C ++运算符重载与继承 [英] C++ operator overloading with inheritance

问题描述

假设我有一个类 Vehicle ，另一个叫 Car ，扩展 类。我想为两个类实现 ++ 运算符。

Let's say I have a class called Vehicle and another called Car that extends Vehicle class. I want to implement ++ operators for both classes.

#include <cstdio>
#include <cmath>
#include <cstring>
#include <ctime>
#include <iostream>
#include <algorithm>
#include <set>
#include <map>
#include <vector>
#include <sstream>
#include <typeinfo>

#define debug(args...) // Just strip off all debug tokens
using namespace std;
// CUT begin
#define debug(args...) {dbg,args;cout<<endl;}
struct debugger{template<typename T> debugger& operator ,(const T& v){cout<<v<<" ";return *this;}}dbg;
template <typename T1,typename T2> inline ostream& operator<<(ostream& os,const pair<T1,T2>& p){return os<<"("<<p.first<<", "<<p.second<<")";}
template<typename T>inline ostream&operator<<(ostream& os,const vector<T>& v){string delim="[";for(unsigned int i=0;i < v.size();i++){os<<delim<<v[i];delim=", ";}return os<<"]";}
template<typename T>inline ostream&operator<<(ostream& os,const set<T>& v){string delim="[";for (typename set<T>::const_iterator ii=v.begin();ii!=v.end();++ii){os<<delim<<*ii;delim=", ";}return os<<"]";}
template<typename T1,typename T2>inline ostream&operator<<(ostream& os,const map<T1,T2>& v){string delim="[";for (typename map<T1,T2>::const_iterator ii=v.begin();ii!=v.end();++ii){os<<delim<<*ii;delim=", ";}return os<<"]";}
// CUT end


class Vehicle
{
public:
    int n;
    Vehicle(int n):n(n){cout<<"Ctor Vehicle "<<n<<endl;}
    Vehicle(Vehicle& v):n(v.n){cout<<"Copy Ctor Vehicle "<<n<<endl;}
    virtual ~Vehicle(){cout<<"Dtor Vehicle "<<n<<endl;}
    virtual ostream& dump(ostream& os){return os<<"Vehicle("<<n<<")";}
    string to_str(){stringstream s; dump(s); return s.str();}
    virtual Vehicle& operator++(){n++;return *this;}
    virtual Vehicle operator++(int x){Vehicle v(*this); operator++(); return v;}
};

class Car: public Vehicle
{
public:
    Car(int n): Vehicle(n){cout<<"Ctor Car "<<n<<endl;}
    virtual ~Car(){cout<<"Dtor Car "<<n<<endl;}
    virtual ostream& dump(ostream& os){return os<<"Car("<<n<<")";}
    virtual Car operator++(int x){Car v(*this); operator++(); return v;}
    /* data */
};
ostream& operator<<(ostream& os,  Vehicle& v)
{
    return v.dump(os);
}

int main(int argc, char const *argv[])
{
    Vehicle * v = new Car(10);
    // cout<<c++<<endl;
    // cout<<c<<endl;
    return 0;
}

使用gcc时出现以下错误：

I get the following error with gcc:

C:\Users\Rajat\Documents\GitHub\interview-preparation\cpp_test.cpp:16:0: warning: "debug" redefined [enabled by default]
C:\Users\Rajat\Documents\GitHub\interview-preparation\cpp_test.cpp:13:0: note: this is the location of the previous definition
C:\Users\Rajat\Documents\GitHub\interview-preparation\cpp_test.cpp:44:14: error: invalid covariant return type for 'virtual Car Car::operator++(int)'
C:\Users\Rajat\Documents\GitHub\interview-preparation\cpp_test.cpp:35:18: error:   overriding 'virtual Vehicle Vehicle::operator++(int)'
C:\Users\Rajat\Documents\GitHub\interview-preparation\cpp_test.cpp: In member function 'virtual Car Car::operator++(int)':
C:\Users\Rajat\Documents\GitHub\interview-preparation\cpp_test.cpp:44:57: error: no matching function for call to 'Car::operator++()'
C:\Users\Rajat\Documents\GitHub\interview-preparation\cpp_test.cpp:44:57: note: candidate is:
C:\Users\Rajat\Documents\GitHub\interview-preparation\cpp_test.cpp:44:14: note: virtual Car Car::operator++(int)
C:\Users\Rajat\Documents\GitHub\interview-preparation\cpp_test.cpp:44:14: note:   candidate expects 1 argument, 0 provided

$ c> ++ 运算符 Car 和 ？

How do I get ++ operators for both Car and Vehicle with minimum number of virtual overrides?

推荐答案

更改

virtual Car operator++(int x){Car v(*this); operator++(); return v;}

至

virtual Vehicle operator++(int x){Car v(*this); Vehicle::operator++(); return v;}

1. 重写operator ++时，不应更改返回类型


2. 明确提及要调用父类的运算符++ Vehicle :: operator ++（）

1. While overriding operator++, return type should not be changed.
2. Explicitly mention that you want to call parent class's operator++ Vehicle::operator++()

更改后，您的程序将生成此输出

With that change, your program produces this output

Ctor Vehicle 10
Ctor Car 10

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