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标题:operator 重载找不到重载函数
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已结贴  问题点数:20 回复次数:5 
operator 重载找不到重载函数
程序代码:
/====sales.h
#ifndef SALES_H
#define SALES_H
#include <iostream>

class Sales
{
    friend std::istream& operator >>(std::istream&,Sales&);
    friend std::ostream& operator <<(std::ostream&,Sales&);
    friend bool operator< (const Sales&, const Sales&);
    friend bool operator== (const Sales&, const Sales&);
public:
    Sales& operator+=(const Sales&);
    Sales(const std::string &book): ISBN(book) { }
    Sales(std::istream &is) { is >> *this; }
    Sales()=default;
    double Avg_price()const{if(Number)return Price/Number;else return 0;}
    std::string isbn() const { return ISBN; }
private:
    std::string ISBN;
    int Number=0;
    double Price=0.0;
};
inline bool compareIsbn (const Sales& a,const Sales& b){
    return a.isbn() == b.isbn();
}

inline bool operator< (const Sales& a, const Sales& b){
    return (a.Price < b.Price);
}

inline bool operator == (const Sales& a, const Sales& b){//这里是我写的operator函数,基本上是照抄C++ Primer 第五版给出的代码
    return compareIsbn(a,b);
}
inline bool operator != (const Sales& a, const Sales& b){
    return !(a==b);
}
#endif // SALES_H

程序代码:
//-------main.cpp
#include <iostream>
//using namespace std;
#include"sales.h"

int main(int argc, char *argv[])
{
    Sales *Head=new Sales[20];
    int n=0;
    while(std::cin >> Head[n++]){
        //    std::cout <<"{"<< *Head<<"} \n";
    }
    for(int i=0;i<n;i++){
        for(int j=i+1;j<n;j++){
            while(Head[i]==Head[j]){  //程序崩溃的时候运行到这里,说是找不到能用的operator==函数
                Head[i]+=Head[j];
                Head[j]=Head[--n];}
        }
    }

    return 0;
}

程序代码:
//------sales.cpp   不过貌似和我所遇到的问题没关系,可以不看
#include <iostream>
#include "sales.h"

Sales& Sales::operator +=(const Sales& s){
    Number+=s.Number;
    Price+=s.Price;
    return *this;
}
Sales operator +(const Sales&a,const Sales& b){
    Sales temp(a);
    temp+=b;
    return temp;
}


std::istream& operator >>(std::istream&in,Sales&s){
    double price;
    in>>s.ISBN>>s.Number>>price;
    if(in)s.Price+=price*s.Number;
    else s=Sales();//reset object to default state
    return in;
}

std::ostream& operator <<(std::ostream&out,Sales&s){
    out<<s.ISBN<<" "<<s.Number<<" "<<s.Price
      <<" "<<s.Avg_price();
         return out;
}

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我检查过几遍Sales operator==部分的代码,和我从官网下载下来的代码包的示例代码基本一致。(除了class的名字以及比较的条件)。
从程序报出的ERROR来看,他是没找到这个重载函数,然后我注意到这里程序要的是operator==(Sales const&,Sales const&)而我所定义的是operator==(const Sales&,const Sales&);是不是这个const放置前后不一致引起的?如果是,应该怎么修改?






2016-09-13 19:39
书生牛犊
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由于篇幅缘故,现将我所模仿的那个.h文件粘贴如下:
程序代码:
/*

 * This file contains code from "C++ Primer, Fifth Edition", by Stanley B.

 * Lippman, Josee Lajoie, and Barbara E. Moo, and is covered under the

 * copyright and warranty notices given in that book:

 *


 * "Copyright (c) 2013 by Objectwrite, Inc., Josee Lajoie, and Barbara E. Moo."

 *


 *


 * "The authors and publisher have taken care in the preparation of this book,

 * but make no expressed or implied warranty of any kind and assume no

 * responsibility for errors or omissions. No liability is assumed for

 * incidental or consequential damages in connection with or arising out of the

 * use of the information or programs contained herein."

 *


 * Permission is granted for this code to be used for educational purposes in

 * association with the book, given proper citation if and when posted or

 * reproduced.Any commercial use of this code requires the explicit written

 * permission of the publisher, Addison-Wesley Professional, a division of

 * Pearson Education, Inc. Send your request for permission, stating clearly

 * what code you would like to use, and in what specific way, to the following

 * address:


 *


 *     Pearson Education, Inc.

 *     Rights and Permissions Department

 *     One Lake Street

 *     Upper Saddle River, NJ  07458

 *     Fax: (201) 236-3290
*/


/* This file defines the Sales_item class used in chapter 1.

 * The code used in this file will be explained in

 * Chapter 7 (Classes) and Chapter 14 (Overloaded Operators)

 * Readers shouldn't try to understand the code in this file

 * until they have read those chapters.
*/

#ifndef SALESITEM_H
// we're here only if SALESITEM_H has not yet been defined

#define SALESITEM_H

// Definition of Sales_item class and related functions goes here
#include <iostream>
#include <string>

class Sales_item {
// these declarations are explained section 7.2.1, p. 270

// and in chapter 14, pages 557, 558, 561
friend std::istream& operator>>(std::istream&, Sales_item&);
friend std::ostream& operator<<(std::ostream&, const Sales_item&);
friend bool operator<(const Sales_item&, const Sales_item&);
friend bool operator==(const Sales_item&, const Sales_item&);
public:
    // constructors are explained in section 7.1.4, pages 262 - 265
    // default constructor needed to initialize members of built-in type
    Sales_item() = default;
    Sales_item(const std::string &book): bookNo(book) { }
    Sales_item(std::istream &is) { is >> *this; }
public:
    // operations on Sales_item objects
    // member binary operator: left-hand operand bound to implicit this pointer
    Sales_item& operator+=(const Sales_item&);
   

    // operations on Sales_item objects
    std::string isbn() const { return bookNo; }
    double avg_price() const;
// private members as before
private:
    std::string bookNo;      // implicitly initialized to the empty string
    unsigned units_sold = 0; // explicitly initialized
    double revenue = 0.0;
};

// used in chapter 10
inline bool compareIsbn(const Sales_item &lhs, const Sales_item &rhs)

{ return lhs.isbn() == rhs.isbn(); }

// nonmember binary operator: must declare a parameter for each operand
Sales_item operator+(const Sales_item&, const Sales_item&);

inline bool operator==(const Sales_item &lhs, const Sales_item &rhs)
{
    // must be made a friend of Sales_item
    return lhs.units_sold == rhs.units_sold &&
           lhs.revenue == rhs.revenue &&
           lhs.isbn() == rhs.isbn();
}

inline bool operator!=(const Sales_item &lhs, const Sales_item &rhs)
{
    return !(lhs == rhs); // != defined in terms of operator==
}

// assumes that both objects refer to the same ISBN
Sales_item& Sales_item::operator+=(const Sales_item& rhs)

{
    units_sold += rhs.units_sold;

    revenue += rhs.revenue;

    return *this;
}

// assumes that both objects refer to the same ISBN
Sales_item operator+(const Sales_item& lhs, const Sales_item& rhs)

{
    Sales_item ret(lhs);  // copy (|lhs|) into a local object that we'll return
    ret += rhs;           // add in the contents of (|rhs|)

    return ret;           // return (|ret|) by value
}

std::istream& operator>>(std::istream& in, Sales_item& s)
{
    double price;
    in >> s.bookNo >> s.units_sold >> price;
    // check that the inputs succeeded
    if (in)
        s.revenue = s.units_sold * price;
    else

        s = Sales_item();  // input failed: reset object to default state
    return in;
}

std::ostream& operator<<(std::ostream& out, const Sales_item& s)
{
    out << s.isbn() << " " << s.units_sold << " "
        << s.revenue << " " << s.avg_price();
    return out;
}

double Sales_item::avg_price() const
{
    if (units_sold)

        return revenue/units_sold;

    else

        return 0;
}
#endif





φ(゜▽゜*)♪
2016-09-13 19:41
yangfrancis
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inline bool operator == (const Sales& a, const Sales& b){
    return compareIsbn(a,b);
}
把它改成return a.isbn()==b.isbn();看能否通过
2016-09-13 21:57
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回复 3楼 yangfrancis
我把它改成了return true; 还是不行。。。
是不是我哪里定义错了?

φ(゜▽゜*)♪
2016-09-13 22:20
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我把关键字inline删掉,然后就行了。。。。问题已经解决,但是不太理解为什么。难道是C17和C11的语言标准不一样?(那本书用的是C11标准,我用的QT刚下载的最新的GUN)

φ(゜▽゜*)♪
2016-09-13 22:49
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嘿嘿,今天在用这段代码的时候这个函数又出现了“重复定义”的问题,然后我就加上了inline的关键字,然后就又没错了。
这两天我用的都是QT环境。编译器也没再换了(最新的了应该是)。
上次有inline说是找不到我写的重载函数,去掉inline就行了。
今天没inline说重复定义了这个函数,我加上inline也又行了。什么鬼,闹哪样?
今天测试的代码“main.cpp”修改如下,其他两个没动
程序代码:
#include <iostream>
//using namespace std;
#include"sales.h"

int main(int argc, char *argv[])
{
    Sales Total;
    if(std::cin>>Total){
        Sales temp;
        while(std::cin>>temp){
            if(temp==Total){
                Total+=temp;
            }else{
                std::cout<<Total;
                Total=temp;
            }
        }
        std::cout<<Total;
    }else std::cout<<"No data!";

    return 0;
}

顺便问一下,我在std::cout<<Total<<std::endl;的时候出现了未定义的现象,去掉std::endl就可以了。请问是不是也要std::endl重载啊?


φ(゜▽゜*)♪
2016-09-15 13:32
快速回复:operator 重载找不到重载函数
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