Can you modify this mex file to accept an array of MATLAB objects?

Hello all,

This page https://www.mathworks.com/help/matlab/matlab_external/use-matlab-objects-in-mex-functions.html expalins how to pass an object from MATLAB to a C++ mex function. The MATLAB object is a simple EmployeeID as follows:

classdef EmployeeID

properties

Name (1,:) char

Picture (1000,800) uint8

end

methods

function obj = EmployeeID(n,p)

if nargin > 0

obj.Name = n;

obj.Picture = p;

end

end

end

end

The mex code is as follows:

#include "mex.hpp"

#include "mexAdapter.hpp"

using matlab::mex::ArgumentList;

using namespace matlab::data;

class MexFunction : public matlab::mex::Function {

std::shared_ptr<matlab::engine::MATLABEngine> matlabPtr = getEngine();

public:

void operator()(ArgumentList outputs, ArgumentList inputs) {

// Move object to variable

Array obj = std::move(inputs[0]);

// Get property value and modify

TypedArray<uint8_t> imageData = matlabPtr->getProperty(obj, u"Picture");

for (auto& elem : imageData) {

if (elem > 240) {

elem = elem - elem/100;

}

}

// Set property value and assign to output

matlabPtr->setProperty(obj, u"Picture", imageData);

outputs[0] = obj;

}

};

Can anyone help me understand how to modify the mex file so that it accepts an array of EmployeeID and iterate through the elements of the array in C++ mex and does something simple, like printing the name of field for each array?

Any help is much appreciated.

Answer 1

[Ali Behboodian]

This was documented on the same page but I have missed it.

The trick is mentioned here:

Get Property Value from Object Array

If the input to the MEX function is an object array, call getProperty with index of the object in the array whose property value you want to get. For example, this code snippet returns the value of the Name property for the fourth element in the object array, objectArray.

matlab::data::Array objectArray(inputs[0]);

matlab::data::CharArray propName = matlabPtr->getProperty(objectArray, 3, u"Name");