虚析构

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//********************************************************//
//------------------什么时候使用虚析构--------------------//
//有两种情况下需使用虚析构函数:(注:构造与析构都不能被继承)
// 1、当用基类指针pBase去new一个派生类对象，delete pBase时
// 2、当类中有一个虚成员函数时，而用基类去调用派生类成员时
//*******************************************************//

实例一

#include <iostream>
using namespace std;

class CBase
{
public:
    CBase()
    {
        cout<<"CBase:CBase()"<<endl;
    }

    ~CBase()
    {
        cout<<"CBase:~CBase()"<<endl;
    }

    void Dosomethings()
    {
        cout<<"CBase::Dosomethings()"<<endl;
    }
};

class CDerived : public CBase 
{
public:
    CDerived()
    {
        cout<<"CDerived:CDerived()"<<endl;
    }
    
    ~CDerived()
    {
        cout<<"CDerived:~CDerived()"<<endl;
    }

    void Dosomethings()
    {
        cout<<"CDerived::Dosomethings()"<<endl;
    }
};


int main(int argc, char* argv[])
{
    CBase *pBase = new CDerived;

    pBase->Dosomethings();
    
    delete pBase;

    return 0;
}

 运行行结果：

CBase::CBase()

CDerived::CDerived()

CBase::Dosomethings()

CBase::~CBase()

当用基类指针pBase new 派生类对象内存，再用delete pBase时，造成只释放了派生类对象中有关基类的那部分，而造成内存泄露。若用虚析构，见实例二

实例二

 

#include <iostream>
using namespace std;

class CBase
{
public:
    CBase()
    {
        cout<<"CBase:CBase()"<<endl;
    }

    virtual ~CBase()
    {
        cout<<"CBase:~CBase()"<<endl;
    }

    void Dosomethings()
    {
        cout<<"CBase::Dosomethings()"<<endl;
    }
};

class CDerived : public CBase 
{
public:
    CDerived()
    {
        cout<<"CDerived:CDerived()"<<endl;
    }
    
    virtual~CDerived()
    {
        cout<<"CDerived:~CDerived()"<<endl;
    }

    void Dosomethings()
    {
        cout<<"CDerived::Dosomethings()"<<endl;
    }
};


int main(int argc, char* argv[])
{
    CBase *pBase = new CDerived;

    pBase->Dosomethings();
    
    delete pBase;

    return 0;
}

 

运行结果：

CBase::CBase()

CDerived::CDerived()

CBase::Dosomethings()

CDerived::~CDerived()

CBase::~CBase()

这样，当delete pBase 时，就会释放全部派生类内存。还有什么时候用虚析构呢？见实例三

实例三

 

#include <iostream>
using namespace std;

class CBase
{
public:
    CBase()
    {
        cout<<"CBase:CBase()"<<endl;
    }

    virtual ~CBase()
    {
        cout<<"CBase:~CBase()"<<endl;
    }

    virtual void Dosomethings()
    {
        cout<<"CBase::Dosomethings()"<<endl;
    }
};

class CDerived : public CBase 
{
public:
    CDerived()
    {
        cout<<"CDerived:CDerived()"<<endl;
    }
    
    virtual~CDerived()
    {
        cout<<"CDerived:~CDerived()"<<endl;
    }

    void Dosomethings()
    {
        cout<<"CDerived::Dosomethings()"<<endl;
    }
};


int main(int argc, char* argv[])
{
    CBase *pBase = new CDerived;

    pBase->Dosomethings();
    
    delete pBase;

    return 0;
}

 

运行结果如实例三

 

 

 

 

 

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