c#调用c++的DLL的实现方法

#pragma once
#include <string>
public ref class Function
{
public:
    Function(void);
    ~Function(void);
    int menber;
    int menberFuncAdd(int a,int b);
    System::String^ say(System::String^ str);
};
 
//.cpp
#include "Function.h"
Function::Function(void)
{
}
Function::~Function(void)
{
}
 
int Function::menberFuncAdd(int a,int b)
{
   return a+b;
}
System::String^ Function::say(System::String^ str)
{
   return str;
}

#include "Function.h"

 Function fun = new Function();
            int a = fun.menberFuncAdd(1, 2);
            string s = fun.say("Hello World");

// stdafx.h : 标准系统包含文件的包含文件，
// 或是经常使用但不常更改的
// 特定于项目的包含文件
//
 
#pragma once
 
#include "targetver.h"
#ifdef A_EXPORTS
#define DLL_API __declspec(dllexport)
#else
#define DLL_API __declspec(dllimport)
#endif
#define WIN32_LEAN_AND_MEAN             //  从 Windows 头文件中排除极少使用的信息
// Windows 头文件:
#include <windows.h>
 
extern "C" DLL_API void MessageBoxShow(); 
 
// TODO: 在此处引用程序需要的其他头文件

#include "stdafx.h"
BOOL APIENTRY DllMain( HMODULE hModule,
                       DWORD  ul_reason_for_call,
                       LPVOID lpReserved
                     )
{
    switch (ul_reason_for_call)
    {
    case DLL_PROCESS_ATTACH:
    case DLL_THREAD_ATTACH:
    case DLL_THREAD_DETACH:
    case DLL_PROCESS_DETACH:
        break;
    }
    return TRUE;
}
 
#ifdef _MANAGED
#pragma managed(push, off)
#endif
 
void MessageBoxShow()
{
    MessageBox(NULL, TEXT("Hello World"), TEXT("In a DLL"), MB_OK);
}
 
 
#ifdef _MANAGED
#pragma managed(pop)
#endif

[DllImport("ll.dll")]
 public extern static void MessageBoxShow();