【CMake】依赖包调用一瞥

语法糖
,

花了一天，终于把 IK 系列连接在了一起，这一波硬读代码，属实有些影响生活了！

本文将列出几个载入外部包的方法，代码已同步至 timrockefeller/IKCMake。

从二进制文件开始

一般来说，我们可以通过 add_executable() 与 add_library() 来创建将要 Build 的对象，并为它提供 SRC、INC、LIB 文件以编译并链接。而当生成的库文件需要被使用者使用时，需要用 install(TARGETS) 声明，下面的代码可以将 target_name 对象作为 ${PROJECT_NAME}Targets 成员对外封装：

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install(
    TARGETS ${target_name}
    EXPORT "${PROJECT_NAME}Targets"
    RUNTIME DESTINATION "bin"
    ARCHIVE DESTINATION "${package_name}/lib"
    LIBRARY DESTINATION "${package_name}/lib"
)

接着就可以通过 export() 将所有来自${PROJECT_NAME}Targets 的编译定义导出。官方文档如此描述该函数：”Export targets from the build tree for use by outside projects”。

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# generate the export targets for the build tree
# needs to be after the install(TARGETS) command
export(
    EXPORT "${PROJECT_NAME}Targets"
    NAMESPACE "KTKR::"
    #FILE "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}Targets.cmake"
)

# install the configuration targets
install(
    EXPORT "${PROJECT_NAME}Targets"
    FILE "${PROJECT_NAME}Targets.cmake"
    NAMESPACE "KTKR::"
    DESTINATION "${package_name}/cmake"
)

refer: CMake命令之export

Package

抛开 CPack 不谈，先看看原生 find_package() 方法。一般来说，find_package() 行为树如下：

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graph TD
A[find_package] --> B(圆角)
    B --> C{CONFIG or NO_MODULE?}
    C --> |Yes| E[[Config Mode]]
    C --> |No| D[[Module Mode]]
    D --> |Not found| E
    E --> |Found| F[End]
    D --> |Found| F[End]

当使用 Config 模式时，需要额外创建一些文件以辅助包导入：

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include(CMakePackageConfigHelpers)
# generate the config file that is includes the exports
configure_package_config_file(
    ${PROJECT_SOURCE_DIR}/config/Config.cmake.in
    "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}Config.cmake"
    INSTALL_DESTINATION "${package_name}/cmake"
    NO_SET_AND_CHECK_MACRO
    NO_CHECK_REQUIRED_COMPONENTS_MACRO
)

# generate the version file for the config file
write_basic_package_version_file(
    "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}ConfigVersion.cmake"
    VERSION ${PROJECT_VERSION}
    COMPATIBILITY SameMinorVersion
)

# install the configuration file
install(FILES
    "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}Config.cmake"
    "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}ConfigVersion.cmake"
    DESTINATION "${package_name}/cmake"
)

refer: Cmake之深入理解find_package()的用法

FetchContent远程导入

CMake 3.11 后提供了一种通过 git 方式载入包的方法，使用例如下：

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set(IKIT_GIT_TAG  ${version})  # 指定版本
set(IKIT_GIT_URL  "https://github.com/timrockefeller/${name}.git")  # 指定git仓库地址
FetchContent_Declare(
    ${name}
    GIT_REPOSITORY    ${IKIT_GIT_URL}
    GIT_TAG           ${IKIT_GIT_TAG}
)
FetchContent_MakeAvailable(${name})

EOF.

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