友谊和运营商重载帮助

Question

我有以下课程

#ifndef Container_H
#define Container_H
#include <iostream>
using namespace std;

class Container{

    friend bool operator==(const Container &rhs,const Container &lhs);
 public:
   void display(ostream & out) const;

 private:
   int sizeC;                // size of Container
   int capacityC;            // capacity of dynamic array
   int * elements;            // pntr to dynamic array
  };
ostream & operator<< (ostream & out, const Container & aCont);
#endif

和这个源文件

#include "container.h"

/*----------------------------*********************************************
note: to test whether capacityC and sizeC are equal, must i add 1 to sizeC?
seeing as sizeC starts off with 0??
*/

Container::Container(int maxCapacity){
    capacityC = maxCapacity;
    elements = new int [capacityC];
    sizeC = 0;
}

Container::~Container(){
    delete [] elements;
}

Container::Container(const Container & origCont){
    //copy constructor?
    int i = 0;
    for (i = 0; i<capacityC; i++){ //capacity to be used here?
        (*this).elements[i] = origCont.elements[i];

    }
}

bool Container::empty() const{
    if (sizeC == 0){
        return true;
    }else{
        return false;
    }
}

void Container::insert(int item, int index){
    if ( sizeC == capacityC ){
        cout << "\n*** Next:  Bye!\n";
        return; // ? have return here?
    }
    if ( (index >= 0) && (index <= capacityC) ){
        elements[index] = item;
        sizeC++;
    }
    if ( (index < 0) && (index > capacityC) ){
        cout<<"*** Illegal location to insert--"<< index << ". Container unchanged. ***\n";
    }//error here not valid? according to original a3? have i implemented wrong?
}

void Container::erase(int index){
    if ( (index >= 0) && (index <= capacityC) ){ //correct here? legal location?
        int i = 0;
        while (i<capacityC){ //correct?
            elements[index] = elements[index+1]; //check if index increases here.
            i++;
        }
        sizeC=sizeC-1; //correct? updated sizeC?
    }else{
        cout<<"*** Illegal location to be removed--"<< index << ". Container unchanged. ***\n";
    }
}

int Container::size()const{
    return sizeC; //correct?
}

/*
bool Container::operator==(const Container &rhs,const Container &lhs){
    int equal = 0, i = 0;
    for (i = 0; i < capacityC ; i++){
        if ( rhs.elements[i] == lhs.elements[i] ){
            equal++;
        }
    }

    if (equal == sizeC){
        return true;
    }else{
        return false;
    }
}

ostream & operator<< (ostream & out, const Container & aCont){
    int i = 0;
    for (i = 0; i<sizeC; i++){
        out<< aCont.elements[i] << " " << endl;
    }
}


*/

我在头文件中没有其他功能(只是一个quikie).无论如何,"/**/"中的最后两个函数我无法工作,我在这里做错了什么？

第一个函数是查看两个数组是否彼此相等

Answer 1

当您将函数声明为friend类的内部时,该函数是非成员函数,就好像它是在封闭的命名空间中声明的一样.所以,在你的情况下,你的朋友声明operator==,

class Container
{
    friend bool operator==(const Container &rhs,const Container &lhs);
};

是一个非成员函数,就好像你已经在类之外声明它一样,如下所示:

class Container
{
};

bool operator==(const Container &rhs,const Container &lhs);

请注意,当您声明友元函数时,该函数也可以访问该类的私有成员,因此这不完全相同.

所以,你的定义operator==好像是一个成员函数是不正确的:

bool Container::operator==(const Container &rhs,const Container &lhs) { ... }

应该

bool operator==(const Container &rhs,const Container &lhs) { ... }

至于你的operator<<重载,它不是朋友Container,因此它无权访问私有elements成员Container.要么成为operator<<好友,要么为该类添加公共访问者,以便它可以通过它们访问私有成员.