__declspec(dllexport) 和 __declspec(dllimport)的作用

operatordll.h

#include <iostream>

#ifdef OPERATORDLL_EXPORTS
#define DLL_EXPORT __declspec(dllexport)
#else
#define DLL_EXPORT __declspec(dllimport)      //不加import 如果把dll和头文件提供给别人使用的时候就会出“unsloved symbol a”的问题。
#endif

class DLL_EXPORT Operatordll
{
public:
static int a;

double mul_double(double a, double b);

double div_double(double a, double b);
};

//////////////////////////////////////////////////////////////////////

operatordll.cpp

#include "operatordll.h"

int Operatordll::a = 0;

double Operatordll::mul_double(double a, double b)
{
return (a * b);
}

double Operatordll::div_double(double a, double b)
{
return (a / b);
}