构造函数，析构函数

最新推荐文章于 2025-01-16 17:31:48 发布

原创最新推荐文章于 2025-01-16 17:31:48 发布 · 263 阅读

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#include <iostream>
using namespace std;
class A{
public:
	A(){ cout << "Construct a" << endl; p(); }
	virtual void p(){ cout << "A" << endl; }
	//~A(){ cout << "Destruct a" << endl; p(); }//析构函数不加virtual
	virtual ~A(){ cout << "Destruct a" << endl; p(); }//析构函数加了virtual 输出结果第三类 A *a1=new B()最后调用了子类的析构函数
};
class B : public A{
public:
	B(){ cout << "Construct b" << endl; p(); }
	void p(){ cout << "B" << endl; }
	~B(){ cout << "Destruct b" << endl; p(); }
};
int main()
{
	cout << "--------------- A *a = new A()  ---------------" << endl;
	A *a = new A();
	a->p();
	delete a;
	cout << "--------------- A *a = new A()  ---------------" << endl<<endl<<endl;
	
	cout << "--------------- B *b = new B()  ---------------" << endl; //输出结果都是先调用父类构造函数，子类构造函数，子类析构函数，父类析构函数

	B *b = new B();
	b->p();
	delete b;
	cout << "--------------- B *b = new B()  ---------------" << endl << endl << endl;

	cout << "--多态实现的精髓- A *a1 = new B()  -父类指针指向子类对象----" << endl;
	A *a1 = new B();
	a1->p();//因为p是虚函数，运行时动态绑定子类中函数p()的地址，所以打印出B
	delete a1;
	cout << "--多态实现的精髓- A *a1 = new B()  -父类指针指向子类对象----" << endl;
	system("pause");
	return 0;
}

#include <iostream>
using namespace std;
class A{
public:
	A(){ cout << "Construct a" << endl; p(); }
	virtual void p(){ cout << "A" << endl; }
	~A(){ cout << "Destruct a" << endl; p(); }//析构函数不加virtual 输出结果第三类 A *a1=new B()最后没有调用子类的析构函数，只调用了父类的析构函数
	//virtual ~A(){ cout << "Destruct a" << endl; p(); }//析构函数加了virtual
};
class B : public A{
public:
	B(){ cout << "Construct b" << endl; p(); }
	void p(){ cout << "B" << endl; }
	~B(){ cout << "Destruct b" << endl; p(); }
};
int main()
{
	cout << "--------------- A *a = new A()  ---------------" << endl;
	A *a = new A();
	a->p();
	delete a;
	cout << "--------------- A *a = new A()  ---------------" << endl<<endl<<endl;
	
	cout << "--------------- B *b = new B()  ---------------" << endl; //输出结果都是先调用父类构造函数，子类构造函数，子类析构函数，父类析构函数
	B *b = new B();
	b->p();
	delete b;
	cout << "--------------- B *b = new B()  ---------------" << endl << endl << endl;

	cout << "--多态实现的精髓- A *a1 = new B()  -父类指针指向子类对象----" << endl;
	A *a1 = new B();
	a1->p();//因为p是虚函数，运行时动态绑定子类中函数p()的地址，所以打印出B
	delete a1;
	cout << "--多态实现的精髓- A *a1 = new B()  -父类指针指向子类对象----" << endl;
	system("pause");
	return 0;
}