C++中继承声明基类析构函数为虚函数，继承关系的内存分布

发布时间：2020-12-16 09:17:19 所属栏目：百科来源：网络整理

导读：? 1，基类析构函数不为虚函数 #include " pch.h " #include iostream class CBase{ public : CBase() { m_one = 0 ; printf( " this is CBase constructn " ); } ~ CBase() { printf( " this is ~CBase deconstructn " ); } void setNumOne( int n) { m_on

1，基类析构函数不为虚函数

#include "pch.h"
#include <iostream>

class CBase
{
public:
    CBase() {
        m_one = 0;
        printf("this is CBase constructn");
    }
    ~CBase() {
        printf("this is ~CBase deconstructn");
    }

    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 constructn");
    }
    ~CDrived() {
        printf("this is ~CDrived deconstructn");
    }

    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 construct
this is CDrived construct
this is ~CBase deconstruct
Hello 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 <iostream>

class CBase
{
public:
    CBase() {
        m_one = 0;
        printf("this is CBase constructn");
    }
    virtual ~CBase() {
        printf("this is ~CBase deconstructn");
    }

    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 constructn");
    }
    ~CDrived() {
        printf("this is ~CDrived deconstructn");
    }

    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 construct
this is CDrived construct
this is ~CDrived deconstruct
this is ~CBase deconstruct
Hello World!

2，

#include "pch.h"
#include <iostream>

class CBase
{
public:
    CBase() {
        m_one = 0;
        printf("this is CBase constructn");
    }
    virtual ~CBase() {
        printf("this is ~CBase deconstructn");
    }

    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 constructn");
    }
    ~CDrived() {
        printf("this is ~CDrived deconstructn");
    }

    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) = %dn",sizeof(CDrived)); // 12
    delete p;
    std::cout << "Hello World!n"; 
}

（编辑：李大同）

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C++中继承声明基类析构函数为虚函数，继承关系的内存分布