注：这个程序是在软件设计师教程上看到，并做了一点点修改得到。。

在一个简化的绘图程序中，支持点（point）和圆（circle）两种图形，在设计过程中采用面向对象思想，认为所有的点和圆都是一种图形（shape），

并定义类型shape_t、point_t、circle_t分别表示基本图形、点和圆，点和圆自然具有基本图形的所有特征。

下面是利用C语言，通过函数指针和可变参数机制实现上面的类层次关系：

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>

// 程序中的两个图形：点和圆
typedef enum {point,circle}shape_type;
// 基本图形类型
typedef struct {
	shape_type type;
	void (*destroy)();
	void (*draw)();
}shape_t;
// 点类
typedef struct {
	shape_t common;
	int x,y;
}point_t;
// 圆类
typedef struct {
	shape_t common;
	point_t *center;
	int radius;
}circle_t;
/*
 
下面是相关方法*/
void destroyPoint(point_t *this)
{
	int x=this->x,y=this->y;
	free(this);
	printf("P(%d,%d) destroyed!\n",x,y);
}
void drawPoint(point_t *this)
{
	printf("P(%d,%d)",this->x,this->y);
}

point_t * createPoint(va_list *ap)
{
	point_t *p_point;
	if ((p_point=(point_t*)malloc(sizeof (point_t)))==NULL)
		return NULL;
	p_point->common.type=point;
	p_point->common.destroy=destroyPoint;
	p_point->common.draw=drawPoint;
	p_point->x=va_arg(*ap,int);
	p_point->y=va_arg(*ap,int);
	return p_point;
}

void destroyCircle(circle_t *this)
{
	int x=this->center->x;
	int y=this->center->y;
	int r=this->radius;
	this->center->common.destroy(this->center);
	free(this);
	printf("C(P(%d,%d),%d) destroyed!\n",x,y,r);
}
void drawCircle(circle_t *this)
{
	printf("C(");
	this->center->common.draw(this->center);
	printf(",%d)",this->radius);
}
circle_t* createCircle(va_list* ap)
{
	circle_t *p_circle;
	if ((p_circle=(circle_t*)malloc(sizeof(circle_t)))==NULL)
		return NULL;
	p_circle->common.type=circle;
	p_circle->common.destroy=destroyCircle;
	p_circle->common.draw=drawCircle;
	p_circle->center=createPoint(ap);
	p_circle->radius=va_arg(*ap,int);
	return p_circle;
}
shape_t* createShape(shape_type st,...)
{
	va_list ap;
	shape_t* p_shape=NULL;
	va_start(ap,st);
	if (st==point) p_shape=(shape_t*)createPoint(&ap);
	if (st==circle) p_shape=(shape_t*)createCircle(&ap);

	va_end(ap);
	return p_shape;
}

int main()
{
	int i;
	shape_t *shapes[2];
	shapes[0]=createShape(point,2,3);
	shapes[1]=createShape(circle,20,40,10);
	for (i=0;i<2;i++) {
		shapes[i]->draw(shapes[i]);
		printf("\n");
	}
	for (i=1;i>=0;i--)
		shapes[i]->destroy(shapes[i]);
	return 0;
}

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