Convert Matlab struct into custom C++ type with C++ Mex API

I am trying to mex a custom C++ code file but am struggeling in how to convert the Matlab-Inputs into whatever type I need for my C++ Code.

Let's assume I have a Matlab struct like this

u = struct(test1 = 5, test2 = 10, test3 = struct(test4 = 1:10))

u = struct with fields:
    test1: 5
    test2: 10
    test3: [1x1 struct]

As u see I have a nested struct with an array inside. Now, in the C++ Mex API I need to read all values of the above struct. How do I do this? I tried indexing into the inputs of the operator() method

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

however, that way I could only retrieve the number of inputs but not their numerical contents.

I guess I have to do something like

matlab::data::TypedArray<Struct> in0 = std::move(inputs[0]);

to get to the values but that alone doesn't help me. How do I proceed?

Answer 1

[埃博拉酱]

Usually you should move-construct a StructArray from inputs[0] and index into it to get a Struct element, which can be then indexed with a fieldname as a C++ string to get a generic Array, with which you can then move-construct a TypedArray of correct type (get its real runtime type with Array::GetType if you can't ensure it at coding time). Finally you should usually index into that TypedArray to get a numeric element, get an iterator like cbegin/begin, or release it as a buffer_ptr_t to get a C++ native pointer.

void Example(matlab::mex::ArgumentList outputs, matlab::mex::ArgumentList inputs)
{
	matlab::data::TypedArray<double> A = matlab::data::StructArray(matlab::data::StructArray(std::move(inputs[0]))[0]["test3"].operator matlab::data::Array())[0]["test4"];
	A.cbegin();//Get an iterator
	A[0];//Get a double element
	const matlab::data::buffer_ptr_t<double> B = A.release();//After this, A becomes invalid
	B.get();//Get a native pointer
}

20241028：Edited for forgetting to provide a type to the buffer_ptr_t

[Friedrich]

Thanks @埃博拉酱, that helped!

Is it also possible to move the content of the Array A to a std::vector<double> v?

Just for the sake of completeness, I guess you forgot to provide a type to the buffer_ptr_t. This compiles:

const matlab::data::buffer_ptr_t<double> B = A.release();

[埃博拉酱]

No. std::vector does not support moving constructs from types other than vector. Copying is inevitable if you really must get a vector.