C++中vitual的用法总结

最新推荐文章于 2024-12-18 17:08:37 发布

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本文通过示例代码详细介绍了C++中虚函数的作用及其如何实现多态性，同时探讨了虚继承如何解决钻石问题并减少基类的重复实例化。

一、修饰成员函数

#include <iostream>
using namespace std;

class A
{
public:A(){}
public:
    virtual void func1(){ cout << "A vitual"; }
    virtual void func2()
    {
        func1();
    }
};

class B :public A
{
public:B(){}
public:
     void func1(){ cout << "B vitual"; }
     void func2(){
        func1();
    }
};

int main()
{
    A *a = new B();
    a->func2();
    while (1);
    return 0;
}

输出结果：
这里写图片描述

二、修饰类

#include <iostream>
using namespace std;

class A{
public:   
    A()
    { 
        cout << "A构造" << endl;
    }

    ~A()
    { 
        cout << "A析构" << endl; 
    }
};

class B : virtual public A
{
public:    
    B()
    { 
        cout << "B构造" << endl; 
    }
    ~B()
    { 
        cout << "B析构" << endl;
    }
};

class C : virtual public A
{
public:     
    C()
    { 
        cout << "C构造" << endl;
    }

    ~C()
    { 
        cout << "C析构" << endl;
    }
};

class D : public B, public C{
public:            
    D()
    { 
        cout << "D构造" << endl; 
    }

    ~D()
    { 
        cout << "D析构" << endl; 
    }
};

int main()
{
    D *d = new D();
    delete d;
    while (1);
    return 0;
}

执行结果:
这里写图片描述

类没有被vitual修饰时：

#include <iostream>
using namespace std;

class A{
public:   
    A()
    { 
        cout << "A构造" << endl;
    }

    ~A()
    { 
        cout << "A析构" << endl; 
    }
};

class B : public A
{
public:    
    B()
    { 
        cout << "B构造" << endl; 
    }
    ~B()
    { 
        cout << "B析构" << endl;
    }
};

class C :  public A
{
public:     
    C()
    { 
        cout << "C构造" << endl;
    }

    ~C()
    { 
        cout << "C析构" << endl;
    }
};

class D : public B, public C{
public:            
    D()
    { 
        cout << "D构造" << endl; 
    }

    ~D()
    { 
        cout << "D析构" << endl; 
    }
};

int main()
{
    D *d = new D();
    delete d;
    while (1);
    return 0;
}

执行结果：
这里写图片描述

三、vitual修饰析构函数

#include <iostream>
using namespace std;


class A{
public:
    A()
    {
        cout << "construct A" << endl;
    }
    virtual ~A()
    {
        cout << "destory A" << endl;
    }   
};

 class B : public A{
public:
    B()
    {          
        cout << "construct B" << endl;
    }

    virtual ~B()
    {              
        cout << "destory B" << endl;
    }   
};

int main()
{   
    A *a = new B();
    delete a;
    while (10);
    return 0;
}

执行结果：

这里写图片描述