cpp虚函数，基类命名指向子类实例必备佳选

Posted 2022-12-07 飞凡可期

简单虚函数

//============================================================================
// Name        : p1022VirtualDeconstructor.cpp
// Author      : perfey
// Version     :
// Copyright   : Your copyright notice
// Description : Hello World in C++, Ansi-style
//============================================================================

#include <iostream>
using namespace std;

class Base

public:
	Base()cout << "Conctructing Base!"<<endl;

	virtual ~Base()cout << "Deconstructing Base!"<<endl;//多一个空格，virtual和~之间
;

class Derive: public Base

public:
	  Derive()cout << "Constructing Derive!"<<endl;
      ~ Derive()cout << "Deconstructing Derive!"<<endl;
     /*
      * 若是不加virtual，只输出构建base, Derive, 解构Base 三步，没有解构 derive？ 这个有问题了
      *
      * */
;


int main() 
	cout << "!!!Hello World!!!" << endl; // prints !!!Hello World!!!

	Base *bptr = new Derive(); //父类指针指向之类实例；
	delete bptr;

	return 0;

结果

Conctructing Base!
Constructing Derive!
Deconstructing Derive!
Deconstructing Base!

（如果没有 tilde~前面那个virtual修饰，那么不会有Deconstructing Derive！这一句）

继续传递，继承下去

//============================================================================
// Name        : p1022VirtualDeconstructor.cpp
// Author      : perfey
// Version     :
// Copyright   : Your copyright notice
// Description : Hello World in C++, Ansi-style
//============================================================================

#include <iostream>
using namespace std;

class Base

public:
	Base()cout << "Conctructing Base!"<<endl;

	virtual ~Base()cout << "Deconstructing Base!"<<endl;//多一个空格，virtual和~之间
;

class Derive: public Base

public:
	  Derive()cout << "Constructing Derive!"<<endl;
      ~ Derive()cout << "Deconstructing Derive!"<<endl;
     /*
      * 若是不加virtual，只输出构建base, Derive, 解构Base 三步，没有解构 derive？ 这个有问题了
      *
      * */
;

class Derive2: public Derive

public:
	  Derive2()cout << "Constructing DeriveSon!"<<endl;
      ~ Derive2()cout << "Deconstructing DeriveSon!"<<endl;
     /*
      * 若是不加virtual，只输出构建base, Derive, 解构Base 三步，没有解构 derive？ 这个有问题了
      *
      * */
;


int main() 
	cout << "!!!Hello World!!!" << endl; // prints !!!Hello World!!!

	Base *bptr = new Derive2(); //父类指针指向之类实例；
	delete bptr;

	return 0;

结果

!!!Hello World!!!
Conctructing Base!
Constructing Derive!
Constructing DeriveSon!
Deconstructing DeriveSon!
Deconstructing Derive!
Deconstructing Base!

可以看到每一个子类都继承虚函数，都调用了Deconstructor这是预期的效果。

继续花样

//============================================================================
// Name        : p1022VirtualDeconstructor.cpp
// Author      : perfey
// Version     :
// Copyright   : Your copyright notice
// Description : Hello World in C++, Ansi-style
//============================================================================

#include <iostream>
using namespace std;

class Base

public:
	Base()cout << "Conctructing Base!"<<endl;

	virtual ~Base()cout << "Deconstructing Base!"<<endl;//多一个空格，virtual和~之间

    virtual void Eat() = 0; //纯需函数，无需在基类中实现，奇怪吧，类似interface中概念
;

class Derive: public Base

public:
	  Derive()cout << "Constructing Derive!"<<endl;

       void Eat()override
    		  
    	  cout <<" 我吃生肉，茹毛饮血！！"<<endl;
              

      ~ Derive()cout << "Deconstructing Derive!"<<endl;
;

/*
 * 若是不加virtual，只输出构建base, Derive, 解构Base 三步，没有解构 derive？ 这个有问题了
 *
 * */

class Derive2: public Derive

public:
	  Derive2()cout << "Constructing DeriveSon!"<<endl;
      ~ Derive2()cout << "Deconstructing DeriveSon!"<<endl;
     void Eat() 
    	  cout <<" 我今晚大口吃肉！"<<endl;
      
;


int main() 
	cout << "!!!Hello World!!!" << endl; // prints !!!Hello World!!!

	Base *bptr = new Derive(); //父类指针指向之类实例；
	bptr->Eat();
	bptr = new Derive2();
	bptr->Eat();

	delete bptr;

	return 0;

纯虚函数来结果

!!!Hello World!!!
Conctructing Base!
Constructing Derive!
我吃生肉，茹毛饮血！！
Conctructing Base!
Constructing Derive!
Constructing DeriveSon!
我今晚大口吃肉！
Deconstructing DeriveSon!
Deconstructing Derive!
Deconstructing Base!