MinGW clibgen build fails to find -llibMatlabDataArray

I am using Matlab2021a. I am trying to wrap an existing C++ library for use in Matlab. I did the wrapping in Linux and I am now trying to do the same thing in Windows. For my comiler, I am using MinGW 6.3.0 as installed by the using the download provided by Mathworks:

https://www.mathworks.com/matlabcentral/fileexchange/52848-matlab-support-for-mingw-w64-c-c-compiler

I was able to run the clibgen.generateLibraryDefinition command, but when I try to do a build, I get linker errors. To narrow down the origin of the problem, I followed a useful simple example case. The instructions are provided at the following link:

https://www.reddit.com/r/matlab/comments/hv426x/calling_c_shared_objects_from_matlab/

I made the libfive.h and libfive.cpp files as per those instructions. I then built a shared library using MinGW's g++.

$ g++ -c -fPIC libfive.cpp -o libfive.o
$ g++ libffive.o -shared -o libfive_win.so

From inside Matlab, I generated a library definition.

>> clibgen.generateLibraryDefinition('libfive.h', 'Libraries', 'libfive_win.so')
Using MinGW64 Compiler (C++) compiler.
Generated definition file definelibfive.mlx and data file 'libfiveData.xml' contain definitions for 1 constructs supported by MATLAB.
Build using build(definelibfive).

The inclusion of the _win suffix is to distinguish that the file is a windows shared library because I did the same test for the Linux case. When I try to do a build, though, I get the following error:

>> build(definelibfive)
Building interface file 'libfiveInterface.dll'.
Error using clibgen.internal.buildHelper (line 62)
Build failed with error:
'C:/ProgramData/MATLAB/SupportPackages/R2021a_1/3P.instrset/mingw_w64.instrset/bin/../lib/gcc/x86_64-w64-mingw32/6.3.0/../../../../x86_64-w64-mingw32/bin/ld.exe:
cannot find -l-LC:\MATLAB\R2021a\extern\lib\win64\mingw64
C:/ProgramData/MATLAB/SupportPackages/R2021a_1/3P.instrset/mingw_w64.instrset/bin/../lib/gcc/x86_64-w64-mingw32/6.3.0/../../../../x86_64-w64-mingw32/bin/ld.exe:
cannot find -llibMatlabDataArray
collect2.exe: error: ld returned 1 exit status
'.

Error in clibgen.LibraryDefinition/build (line 1297)
            clibgen.internal.buildHelper(obj, obj.LibraryInterface, '', directBuild);

The error is the same for both this simple example case and the more complex case. In C:\MATLAB\R2021a\extern\lib\win64\mingw64, the libMatlabDataArray.lib is present.

Answer 1

[Nathan Parrish]

The cause of this problem was that Matlab failed to fill in the library name that needs to be provided to the linker (which is libfive_win.so). Libraries built from MinGW must have a .lib file extension. This is because the clibgen.internal.build function uses

idx = strfind(nameExt, '.lib');
res = nameExt(1:idx-1);
name = ['-l', res];

In my example, the MinGW extension was set up as .so causing strfind to return an empty array and name became nothing but the -l.

The linker then parsed '-l -LC:\MATLAB\R2021a\extern\lib\win64\mingw64' as one token leading to this error.

If you simply rename the library file, it will lead to link errors because internally the generated library will look for a library with the old name so it will cause

Error using which
Unable to load interface library: '[...]\libfive\libfiveInterface.dll'. Reason: The specified module
could not be found.
Ensure the C++ dependent libraries for the interface library are added to run-time path.

Related documentation

The solution was to rebuild the library so that the output had the name libfive.lib and then follow the normal pattern.

doc clib.libfive.five % Show documentation
clib.libfive.five() % Run the function