Using function from FindMatlab.cmake - matlab

Question

I'm trying to use matlab_get_all_valid_matlab_roots_from_registry() from FindMatlab.cmake and print the results using this script:
cmake_minimum_required(VERSION 2.8)
find_package(Matlab REQUIRED)
matlab_get_all_valid_matlab_roots_from_registry(a b)
message("!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!")
message(STATUS " !!!!! ${a} ${b} ${Matlab_ROOT_DIR} ####")
message("!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!")
Is it necessary that I first call find_package() before calling matlab_get_all_valid_matlab_roots_from_registry() ?
The output of the script doesn't print the contents of the variables a and b that are return values of that function. This is the output:
1> Command line: c:\program files (x86)\microsoft visual studio\2017
\community\common7\ide\commonextensions\microsoft\cmake\CMake\bin\cmake.exe -G "Ninja" -DCMAKE_INSTALL_PREFIX:PATH="C:\Users\AppTeam\CMakeBuilds\6f0f93b4-4e73-e838-98c8-2bfd807d82bf\install\x64-Debug (default)" -DCMAKE_CXX_COMPILER="C:/Program Files (x86)/Microsoft Visual Studio/2017/Community/VC/Tools/MSVC/14.16.27023/bin/HostX64/x64/cl.exe" -DCMAKE_C_COMPILER="C:/Program Files (x86)/Microsoft Visual Studio/2017/Community/VC/Tools/MSVC/14.16.27023/bin/HostX64/x64/cl.exe" -DCMAKE_BUILD_TYPE="Debug" -DCMAKE_MAKE_PROGRAM="c:\program files (x86)\microsoft visual studio\2017\community\common7\ide\commonextensions\microsoft\cmake\Ninja\ninja.exe" "C:\Users\AppTeam\Documents\bil\matlab\codegen\lib\mcadd"
1> Working directory: C:\Users\AppTeam\CMakeBuilds\6f0f93b4-4e73-e838-98c8-2bfd807d82bf\build\x64-Debug (default)
1> -- !!!!! C:/Program Files/MATLAB/R2018b ####
1> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
1> !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
1> -- Configuring done
It seems that Matlab_ROOT_DIR variable is OK, but I would like to find all MATLAB installations by using matlab_get_all_valid_matlab_roots_from_registry() but the output variables are not displayed. What am I doing wrong?

Answer 1

The proper syntax is:
matlab_get_all_valid_matlab_roots_from_registry(matlab_versions, matlab_roots)
where matlab_versions is an input argument, and should contain a list of the MATLAB versions you want the roots for. Since you pass an empty list as input, you get zero roots back.
According to the sources, matlab_versions comes either from extract_matlab_versions_from_registry_brute_force or matlab_extract_all_installed_versions_from_registry. The former is an internal macro, and the latter is a function available only on Windows. So on Windows you can do:
find_package(Matlab REQUIRED)
set(matlab_versions)
matlab_extract_all_installed_versions_from_registry(ON matlab_versions)
matlab_get_all_valid_matlab_roots_from_registry(matlab_versions, matlab_roots)
message(STATUS " !!!!! ${matlab_versions} ${matlab_roots} ${Matlab_ROOT_DIR} ####")
Also, yes, you do need to issue find_package(Matlab) to make the functions defined therein available.
Note regarding cmake_minimum_required(VERSION 2.8):
If a user has a version of CMake that old (2.8 was released in 2009!), you might find that the user's MATLAB will not be found. The script has a list of known versions of MATLAB to look for, so you need to always use the newest version of the script to find the newest versions of MATLAB (or explicitly add information about the release you are using). The version of the FindMatlab.cmake script in 2009 explicitly looked for MATLAB 7.0 and 7.0 SP1, which were released in 2004, already 5 years outdated at that time, and didn't have the possibility to look for newer versions of MATLAB. This script also did not define a function matlab_get_all_valid_matlab_roots_from_registry.
So, in general, I recommend that you look for the CMake features you are using, and require a version of CMake that supports those features. I know it is common to see "require 2.8" in CMake scripts, but this is not always the best choice. In the case of MATLAB, it certainly is not the best choice.