MATLAB Coder: Including a DLL function in C# which returns dynamic sized data

Hello,

I have got a simple method

function res = returnArray(a)
    res = zeros(a, a);
end

which returns a 2D array of doubles. How can I include it in my C# client?

I exported it in a DLL and tried to import it like this (using the method signature created by the Coder):

using System.Runtime.InteropServices;

class Programm
{
    [DllImport("returnArray.dll", CallingConvention = CallingConvention.Cdecl)]
    public static extern void returnArray(double a, emxArray_real_T resArr);
    
    static void Main()
    {
    double a = 1;
    emxArray_real_T resArr = new emxArray_real_T();
    returnArray(a, resArr);
    }
}

This produces System.AccessViolationException: "Attempted to read or write protected memory. This is often an indication that other memory is corrupt."

[Sumit Ghosh]

You can try to avoid generation of emxArray types in the DLL by not relying on variable size arrays. This will result in generation primitive types like double arrays, which you can interface with C#.

To avoid using variable-size arrays, you can change the config settings related to Dynamic Memory Allocation. for this, you can use coder.EmbeddedCodeConfig

https://www.mathworks.com/help/coder/ref/coder.embeddedcodeconfig.html

Option 1: Set the DynamicMemoryAllocation property to Off to disable variable-size arrays for all arrays in your code

Option 2: By default, DynamicMemoryAllocation is set to Threshold, and you can adjust the threhold value to something within which your array will not use variable-size. To do this, you can use the property DynamicMemoryAllocationThreshold (default vaue is 65536).

You can look at examples in https://www.mathworks.com/help/coder/ug/use-c-arrays-in-the-generated-function-interfaces.html to see how to generate the C function interface using primitive types instead of emxArrays.

[Philipp]

Thank you for yor answer! Turning off DynamicMemoryAllocaton leads to problems with my other code (which does not appear in this example).

I succeeded doing it with swig (https://github.com/mathworks/coder-swig) and using the implemented interface.

Answer 1

[Sumit Ghosh]

You can try to avoid generation of emxArray types in the DLL by not relying on variable size arrays. This will result in generation primitive types like double arrays, which you can interface with C#.

To avoid using variable-size arrays, you can change the config settings related to Dynamic Memory Allocation. for this, you can use coder.EmbeddedCodeConfig

https://www.mathworks.com/help/coder/ref/coder.embeddedcodeconfig.html

Option 1: Set the DynamicMemoryAllocation property to Off to disable variable-size arrays for all arrays in your code

Option 2: By default, DynamicMemoryAllocation is set to Threshold, and you can adjust the threhold value to something within which your array will not use variable-size. To do this, you can use the property DynamicMemoryAllocationThreshold (default vaue is 65536).

You can look at examples in https://www.mathworks.com/help/coder/ug/use-c-arrays-in-the-generated-function-interfaces.html to see how to generate the C function interface using primitive types instead of emxArrays.