C++ Primer（第5版） 练习 15.30
练习 15.30 编写你自己的Basket类，用它计算上一个练习中交易记录的总价格。
环境：Linux Ubuntu（云服务器）
工具：vim
代码块：
#include<iostream>
#include<vector>
#include<memory>
#include<set>
using namespace std;class Quote{public:Quote() = default;Quote(const std::string &book, double sales_price): bookNo(book), price(sales_price) {}std::string isbn() const { return bookNo; }virtual double net_price(std::size_t n) const { return n * price; }virtual ~Quote() = default;virtual Quote* clone() const &{ return new Quote(*this); }virtual Quote* clone() && { return new Quote(std::move(*this)); }private:std::string bookNo;protected:double price = 0.0;
};class Disc_quote: public Quote{public:Disc_quote() = default;Disc_quote(const std::string &book, double price, std::size_t qty, double disc): Quote(book, price), quantity(qty), discount(disc) {}double net_price(std::size_t) const = 0;protected:std::size_t quantity = 0;double discount = 0.0;
};class Bulk_quote: public Disc_quote{public:Bulk_quote() = default;Bulk_quote(const std::string& book, double price, std::size_t qty, double disc): Disc_quote(book, price, qty, disc) {}double net_price(std::size_t) const override;Bulk_quote* clone() const & { return new Bulk_quote(*this); }Bulk_quote* clone() && { return new Bulk_quote(std::move(*this)); }
};double Bulk_quote::net_price(size_t cnt) const{if (cnt >= quantity){return cnt * (1 - discount) * price;}else{return cnt * price;}
}double print_total(ostream &os, const Quote &item, size_t n){double ret = item.net_price(n);os<<"ISBN: "<<item.isbn()<<" # sold: "<<n<<" total due: "<<ret<<endl;return ret;
}class Basket {public:void add_item(const Quote& sale){items.insert(std::shared_ptr<Quote>(sale.clone()));}void add_item(Quote&& sale){items.insert(std::shared_ptr<Quote>(std::move(sale).clone()));}double total_receipt(std::ostream&) const;private:static bool compare(const std::shared_ptr<Quote> &lhs, const std::shared_ptr<Quote> &rhs){return lhs->isbn() < rhs->isbn();}std::multiset<std::shared_ptr<Quote>, decltype(compare)*> items{compare};
};double Basket::total_receipt(ostream &os) const{double sum = 0.0;for(auto iter = items.cbegin(); iter != items.cend(); iter = items.upper_bound(*iter)){sum += print_total(os, **iter, items.count(*iter));}os<<"Total Sales: "<<sum<<endl;return sum;
}int main(){Basket obj;obj.add_item(Quote("0-101-13456-X", 10));obj.add_item(Bulk_quote("0-102-34567-Y", 15, 20, 0.5));obj.add_item(Bulk_quote("0-103-32467-X", 5, 30, 0.5));obj.total_receipt(cout);return 0;
}
运行结果显示如下：
