如何将虚拟析构函数删除派生类内存 [英] How to virutal destructor will delete the derived class memory

问题描述

计划：

Program:

//============================================================================
// Name        : revision6.cpp
// Author      : 
// Version     :
// Copyright   : Your copyright notice
// Description : Hello World in C++, Ansi-style
//============================================================================

#include <iostream>
using namespace std;

class innova {
public:
	innova() {
		cout << "innova constructor called" << endl;
	}
	virtual void speed() {
		cout << "The speed of innova is: 160kmph" << endl;
	}

	virtual ~innova() {
		cout << "innova destructor called" << endl;
	}
};

class nano : public innova {
public:
	nano() {
		cout << "nano constructor called" << endl;
	}
	void speed() {
		cout << "The speed of nano is: 60kmph" << endl;
	}
	~nano() {
		cout << "Nano destructor called" << endl;
	}
};
int main() {
	innova *inobj = new nano;
	inobj->speed();
	delete inobj; 
	return 0;
}

输出：

Output:

innova constructor called
nano constructor called
The speed of nano is: 60kmph
Nano destructor called
innova destructor called

我的问题：

在main函数中我删除了innova指针（删除inobj），这里它调用了两个类析构函数，我不知道它是如何使用虚拟析构函数在内部调用的。



你能否澄清这个问题。



提前致谢

Paramaraj

My question:
In main function I am deleting the innova pointer (delete inobj), Here its calling the both class destructor , i dont how it is calling internally using virtual destructor.

Could you please clarify this problem.

Thanks in advance
Paramaraj

推荐答案

最有可能通过 vtables 发生（据我所知，这些细节留给实施者）。这是一种语言功能，您可以在这里找到一些信息 [ ^ ]。

It happens most likely through vtables (such details are left to implementators, as far as I know). This is a language feature, you may find some info here[^].

因为构造函数可以被调用名字，但在destrctors的情况下，它不是真的。 ..

自动调用析构函数。

As constructors can be called by name but in case of destrctors it is not true. ..
destructor is called automatically.

#include <iostream>
using namespace::std;

class Base
{
public:
	Base(){cout << "Base constructor" << endl;}
	virtual ~Base(){cout << "Base destructor" << endl;} // virtual 
	virtual void f(){cout << "f in the Base class" << endl;}
	void g(){cout << "g in the Base (invoked)" << endl;}
};
class Derived:public Base
{
    public:
	Derived(){cout << "Derived constructor" << endl;}
	~Derived(){cout << "Derived destructor" << endl;}
	void f(){cout << "f in the Derived class" << endl;}
	void g(){cout << "g in the Derived (invoked)" << endl;}
};

int main()
{
	Base *x,*y;
	x = new Base;
	y = new Derived;
	x->f();
	y->f();
	x->g();
	y->g(); // g of Base called again, as this is not declared as virtual ..
	delete x;
	delete y; // again destructor of Base called, not the Derived ..
        // hence constructor is called by name, but the destructors don't,
       // so, the destructor of Base class should be virtual ..
	return 0;
}

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