Unix/C/C++进阶--通过基类释放子对象

Unix/C/C++进阶--通过基类释放子对象

• 1 概述
• 2 情况分类
• • 2.1 父类指针，父类对象
  • 2.2 子类指针，子类对象 【父类析构函数为虚函数】
  • 2.3 父类指针，子类对象
  • • 父类析构函数为虚函数，删除父指针
    • 父类析构函数为虚函数，父指针做子类型转换后再删除
    • 父类析构函数不实现，删除父指针
    • 父类析构函数不实现，父指针做子类型转换后再删除
• 3 结构体
• 4 详解
• 参考

1 概述

如下图，子类继承父类，delete就是依据指针指向的内存地址以及虚表指针。

2 情况分类

具体删除内存多少与指针类型和虚表指针相关。

2.1 父类指针，父类对象

正常释放自身。

#include 
#include 
using namespace std;

class Father
{
public:
    Father() { cout << "father" << endl; }
    // virtual ~Father() {}
    virtual ~Father() { cout << "~father" << endl; }
};


class Son: public Father
{
public:
    Son()  { cout << "son" << endl; }
    ~Son() {  cout << "~son" << endl; }
};

int main()
{
    Father father;
}

• 结果

father
~father

2.2 子类指针，子类对象 【父类析构函数为虚函数】

父类析构函数为虚函数，释放子类自身以及父类。

#include 
#include 
using namespace std;

class Father
{
public:
    Father() { cout << "father" << endl; }
    // virtual ~Father() {}
    virtual ~Father() { cout << "~father" << endl; }
};


class Son: public Father
{
public:
    Son()  { cout << "son" << endl; }
    ~Son() {  cout << "~son" << endl; }
};

int main()
{
    Son son;
}

• 结果

father
son
~son
~father

2.3 父类指针，子类对象 父类析构函数为虚函数，删除父指针

#include 
#include 
using namespace std;

class Father
{
public:
    Father() { cout << "father" << endl; }
    // virtual ~Father() {}
    virtual ~Father() { cout << "~father" << endl; }
};


class Son: public Father
{
public:
    Son()  { cout << "son" << endl; }
    ~Son() {  cout << "~son" << endl; }
};

int main()
{
    Father *father = new Son();
    delete father;
}

• 结果

father
son
~son
~father

父类析构函数为虚函数，父指针做子类型转换后再删除

#include 
#include 
using namespace std;

class Father
{
public:
    Father() { cout << "father" << endl; }
    // virtual ~Father() {}
    virtual ~Father() { cout << "~father" << endl; }
};


class Son: public Father
{
public:
    Son()  { cout << "son" << endl; }
    ~Son() {  cout << "~son" << endl; }
};

int main()
{
    Father *father = new Son();
    delete (Son *)father;
}

• 结果

father
son
~son
~father

父类析构函数不实现，删除父指针

#include 
#include 
using namespace std;

class Father
{
public:
    Father() { cout << "father" << endl; }
    // virtual ~Father() {}
    // virtual ~Father() { cout << "~father" << endl; }
};


class Son: public Father
{
public:
    Son()  { cout << "son" << endl; }
    ~Son() {  cout << "~son" << endl; }
};

int main()
{
    Father *father = new Son();
    delete father;
}

• 结果

father
son

父类析构函数不实现，父指针做子类型转换后再删除

#include 
#include 
using namespace std;

class Father
{
public:
    Father() { cout << "father" << endl; }
    // virtual ~Father() {}
    // virtual ~Father() { cout << "~father" << endl; }
};


class Son: public Father
{
public:
    Son()  { cout << "son" << endl; }
    ~Son() {  cout << "~son" << endl; }
};

int main()
{
    Father *father = new Son();
    delete (Son*)father;
}

• 结果

father
son
~son

3 结构体

C++类就是对结构体的拓展，所以结构体和类的使用一致。

#include 
#include 
using namespace std;

struct Father
{
public:
    Father() { cout << "father" << endl; }
    // virtual ~Father() {}
    virtual ~Father() { cout << "~father" << endl; }
};


struct Son: public Father
{
public:
    Son()  { cout << "son" << endl; }
    ~Son() {  cout << "~son" << endl; }
};

int main()
{
    Father *father = new Son();
    delete father;
}

• 结果

father
son
~son
~father

4 详解

2.7 多态与虚函数

参考

1、C++概述
2、C++多态的delete调用的是父类析构函数，那么子类对象的内存释放了吗？
3、delete基类指针释放子类对象
4、C++中虚函数和纯虚函数的区别