How to copy DLL files into the same folder as the executable using CMake?

Question

I'd use add_custom_command to achieve this along with cmake -E copy_if_different.... For full info run

cmake --help-command add_custom_command
cmake -E

So in your case, if you have the following directory structure:

/CMakeLists.txt
/src
/libs/test.dll

and your CMake target to which the command applies is MyTest, then you could add the following to your CMakeLists.txt:

add_custom_command(TARGET MyTest POST_BUILD        # Adds a post-build event to MyTest
    COMMAND ${CMAKE_COMMAND} -E copy_if_different  # which executes "cmake - E copy_if_different..."
        "${PROJECT_SOURCE_DIR}/libs/test.dll"      # <--this is in-file
        $<TARGET_FILE_DIR:MyTest>)                 # <--this is out-file path

If you just want the entire contents of the /libs/ directory copied, use cmake -E copy_directory:

add_custom_command(TARGET MyTest POST_BUILD
    COMMAND ${CMAKE_COMMAND} -E copy_directory
        "${PROJECT_SOURCE_DIR}/libs"
        $<TARGET_FILE_DIR:MyTest>)

If you need to copy different dlls depending upon the configuration (Release, Debug, eg) then you could have these in subdirectories named with the corresponding configuration: /libs/Release, and /libs/Debug. You then need to inject the configuration type into the path to the dll in the add_custom_command call, like this:

add_custom_command(TARGET MyTest POST_BUILD
    COMMAND ${CMAKE_COMMAND} -E copy_directory
        "${PROJECT_SOURCE_DIR}/libs/$<CONFIGURATION>"
        $<TARGET_FILE_DIR:MyTest>)

I put these lines in my top-level CMakeLists.txt file. All the libraries and executables compiled by CMake will be placed in the top level of the build directory so that the executables can find the libraries and it is easy to run everything.

set (CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR})
set (CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR})

Note that this doesn't solve the OP's problem of copying precompiled binaries from the project's source directory.

I've had this problem today when tried to make a Windows build of my program. And I ended up doing some research myself since all these answers didn't satisfy me. There were three main issues:

• I wanted debug builds to be linked with debug versions of libraries and release builds to be linked with release builds of libraries, respectively.

• In addition to that, I wanted correct versions of DLL files (Debug/Release) to be copied to output directories.

• And I wanted to achieve all this without writing complex and fragile scripts.

After browsing some CMake manuals and some multiplatform projects at github I've found this solution:

Declare your library as a target with "IMPORTED" attribute, reference its debug and release .lib and .dll files.

add_library(sdl2 SHARED IMPORTED GLOBAL)
set_property(TARGET sdl2 PROPERTY IMPORTED_IMPLIB_RELEASE "${SDL_ROOT_PATH}/lib/SDL2.lib")
set_property(TARGET sdl2 PROPERTY IMPORTED_LOCATION_RELEASE "${SDL_ROOT_PATH}/bin/SDL2.dll")
set_property(TARGET sdl2 PROPERTY IMPORTED_IMPLIB_DEBUG "${SDL_ROOT_PATH}/lib/SDL2d.lib")
set_property(TARGET sdl2 PROPERTY IMPORTED_LOCATION_DEBUG "${SDL_ROOT_PATH}/bin/SDL2d.dll")

Link this target with your project as usual

target_link_libraries(YourProg sdl2 ...)

Make custom build step to copy dll file to its destination if it has been altered somehow since previous build

add_custom_command ( TARGET YourProg POST_BUILD
    COMMAND ${CMAKE_COMMAND} -E copy_if_different
    $<TARGET_FILE:sdl2> $<TARGET_FILE_DIR:YourProg>
)

An addendum to the accepted answer, added as a separate answer so I get code formatting:

If you are building your dlls in the same project, they will usually be in Release, Debug, etc. directories. You'll have to use the Visual Studio environment variables to correctly copy them. e.g.:

"${PROJECT_BINARY_DIR}/your_library/\$\(Configuration\)/your_library.dll"

for the source and

"${CMAKE_CURRENT_BINARY_DIR}/\$\(Configuration\)/your_library.dll"

for the destination. Note the escaping!

You can't use the CMake CMAKE_BUILD_TYPE variable for the configuration since it's resolved at VS project generation time and will always be whatever the default is.

You can also use the command find_library:

find_library(<some_var> NAMES <name_of_lib> PATHS "<path/to/lib>")

With a defined EXECUTABLE_PATH, for instance:

set(EXECUTABLE_OUTPUT_PATH ${PROJECT_BINARY_DIR}/bin)

you could move the .dll files that your executable need, with

file(COPY ${<some_var>}
    DESTINATION ${EXECUTABLE_OUTPUT_PATH})