how to pass 2D array from c++ to matlab via mex new c++ api

Hi, i am trying to understand how to cast matlab variables and c++ variables

lets say i want to pass matrix i created in c++ (2D or 1D float array) to matlab.

i am using the new C++ api

i have tried something like:

CMatrixType2D<float> m_mfImage; //create matrix
m_mfImage.Init(m_Alg.mConfig.uiHeight, m_Alg.mConfig.uiWidth);//init matrix
aOutput.m_pmuiImage = &m_mfImage;

//Execute Algorithm
m_Alg.Execute(&aInput, &aOutput);//create frame output
outputs[0] = factory.createArray<float>({ m_Alg.mConfig.uiHeight , m_Alg.mConfig.uiWidth }, aOutput.m_pmuiImage);

but i cant figure how to convers/cast TypedArray to cpp array or get a pointer to work with.

Answer 1

[Zehui Lu]

I'm using Savyasachi Singh's template here to get the pointer of a TypedArray. Then I map this pointer to an Eigen matrix for the heavy computation. The example is like the following. Note that to use external c++ libraries with C++ MEX API, we need to write a wrapper (e.g. compute_something_with_eigen.cpp), and operator() can internally use this function. After we finish the computation with external libraries, we can find the pointer of this result matrix and map it back to a TypedArray.

// Assign the input, assume it's a 2D matrix
TypedArray<double> matrix = std::move(inputs[0]);
// Use the template I mentioned above
double* ptr = getPointer(matrix);
// Get the dimension of input
size_t size_input = matrix.getDimensions();

// Don't do the following in your C++ MEX main file
MatrixXd mat_eig = Map<MatrixXd>(ptr,size_input[0],size_input[1]);
// Do your algorithm