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最新推荐文章于 2021-12-26 00:19:54 发布

原创最新推荐文章于 2021-12-26 00:19:54 发布 · 323 阅读

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本文介绍了一个使用C++实现的销售数据类(Sales_data)的设计与实现细节，包括构造函数、成员函数及友元函数等。展示了如何通过不同构造函数初始化对象，以及如何进行数据读取、打印和合并操作。

7.41

#include <string>
#include <iostream>

class Sales_data {
    friend std::istream &read(std::istream &is, Sales_data &item);
    friend std::ostream &print(std::ostream &os, const Sales_data &item);
    friend Sales_data add(const Sales_data &lhs, const Sales_data &rhs);

public:
    Sales_data(const std::string &s, unsigned n, double p) :bookNo(s), units_sold(n), revenue(n*p)
    {
        std::cout << "Sales_data(const std::string&, unsigned, double)" << std::endl;
    }

    Sales_data() : Sales_data("", 0, 0.0)
    {
        std::cout << "Sales_data()" << std::endl;
    }

    Sales_data(const std::string &s) : Sales_data(s, 0, 0.0)
    {
        std::cout << "Sales_data(const std::string&)" << std::endl;
    }

    Sales_data(std::istream &is);

    std::string isbn() const { return bookNo; }
    Sales_data& combine(const Sales_data&);

private:
    inline double avg_price() const;

private:
    std::string bookNo;
    unsigned units_sold = 0;
    double revenue = 0.0;
};

inline
double Sales_data::avg_price() const
{
    return units_sold ? revenue / units_sold : 0;
}

// declarations for nonmember parts of the Sales_data interface.
std::istream &read(std::istream &is, Sales_data &item);
std::ostream &print(std::ostream &os, const Sales_data &item);
Sales_data add(const Sales_data &lhs, const Sales_data &rhs);

Sales_data::Sales_data(std::istream &is) : Sales_data()
{
    std::cout << "Sales_data(istream &is)" << std::endl;
    read(is, *this);
}

// member functions.
Sales_data& Sales_data::combine(const Sales_data& rhs)
{
    units_sold += rhs.units_sold;
    revenue += rhs.revenue;
    return *this;
}

// friend functions
std::istream &read(std::istream &is, Sales_data &item)
{
    double price = 0;
    is >> item.bookNo >> item.units_sold >> price;
    item.revenue = price * item.units_sold;
    return is;
}

std::ostream &print(std::ostream &os, const Sales_data &item)
{
    os << item.isbn() << " " << item.units_sold << " " << item.revenue;
    return os;
}

Sales_data add(const Sales_data &lhs, const Sales_data &rhs)
{
    Sales_data sum = lhs;
    sum.combine(rhs);
    return sum;
}
using std::cout; using std::endl;

int main()
{
    cout << "1. default way: " << endl;
    cout << "----------------" << endl;
    Sales_data s1;

    cout << "\n2. use std::string as parameter: " << endl;
    cout << "----------------" << endl;
    Sales_data s2("CPP-Primer-5th");

    cout << "\n3. complete parameters: " << endl;
    cout << "----------------" << endl;
    Sales_data s3("CPP-Primer-5th", 3, 25.8);

    cout << "\n4. use istream as parameter: " << endl;
    cout << "----------------" << endl;
    Sales_data s4(std::cin);

    return 0;
}

7.42

#include <iostream>
#include <string>

class Book 
{
public:
    Book(unsigned isbn, std::string const& name, std::string const& author, std::string const& pubdate)
        :isbn(isbn), name(name), author(author), pubdate(pubdate)
    { }

 Book(std::istream &in) 
    { 
        in >> isbn >> name >> author >> pubdate;
    }

private:
    unsigned isbn;
    std::string name;
    std::string author;
    std::string pubdate;
};