在C#中导入C++ DLL

// CPP_DLL.h
#pragma once

extern "C" __declspec(dllexport) int Add(int a, int b);

// CPP_DLL.cpp
#include "stdafx.h"
#include "CPP_DLL.h"

extern "C" __declspec(dllexport) int Add(int a, int b)
{
    return a + b;
}

using System;
using System.Runtime.InteropServices;

namespace CSharp_DLL
{
    class Program
    {
        [DllImport("CPP_DLL.dll", CallingConvention = CallingConvention.Cdecl)]
        public static extern int Add(int a, int b);

        static void Main(string[] args)
        {
            int result = Add(10, 20);
            Console.WriteLine("10 + 20 = " + result);
        }
    }
}