Using the _CDECL calling convention in C# (changing compiler service)

using System;
using System.Runtime.InteropServices;
using System.Collections;


namespace CallDLLFromDotNet
{
	/// <summary>
	/// Summary description for Class1.
	/// </summary>
	
	
	class CallDll
	{

		[DllImport("Sum.dll",CallingConvention=CallingConvention.Cdecl)]
			public static extern int testfuncptr(int a,int b,MulticastDelegate callbk);
		[DllImport("Sum.dll",CallingConvention=CallingConvention.Cdecl)]
			private static extern int Sum(int a, int b);

	[Callconv]public delegate int mydg(int a,int b);


		[STAThread]
		static void Main(string[] args)
		{

			mydg dg = new mydg(mytest);
			int a = 10;
			int b = 10;

			a = testfuncptr(a,b,dg);
			

			Console.WriteLine(a.ToString());
			Console.ReadLine();
		
		}



		public static int mytest(int a,int b)
		{
			return (a+b);
		}

		

	}
}