Adding a Native .dll file from SIMULINK to Visual Studios C#

Question

I have created a .dll file using SIMULINK's embedded coder. (System target file is set to : ert_shrlib.tlc) It successfully builds into Model_win64.dll. Now I want to reference it from Visual studios.

I first tried using the "add reference" tool but got the following error: A reference to 'file path\\Model_win64.dll'

I then searched around for a solution online and am getting that this error is cause by the .dll file being a native .dll so I should use the DllImportAttribute Class https://msdn.microsoft.com/en-us/library/system.runtime.interopservices.dllimportattribute.aspx

So the code I have currently is

using System;
using System.Runtime.InteropServices; 

namespace GUI_Interface
{
    class Main
    {
    [DllImport("Modbot_Model_win64.dll", CharSet = CharSet.Unicode)]
    public static extern int[] MPC(double x, double y, double theta, double Vx, double Vy, double Vtheta);

    public static BackgroundWorker test()
    {
        ints = MPC(0, 0, 0, 0, 0, 0);
    }
}

And I get the runtime error:Cannot marshal 'return value': Invalid managed/unmanaged type combination. I've tried reading up on managed/unmanaged types but I just can't wrap my head around it in order to solve this issue. Any proposed solutions or info on managed/unmanaged would be greatly appreciated.

Answer 1

You can not directly use int[] as return type. It's managed but the dll returned is not.

Change return type to "IntPtr" to receive a pointer.

[DllImport("Modbot_Model_win64.dll", CharSet = CharSet.Unicode)]
public static extern IntPtr MPC(double x, double y, double theta, double Vx, double Vy, double Vtheta);

Then use Marshall copy to get the data

IntPtr ints = MPC(0, 0, 0, 0, 0, 0);
int ret[] = new int[N]; //N is the number of elements
Marshall.Copy(ints, ret, 0, N);