基类和派生类文件链接

        class Item_base{
public:
Item_base(const std::string &book="",double sales_price=0.0):isbn(book),price(sales_price){
   
}

std::string book()const{
    return isbn;
}
virtual double net_price(std::size_t n)const {
    return n*price;
}
virtual ~Item_base(){
   
}


private:
std::string isbn;
protected:
double     price;


};
class Bulk_item:public  Item_base{                                                         
                                                                                            
                                                                                            
                                                                                            
public :                                                                                    
                                                                                            
Bulk_item(const std::string &book="",double sales_price=0.0,size_t qty,double dis):         
Item_base(book,price),min_qty(qty),discount(dis){    }                                      
double net_price(std::size_t)const;                                                            
private:                                                                                    
std::size_t min_qty;                                                                        
double discount;                                                                              
};                                                                                          
                                                                                            
double Bulk_item::net_price(size_t cnt)const{                                               
    if(cnt>=min_qty)                                                                           
    return cnt*(1-discount)*price;                                                            
else                                                                                       
return cnt*price;                                                                           
};   

                                                                                            
                                                                                               
            

#include<iostream>
#include<string>
#include<vector>
#include"Item_base.hpp"

using namespace std;
int main(){
    vector<Item_base>itemvec;
    string isbn;
    double price,qty,discount;
    cout<<"Enter some Bulk_item objects"<<endl;
    while(cin>>isbn>>price>>qty>>discount){
        itemvec.push_back(Bulk_item(isbn,price,qty,discount));
    }
   
    double sum=0.0;
    for(vector<Item_base>::iterator iter=itemvec.begin();
    iter!=itemvec.end();++iter)
    sum+=iter->net_price(100);
    cout<<sum<<endl;
    return 0;
   
   
   
}