C++ 入门 : Exercises involving Sales_item. h

Question

这是 C++ Primer 4th Edition 的问题。我正在使用这个版本，因为它是我唯一可以访问的版本。

Question:

The Web site (http://www.awprofessional.com/cpp_primer) contains a copy of Sales_item.h in the Chapter 1 code directory. Copy that file to your working directory. Write a program that loops through a set of book sales transactions, reading each transaction and writing that transaction to the standard output.

它提供的链接不起作用，所以我从另一个网站下载了 Sales_item.h。

我把头文件的内容贴在了最下面

Proposed Solution

#include <iostream>
#include "Sales_item.h"
using namespace std;

int main()
{
   Sales_item item1;
   cout<<"Enter sales item one"<<endl;
   cin>>item1;
   cout<<"Item one is " <<item1;
   return 0;


}

好吧，我可能不明白这个模棱两可的问题，但这不是这里的问题。当我用命令编译文件时:

g++ salesitem1.cpp -o salesitem1

我收到这个错误

In file included from salesitem1.cpp:2:0:
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/../../../../include/Sales_item.h:70:27: er
ror: ISO C++ forbids initialization of member 'units_sold' [-fpermissive]
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/../../../../include/Sales_item.h:70:27: er
ror: making 'units_sold' static [-fpermissive]
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/../../../../include/Sales_item.h:70:27: er
ror: ISO C++ forbids in-class initialization of non-const static member 'units_s
old'
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/../../../../include/Sales_item.h:71:22: er
ror: ISO C++ forbids initialization of member 'revenue' [-fpermissive]
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/../../../../include/Sales_item.h:71:22: er
ror: making 'revenue' static [-fpermissive]
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/../../../../include/Sales_item.h:71:22: er
ror: ISO C++ forbids in-class initialization of non-const static member 'revenue
'

所以我的问题是:为什么会这样？这本书有什么问题吗？如果是，我该如何继续练习？另外，我尝试编译书中的示例并收到类似的错误消息。

感谢您耐心看完这个问题。任何好的答案将不胜感激。

Sales_item.h源码

/*
 * 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

Answer 1

我很确定您不小心得到了 C++ Primer 5 的源代码，它使用 C++11，其中的代码是合法的。查找您正在使用的版本的源代码。我相信this link应该可以。