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); }