How to find size of CellArray in mex c++?

I am attempting to write a c++ program to mex in Matlab. I am passing in a cell array that I need to find the size of. Here is a MWE called myMatlabFunction.cpp

#include "mex.hpp"
#include "mexAdapter.hpp"

using namespace matlab::data;
using matlab::mex::ArgumentList;

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

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

      CellArray myCell = std::move(inputs[0]);
      // What goes here to find number of cells? 

      outputs[0] = myCell;

    }

};

And the corresponding Matlab command would be

% Initialize cell  
mcell = cell(3,1);
mcell{1,1} = ones(1,3);
mcell{2,1} = ones(1,2);
mcell{3,1} = ones(1,4);

% call c++ function
out = myMatlabFunction(mcell);

Following this matlab url, I am moving the input cell array to a matlab::data::CellArray. If I write

matlab::data::TypedArrayRef<double> ref myCell[0];

then I can access all the elements in the first cell of the cell array. But how do I found out the number of cells that are there? I'm having difficulty locating documentation on how to find the size.

Answer 1

[OCDER]

To get the size of the cell array, use mxGetM for number of rows, mxGetN for number of columns, or mxGetNumberOfElements for number of elements.

mwSize NRow = mxGetM(prhs[0]);
mwSize NCol = mxGetN(prhs[0]);
mwSize NElem = mxGetNumberOfElements(prhs[0]);

To get the number of elements within a cell array element, extract the cell element pointer, and then use the same functions.

mxArray *pCell = mxGetCell(prhs[0], j); //Get pointer to jth element of a cell array
mwSize NumRow = mxGetM(pCell);
mwSize NumCol = mxgetN(pCell);
mwSize NumElem = mxGetNumberOfElements(pCell);

https://www.mathworks.com/help/matlab/apiref/mxgetm.html https://www.mathworks.com/help/matlab/apiref/mxgetn.html https://www.mathworks.com/help/matlab/apiref/mxgetnumberofelements.html https://www.mathworks.com/help/matlab/apiref/mxgetcell.html

[Andrew Rhodes]

All of the functions in your answer are referring to c code. I am trying to use the c++ mex application https://www.mathworks.com/help/matlab/cpp-mex-file-applications.html.

Answer 2

[Zehui Lu]

According to this website, there is a function called getDimensions() under matlab::data::Array can return the size of matlab input matrix in C++ API.

Basically, what I did for matrix is the following. However, I haven't tried it on other data type. But I think the MATLAB Data API documentation for C++ API might be helpful.

https://www.mathworks.com/help/matlab/matlab-data-array.html

//This is the input matrix
TypedArray<double> matrix = std::move(inputs[0]);

//Get the dimension
std::vector<unsigned long int> size_test = matrix.getDimensions();

//We can slice this size vector
std::cout << "test_size =" << std::endl << size_test[0] << std::endl;
std::cout << "test_size =" << std::endl << size_test[1] << std::endl;

//Get the size of this size vector
std::cout << "size of size =" << std::endl << size_test.size() << std::endl;