c/c++ 继承与多态 容器与继承2

说明了容器里使用继承关系的方法，这里再弄一个练习，巩固一下。

做一个类basket，它有个multiset成员，key是智能指针std::shared_ptr<quote>，由于key是自定义对象，所有必须给一个比较key的函数decltype(compare)*，关于自定义key的set，参考 。有个公有的additem成员方法，

quote3.h

#ifndef __quote3_h__
#define __quote3_h__

#include <iostream>

class quote{
 public:
  quote() = default;
  quote(const std::string& book, double pri)
    :bookno(book), price(pri){}
  std::string isbn() const{return bookno;}
  virtual double net_price(std::size_t n)const{
    return n * price;
  }
  virtual void debug()const{
    std::cout << bookno << " " << price << std::endl;
  }
  virtual ~quote() = default;
 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 qyn, double disc):quote(book, price),
    quantity(qyn), discount(disc){}
  
  double net_price(std::size_t) const override = 0;
 protected:
  std::size_t quantity = 0;//折扣适用的数量
  double discount = 0.0;   //折扣率
};

class bulk_quote : public disc_quote{
 public:
  
  bulk_quote() = default;
  
  bulk_quote(const std::string& book, double price,
  std::size_t qyn, double disc)
  :disc_quote(book, price, qyn, disc){}
  
  double net_price(std::size_t) const override;
};

class min_quote : public disc_quote{
 public:
  
  min_quote() = default;
  min_quote(const std::string& book, double price,
       std::size_t qyn, double disc)
   :disc_quote(book, price, qyn, disc){}
  
  double net_price(std::size_t) const override;
};

#endif

quote3.cpp

#include "quote3.h"

double bulk_quote::net_price(std::size_t cnt) const{
  if(cnt >= quantity){
    return cnt * (1 - discount) * price;
  }
  else{
    return cnt * price;
  }
}


double min_quote::net_price(std::size_t cnt) const{
  if(cnt < quantity){
    return cnt * (1 - discount) * price;
  }
  else{
    return cnt * price;
  }
}

basket.h

#ifndef __basket_h__
#define __basket_h__
#include "quote3.h"
#include <set>
#include <memory>


class basket{
 public:
  void add_item(const std::shared_ptr<quote>& sale){
    items.insert(sale);
  }
  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};
};

#endif

basket.cpp

#include "basket.h"

double print_total(std::ostream& os,
           const quote& item, size_t n);
double basket::total_receipt(std::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 sale: " << sum << std::endl;
  return sum;
}

main.cpp

#include "quote3.h"
#include "basket.h"
#include <vector>
#include <iostream>

double print_total(std::ostream& os,
           const quote& item, size_t n){
  double ret = item.net_price(n);
  os << "isbn: " << item.isbn()
     << " # sold: " << n << " total due: " << ret << std::endl;
  return ret;

}

int main(){
  basket bsk;
  //bsk.add_item(std::make_shared<quote>("01", 100));
  bsk.add_item(std::make_shared<bulk_quote>("01", 100, 2, 0.1));
  bsk.add_item(std::make_shared<bulk_quote>("01", 100, 2, 0.1));
  bsk.add_item(std::make_shared<bulk_quote>("01", 100, 2, 0.1));
  bsk.total_receipt(std::cout);
}

执行结果1：

isbn: 01 # sold: 3 total due: 270
total sale: 270

把main函数改成下面：

int main(){
  basket bsk;
  bsk.add_item(std::make_shared<quote>("01", 100));
  //bsk.add_item(std::make_shared<bulk_quote>("01", 100, 2, 0.1));
  bsk.add_item(std::make_shared<bulk_quote>("01", 100, 2, 0.1));
  bsk.add_item(std::make_shared<bulk_quote>("01", 100, 2, 0.1));
  bsk.total_receipt(std::cout);
}

执行结果2：

isbn: 01 # sold: 3 total due: 300
total sale: 300

代码有点长，主要的关注点：

• 容器里放的是智能指针
• 第一次添加的智能指针，如果是quote类型，执行结果就是执行结果2；如果是bulk_quote类型，执行结果就是执行结果1；

c/c++ 学习互助qq群：877684253

本人微信：xiaoshitou5854