Passing struct to Mex file with C++ interface

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Torsten Knüppel 2020-2-21

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Hi all,

I'm trying to pass a struct to a Mex-File and would like to know what is the suggested way to access its fields.

Here is a short script for a illustrating the problem:

mex mexStructTest.cpp
strct = struct('a', 10);
mexStructTest(strct);

The corresponding Mex-file is

#include "mex.hpp"
#include "mexAdapter.hpp"
using namespace matlab::data;
using matlab::mex::ArgumentList;
using matlab::engine::convertUTF8StringToUTF16String;
class MexFunction : public matlab::mex::Function {
public:
    void operator()(ArgumentList outputs, ArgumentList inputs) {
        if(inputs[0].getType() == matlab::data::ArrayType::STRUCT){
            
            // Working
            StructArray s(inputs[0]);
            matlab::data::Reference<Struct> s2 = s[0];
//             Struct s2 = StructArray(inputs[0])[0];
            
            // Not working -> Crash
//             matlab::data::Reference<Struct> s2 = StructArray(inputs[0])[0]; 
//             Struct s2 = StructArray(inputs[0])[0];            
                    
            double a = TypedArray<double>(s2["a"])[0];
            std::cout << a << "\n";
        }
    }
};

The way I managed to get it working requires to first use a StructArray and then access its fields. However, I would prefer to have this thing as a one-liner (one of the options in the not-working category) or at least understand, why it is crashing.

Thanks in advance and best regards,

Torsten