析构函数为虚函数

编码实现C++类的时候，一般都会把析构函数定义为虚函数，不管这个类是基类还是继承类。

先代码实验

1.析构函数为非虚构

#include <iostream>using namespace std;class CBase{public:    CBase(){}    ~CBase(){cout << "base destructor" << endl;}};class CDerived : public CBase{public:    CDerived(){}    ~CDerived(){cout << "derived destructor" << endl;}};int main(){    CDerived* cd = new CDerived();    delete cd;    cout << "-----------------" << endl;    CBase* cb = new CBase();    delete cb;    cout << "-----------------" << endl;    CBase* p = new CDerived();    delete p;<pre name="code" class="html">    return 0;}

运行结果：

derived destructorbase destructor-----------------base destructor-----------------base destructor

可以发现，使用多态的时候，出问题了。

2.析构函数为虚函数

#include <iostream>using namespace std;class CBase{public:    CBase(){}    virtual ~CBase(){cout << "base destructor" << endl;}};class CDerived : public CBase{public:    CDerived(){}    ~CDerived(){cout << "derived destructor" << endl;}};int main(){    CDerived* cd = new CDerived();    delete cd;    cout << "-----------------" << endl;    CBase* cb = new CBase();    delete cb;    cout << "-----------------" << endl;    CBase* p = new CDerived();    delete p;<pre name="code" class="html">    return 0;}

和上一段代码比较，这段代码只把CBase类的析构函数定义为虚函数了。运行结果为：

derived destructorbase destructor-----------------base destructor-----------------derived destructorbase destructor

这就正常了。

3.原因

对于

CDerived* cd = new CDerived();delete cd;

指针cd指向CDerived对象，调用CDerived类的析构函数，因为析构了继承类，所以，之后会析构基类

对于

CBase* cb = new CBase();delete cb;

指针cb指向CBase类的对象，调用CBase类的析构函数。

对于

CBase* p = new CDerived();delete p;

基类使用虚析构函数时，动态联编，指针指向的是CDerived类的对象，调用CDerived类的析构函数，因为析构了继承类，所以，之后会析构基类

基类没使用虚析构函数时，静态联编，指针指向CBase类的对象，调用CBase类的析构函数。就不会调用继承类的析构函数了。