了第三方库（它本身对 CMake 一无所知）的二进制文件，并且您知道只需通过检查文件系统的内容来找到它们。此处不是这种情况，因为您将依赖项构建为同一 CMake 配置运行的一部分。

您想要做的是直接依赖于依赖项的目标。所以不要这样做：

find_library(LIBRARY_A A)
target_link_libraries(B ${LIBRARY_A}) 

你会直接写

target_link_libraries(B A)

这当然只有在 A 是一个已知目标时才有效，这是您应该关注的问题。

只要您将库作为同一 CMake 运行的一部分继续构建，这非常简单：如果目标是由父目录或同级目录添加的，您应该可以立即使用它。在您的情况下，使事情复杂化的是，您还希望能够单独构建不同的库。这意味着您需要一种将目标导入到构建中的机制，以便看起来该目标是作为同一 CMake 运行的一部分再次生成的。

您可以通过添加imported target 并设置其接口属性来手动执行此操作，也可以使用CMake 的packaging mechanism 以自动方式完成此操作。请注意，这些都不是微不足道的，因此您可能希望从简单的情况开始，即一切都发生在一次 CMake 运行中，然后在您更习惯使用 CMake 后添加对分离构建的支持。