我如何在不使用virtual关键字的情况下覆盖此C ++继承的成员函数? [英] How am i overriding this C++ inherited member function without the virtual keyword being used?

问题描述

我有一个小程序来演示简单的继承.我正在定义一个源自哺乳动物的Dog类.这两个类共享一个称为ToString()的简单成员函数.当我不使用virtual关键字时，Dog如何覆盖Mammal类中的实现? (我什至需要使用virtual关键字来覆盖成员函数吗?)

I have a small program to demonstrate simple inheritance. I am defining a Dog class which is derived from Mammal. Both classes share a simple member function called ToString(). How is Dog overriding the implementation in the Mammal class, when i'm not using the virtual keyword? (Do i even need to use the virtual keyword to override member functions?)

mammal.h

#ifndef MAMMAL_H_INCLUDED
#define MAMMAL_H_INCLUDED

#include <string>

class Mammal
{
    public:
        std::string ToString();
};

#endif // MAMMAL_H_INCLUDED

mammal.cpp

mammal.cpp

#include <string>
#include "mammal.h"

std::string Mammal::ToString()
{
    return "I am a Mammal!";
}

dog.h

#ifndef DOG_H_INCLUDED
#define DOG_H_INCLUDED

#include <string>
#include "mammal.h"

class Dog : public Mammal
{
    public:
        std::string ToString();
};

#endif // DOG_H_INCLUDED

dog.cpp

#include <string>
#include "dog.h"

std::string Dog::ToString()
{
    return "I am a Dog!";
}

main.cpp

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

using namespace std;

int main()
{
    Dog d;
    std::cout << d.ToString() << std::endl;
    return 0;
}

输出

I am a Dog!

我正在Windows上通过Code :: Blocks使用MingW.

I'm using MingW on Windows via Code::Blocks.

推荐答案

它不是覆盖基类中的ToString方法，因为基类方法不是virtual.只是用具有相同签名的函数来隐藏该函数.

It's not overriding the ToString method in the base class as the base class method is not virtual. It is simply hiding that function with a function with an identical signature.

在Dog对象上调用ToString()时，将调用Dog::ToString方法.为什么还要调用任何其他ToString()方法? Dog::声明是找到的第一个? virtual仅在通过指针或对基类对象的引用进行调用时才会发生(并且仅在需要时)分派.

When you call ToString() on a Dog object the Dog::ToString method is called. Why would it call any other ToString() method; the Dog:: declaration is the first one found? virtual dispatch would only happen (and only be needed) when being called through a pointer or reference to a base class object.

如果需要在Dog对象上调用基类方法，则必须明确地限定它.

If you needed to call the base class method on a Dog object you would have to qualify it explicitly.

d.Mammal::ToString()

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