C# 访问 C DLL

using System;
using System.Runtime.InteropServices;
namespace zzzili
{
    class Test{
        [DllImport("dllTest.dll")]
        public static extern int MyDll_Add(int a, int b);               
        static void Main()
        {
           Console.WriteLine(MyDll_Add(1,2).ToString());
        }
    }
}
dllTest.C
extern "C"  __declspec(dllexport) int MyDll_Add(int a,int b);
int MyDll_Add(int a,int b)
{
 return a+b;
}