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1. 目的

在基于 CMake 构建的 C/C++ 工程中，拷贝当前工程需要的每个DLL文件到 Visual Studio 工程的启动路径下， 让可执行目标在运行阶段正常运行，解决“DLL找不到”导致的程序终止、异常退出等问题，解决“每次都要手动拷贝，有时候忘记拷贝”的问题。

举例：

• OpenCV： 官方预编译版本，包含的 opencv_world.dll, 以及读取某些视频时需要的 opencv_ffmpeg dll 文件
• windows-pthreads 的 DLL 文件
• 其他依赖库当中，提供的 DLL 文件

实际上不仅限于 Windows 平台的 DLL， 在 Linux / MacOSX 上也同样有这样的问题，此时只需要增加 .so 和 .dylib 文件后缀的动态库支持即可。

本文给出基于 CMake 语言的解决方案。

2. 设计

整体思路

枚举所有 target， 筛选出 SHARED_LIBRARRY 类型的 target， 获取它们的动态库的路径 shared_library_path, 然后拷贝到用户指定的目录 dstDir.

此外有些 dll 文件并没有被 xxx-config.cmake 等配置文件所配置， 需要额外扫描和拷贝，例如 opencv 预编译库中的 ffmpeg 的 dll 文件。

多层依赖的处理

有时候工程比较复杂， target 至少包括三层， 最后一层是可执行文件， 第二层可能没有DLL，但第二层依赖的第一层则可能存在DLL文件，这就导致枚举 target 时不能只枚举一层。换言之，枚举 target 的过程是一个递归过程， 需要使用深度优先搜索 DFS 算法。

获取 DLL 所在目录

这个问题比较简单， 用 cmake 的 get_target_property 函数获取。

探测剩余的 DLL 文件

包括两种情况：

• target 本身是动态库类型， 那么它的 DLL 文件所在的目录应该被扫描，扫描出的新的 DLL 文件也应该被拷贝
• target 本身是静态库类型， 但它所在目录的上一级目录中， 有一个 bin 目录， bin 目录里存放有 DLL 文件

3. 代码实现

代码实现过程中遇到一些“难点”，主要是对 cmake 不够足够熟悉， 简单列举：

判断 stack 是否为空

• DFS 算法的实现过程中， 怎样判断 stack 为空？获取 stack 首部元素？依赖于对 list 的操作， 包括将“列表是否为空”封装为函数

#======================================================================
# Determine if a list is empty
#======================================================================
# Example:
# cvpkg_is_list_empty(testbed_requires testbed_requires_empty)
# message(STATUS "testbed_requires_empty: ${testbed_requires_empty}")
#----------------------------------------------------------------------
function(cvpkg_is_list_empty the_list ret)list(LENGTH ${the_list} the_list_length)if(${the_list_length} EQUAL 0)set(${ret} TRUE PARENT_SCOPE)else()set(${ret} FALSE PARENT_SCOPE)endif()
endfunction()

判断 stack 是否为空

通过判断元素是否在列表中来实现。封装为了函数

#======================================================================
# Determine if item is in the list
#======================================================================
# Example: 
# cvpkg_is_item_in_list(testbed_requires "protobuf" protobuf_in_the_lst)
# message(STATUS "protobuf_in_the_lst: ${protobuf_in_the_lst}")
# 
# cvpkg_is_item_in_list(testbed_requires "opencv" opencv_in_the_lst)
# message(STATUS "opencv_in_the_lst: ${opencv_in_the_lst}")
#----------------------------------------------------------------------
function(cvpkg_is_item_in_list the_list the_item ret)list(FIND ${the_list} ${the_item} index)if(index EQUAL -1)set(${ret} FALSE PARENT_SCOPE)else()set(${ret} TRUE PARENT_SCOPE)endif()
endfunction()

获取所有 target

原本的依赖关系是 hierarchical 的， 怎样拍平，得到一维的依赖列表？并且不能有重复元素？答案是用 DFS。

#======================================================================
# 4. Recursively get required packages for a package. No duplicated.
#======================================================================
# Example: 
# cvpkg_get_flatten_requires(testbed flatten_pkgs)
# message(STATUS "flatten_pkgs: ${flatten_pkgs}")
#----------------------------------------------------------------------
function(cvpkg_get_flatten_requires input_pkg the_result)list(LENGTH input_pkg input_pkg_length)if(NOT (${input_pkg_length} EQUAL 1))cvpkg_error("input_pkg should be single element list")endif()set(visited_pkgs "")set(pkg_stack ${input_pkg})while(TRUE)cvpkg_is_list_empty(pkg_stack pkg_stack_empty)if(${pkg_stack_empty})break()endif()cvpkg_debug("pkg_stack: ${pkg_stack}")# pop the last elementlist(POP_BACK pkg_stack pkg)cvpkg_debug("pkg: ${pkg}")# mark the element as visitedcvpkg_is_item_in_list(visited_pkgs "${pkg}" pkg_visited)if(NOT ${pkg_visited})cvpkg_debug(" visiting ${pkg}")list(APPEND visited_pkgs ${pkg})# traverse it's required dependencies and put into pkg_stackget_target_property(subpkgs ${pkg} LINK_LIBRARIES)cvpkg_debug("LINK_LIBRARIES: ${subpkgs}")if(subpkgs)foreach(subpkg ${subpkgs})if(TARGET ${subpkg}) # if called target_link_libraries() more than once, subpkgs contains stuffs like `::@(000001FAFA8C75C0)`cvpkg_debug("  subpkg: ${subpkg}")list(APPEND pkg_stack ${subpkg})endif()endforeach()endif()get_target_property(subpkgs ${pkg} INTERFACE_LINK_LIBRARIES)cvpkg_debug("INTERFACE_LINK_LIBRARIES: ${subpkgs}")if(subpkgs)foreach(subpkg ${subpkgs})if(TARGET ${subpkg}) # if called target_link_libraries() more than once, subpkgs contains stuffs like `::@(000001FAFA8C75C0)`cvpkg_debug("  subpkg: ${subpkg}")list(APPEND pkg_stack ${subpkg})endif()endforeach()endif()endif()endwhile()list(POP_FRONT visited_pkgs visited_pkgs)set(${the_result} ${visited_pkgs} PARENT_SCOPE)
endfunction()

检测并拷贝 DLL

这是代码最多的函数， 不过思路上前面已经提到过， 并不复杂。

代码多的几个原因：

• 支持 .dll 的同时， 要支持 .so 和 .dylib
• windows 上的 target， 可能 debug 和 release 库的文件不是同一个，都需要拷贝，因此需要枚举5个属性

  set(prop_lst "IMPORTED_LOCATION;IMPORTED_LOCATION_DEBUG;IMPORTED_LOCATION_RELEASE")

• 去重： 拷贝过的文件要忽略， 重复的目录要合并

Talk is cheap, show me the code:

#======================================================================
# Copy imported lib for all build types
# Should only be used for shared libs, e.g. .dll, .so, .dylib
#======================================================================
# Example: 
# cvpkg_copy_imported_lib(testbed ${CMAKE_BINARY_DIR}/${testbed_output_dir})
#----------------------------------------------------------------------
function(cvpkg_copy_imported_lib targetName dstDir)set(prop_lst "IMPORTED_LOCATION;IMPORTED_LOCATION_DEBUG;IMPORTED_LOCATION_RELEASE")if(NOT (TARGET ${targetName}))return()endif()if(CMAKE_SYSTEM_NAME MATCHES "Windows")set(shared_library_filename_ext ".dll")elseif(CMAKE_SYSTEM_NAME MATCHES "Linux")set(shared_library_filename_ext ".so")elseif(CMAKE_SYSTEM_NAME MATCHES "Darwin")set(shared_library_filename_ext ".dylib")endif()get_target_property(pkg_type ${targetName} TYPE)if(NOT (${pkg_type} STREQUAL "SHARED_LIBRARY"))if(${pkg_type} STREQUAL "STATIC_LIBRARY")if(CMAKE_SYSTEM_NAME MATCHES "Windows")set(static_library_filename_ext ".lib")elseif(CMAKE_SYSTEM_NAME MATCHES "Linux")set(static_library_filename_ext ".a")elseif(CMAKE_SYSTEM_NAME MATCHES "Darwin")set(static_library_filename_ext ".a")endif()### for static library targets, there might be `bin` directory, parallel to `lib` directory.# 先获取静态库文件路径foreach(prop ${prop_lst})get_target_property(static_library_path ${pkg} ${prop})if(static_library_path)# 获取静态库所在目录get_filename_component(static_library_live_directory ${static_library_path} DIRECTORY)# 获取静态库目录的上层目录get_filename_component(static_library_parent_directory ${static_library_live_directory} DIRECTORY)set(candidate_bin_dir "${static_library_parent_directory}/bin")# 判断上层目录是否存在 bin 目录, 如果存在 bin 目录， 执行扫描和拷贝if(EXISTS "${candidate_bin_dir}")set(glob_pattern "${candidate_bin_dir}/*${shared_library_filename_ext}")file(GLOB shared_library_path_lst "${glob_pattern}")foreach(shared_library_path ${shared_library_path_lst})list(APPEND copied_shared_library_path_lst "${shared_library_path}")cvpkg_info("Copy ${shared_library_filename_ext} file (for static library, we detect and copy them!)")cvpkg_info("  - shared library file: ${prop}=${static_library_path}")cvpkg_info("  - dstDir: ${dstDir}")execute_process(COMMAND ${CMAKE_COMMAND} -E copy ${shared_library_path} ${dstDir})endforeach()endif()endif()endforeach()endif()return()endif()### copy as the package description file (xxx-config.cmake or xxx.cmake) decribedset(pkg ${targetName})set(copied_shared_library_path_lst "")foreach(prop ${prop_lst})cvpkg_debug("!! prop: ${prop}")get_target_property(shared_library_path ${pkg} ${prop})if(shared_library_path)list(APPEND copied_shared_library_path_lst "${shared_library_path}")cvpkg_info("Copy ${shared_library_filename_ext} file")cvpkg_info("  - package(target): ${pkg}")cvpkg_info("  - prop: ${prop}=${shared_library_path}")cvpkg_info("  - dstDir: ${dstDir}")execute_process(COMMAND ${CMAKE_COMMAND} -E copy ${shared_library_path} ${dstDir})endif()endforeach()### copy un-tracked shared library files that under same directory of each tracked shared library filescvpkg_is_list_empty(copied_shared_library_path_lst copied_shared_library_path_lst_empty)if(${copied_shared_library_path_lst_empty})return()endif()# get directories of each copied shared library filesset(shared_library_live_directory_lst "")foreach(copied_shared_library_path ${copied_shared_library_path_lst})get_filename_component(shared_library_live_directory ${copied_shared_library_path} DIRECTORY)list(APPEND shared_library_live_directory_lst "${shared_library_live_directory}")endforeach()# remove duplicated directorieslist(REMOVE_DUPLICATES "${shared_library_live_directory_lst}")# for each candidate directory, scan shared library filesforeach(shared_library_live_directory ${shared_library_live_directory_lst})set(glob_pattern "${shared_library_live_directory}/*${shared_library_filename_ext}")file(GLOB shared_library_path_lst "${glob_pattern}")foreach(shared_library_path ${shared_library_path_lst})# if the scanned shared library file is not copied, do a copycvpkg_is_item_in_list(copied_shared_library_path_lst "${shared_library_path}" shared_library_already_copied)if(NOT shared_library_already_copied)list(APPEND copied_shared_library_path_lst "${shared_library_path}")cvpkg_info("Copy ${shared_library_filename_ext} file (xxx-config.cmake forget this file, but we copy them!)")cvpkg_info("  - package(target): ${pkg}")cvpkg_info("  - prop: ${prop}=${shared_library_path}")cvpkg_info("  - dstDir: ${dstDir}")execute_process(COMMAND ${CMAKE_COMMAND} -E copy ${shared_library_path} ${dstDir})endif()endforeach()endforeach()endfunction()

4. 使用

从使用的角度非常简单:调用 cvpkg_copy_required_dlls() 函数即可，它的实现代码为：

#======================================================================
# Recursively copy required DLL files into destination directory
#======================================================================
# Example: 
# cvpkg_copy_required_dlls(testbed ${CMAKE_BINARY_DIR})
# cvpkg_copy_required_dlls(testbed ${CMAKE_BINARY_DIR}/${testbed_output_dir})
#----------------------------------------------------------------------
function(cvpkg_copy_required_dlls targetName dstDir)cvpkg_get_flatten_requires(testbed flatten_pkgs)#cvpkg_debug("flatten_pkgs: ${flatten_pkgs}")message(STATUS "flatten_pkgs: ${flatten_pkgs}")foreach(pkg ${flatten_pkgs})cvpkg_copy_imported_lib(${pkg} ${dstDir})endforeach()
endfunction()

调用代码为:

cvpkg_copy_required_dlls(testbed ${CMAKE_BINARY_DIR})