On Fri, Jul 6, 2018 at 8:25 PM, Mads Andreasen <te...@andreasen.cc> wrote:
> Hi, > > I am trying to work with FetchContent in cmake 3.11. > I want to use the jsoncpp library and use FetchContent to get and build it. > FetchContent can only download it. You need to build it as a separate step (you should avoid building things during the configure phase as much as possible). The expected pattern is to add the downloaded contents to your existing build via add_subdirectory(). If you want to keep the build isolated from your main build, then use ExternalProject directly rather than FetchContent. > > I also want to configure the jsoncpp build with some cmake arguments and I > can't seem to get that right. > > My CMakeLists.txt looks like this: > ************************************************************** > cmake_minimum_required(VERSION 3.11) > project(Foo) > > include(FetchContent) > > FetchContent_Declare(jsoncpp > URL "c:/project/jsoncpp-src" > CMAKE_ARGS "-DJSONCPP_WITH_CMAKE_PACKAGE=ON;-DJSONCPP_WITH_PKGCONFIG_ > SUPPORT=OFF" > ) > > FetchContent_Populate(jsoncpp) > > add_executable(Foo main.cpp) > ************************************************************** > The configure, build, test and install steps of ExternalProject do not apply to FetchContent, that's why CMAKE_ARGS has no effect. > > > FetchContent downloads and configures the jsoncpp as an ExternalProject. > No, it only downloads, not configures. > That part looks like this: > ********************************************* > ExternalProject_Add(jsoncpp-populate > "UPDATE_DISCONNECTED" "False" "URL" > "c:/project/jsoncpp-src" "CMAKE_ARGS" "-DJSONCPP_WITH_CMAKE_PACKAGE=ON" > "-DJSONCPP_WITH_PKGCONFIG_SUPPORT=OFF" > SOURCE_DIR "C:/temp/foo/build/_deps/ > jsoncpp-src" > BINARY_DIR "C:/temp/foo/build/_deps/ > jsoncpp-build" > CONFIGURE_COMMAND "" > BUILD_COMMAND "" > INSTALL_COMMAND "" > TEST_COMMAND "" > ) > ******************************************************* > > For the external project - the CMAKE_ARGS are no longer a list, but > individual arguments. > > I have tried different things, like escaping the ; with \\; and stuff like > that, and I can't get it to work. > I'm thinking there is something obvious I am missing? > Assuming jsoncpp doesn't assume it is a top level project (I haven't checked), the canonical pattern as explained in the docs <https://cmake.org/cmake/help/latest/module/FetchContent.html#overview> would be: FetchContent_Declare(jsoncpp URL "c:/project/jsoncpp-src" ) FetchContent_GetProperties(jsoncpp) if(NOT jsoncpp_POPULATED) FetchContent_Populate(jsoncpp) add_subdirectory(${jsoncpp_SOURCE_DIR} ${jsoncpp_BINARY_DIR}) endif() The reason why FetchContent has all but download steps disabled is the projects should avoid doing time-consuming things during the configure stage. A configure stage will be inherently non-parallel as well, so it hurts you twice. Build steps should be deferred to the build stage as much as possible. If you find yourself wanting to pull some external project's build earlier into the configure stage, chances are you really should be using a superbuild if you truly need a build to be complete before the configure logic of a different project is executed. -- Craig Scott Melbourne, Australia https://crascit.com
-- Powered by www.kitware.com Please keep messages on-topic and check the CMake FAQ at: http://www.cmake.org/Wiki/CMake_FAQ Kitware offers various services to support the CMake community. For more information on each offering, please visit: CMake Support: http://cmake.org/cmake/help/support.html CMake Consulting: http://cmake.org/cmake/help/consulting.html CMake Training Courses: http://cmake.org/cmake/help/training.html Visit other Kitware open-source projects at http://www.kitware.com/opensource/opensource.html Follow this link to subscribe/unsubscribe: https://cmake.org/mailman/listinfo/cmake
