C++ Primer 课后习题提问！

[liwenchao0309]

程序一：#include"Item.hpp"
#include<vector>
#include<string>
#include<iostream>
#include<utility>
using namespace std;

int main()
{
vector<Item_base>itemVec;
string isbn;
double price,qty,discount;
//
cout<<"Enter some Bulk_item objects(Ctrl+Z to end): "
<<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<<"summation of net_price: "<<sum<<endl;

return 0;
}
程序二：
#include"Item.hpp"
#include<vector>
#include<string>
#include<iostream>
#include<utility>
using namespace std;

int main()
{
vector<Item_base*>itemVec;
string isbn;
double price,qty,discount;
//
cout<<"Enter some Bulk_item objects(Ctrl+Z to end): "
<<endl;
while(cin>>isbn>>price>>qty>>discount) {
Bulk_item* p=new Bulk_item(isbn,price,qty,discount);
itemVec.push_back(p);
}
//
double sum=0.0;
for(vector<Item_base*>::iterator iter=itemVec.begin();
iter!=itemVec.end();++iter)
sum+=(*iter)->net_price(100);
//
cout<<"summation of net_price: "<<sum<<endl;
//
for(vector<Item_base*>::iterator it=itemVec.begin();
it!=itemVec.end();++it)
delete *it;

return 0;
}

Item.hpp文件：
#include<string>
#include<iostream>
using namespace std;
class Item_base{
public:
Item_base(const string& book="",double sales_price=0.0):
isbn(book),price(sales_price){}
string book() const
{
return isbn;
}
virtual double net_price(size_t n) const
{
return n*price;
}
virtual ~Item_base() {}
private:
string isbn;
protected:
double price;
};

class Bulk_item:public Item_base {
public:
Bulk_item(const string& book="",double sales_price=0.0,size_t qty=0,double dis_date=0.0):
Item_base(book,sales_price),min_qty(qty),discount(dis_date){}
double net_price(size_t cnt)
{
if(cnt>=min_qty)
return cnt*(1-discount)*price;
else
return cnt*price;
}
private:
size_t min_qty;
double discount;
};
问题：
程序一”sum+=iter->net_price(100);“这段代码调用的应该是基类Item_base的net_price，
程序二采用指针，动态绑定，“sum+=(*iter)->net_price(100);”调用的应该是派生类Bulk_item的net_price，
运行结果应该不同才对，
可是我运行程序一的结果和程序二的运行结果相同，大家帮着看看问题出在哪里，先谢谢了！

[liubuweiright]

顶

[wbgxx]

int i=0;

[ysysbaobei]

顶

[effective_person]

用代码贴,这样看着很累！，如下：

int a =10;