cmake find_library and CMAKE_FIND_ROOT_PATH
c, c++, cmake
Solution
I have met the same problem when doing cross-compiling of openwrt, with an external toolchain specified.
Like the problem described, I have set the `CMAKE_FIND_ROOT_PATH` to the toolchain's directory, but still, `rpcd` complains about missing crypt library.
Then I noticed this thread and figured may be it is because of implied lib search path of `./usr/lib` and `./lib`. As such, I changed the `CMAKE_FIND_ROOT_PATH` to be the sysroot of the toolchain, which includes `./usr/lib` and `./lib` for the target platform, then the problem is gone.
Getting back to the original problem, I think maybe if you can try to set `CMAKE_FIND_ROOT_PATH` to be `C:/DEV`, and place the library to be linked to under `C:/DEV/lib`.
That being said, if you are not doing a cross-compiling, this may not be the most sensible solution.
Problem
In the documentation for cmake's `find_library` function, we have The CMake variable CMAKE_FIND_ROOT_PATH specifies one or more directories to be prepended to all other search directories. This effectively “re-roots” the entire search under given locations. Paths which are descendants of the CMAKE_STAGING_PREFIX are excluded from this re-rooting, because that variable is always a path on the host system. By default the CMAKE_FIND_ROOT_PATH is empty. The CMAKE_SYSROOT variable can also be used to specify exactly one directory to use as a prefix. Setting CMAKE_SYSROOT also has other effects. See the documentation for that variable for more. These variables are especially useful when cross-compiling to point to the root directory of the target environment and CMake will search there too. By default at first the directories listed in CMAKE_FIND_ROOT_PATH are searched, then the CMAKE_SYSROOT directory is searched, and then the non-rooted directories will be searched. The default behavior can be adjusted by setting CMAKE_FIND_ROOT_PATH_MODE_LIBRARY. This behavior can be manually overridden on a per-call basis. By using CMAKE_FIND_ROOT_PATH_BOTH the search order will be as described above. If NO_CMAKE_FIND_ROOT_PATH is used then CMAKE_FIND_ROOT_PATH will not be used. If ONLY_CMAKE_FIND_ROOT_PATH is used then only the re-rooted directories and directories below CMAKE_STAGING_PREFIX will be searched. (see http://www.cmake.org/cmake/help/v3.0/command/find_library.html) I'm not sure how you read that, but to me, it seems implied that `find_library` will use `CMAKE_FIND_ROOT_PATH` to look for libraries. I've written the following `cmakelists.txt`: ``` cmake_minimum_required( VERSION 3.0 ) project( "cmakefindlibtest" ) message( "CMAKE_FIND_ROOT_PATH is ${CMAKE_FIND_ROOT_PATH}" ) list( APPEND CMAKE_FIND_ROOT_PATH "C:/DEV/lib/" ) message( "CMAKE_FIND_ROOT_PATH is now ${CMAKE_FIND_ROOT_PATH}" ) #find_library( punycode_library_test punycode PATHS "C:/DEV/lib" ) find_library( punycode_library_test punycode ) message( "punycode_library_test is now ${punycode_library_test}" ) add_executable( cmakefindlibtest main.cpp ) target_link_libraries( cmakefindlibtest ${punycode_library_test} ) ``` `main.cpp` is just hello world. In `C:\DEV\lib`, I've put a library named `punycode.lib` (this is on Windows). I've pointed `CMAKE_FIND_ROOT_PATH` to the directory. And then when I call `find_library`, I get: ``` c:\DEV\cmakefindtest\_build>cmake .. -- Building for: Visual Studio 11 2012 CMAKE_FIND_ROOT_PATH is CMAKE_FIND_ROOT_PATH is now C:/DEV/lib/ punycode_library_test is now punycode_library_test-NOTFOUND CMake Error: The following variables are used in this project, but they are set to NOTFOUND. Please set them or make sure they are set and tested correctly in the CMake files: punycode_library_test linked by target "cmakefindlibtest" in directory C:/DEV/cmakefindtest -- Configuring incomplete, errors occurred! See also "C:/DEV/cmakefindtest/_build/CMakeFiles/CMakeOutput.log". ``` Note that when I add the directory to the PATHS part of `find_library`'s invocation ``` find_library( punycode_library_test punycode PATHS "C:/DEV/lib" ) ``` everything works: ``` c:\DEV\cmakefindtest\_build>cmake .. -- Building for: Visual Studio 11 2012 CMAKE_FIND_ROOT_PATH is CMAKE_FIND_ROOT_PATH is now C:/DEV/lib/ punycode_library_test is now C:/DEV/lib/punycode.lib -- Configuring done -- Generating done -- Build files have been written to: C:/DEV/cmakefindtest/_build ``` So does `find_library` just not use `CMAKE_FIND_ROOT_PATH`? Update: It looks like CMAKE_LIBRARY_PATH mostly does what I want it to do here, and according to http://public.kitware.com/pipermail/cmake-developers/2012-January/002850.html, it looks like that's what I should be using it for in this case anyways. But, I'm still trying to figure out why `CMAKE_FIND_ROOT_PATH` doesn't work with `find_library`. The documentation at http://www.cmake.org/Wiki/CMake_Cross_Compiling says of `CMAKE_FIND_ROOT_PATH`, this is a list of directories, each of the directories listed there will be prepended to each of the search directories of every FIND_XXX() command. which doesn't seem to be true in this case, unless there's some sort of set-up or another variable that I've missed.