C模拟实现C++的多态

用c语言中的结构体模拟类，用函数指针模拟虚函数表。

整个程序用于模拟C++中的多态性，即用基类访问派生类的函数。

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//  c语言模拟多态性



#include "stdio.h"

#include "stdlib.h"



enum ShapeType{CIRCLE,SQUARE,RECTANGLE};//形状类型





//建立虚函数表,2个虚函数

typedef struct  

{

    void (*ShowShape)();  

    double (*CalArea)(int w);

}vtable;



//建立基类

typedef struct

{

    vtable *vptr_base;

    ShapeType  type;

}BaseShape;





//建立三个派生类

typedef struct

{

    BaseShape  itsType;

    int r;

}Circle;



typedef struct

{

    BaseShape itsType;

    int w;

}Square;



typedef struct  

{

    BaseShape itsType;

    int w,h;

}Rectangle;



//子类重写虚函数 

//Circle

void showCircle()

{

    printf("I'm a Circle!\n");

}



double calArea_Circle(int r)

{

    return 3.14*r*r;

}



//Square

void showSquare()

{

    printf("I'm a Square!\n");

}



double calArea_Square(int w)

{

    return w*w;

}





//Rectangle

void showRectangle()

{

    printf("I'm a Rectangle!\n");

}



double calArea_Rectangle(int w)

{

    return w*w*2;  //假设高是宽的2倍

}



//测验多态，只需要传递基类指针ShapePointer。  

void virtualShow(BaseShape *base)

{

    base->vptr_base->ShowShape();

}



void virtualCalArea(BaseShape *base, int w)

{

    printf("     面积为: %2.2f\n", base->vptr_base->CalArea(w));

}



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

void main()

{

    Circle m_c = {(vtable *)malloc(sizeof(vtable)), CIRCLE, 1};

    Square m_s = {(vtable *)malloc(sizeof(vtable)), SQUARE, 1};

    Rectangle m_r = {(vtable *)malloc(sizeof(vtable)), RECTANGLE, 1,2};



    printf("圆的半径为1，正方形的宽为1，长方形的宽高分别为1,2\n");



    //各子类对象的虚函数表初始化

    m_c.itsType.vptr_base->ShowShape = showCircle;

    m_c.itsType.vptr_base->CalArea = calArea_Circle;



    m_s.itsType.vptr_base->ShowShape = showSquare;

    m_s.itsType.vptr_base->CalArea = calArea_Square;



    m_r.itsType.vptr_base->ShowShape = showRectangle;

    m_r.itsType.vptr_base->CalArea = calArea_Rectangle;



    //基类指针指向派生类

    BaseShape *pB_c = (BaseShape *)&m_c;

    BaseShape *pB_s = (BaseShape *)&m_s;

    BaseShape *pB_r = (BaseShape *)&m_r;



    //测试多态性

    virtualShow(pB_c);

    virtualCalArea(pB_c,1);



    virtualShow(pB_s);

    virtualCalArea(pB_s,1);



    virtualShow(pB_r);

    virtualCalArea(pB_r,1);

    







}