CMake：导入的库作为另一个自定义命令或目标的 OUTPUT 或 BYPRODUCTS

Question

我想从 ZIP 文件中提取一个静态库并链接到它。

具有以下设置：

add_library(COMSDK_LIB STATIC IMPORTED GLOBAL)
set_property(TARGET COMSDK_LIB PROPERTY IMPORTED_LOCATION "/tmp/lib/libRTSClientSdk.a")

而导入的库正在另一个CMakeLists.txt中使用：

target_link_libraries(mylib COMSDK_LIB)

会不会是导入的库是由另一个add_custom_command或add_custom_target生成的？

我尝试了以下方法，但它确实不工作：

add_custom_command(
    OUTPUT "/tmp/lib/libRTSClientSdk.a"
    COMMAND unzip -x client_sdk.zip -o /tmp
    DEPENDS client_sdk.zip
)

给定的错误信息是：

$ ninja
ninja: error: '/tmp/lib/libRTSClientSdk.a', needed by 'mylib.dll', missing and no known rule to make it

Answer 1

问题是您的自定义命令正在make 步骤期间执行，并且它期望在cmake 执行期间更早提取依赖项。因此，基本上，您需要从 SDK 在在 CMake 规则中或在链接本身期间使用它之前获取该静态库。

CMake mailing list 中列出了两种可能的解决方案。

解决方案#1：（在 CMake 端执行）

重新表述代码 sn-ps 之一，在 CMake 执行期间正在完成下载和解压缩：

set(CLIENTSDK_ZIP "cliendsdk.zip")
set(CLIENTSDK_URL "http://example.com/${CLIENTSDK_ZIP}")
set(CLIENTSDK_LIB "libRTSClientSdk.a")
set(CLIENTSDK_OUTPUT_DIR "/tmp/sdk/dir")

# Basically just downloading zip file:
message(STATUS "Downloading ${CLIENTSDK_URL}")
execute_process(COMMAND wget ${CLIENTSDK_URL}
  WORKING_DIRECTORY ${CLIENTSDK_OUTPUT_DIR}
  RESULT_VARIABLE errno
  ERROR_VARIABLE err)

if (NOT ${errno} EQUAL 0)
  message(ERROR "Failed downloading ${CLIENTSDK_URL}. Code: ${err}")
endif()

# Extracting downloaded zip file:
message(STATUS "Extracting ${CLIENTSDK_ZIP})
execute_process(COMMAND unzip ${CLIENTSDK_ZIP}
  WORKING_DIRECTORY ${CLIENTSDK_OUTPUT_DIR}
  RESULT_VARIABLE errno
  ERROR_VARIABLE err)

if (NOT ${errno} EQUAL 0)
  message(ERROR "Failed extracting ${CLIENTSDK_ZIP}. Code: ${err}")
endif()

# Importing into CMake scope one library from extracted zip:
add_library(specific_sdk_lib STATIC IMPORTED)
set_target_properties(specific_sdk_lib
  PROPERTIES IMPORTED_LOCATION ${CLIENTSDK_OUTPUT_DIR}/lib/${CLIENTSDK_LIB})

# Adding rule for linking to specific static library from extracted zip:
target_link_libraries(mylib specific_sdk_lib)

解决方案 #2（在 make 端执行）：

# We must include ExternalProject CMake module first!
include("ExternalProject")

set(CLIENTSDK_URL "http://example.com/clientsdk.zip")
set(CLIENTSDK_LIB "libRTSClientSdk.a")
set(CLIENTSDK_PREFIX "3rd_party")
set(CLIENTSDK_EXTRACTED_DIR
    "${CMAKE_CURRENT_BINARY_DIR}/${CLIENTSDK_PREFIX}/src/DownloadClientSDK/")

ExternalProject_Add("DownloadClientSDK"
    PREFIX ${CLIENTSDK_PREFIX}
    URL "${CLIENTSDK_URL}"
    # Suppress ExternalProject configure/build/install targets:
    CONFIGURE_COMMAND ""
    BUILD_COMMAND ""
    INSTALL_COMMAND "")

add_library(COMSDK_LIB STATIC IMPORTED)
set_target_properties(COMSDK_LIB PROPERTIES IMPORTED_LOCATION
    ${CLIENTSDK_EXTRACTED_DIR}/${CLIENTSDK_LIB})

# Require all that download/unzip mumbojumbo only for COMSDK_LIB:
add_dependencies(COMSDK_LIB DownloadClientSDK)

target_link_libraries(my_library COMSDK_LIB)

基本上，CMake 和它的ExternalProject 模块负责（生成正确的make 目标）识别存档格式，解压缩它，如果需要 - 配置，构建和安装。