一、概述
二、测试代码
三、输出
四、总结
一、概述c++的virtual提供了运行时的多态，可以用基类的指针调用子类对象的函数，通过override可以强制要求基类有对应的虚函数。
二、测试代码#pragma once
#include <stdio.h>
class Base
{
public:
void A_1()
{
printf("Base::A_1\n");
};
virtual void A_2()
{
printf("Base::A_2\n");
}
virtual void A_3()
{
printf("Base::A_3\n");
}
virtual void A_4()
{
printf("Base::A_4\n");
}
void A_5()
{
printf("Base::A_5\n");
}
};
class Drived : public Base
{
public:
void A_1() //覆盖了基类的函数，用基类指针调用时调用到的时基类的A_1，用子类指针调用时调用到的时子类的A_1
{
printf("Drived::A_1\n");
};
virtual void A_2() //用基类或子类指针都调用到的是子类的A_2,之类的virtual说明的是是子类的A_2还可以被virtual
{
printf("Drived::A_2\n");
}
void A_3() //用基类或子类指针都调用到的是子类的A_2
{
printf("Drived::A_3\n");
}
virtual void A_4() override //子类加上override，如果基类没有对应virtual函数就会编译错误。避免拼错和记错没有重写基类函数
{
printf("Drived::A_4\n");
}
/*
void A_5() override //编译错误 'Drived::A_5': method with override specifier 'override' did not override any base class methods
{
printf("Drived::A_5\n");
}
*/
};
class Drived2 : public Drived
{
public:
void A_2() override
{
printf("Drived2::A_2\n");
}
void A_3() override//用基类或子类指针都调用到的是子类的A_2
{
printf("Drived2::A_3\n");
}
};
class VirtualTest
{
public:
void DoTest()
{
Drived *drived = new Drived();
Base *base = drived;
base->A_1();
drived->A_1();
printf("\n");
base->A_2();
drived->A_2();
printf("\n");
base->A_3();
drived->A_3();
printf("\n");
base->A_4();
drived->A_4();
printf("\n");
Drived2 *drived2 = new Drived2();
base = drived2;
drived = drived2;
base->A_2();
drived->A_2();
drived2->A_2();
printf("\n");
base->A_3();
drived->A_3();
drived2->A_3();
}
};
三、输出
四、总结Base::A_1
Drived::A_1Drived::A_2
Drived::A_2Drived::A_3
Drived::A_3Drived::A_4
Drived::A_4Drived2::A_2
Drived2::A_2
Drived2::A_2Drived2::A_3
Drived2::A_3
Drived2::A_3
1、基类函数没加virtual，子类有相同函数，实现的是覆盖。用基类指针调用时，调用到的是基类的函数；用子类指针调用时，调用到的是子类的函数。
2、基类函数加了virtual时，实现的时重写。用基类指针或子类指针调用时，调用到的都是子类的函数。
3、函数加上override，强制要求基本相同函数需要是虚函数，否则会编译报错。
4、子类的virtual可加可不加，建议加override不加virtual。
以上为个人经验，希望能给大家一个参考，也希望大家多多支持软件开发网。