C++類繼承--基類析構函數加上Virtual

下面的內容要說明兩個問題：1. 基類的析構函數爲何要加上Virtual--防止內存泄露

1. 基類虛構函數無virtual，派生類沒法析構，會致使內存泄露

#include <stdio.h>

class Base
{
public:
	int a;
	Base(){
		a=0;
	}
	~Base(){
		printf("base delete");
	}
	virtual void setA()=0;
};

class A:public Base
{
public:
	A(){
		a = 10;
	}
	~A(){
		printf("A class delete\n");
	}
	virtual void setA()
	{
		a = 2;
	}
};

class B:public Base
{
public:
	B(){
		a=20;
	}
	~B(){
		a=-20;
	}
	
	virtual void setA()
	{
		a = 3;
	}
};

int main()
{
	
	Base *ax = new A();
	Base *bx = new B();
	Base *aClass =  ax;
	Base *bClass = bx;
	printf("a value of a construct %d\n", aClass->a);
	printf("a value of b construct %d\n", bClass->a);

	aClass->setA();
	bClass->setA();
	printf("a value of a %d\n", aClass->a);
	printf("a value of b %d\n", bClass->a);

	delete aClass;
	
	return 0;
}

　　運行結果爲：

2. 若在基類析構函數前加上Virtual

class Base
{
public:
	int a;
	Base(){
		a=0;
	}
	virtual ~Base(){
		printf("base delete");
	}
	virtual void setA()=0;
	
};

　　運行結果爲：