mapbasic 调用dll时总出错，以下是dll内容，请大侠帮看下

[mysummering]

//头文件：
//#pragma once
#ifdef sayhello_EXPORTS
#define sayhello_API __declspec(dllexport)
#else
#define sayhello_API __declspec(dllimport)
#endif

namespace say
{
// This class is exported from the MathFuncsDll.dll
class Myhello
{
public:
// Returns a + b
static sayhello_API int sayhello();


};
}

//cpp文件：
#include "stdafx.h"
#include "sayhello.h"
#include <stdexcept>

using namespace std;

namespace say
{
int Myhello::sayhello()
{
return 1;
}
}

//def文件：

LIBRARY
EXPORTS
sayhello