虚析构函数

作者：jicanmeng

时间：2014年12月05日

先看一个程序： 

#include <iostream>
using namespace std;

class Base
{
public:
    ~Base(){
        cout << "Calling ~Base()" << endl;
    }
};

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

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

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

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

    return 0;
}

上面的程序中，程序退出之前，我们调用delete pBase;，但是这行代码只会调用Base的析构函数，不会调用Derived的析构函数，会产生内存泄露。可以通过将Base的析构函数设置为虚函数来解决这个问题。 

#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;
}

参考资料

  1. <<C++实用教程>> 电子工业出版社 郑阿奇 主编 丁有和 编著
  2. The C++ Tutorial:
    http://www.learncpp.com/cpp-tutorial/123-virtual-destructors-virtual-assignment-and-overriding-virtualization/