How to send std::map from Mex function back to Matlab?

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

public:

void operator()(matlab::mex::ArgumentList outputs, matlab::mex::ArgumentList inputs)

{

ArrayFactory factory;

std::map<int, std::string > test_map {

{1, "Bla-bla"},

{2, "cla-cla"},

{3, "dla-dla"},

};

outputs[0] = ... // how to pass back test_map?

}

};

Answer 1

[Rishav]

Hi Rakesh,

To send a std::map from a Mex function back to MATLAB, it needs to be converted into a MATLAB data type that MATLAB can understand.

Here is the updated code to do the same:

class MexFunction : public matlab::mex::Function {
public:
    void operator()(matlab::mex::ArgumentList outputs, matlab::mex::ArgumentList inputs) {
        matlab::data::ArrayFactory factory;

        std::map<int, std::string> test_map {
            {1, "Bla-bla"},
            {2, "cla-cla"},
            {3, "dla-dla"},
        };

        // Convert std::map to MATLAB cell array
        matlab::data::CellArray cellArray = factory.createCellArray({1, test_map.size()});
        int idx = 0;
        for (const auto& pair : test_map) {
            cellArray[idx++] = factory.createCharArray(pair.second.c_str());
        }

        // Assign the MATLAB cell array to the output
        outputs[0] = cellArray;
    }
};

Also, make sure to include the appropriate headers for the MATLAB Data API.