学步园

C++中虚析构函数的作用,当用一个基类的指针删除一个派生类的对象时，派生类的析构函数会被调用，否则派生类对象的析构函数不会被调用。并不是要把所有类的析构函数都写成虚函数。因为当类里面有虚函数的时候，编译器会给类添加一个虚函数表，里面来存放虚函数指针，这样就会增加类的存储空间。所以，只有当一个类被用来作为基类的时候，才把析构函数写成虚函数。

代码：

#include <iostream>
using namespace std;

class ClxBase
{
        public:
                ClxBase()
                {
                        cout << "in ClxBase() " << endl;
                };
                virtual ~ClxBase()
                {
                        cout << "in  virtual ~ClxBase() "<< endl;
                };

                virtual void DoSomething() { cout << "Do something in class ClxBase!" << endl; };
};

class ClxDerived : public ClxBase
{
        public:
                ClxDerived()
                {
                        cout << "in ClxDerived() " << endl;
                };

                ~ClxDerived() { cout << "in ~ClxDerived()" << endl; };

                void DoSomething() { cout << "Do something in class ClxDerived!" << endl; };
};
int main()
{
        ClxBase *pTest = new ClxDerived;
        //pTest->DoSomething();
        delete pTest;
        cout << "========================" << endl ;
        ClxDerived test;
}

运行：huangxw3%./test
in ClxBase()
in ClxDerived()
in ~ClxDerived()
in  virtual ~ClxBase()
========================
in ClxBase()
in ClxDerived()
in ~ClxDerived()
in  virtual ~ClxBase()