【zz】DLL 导出类

短命女 2022-07-12 04:16 204阅读 0赞

## [DLL导出类][DLL] ##

**DLL导出类**  
  
　　DLL中定义的类可以在应用工程中使用。  
  
　　下面的例子里，我们在DLL中定义了point和circle两个类，并在应用工程中引用了它们。

//文件名：point.h，point类的声明  
  
\#ifndef POINT\_H  
  
\#define POINT\_H  
  
\#ifdef DLL\_FILE  
  
class \_declspec(dllexport) point //导出类point  
  
\#else  
  
class \_declspec(dllimport) point //导入类point  
  
\#endif  
  
\{  
  
public:  
  
float y;  
  
float x;  
  
point();  
  
point(float x\_coordinate, float y\_coordinate);  
  
\};  
  
\#endif  
  
  
//文件名：point.cpp，point类的实现  
  
\#ifndef DLL\_FILE  
  
\#define DLL\_FILE  
  
\#endif  
  
\#include "point.h"  
  
//类point的缺省构造函数  
  
point::point()  
  
\{  
  
x = 0.0;  
  
y = 0.0;  
  
\}  
  
//类point的构造函数  
  
point::point(float x\_coordinate, float y\_coordinate)  
  
\{  
  
x = x\_coordinate;  
  
y = y\_coordinate;  
  
\}  
  
  
//文件名：circle.h，circle类的声明  
  
\#ifndef CIRCLE\_H  
  
\#define CIRCLE\_H  
  
\#include "point.h"  
  
\#ifdef DLL\_FILE  
  
class \_declspec(dllexport)circle //导出类circle  
  
\#else  
  
class \_declspec(dllimport)circle //导入类circle  
  
\#endif  
  
\{  
  
public:  
  
void SetCentre(const point ¢rePoint);  
  
void SetRadius(float r);  
  
float GetGirth();  
  
float GetArea();  
  
circle();  
  
private:  
  
float radius;  
  
point centre;  
  
\};  
  
\#endif  
  
  
//文件名：circle.cpp，circle类的实现  
  
\#ifndef DLL\_FILE  
  
\#define DLL\_FILE  
  
\#endif  
  
\#include "circle.h"  
  
\#define PI 3.1415926  
  
//circle类的构造函数  
  
circle::circle()  
  
\{  
  
centre = point(0, 0);  
  
radius = 0;  
  
\}  
  
//得到圆的面积  
  
float circle::GetArea()  
  
\{  
  
return PI \*radius \* radius;  
  
\}  
  
//得到圆的周长  
  
float circle::GetGirth()  
  
\{  
  
return 2 \*PI \* radius;  
  
\}  
  
//设置圆心坐标  
  
void circle::SetCentre(const point ¢rePoint)  
  
\{  
  
centre = centrePoint;  
  
\}  
  
//设置圆的半径  
  
void circle::SetRadius(float r)  
  
\{  
  
radius = r;  
  
\}  
  
类的引用：

\#include "../circle.h"　　//包含类声明头文件  
  
\#pragma comment(lib,"dllTest.lib");  
  
  
int main(int argc, char \*argv\[\])  
  
\{  
  
circle c;  
  
point p(2.0, 2.0);  
  
c.SetCentre(p);  
  
c.SetRadius(1.0);  
  
printf("area:%f girth:%f", c.GetArea(), c.GetGirth());  
  
  
return 0;  
  
\}

从上述源代码可以看出，由于在DLL的类实现代码中定义了宏DLL\_FILE，故在DLL的实现中所包含的类声明实际上为：

class \_declspec(dllexport) point //导出类point  
  
\{  
  
…  
  
\}

和

class \_declspec(dllexport) circle //导出类circle  
  
\{  
  
…  
  
\}

而在应用工程中没有定义DLL\_FILE，故其包含point.h和circle.h后引入的类声明为：

class \_declspec(dllimport) point //导入类point  
  
\{  
  
…  
  
\}

和

class \_declspec(dllimport) circle //导入类circle  
  
\{  
  
…  
  
\}

[DLL]: http://www.cppblog.com/ivenher/articles/1318.html