MATLAB coder - selecting output type for entry point function

I'm trying to use matlab coder to create C++ code, compile into a DLL and use this inside a C# project. I have a single entry point function that returns a 1x3 array in matlab, i.e.

 function oneByThreeArray = exampleFunction(input1, input2, input3,...){...}

When coder is run, the default behaviour is to convert this entry point to

   void exampleFunction(const double input1, const double input2, const double input3,..., double oneByThreeArray[3])

So my two questions are

• is it possible to set the C++ output type (rather than void) of my entry point function so that it returns a value for oneByThreeArray (e.g. std::array) before the code is generated by the coder?
• if not, how should this C++ code be called from within C#? If oneByThreeVector is initialised just before the function call, will it be filled with the desired output values afterwards?

Answer 1

[Yoke Peng Leong]

You can consider creating the function such that the output oneByThreeArray is pass by reference:

https://www.mathworks.com/examples/matlab-coder/mw/coder-ex37517449-pass-structure-arguments-by-reference-or-by-value-in-generated-code

Answer 2

[Simone Pagliuca]

I know this is old but since I encountered the same problem, I'll post the solution anyway.

In my testing using an array creates some problems (I'll edit if i find a solution), but you can pull it off with multiple values:

So instead of

function array = myfunction(arg1, arg2)

you write it like

function [value1, value2, value3] = myfunction(arg1, arg2)

where the 3 values are you arrays elements.

Then, you generate the DLL.

Then, C#:

First of all, import the dll:

 [DllImport("myfunction.dll",
          CallingConvention = CallingConvention.Cdecl)]
        public static extern void myfunction(Double arg1, Double arg2, out Double value1, out Double value2, out Double value3);

note that the function is of type void and the outputs are set as arguments with the prefix out.

Then to use it:

        double value1;
        double value2;
        double value3;
        
        sg_geometry(arg1, arg2, arg3, out value1, out value2, out value3);

So now you have your results in the variables value1, value2, value3.