a.cpp

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// 测试a.h中定义的类
#include <iostream >
#include "a.h"
using namespace std;

void foo( A* obj)  
{ 
	//根据type值的情况，选择不同的函数输出，
	switch ( obj->GetType() )
	{
		case 0:
			((A*)obj )-> Display();    // 强制类型转换
			break;
		case 1:
			((B*)obj )-> Display();
			break;
		case 2:
			((C*)obj ) -> Display();
			break;
		default:
			cout << "error\n";
			break;
	}
}

int main()
{
	A	a;
	B	b;
	C	c;
	foo( &a );
	foo( &b );
	foo( &c );

	return 0;
}