C++多态为什么要定义虚析构函数

来源：互联网发布：外国人来中国旅游数据编辑：程序博客网时间：2024/06/06 02:00

请看父类Base类没有定义虚析构函数的例子：

#include <iostream>class Base{public:virtual int start(){std::cout<<"Base::start"<<std::endl;}~Base(){std::cout<<"Base::~Base() "<<std::endl;}};class Derived : public Base{public:    virtualint start(){m_pInt = new int [10];std::cout<<"Derived::start()"<<std::endl;}~Derived(){std::cout<<"Derived::~Derived()"<<std::endl;if(NULL != m_pInt){delete m_pInt;m_pInt = NULL;}}private:int *m_pInt;};int main(){Base *pBase = new Derived();pBase->start();delete pBase;pBase = NULL;return 0;}

执行结果

对不起，使用基类指向派生类，释放类对象时，没有执行到Derived类的析构函数，使得Derived类申请有堆内存或者申请有资源的情况，会造成内存泄漏或资源泄漏。

解决方法：基类的析构函数定义为虚析构函数，这样的使用基类指向派生类，删除基类指针时，能执行到Derived类的析构函数。

#include <iostream>class Base{public:virtual int start(){std::cout<<"Base::start"<<std::endl;}virtual ~Base(){std::cout<<"Base::~Base() "<<std::endl;}};class Derived : public Base{public:    virtualint start(){m_pInt = new int [10];std::cout<<"Derived::start()"<<std::endl;}virtual ~Derived(){std::cout<<"Derived::~Derived()"<<std::endl;if(NULL != m_pInt){delete m_pInt;m_pInt = NULL;}}private:int *m_pInt;};int main(){Base *pBase = new Derived();pBase->start();delete pBase;pBase = NULL;return 0;}

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