1，基类析构函数不为虚函数

#include "pch.h"#include 
     
      class CBase{public:    CBase() {        m_one = 0;        printf("this is CBase construct\n");    }    ~CBase() {        printf("this is ~CBase deconstruct\n");    }    void setNumOne(int n)    {        m_one = n;    }    int getNumOne()    {        return m_one;    }private:    int m_one;};class CDrived:public CBase{public:    CDrived() {        m_two = 0;        printf("this is CDrived construct\n");    }    ~CDrived() {        printf("this is ~CDrived deconstruct\n");    }    void setNumTwo(int n)    {        m_two = n;    }    int getNumTwo()    {        return m_two;    }private:    int m_two;};int main(){    CBase *p = new CDrived;    delete p;    std::cout << "Hello World!\n"; }
     

输出：

this is CBase constructthis is CDrived constructthis is ~CBase deconstructHello World!

可以发现继承类析构函数没有调用，若继承类中有一些资源需要释放，则不能释放，故需要将基类析构函数声明为虚函数。

 

#include "pch.h"#include 
     
      class CBase{public:    CBase() {        m_one = 0;        printf("this is CBase construct\n");    }    virtual ~CBase() {        printf("this is ~CBase deconstruct\n");    }    void setNumOne(int n)    {        m_one = n;    }    int getNumOne()    {        return m_one;    }private:    int m_one;};class CDrived:public CBase{public:    CDrived() {        m_two = 0;        printf("this is CDrived construct\n");    }    ~CDrived() {        printf("this is ~CDrived deconstruct\n");    }    void setNumTwo(int n)    {        m_two = n;    }    int getNumTwo()    {        return m_two;    }private:    int m_two;};int main(){    CBase *p = new CDrived;    delete p;    std::cout << "Hello World!\n"; }
     

输出：

this is CBase constructthis is CDrived constructthis is ~CDrived deconstructthis is ~CBase deconstructHello World!

 

2，

#include "pch.h"#include 
     
      class CBase{public:    CBase() {        m_one = 0;        printf("this is CBase construct\n");    }    virtual ~CBase() {        printf("this is ~CBase deconstruct\n");    }    virtual void setNumOne(int n)    {        m_one = n;    }    virtual int getNumOne()    {        return m_one;    }private:    int m_one;};class CDrived:public CBase{public:    CDrived() {        m_two = 0;        printf("this is CDrived construct\n");    }    ~CDrived() {        printf("this is ~CDrived deconstruct\n");    }    void setNumTwo(int n)    {        m_two = n;    }    int getNumTwo()    {        return m_two;    }private:    int m_two;};int main(){    CDrived *p = new CDrived;    printf("sizeof(CDrived) = %d\n", sizeof(CDrived)); // 12    delete p;    std::cout << "Hello World!\n"; }
     

 

 

3，多继承

单继承只有一个虚表指针，而多继承往往有多个

#include "pch.h"#include 
     
      class CFather{public:    CFather() {        }    ~CFather() {    }    virtual void setTall(int tall)    {        m_tall = tall;    }private:    int m_tall;};class CMother{public:    CMother() {    }    ~CMother() {    }    virtual void setWeight(int weight)    {        m_weight = weight;    }private:    int m_weight;};class CSon:public CFather,public CMother{public:    CSon() {    }    ~CSon() {    }    virtual void setAge(int age) // 地址存放在第一个虚表指针后面    {        m_age = age;    }private:    int m_age;};int main(){    CSon cSon;    cSon.setAge(8);    printf("sizeof(CSon) = %d\n", sizeof(CSon)); // 20    std::cout << "Hello World!\n"; }