C ++中的虚拟析构函数 [英] virtual destructor in c++

问题描述

在下面的代码中，为什么自动调用~Derived()析构函数?

In the code below, why is the ~Derived() destructor called automatically?

#include<iostream>
using namespace std;
class Base
{
public:
    virtual ~Base()
    {
        cout << "Calling ~Base()" << endl;
    }
};

class Derived: public Base
{
private:
    int* m_pnArray;

public:
    Derived(int nLength)
    {
        m_pnArray = new int[nLength];
    }

    virtual ~Derived()
    {
        cout << "Calling ~Derived()" << endl;
        delete[] m_pnArray;
    }
};

int main()
{
    Derived *pDerived = new Derived(5);
    Base *pBase = pDerived;
    delete pBase;

    return 0;
}

推荐答案

因为您的基类析构函数是虚拟的

Because your base class destructor is virtual

virtual ~Base();

对指向基类的指针的delete调用会导致对析构函数的虚拟调用，并且任何虚拟调用都会分派到派生类中的匹配函数.这不仅好，而且是必要的；否则，行为是不确定的.

the call to delete on a pointer to a base class results in virtual call to destructor and as any virtual call is dispatched to matching function in derived class. It is not only good, but necessary: otherwise the behavior is undefined.

这对于析构函数不是空函数的派生类至关重要.非虚拟调用会导致调用基类析构函数，派生资源被泄漏等.

This is crucial for a derived classes which destructor is not an empty function. Non-virtual call would otherwise result in calling base class destructor, derived resources being leaked, etc.

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