在基类中使用了 C++ 中的虚拟析构函数，因此派生类对象也可以被销毁。 虚拟析构函数是通过使用 ~ 波浪号运算符，然后在构造函数之前使用 virtual 关键字来声明的。

注意：构造函数不能是虚函数，但析构函数可以是虚函数。

不使用虚拟析构函数的示例

#include <iostream>  
using namespace std;  
class Base  
{  
    public:  
    Base()  
    {  
        cout<<"Base constructor is called"<<"\n";  
    }  
    ~Base()  
    {  
        cout<<"Base class object is destroyed"<<"\n";  
    }  
};  
class Derived:public Base  
{  
    public:  
    Derived()  
    {  
        cout<<"Derived class constructor is called"<<"\n";  
    }  
    ~Derived()  
    {  
        cout<<"Derived class object is destroyed"<<"\n";  
    }  
};  
int main()   
{  
  Base* b= new Derived;  
  delete b;  
  return 0;  

}

输出结果：

Base constructor is called
Derived class constructor is called
Base class object is destroyed

在上面的例子中，delete b 只会调用基类析构函数，因为派生类析构函数保持未销毁。 这会导致内存泄漏。

带有虚拟析构函数的示例：

#include <iostream>  
using namespace std;  
class Base  
{  
    public:  
    Base()  
    {  
        cout<<"Base constructor is called"<<"\n";  
    }  
    virtual ~Base()  
    {  
        cout<<"Base class object is destroyed"<<"\n";  
    }  
};  
class Derived:public Base  
{  
    public:  
    Derived()  
    {  
        cout<<"Derived class constructor is called"<<"\n";  
    }  
    ~Derived()  
    {  
        cout<<"Derived class object is destroyed"<<"\n";  
    }  
};  
int main()   
{  
  Base* b= new Derived;  
  delete b;  
  return 0;  

}

运行结果：

Base constructor is called
Derived class constructor is called
Derived class object is destroyed
Base class object is destroyed

当我们使用虚析构函数时，那么先调用派生类析构函数，再调用基类析构函数。