CMake how to copy dll after find_package()

Question

Trying out a CMAKE Project in Visual Studio 2022 for the first time and I am trying to adapt CmakeLists.txt from this repository in order to use the Open3D library.

As far as I understand, the following section means that on windows and in case Open3D was build as shared library, then the .dll file should be copied to the output folder of the project.

if(WIN32)
    get_target_property(open3d_type Open3D::Open3D TYPE)
    if(open3d_type STREQUAL "SHARED_LIBRARY")
        message(STATUS "Copying Open3D.dll to ${CMAKE_CURRENT_BINARY_DIR}/$<CONFIG>")
        add_custom_command(TARGET Draw POST_BUILD
                           COMMAND ${CMAKE_COMMAND} -E copy
                                   ${CMAKE_INSTALL_PREFIX}/bin/Open3D.dll
                                   ${CMAKE_CURRENT_BINARY_DIR}/$<CONFIG>)
    endif()
endif()

However, on my machine the variable ${CMAKE_INSTALL_PREFIX} points to <project-root>/out/install/x64-debug which seems to be generated from VS2022(?).

What I have done

So far I have added system variable to my windows environment variables called OPEN3D_DIR, which points to the root of the open3d binaries (=the folder containing bin, CMake, include and lib folder of the library) With that find_package(OPEN3D REQUIRED) seems to work, however in the script, the variable ${OPEN3D_DIR} points to <OPEN3D-root>/CMake

Basically, in short my question is how finding package paths is normally handled, where does the value for ${CMAKE_INSTALL_PREFIX} come from and in general, how would one set variables, which would normally be set in the CMAKE GUI?

try `$` in place of `${CMAKE_INSTALL_PREFIX}/bin/Open3D.dll` — Alan Birtles, Aug 09 '23 at 12:48
@AlanBirtles thank you this seems to do the trick, the dll is now copied to the output. Thank you. — Roland Deschain, Aug 09 '23 at 12:59

score 1 · Accepted Answer · answered Aug 09 '23 at 13:06

You can use $<TARGET_FILE:Open3D::Open3D> to get the path to the DLL from the target, you can also simplify the output directory to $<TARGET_FILE_DIR:Draw>

copy_if_different might be better than copy to make your build a bit faster.

e.g.:

if(WIN32)
    get_target_property(open3d_type Open3D::Open3D TYPE)
    if(open3d_type STREQUAL "SHARED_LIBRARY")
        message(STATUS "Copying Open3D.dll to $<TARGET_FILE_DIR:Draw>")
        add_custom_command(TARGET Draw POST_BUILD
                           COMMAND ${CMAKE_COMMAND} -E copy_if_different
                                   $<TARGET_FILE:Open3D::Open3D>
                                   $<TARGET_FILE_DIR:Draw>)
    endif()
endif()

See https://cmake.org/cmake/help/latest/manual/cmake-generator-expressions.7.html for more useful expressions.

CMake how to copy dll after find_package()

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