c++ - MATLAB array conversion with clibgen

Hello,

I am binding my c++ toolsets to MATLAB. The code is very Object Oriented so I cannot just use simple mex functions and have to use clibgen.

Ideally I'd only need 2 functions: one that convert 1D MATLAB array into c++ vectors, and another one converting c++ vectors to 1D MATLAB array. The first eventually work (with data copy, not references), but getting a vector out does not.

Here is a simple example, on Windows with minGW installed through MATLAB:

// c++ code in main.hpp file:
#include "MatlabDataArray.hpp"


// DUmmy function adding 5 to an array
matlab::data::Array add5(std::vector<double> foo)
{
	std::vector<double> bar(foo);
	for(auto &v:bar)
		v+=5;

	matlab::data::ArrayFactory fac;
	return fac.createArray({bar.size()}, bar.begin(),bar.end());
}

// MATLAB side:
% getting the library path
library_files = [fullfile(matlabroot,"extern","lib","win64","mingw64","libMatlabDataArray.lib"),...
    fullfile(matlabroot,"extern","lib","win64","mingw64","libMatlabEngine.lib")];
% generating headers
clibgen.generateLibraryDefinition("main.hpp",... % Headers
    "OverwriteExistingDefinitionFiles",true, ... 
    "Libraries",library_files, ... % Uses the MATLAB libraries (.lib linked to MinGW)
    PackageName="test"); % in clib, the package will be ingested as DAGGER
% compiling and adding to path
build(definetest);
addpath("test");

% Then generating MATLAB array
arr = zeros(1,5)+2;
% adding 5 to each elements
arr2 = clib.DAGGER.add5(arr);
% so far so good
% But the following line throw an error:
arr2 + arr

arr2 is not a MATLAB array and cannot be used in simple operation with other arrays, or figures, ...

I get errors like that...

Operator '+' is not supported for operands of type 'clib.test.matlab.data.Array'

The real questions are: Is there a way, on the c++ side to return MATLAB arrays usable in MATLAB (eventually without data copy)? and is there an easy way to convert it back from MATLAB (although it would add a LOT of code overhead)?

Thanks in advance,

B.

Answer 1

[Divyanshu]

According to the code snippet of “main.hpp” file, you are trying to create a MATLAB array using ArrayFactory and want to transfer it to the MATLAB workspace from C++ program.

You can go through the following documentation which explains in detail that how one can use the array created in C++ in the MATLAB workspace. Moreover, it has an example with code where an array is created in C++ and is then moved to the workspace of MATLAB and after certain calculations the result is fetched from MATLAB workspace and displayed in the C++ program.

Pass Variables from C++ to MATLAB - MATLAB & Simulink (mathworks.com)