生成依赖外部资源的header-only个库的.lib

Question

编辑： 我已经阅读并了解最初的问题是由于 scanning-header-only 没有 cpp 文件，因此没有生成 lib 文件。编辑问题以反映额外的理解：

我当前的项目文件夹结构和相关CMakeLists内容：

leveling
├── CMakeLists.txt: add_subdirectory(deps) 
└── deps
    ├── CMakeLists.txt: add_subdirectory(scanning-header-only)
    └── scanning
        ├── CMakeLists.txt: add_subdirectory(deps)
        │                   add_library(scanning-header-only file.h)
        │                   target_include_directories(scanning-header-only PUBLIC ${CMAKE_CURRENT_LIST_DIR}/deps/tinyxml2)
        │                   target_link_libraries(scanning-header-only PUBLIC tinyxml2)
        └── deps
            ├── CMakeLists.txt: add_subdirectory(tinyxml2)
            └── tinyxml2

但是没有生成scanning-header-only库文件，因此根项目不能target_link_libraries（升级scanning-header-only），不得不target_include_directories(leveling ${CMAKE_CURRENT_LIST_DIR}/deps/scanning-header-only/deps/tinyxml2)

是否可以target_link_library一个依赖外部资源的header-only库？

我看到没有外部资源依赖的 header-only 库可能是 add_library(.. INTERFACE)，但我没有这样做，因为依赖 tinyxml2

一个肮脏的解决方法是将 cpp 文件添加到 scanning-header-only 并生成一个 lib 文件，但是有正确的方法吗？

这是最小示例 v1：https://www.dropbox.com/s/r1lbajz3xoat1bg/leveling-header-only-test%20v1.zip?dl=0

练级CMakeLists.txt: cmake_minimum_required（版本 3.8）

set(LEVELING_NAME leveling)

project(${LEVELING_NAME})

#
# To put tinyxml.dll next to the executable, to workaround having to make tinyxml2.dll reachable in PATH
#
set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)

math(EXPR platform_bits "${CMAKE_SIZEOF_VOID_P} * 8")
set(platform_dir bin/${CMAKE_SYSTEM_NAME}-${platform_bits})

foreach(config DEBUG RELEASE RELWITHDEBINFO MINSIZEREL)
    foreach(var
            CMAKE_ARCHIVE_OUTPUT_DIRECTORY_${config}
            CMAKE_LIBRARY_OUTPUT_DIRECTORY_${config}
            CMAKE_RUNTIME_OUTPUT_DIRECTORY_${config}
            )
        set(${var} "${CMAKE_BINARY_DIR}/${platform_dir}/${config}")
        string(TOLOWER "${${var}}" ${var})
    endforeach()
endforeach()
#
# ----------------------------------------------------------------------
#

add_subdirectory(deps)

add_executable(${LEVELING_NAME} main.cpp)

target_include_directories(${LEVELING_NAME} PUBLIC
    ${CMAKE_CURRENT_LIST_DIR}/deps/scanning 
)

target_link_libraries(${LEVELING_NAME} 
    xml-reading
)

set_property(DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR} PROPERTY VS_STARTUP_PROJECT ${LEVELING_NAME}) # Set Startup Project in VS. Implemented in CMake v3.6
set_target_properties(${LEVELING_NAME} PROPERTIES VS_DEBUGGER_WORKING_DIRECTORY "${CMAKE_SOURCE_DIR}") # Set Working Directory of project in VS. Implemented in CMake v3.8

正在扫描CMakeLists.txt

cmake_minimum_required(VERSION 3.8)

set(XML_NAME xml-reading)

project(${XML_NAME})

#
# To put tinyxml.dll next to the executable, to workaround having to make tinyxml2.dll reachable in PATH
#
set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)

math(EXPR platform_bits "${CMAKE_SIZEOF_VOID_P} * 8")
set(platform_dir bin/${CMAKE_SYSTEM_NAME}-${platform_bits})

foreach(config DEBUG RELEASE RELWITHDEBINFO MINSIZEREL)
    foreach(var
            CMAKE_ARCHIVE_OUTPUT_DIRECTORY_${config}
            CMAKE_LIBRARY_OUTPUT_DIRECTORY_${config}
            CMAKE_RUNTIME_OUTPUT_DIRECTORY_${config}
            )
        set(${var} "${CMAKE_BINARY_DIR}/${platform_dir}/${config}")
        string(TOLOWER "${${var}}" ${var})
    endforeach()
endforeach()
#
# ----------------------------------------------------------------------
#

add_subdirectory(deps)

add_library(${XML_NAME} INTERFACE CamerasXML.h)
target_include_directories(${XML_NAME} INTERFACE
    ${CMAKE_CURRENT_LIST_DIR}/deps/tinyxml2
)
target_link_libraries(${XML_NAME} 
    INTERFACE tinyxml2
)

产生

CMake Error at deps/scanning/CMakeLists.txt:33 (add_library): 
  add_library INTERFACE library requires no source arguments.

Answer 1

A .lib 是当您在 Windows 上创建 STATIC (.lib) 或 SHARED（.lib 和 .dll）库时。您想要的是一个 INTERFACE 库，它不生成任何文件。 http://mariobadr.com/creating-a-header-only-library-with-cmake.html has an example. Then you can use the following commands listed here, https://cmake.org/cmake/help/latest/command/add_library.html#interface-libraries，填充界面。请注意，它使用的是 INTERFACE 而不是 PUBLIC.

target_link_libraries(INTERFACE),
target_link_options(INTERFACE),
target_include_directories(INTERFACE),
target_compile_options(INTERFACE),
target_compile_definitions(INTERFACE), and
target_sources(INTERFACE),

我从来没有真正使用过这个，但我认为它可以像文档中描述的那样工作。

Answer 2

一个简单的 add_library(${XML_NAME} INTERFACE)（不指定任何源文件），而 target_include_directories(${XML_NAME} INTERFACE ${CMAKE_CURRENT_LIST_DIR}/deps/tinyxml2) 和 target_link_libraries(${XML_NAME} INTERFACE tinyxml2) 就可以了。

父项目可以使用 tinyxml2 包含的内容，并且在父项目中链接了 tinyxml2 库。

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