Question

C++，继承类中析构函数问题

#include <iostream>
using namespace std;
class CBase {
public:
CBase(int i){ m_data = i;cout << "Constructor of CBase. m_data=" << m_data <<endl; }
~CBase(){ cout << "Destructor of CBase. m_data=" << m_data <<endl; }
protected:
int m_data;
};
class CDerived: public CBase
{
public:
CDerived(const char *s): CBase(strlen(s)){ m_data = new char[strlen(s) + 1];
strcpy(m_data, s);cout << "Constructor of CDerived. m_data = " << m_data << endl; }
~CDerived(){ delete m_data;cout << "Destructor of CDerived. m_data = " << m_data <<endl;}
private:
char *m_data;
};
int main()
{
CBase *p ;
p = new CDerived ("abcd");
delete p;
return 0;
}
此过程中为什么不执行子类的析构函数呢？

Answer 1

因为基类的析构函数不是虚析构函数，所以是根据指针的类型调用析构函数，而不是根据指针指向对象的类型调用析构函数。

虚函数是在基类中被声明为 virtual，并在派生类中重新定义的成员函数，可实现成员函数的动态重载。

当一个类作为基类时，它的析构函数应该为虚析构函数。

Answer 2

解析函数要 virtual

#include <iostream>
using namespace std;
class CBase {
public:
CBase(int i){ m_data = i;cout << "Constructor of CBase. m_data=" << m_data <<endl; }
virtual ~CBase(){ cout << "Destructor of CBase. m_data=" << m_data <<endl; }
^^^^^^^^注意
protected:
int m_data;
};
class CDerived: public CBase
{
public:
CDerived(const char *s): CBase(strlen(s)){ m_data = new char[strlen(s) + 1];
strcpy(m_data, s);cout << "Constructor of CDerived. m_data = " << m_data << endl; }
virtual ~CDerived(){ delete m_data;cout << "Destructor of CDerived. m_data = " << m_data <<endl;}
^^^^^^^^注意
private:
char *m_data;
};
int main()
{
CBase *p ;
p = new CDerived ("abcd");
delete p;
return 0;
}