C++入門：涉及Sales_item.h的練習

Question

這是C++ Primer第4版的一個問題。我正在使用這個版本，因爲它是我唯一可以訪問的版本。

問：

的網站（http://www.awprofessional.com/cpp_primer）包含在第1章代碼目錄Sales_item.h的副本。將該文件複製到您的工作目錄。編寫一個循環遍歷一系列圖書銷售交易的程序，讀取每筆交易並將該交易寫入標準輸出。

它提供的鏈接不起作用，所以我從另一個網站下載了Sales_item.h。

我粘貼了底部頭文件的內容。

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，我可能不明白的曖昧問題，但在這裏，是沒有問題的。當我編譯命令文件：

g++ salesitem1.cpp -o salesitem1 

我得到這個錯誤

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 
' 

所以我的問題是：爲什麼會發生這種情況？這本書有什麼問題嗎？如果是這樣，我該如何繼續這項練習？在旁邊的筆記我試圖編譯書中的例子，並得到類似的錯誤信息。

感謝您耐心閱讀此問題。任何好的答案將不勝感激。

Sales_item.h的源代碼

/* 
* 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

我敢肯定，你意外地得到了源代碼，C++入門5，它使用C++ 11，其中的代碼是合法的。找到您正在使用的版本的源代碼。我認爲this link應該工作。