dll导出类的两种方法！

方法一：

 

不罗嗦了，直接上代码吧！

// MathFuncsDll.h

 

namespace MathFuncs
{
 class  __declspec(dllexport) MyMathFuncs
 {
 public:
  double Add(double a, double b);

  double Subtract(double a, double b);

  double Multiply(double a, double b);

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

 

// MathFuncsDll.cpp

#include "MathFuncsDll.h"

#include <stdexcept>

using namespace std;

namespace MathFuncs
{
 double MyMathFuncs::Add(double a, double b)
 {
  return a + b;
 }

 double MyMathFuncs::Subtract(double a, double b)
 {
  return a - b;
 }

 double MyMathFuncs::Multiply(double a, double b)
 {
  return a * b;
 }

 double MyMathFuncs::Divide(double a, double b)
 {
  if (b == 0)
  {
   throw new invalid_argument("b cannot be zero!");
  }

  return a / b;
 }
}

 

#include <iostream>

#include "MathFuncsDll.h"
#include <windows.h>
#include <stdio.h>

using namespace std;
using namespace MathFuncs;

int main()
{
 double a = 7.4;
 int b = 99;
 MyMathFuncs *p = new MyMathFuncs;

 cout << "a + b = " <<
  p->Add(a, b) << endl;

 cout << "a - b= " <<
  p->Subtract(a,b)<<endl;

 Sleep(10000);

 return 0;
}

 

方法（二）

// MathFuncsDll.h

namespace MathFuncs
{
 class MyMathFuncs
 {
 public:
  virtual double Add(double a, double b);       //注意，这里必须是虚函数后者纯虚函数。

  virtual double Subtract(double a, double b);

  virtual double Multiply(double a, double b);

  virtual double Divide(double a, double b);
 };

 __declspec(dllimport) MyMathFuncs* CreateMathFuncsInstance();
 __declspec(dllimport) void ReleaseMathFuncsInstance(MyMathFuncs* &);
}

 

#include "MathFuncsDll.h"

#include <stdexcept>

using namespace std;

namespace MathFuncs
{
 MyMathFuncs* CreateMathFuncsInstance()
 {
  MyMathFuncs *p = NULL;
  p = new MyMathFuncs;
  return p;
 }

 void ReleaseMathFuncsInstance(MyMathFuncs* &p)
 {
  if (p)
  {
   delete p;
  }
 }

 double MyMathFuncs::Add(double a, double b)
 {
  return a + b;
 }

 double MyMathFuncs::Subtract(double a, double b)
 {
  return a - b;
 }

 double MyMathFuncs::Multiply(double a, double b)
 {
  return a * b;
 }

 double MyMathFuncs::Divide(double a, double b)
 {
  if (b == 0)
  {
   throw new invalid_argument("b cannot be zero!");
  }

  return a / b;
 }
}

 

 

#include <iostream>

#include "MathFuncsDll.h"
#include <windows.h>
#include <stdio.h>

using namespace std;
using namespace MathFuncs;

int main()
{
 double a = 7.4;
 int b = 99;
 MyMathFuncs *p = CreateMathFuncsInstance();

 cout << "a + b = " <<
  p->Add(a, b) << endl;

 cout << "a - b= " <<
  p->Subtract(a,b)<<endl;

 ReleaseMathFuncsInstance(p);

 Sleep(10000);

 return 0;
}